# Antipredator responses of native amphibian tadpoles to the presence of invasive alien African clawed frogs

Tatiana Colchen, Olivier Pays, Clément Harmange, Julien Morin, Eléonore Moreau, Manon Bonnet, Alain Pagano

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Tatiana Colchen, Olivier Pays, Clément Harmange, Julien Morin, Eléonore Moreau, et al. | An-tipredator responses of native amphibian tadpoles to the presence of invasive alien African clawed frogs. Animal Behaviour, 2025, 226, pp.123255. 10.1016/j.anbehav.2025.123255. hal-05153173

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# Antipredator responses of native amphibian tadpoles to the presence of invasive alien African clawed frogs

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Tatiana Colchen<sup>a, * ID</sup>, Olivier Pays<sup>a, b</sup>, Clément Harmange<sup>a ID</sup>, Julien Morin<sup>a</sup>, Eléonore Moreau<sup>a ID</sup>, Manon Bonnet<sup>a, b ID</sup>, Alain Pagano<sup>a ID</sup>

ARTICLE INFO

Article history:

Received 12 September 2024

Initial acceptance 11 December 2024

Final acceptance 8 April 2025

Available online xxx

MS. number: 24-00567R

Keywords:

African clawed frog

aggregation

nonconsumptive effect

predation-risk effect

tadpole

Xenopus laevis

Biological invasions are a primary driver of global environmental changes. Invasive alien species can affect ecosystem dynamics, including interspecific relationships such as competition and predation. Although widely recognized, the impacts of invasive predators on native prey remain sparsely documented, particularly in amphibians. African clawed frog, *Xenopus laevis*, which is native to South Africa, has successfully established populations in western France and has expanded its range in recent decades. African clawed frog is known to prey on native amphibians; however, the indirect effects of predation risk remain unknown. Using 10 min video recordings, whether *Pelophylax* spp. tadpoles, which is a native frog common in French wetlands, showed antipredator responses to the invasive African clawed frog was tested. These responses were compared with those to other predators, including native Odonata larvae and alien red swamp crayfish, *Procambarus clarkii*. Native tadpoles displayed the greatest distance from the predator, and they were more aggregated (with a smaller nearest neighbour distance) when exposed to African clawed frogs compared with other predators. However, the time individuals spent swimming and exploring as well as the average speed during exploration did not differ among predators. This study focuses on the ability of native tadpoles to recognize and respond to invasive predators, emphasizing the ecological challenges faced by native populations.

© 2025 The Author(s). Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Biological invasions are regarded as primary drivers of global environmental change, with the introduction of invasive alien species (IAS) beyond their native ranges facilitated by international trade and transport (Blackburn et al., 2011). IAS pose a major threat because of their novel and significant impacts on native biodiversity (Early et al., 2016; Gentili et al., 2021). The resulting loss of biodiversity and ecosystem services has resulted in warnings from scientists about the substantial impacts of IAS on ecosystems, environmental health and species extinctions (Pysek et al., 2020; Roy et al., 2024). In particular, IAS can affect interspecies relationships such as competition, hybridization, transmission of diseases and predation (Wittenberg, 2005). For

example, invasive alien predators can prey on native species, which may lead to local declines and extinctions in prey populations (Anson & Dickman, 2013; Sih et al., 2010).

Predators influence prey demography through direct consumptive effects (Hebblewhite et al., 2002). However, predators induce phenotypic changes in prey because of the indirect effects of their presence, which are known as predation-risk effects (Creel & Christianson, 2008). These predation-risk effects encompass the costs of antipredator behavioural responses, which can have cascading effects on intra and interspecific interactions (Peacor et al., 2020). Such effects are documented across various taxa, including mammals (Basille et al., 2015; Le Roux et al., 2018; Moll et al., 2016; Willems & Hill, 2009), insects (Buchanan et al., 2017; Hermann & Landis, 2017), fishes (Hill & Heck, 2015; Mitchell & Harborne, 2020) and amphibians (Davenport et al., 2020; Jarvis, 2010; Kloskowski, 2018). Prey responses to predation risk can be morphological, physiological or behavioural (Creel & Christianson, 2008; Peacor et al., 2020; Zanette et al., 2014), including changes in foraging behaviour (Altendorf et al., 2001;

<footnote><sup>a</sup> Univ Angers, BIODIVAG, Angers, France</footnote>

<footnote><sup>b</sup> REHABS International Research Laboratory, CNRS-Université Lyon 1-Nelson Mandela University, George Campus, George, South Africa</footnote>

<footnote>* Corresponding author.</footnote>

<footnote>E-mail addresses: tatiana.colchen@gmail.fr, tatiana.colchen@univ-angers.fr (T. Colchen), olivier.pays@univ-angers.fr (O. Pays), c.harmange.pro@gmail.com (C. Harmange), morin.julienpro@gmail.com (J. Morin), eleonore.moreau@univ-angers.fr (E. Moreau), manon.bonnet@univ-angers.fr (M. Bonnet), alain.pagano@univ-angers.fr (A. Pagano).</footnote>
Verdolin, 2006), habitat use (Bland & Temple, 1990; Werner et al., 1983), vigilance (Creel et al., 2014; Pays et al., 2021), activity patterns (Crawford et al., 2020; Ross et al., 2013) and aggregation (Dittmann & Schausberger, 2017; Sorato et al., 2012). For example, the benefits of aggregation in reducing predation rates have been well documented (Hammer et al., 2023), and they involve mechanisms such as the 'dilution effect' (Lehtonen et al., 1996), 'many eyes' theory (Lima, 1995), 'selfish herd' hypothesis (Hamilton, 1971) or 'confusion effect' (Landeau & Terborgh, 1986). However, the costs associated with these antipredator responses can reduce survival, growth or reproduction (Nelson et al., 2004; Sheriff et al., 2020; Sih, 1994). Therefore, the consequences of predation-risk effects on prey dynamics can be as significant as, if not greater than, the direct effects of predation (Creel & Christianson, 2008; Zanette et al., 2011). Most previous studies have focused on the direct impacts of predation on individual fitness or prey density (Gliwicz, 1994; Peacor & Werner, 2001). However, research on the effects of predation risk has gained considerable interest over the past decade (Creel & Christianson, 2008).

Predation-risk effects can be exacerbated when prey are faced with alien predators (Blackburn et al., 2004; Woinarski et al., 2015). Considering the evolutionary naivety with IAS, native prey may lack appropriate mechanisms for detecting, recognizing and escaping from alien predators (Blumstein et al., 2004; Carthey et al., 2017; Sih et al., 2009, 2011). Consequently, IAS can compound the effects of native predators, thereby affecting prey through direct (lethal) or indirect (sub or nonlethal) effects on their phenotypes (Melotto et al., 2021; Pysek et al., 2020). For example, the clutch size, mass and reproductive age of three-spined stickleback, *Gasterosteus aculeatus*, declined after the initial introduction of northern pike, *Esox lucius* (Heins et al., 2016). In addition, the introduction of European red fox, *Vulpes vulpes*, reduced the foraging activity in two small Australian mammals (Kovacs et al., 2012). Despite growing interest in literature on the impacts of IAS on native biodiversity, relatively few studies have examined the antipredator responses of native prey to alien predators. For native aquatic amphibians exposed to cues of introduced predators, studies have shown variable responses, with some species being unable to detect cues of introduced predators while others being able to detect and avoid such cues (Flores et al., 2024; Gall & Mathis, 2010; Méndez-Méndez et al., 2023; Polo-Cavia et al., 2010).

The African clawed frog, *Xenopus laevis*, which is native to South Africa, has invaded four continents, making it the world's most widespread amphibian (Measey et al., 2012). It is commonly used as an animal model in biological research and pet trade networks, which has led to its accidental escape from captivity and deliberate releases, resulting in the establishment of invasive populations in Europe (Van Sittert & Measey, 2016). African clawed frogs are highly flexible and resilient, thriving in diverse habitats, including ponds, streams and wetlands, which facilitates their rapid establishment and spread in freshwater ecosystems (Moreira et al., 2017). African clawed frogs have been recently introduced to ponds in western France, approximately 40 years ago (Fouquet, 2001), whereas other IAS, such as the crayfish, *Procambarus clarkii*, has been established for 100 years (Gherardi, 2006). Given this accumulation of alien predators, native species need efficient antipredator strategies to cope with the predation risk. Understanding the antipredator responses of local amphibians to the rapid invasion of African clawed frogs is essential for predicting their impact on local populations, including disturbance, displacement or decline and for developing effective conservation strategies. This information is relevant for amphibians, which are among the most affected vertebrates, with 6% of species being threatened by IAS worldwide (Luedtke et al., 2023; Nunes et al., 2019).

In this study, whether the invasive African clawed frog was perceived as a predator by tadpoles of the common native amphibian *Pelophylax* spp. was investigated. In particular, the effects of the presence of African clawed frogs on the antipredator behavioural responses of *Pelophylax* spp. tadpoles were examined, and these antipredator responses were compared with those showed upon exposure to other native (Odonata larvae) or alien (red swamp crayfish, *Procambarus clarkii*) predators and neutral treatments (adult water frogs, *Pelophylax* spp. and plastic frog models). This study focused on *Pelophylax* spp. tadpoles because the aquatic larval stages of amphibians are particularly vulnerable to IAS compared with their terrestrial adult counterparts (Cox & Lima, 2006). In addition, these tadpoles experience substantial predation pressure from a variety of native and alien aquatic predators, including adult African clawed frogs, which are known to prey on amphibian larvae (Courant et al., 2017; Thorp et al., 2019; N. J. N. J. Wilson & Williams, 2014). Local populations of *Pelophylax* spp. also co-occur with African clawed frogs at the adult and larval stages in western France (Courant et al., 2018).

We first hypothesized that if native tadpoles did not recognize alien predators because of evolutionary naivety (Polo-Cavia et al., 2010; Pujol-Buxó et al., 2013), then they should not show anti-predator behavioural responses to African clawed frogs, which shows responses similar to those with neutral treatments (i.e. adult water frog and plastic frog; Balestrieri et al., 2019; Fraker, 2010; Saidapur et al., 2009). By contrast, if African clawed frogs were recognized as a predator, then significant antipredator behavioural responses can be observed compared with those elicited by neutral treatments. In addition, tadpole responses to crayfish, which was introduced 100 years ago, should be similar to or more pronounced than their responses to African clawed frog, which was introduced approximately 40 years ago. The possible antipredator responses of tadpoles included (1) aggregating into a clumped group as a result of dilution, confusion selfish herd and many-eyes mechanisms (Hammer et al., 2023), which might reduce the predation rate per capita (Spieler, 2003), (2) increasing the distance from the predator as part of an escape behaviour (Cooper & Blumstein, 2015) and (3) reducing activity to decrease the probability of detection by predators (i.e. freezing behaviour; Stynoski & Noble, 2012).

## METHODS

### Ethical Note

All experiments complied with French laws on animal experimentation in accordance with the guidelines of the Council of the European Union (2010/63/UE). Permission to capture and handle amphibians was provided by the authority Direction Départementale des Territoires du Maine-et-Loire (approval number DDT49/SEEB/CVB 2023-28). This study was approved by the French Animal Care Guidelines (animal approval number 2023032913264138/APAFIS 42162V2). The experiments were observational without any physical invasive manipulations. The holding tanks included flow pipes and floating polystyrene plates, which were used as shelters by individuals and aquatic plants collected from the ponds to reproduce natural conditions. All individuals were maintained under a natural photoperiod with light from 0730 hours to 2030 hours. Predator and tadpole tanks were visually isolated during rearing periods. Individuals were transferred with care by hand netting from the holding tank to the arena and back. All tests began with an acclimatization period of 15 min. At the end of the experiments, all water frogs (tadpoles and adults) and Odonata larvae were released in their ponds of origin. Red swamp crayfish and African clawed frogs were killed
with an overdose of tricaine methane-sulphonate (MS-222, 3 g/litre) after an anaesthesia of MS-222 (300 mg/litre, Sigma-Aldrich, France) because of their IAS status.

## Origin and Rearing Conditions of Tadpoles and Predators

Water frog *Pelophylax* spp. clutch was collected on 12 May 2023, from a pond at La Cantinerie (47°16'6" N 0°36'49" W, Maine-et-Loire Department, Western France), a site where African clawed frog juveniles and adults were present. Approximately 500 tadpoles, which were obtained from the same clutch, hatched between 19 May and 21 May, 2023, under controlled conditions in the laboratory (approved establishment EU0738–SIFCIR/Sciences) located at the Faculty of Sciences of the University of Angers (France). After hatching, 60 tadpoles were divided into six groups, with 10 tadpoles each group, and maintained at a density of 2–3 tadpoles per litre in plastic tanks (32 cm × 18 cm) with 4 litres of dechlorinated tap water mixed with pond water (50:50 ratio). The tanks were enriched with small flow pipes (4 cm with a 1 cm diameter), floating polystyrene plates (15 cm × 10 cm) used as shelters and aquatic plants collected from the pond. The tadpoles were maintained under a natural photoperiod with light from 0730 hours to 2030 hours. A third of the water was renewed every 2 days, and the water quality was measured once a week (NO₂ = 1.2 ± 1.1 mg/litre; NO₃ = 42.0 ± 28.9 mg/litre; pH = 7.2 ± 0.2; temperature = 20.1 °C ± 1.1 °C). All the tanks were provided with three granules of rabbit food every day throughout the study period.

Predators, including three African clawed frogs, three Odonata larvae and two red swamp crayfish, were collected from the same pond as the tadpoles. Three water frogs, which were used for neutral treatments, were collected from a pond at the University of Angers (i.e. 24 km from the pond of La Cantinerie). Between 19 June and 23 June, 2023, Odonata larvae and crayfish were maintained in plastic tanks for 5 days (32 cm × 18 cm with 4 litres of water). One tank was used for all three Odonata larvae, while each crayfish was kept in a separate tank to avoid interindividual attacks. The African clawed frogs and water frogs were kept in glass aquaria (1 m × 50 cm with 40 litres of water; separated into two aquaria of three individuals). The rearing conditions, including water quality, light and temperature, were the same as those used for the tadpoles. All glass aquaria and plastic tanks were enriched with shelters (flowing pipes measuring 20 cm × 10 cm and floating plates measuring 15 cm × 10 cm) and aquatic plants. For water frogs, small stones were added as substrate in part of the aquarium to allow them to emerge from the water. Predators were fed once a day with fish granules containing 47.5% animal protein.

## Experimental Design and Apparatus

The experimental apparatus comprised a transparent plastic arena (32 cm × 18 cm) filled with 4 litres of dechlorinated tap water mixed with pond water in a 50:50 ratio, which was replaced between each group. A fixed transparent divider with holes (1 mm diameter), which separated the arena into two parts, was also used to allow water circulation. The first chamber (19 cm × 18 cm) housed the tadpoles, whereas the second chamber (13 cm × 18 cm) contained the predator (hereafter referred to as the 'predator chamber'). Each group of 10 tadpoles was transferred from their rearing tanks to the first chamber for 15 min before the predator was introduced into the second chamber for an additional 15 min. At the end of the 30 min test, the tadpoles and predators were returned to their rearing tanks.

Over 5 days, each group of tadpoles was exposed to five treatments, including African clawed frog (CF; snout–vent length (SVL) ± SD = 87.46 ± 7.96 mm), Odonata larvae (OL; total length (TL) ±

SD = 14.85 ± 6.95 mm), red swamp crayfish (CR; TL ± SD = 71.52 ± 3.94 mm), water frog (WF; SVL ± SD = 45.52 ± 11.94 mm) and plastic frog (PF; SVL ± SD = 80.50 mm), with the latter two being considered as neutral treatments. The six groups of 10 tadpoles, aged 30–35 days posthatching (dph), were exposed to one treatment per day (= day of testing), with a 24 h interval between each test. The order of the treatments was randomly determined between two draws to avoid bias of the previous predator exposition 24 h earlier (three groups [= replicates] were tested for each draw [= order of presentation]). The Odonata larvae represented the native predator of frog tadpoles, whereas the African clawed frog and red swamp crayfish were the alien predators. A green plastic frog was used as the first neutral treatment to observe the behavioural response of tadpoles to an inert object that visually mimics a frog. A live adult water frog was used as the second neutral treatment to evaluate the responses to a conspecific that may produce chemical signals. Furthermore, by randomly selecting the testing predator among three (for African clawed frogs and water frogs) or between two (for red swamp crayfish) individuals for each group, the variability in behaviour was ensured, and the representative behavioural responses of prey were obtained. Whenever possible, a predator tested with a group of tadpoles was not reused for another test on the same day. All tests and acclimatization periods were video recorded using a camera (GigE, objective 4.4–11 mm, Noldus) installed 30 cm above the arena. The experimental apparatus was isolated in a dark chamber, which was uniformly illuminated by artificial light to avoid shadow zones in the test area. All trials were conducted from 0830 hours to 1600 hours.

## Behavioural Responses

During the 30 min recording, the behaviour of tadpoles was quantified in two 10 min periods, each preceded by a 5 min acclimation phase. The first 5 min following the introduction of tadpoles into the experimental apparatus constituted the first acclimation phase. Then, tadpole behaviour was quantified during the subsequent 10 min as a baseline control before the introduction of the predator or neutral treatment (hereafter referred to as the 'pre-exposure period'). After the introduction of the predator or neutral treatment, tadpole behaviour was video recorded for 5 min but not analysed, as this period served as the second acclimation phase to the water perturbations caused by the introduction of the predator or neutral treatment. Finally, tadpole behaviour was quantified for 10 min after the introduction of the predator or neutral treatment (hereafter referred to as the 'predator exposure period'). Although we did not monitor the activity of predators during the predator exposure period, the experiments for all the testing groups were standardized by checking whether the predators were active (except for the plastic frog), did not move much and did not show any evident abnormal behaviours during the experiments.

Tadpoles were individually tracked using AnimalTA software (Chiara & Kim, 2023) during 10 min periods before and after the introduction of treatment with nine frames per second (i.e. 5401 frames for 600 s). All tracks were screened and manually corrected frame by frame to ensure that there was no inversion between tracked individuals and no missing values. For both video segments, the following behavioural parameters, which were defined and explained in Table 1, were calculated on the basis of the x–y coordinates of the barycentre of each tadpole: interindividual distances (cm), dependent on the group size and representative of cohesion (Buske & Gerlai, 2011), mean nearest neighbour distance (cm) independent of the group size and representative of the dispersion of individuals (Buske & Gerlai, 2011), mean distance to the predator or neutral treatment chamber (cm), total distance
<table><caption>**Table 1**
Definitions and calculation methods of behavioural response variables measured in an arena containing 10 *Pelophylax* spp. tadpoles</caption><thead><tr><th>Behavioural response variables</th><th>Definitions</th><th>Calculating methods</th></tr></thead><tbody><tr><td>Interindividual distances (cm)</td><td>The distance between the target and all the other individuals in the group</td><td>All distances between all the targets were summed within the arena. Distances were calculated on the basis of the x-y coordinates of the barycentre of each tadpole. This parameter was measured for each frame and then averaged over the 10 min pre-exposure period and the 10 min exposure period</td></tr><tr><td>Nearest neighbour distances (cm)</td><td>The distance between the target and the closest neighbour</td><td>Distances were calculated on the basis of the x-y coordinates of the barycentre of each tadpole. This parameter was measured for each tadpole in each frame and then averaged over the 10 min pre-exposure period and the 10 min exposure period</td></tr><tr><td>Distance to treatment (cm)</td><td>The distance between the target and the predator or neutral treatment chamber</td><td>The divider between the treatment and tadpoles was considered as a border. The mean distance to the border is the averaged shortest distance between the target (centre of the mass of each tadpole) and the border. This parameter was calculated for each tadpole and averaged on the 10 tadpoles over the 10 min pre-exposure period and the 10 min exposure period</td></tr><tr><td>Exploration (cm²)</td><td>The absolute exploration score of the target by measuring the surface it visited</td><td>The 'individual centred method' was used. This method assumes that a target explores a circular area around it (calibrated at 0.99 ± 0.01 cm²) during each frame. Each pixel that falls within this circular area at least once during the video is considered as visited, whereas others are considered as unvisited. The measure of exploration obtained is the total visited surface. This parameter was calculated for each tadpole and then averaged on the 10 tadpoles over the 10 min pre-exposure period and the 10 min exposure period.</td></tr><tr><td>Travelled distances (cm)</td><td>Total distance travelled by the target</td><td>The total distance travelled by the target was summed. This parameter was calculated for each tadpole and averaged across the 10 tadpoles for the entire vide</td></tr><tr><td>Average speed (cm/s)</td><td>The averaged displacement speed of the target between each frame</td><td>The displacement speed between each frame was calculated and averaged for the entire video. This parameter was calculated for each tadpole and averaged on the 10 tadpoles over the 10 min pre-exposure period and the 10 min exposure period</td></tr><tr><td>Proportion time moving</td><td>Proportion of time the target is considered as moving</td><td>The proportion of frames in which the target is moving faster than the moving threshold (set at 0.2 cm to smooth trajectories and avoid microdisplacement inaccuracies of the tracking point). This parameter was calculated for each tadpole and averaged on the 10 tadpoles over the 10 min pre-exposure period and the 10 min exposure period</td></tr></tbody></table>

‘Target’ corresponding to one tadpole. The definitions and calculation methods are in accordance with the AnimalTA Guidelines (Chiara & Kim, 2023).

travelled (cm), average speed (cm/s), exploration (cm²) and proportion of time moving. All behavioural variables were averaged for both video segments (that is, pre-exposure and predator exposure periods), and the differences between these two segments were calculated. The results are presented as the difference between the measurements taken after subtraction before treatment.

## Data Analysis

In comparing the antipredator responses of tadpoles exposed to different native and invasive alien predators, linear mixed-effect models (LMMs) were first run using each behavioural variable as a dependent variable and treatment with three predators (African clawed frog, Odonata larvae and red swamp crayfish) and two neutral treatments (adult water frog versus plastic frog) as the independent variable (fixed factor). The replicate ID (three replicates: from R1 to R3 for each presentation order), order of predator presentation (two presentation orders: P1 [WF-PF-OL-CR-CF] and P2 [OL-CF-CR-WF-PF] and days of testing [five days: from D1 to D5]) were included as the nested random factors. These LMMs were referred to as full models. Then, the same LMMs were run without including the fixed factor treatment (referred to as null models) to control the effect of variables caused by the experiment. For each behavioural variable, the full and null models were compared using likelihood ratio tests (i.e. χ²) to test for the effects of treatment (Faraway, 2006). Whether the baseline value of the studied behaviour during the pre-exposure period affected the effect of the predator treatment on the studied behavioural response, including the pre-exposure period as a covariate and the two-way interaction pre-exposure period × predator treatment, was also tested. When treatment showed a significant effect on a behavioural variable, a post hoc Tukey test was used for multiple comparisons to examine the differences between all treatment levels. The normality of residuals and the distribution of residuals against the fitted values were checked for each variable. All statistical tests were performed using R software (R Core Team, 2022). The models were analysed using the NLME package (Pinheiro et al.,

2024), and multiple comparisons were performed using the MULTCOMP package (Hothorn et al., 2002). The results are presented as means ± SD.

## RESULTS

The treatment affected the mean interindividual distances between tadpoles, the mean nearest neighbour distance and the distance to the predator chamber (Table 2). The mean interindividual distances between tadpoles were significantly shorter when they were exposed to African clawed frogs (9.67 ± 1.81 cm) than when they were exposed to plastic frog (11.13 ± 1.11 cm; *P* = 0.006), red swamp crayfish (11.58 ± 1.49 cm; *P* < 0.001) or Odonata larvae (11.49 ± 1.05 cm; *P* = 0.009). However, such distances did not (but marginally) differ when they were exposed to water frog (11.55 ± 0.97 cm; *P* = 0.074; Fig. 1a, Table 3). The mean nearest neighbour distance between tadpoles was significantly shorter when they were exposed to African clawed frogs (2.88 ± 1.35 cm) than when they were exposed to water frog (3.32 ± 1.22 cm; *P* = 0.018), plastic frog (3.65 ± 1.02 cm; *P* = 0.006) or Odonata larvae (3.64 ± 0.94 cm; *P* = 0.005; Fig. 1b–Table 3). In addition, tadpoles increased their distance from the predator chamber significantly more when the predator was African clawed frog (15.10 ± 3.20 cm) than when it was plastic frog (9.73 ± 5.67 cm; *P* < 0.001), crayfish (11.24 ± 4.66 cm; *P* < 0.001) or Odonata larvae (10.41 ± 4.69 cm; *P* < 0.001; Fig. 1c–Table 3). Moreover, treatment (predator or neutral) showed no effect on exploration, distance travelled, average speed or the proportion of time spent moving in tadpoles (Table 2; see Table S1 for more details on the estimates). Finally, our analyses showed that all behavioural responses, except for the interindividual distance and nearest neighbour distance, decreased when the corresponding behaviours during the pre-exposure period were low (Table 2).

## DISCUSSION

The presence of invasive African clawed frogs led to the highest aggregation patterns, distance from the predator chamber and
<caption>**Table 2**</caption>

Effects of the predator treatment and pre-exposure period on the difference in the mean interindividual distances, the nearest neighbour distances, the distance to treatment (predator or neutral), the exploration value, the distance travelled, the average speed during exploration and the proportion of time moving assessed between the pre-exposure and the predator exposure periods

<table><thead><tr><th>Behavioural response variables</th><th>Fixed effects</th><th>χ<sup>2</sup></th><th>df</th><th>P</th><th>β ± SE</th><th>Random factors (SD)</th></tr></thead><tbody><tr><td rowspan="3">Interindividual distances</td><td>Treatment</td><td><strong>15.599</strong></td><td><strong>4</strong></td><td><strong>0.004</strong></td><td>Table 3</td><td></td></tr><tr><td>Pre-exposure period</td><td>2.166</td><td>1</td><td>0.141</td><td></td><td>0.732</td></tr><tr><td>Treatment*pre-exposure</td><td>3.001</td><td>4</td><td>0.558</td><td></td><td></td></tr><tr><td rowspan="3">Nearest neighbour distances</td><td>Treatment</td><td><strong>20.329</strong></td><td><strong>4</strong></td><td><strong>&lt;0.004</strong></td><td>Table 3</td><td></td></tr><tr><td>Pre-exposure period</td><td>0.047</td><td>1</td><td>0.828</td><td></td><td>0.355</td></tr><tr><td>Treatment*pre-exposure</td><td><strong>13.363</strong></td><td><strong>4</strong></td><td><strong>0.010</strong></td><td>Table 3</td><td></td></tr><tr><td rowspan="3">Distance to treatment</td><td>Treatment</td><td><strong>39.482</strong></td><td><strong>4</strong></td><td><strong>&lt;0.001</strong></td><td>Table 3</td><td></td></tr><tr><td>Pre-exposure period</td><td><strong>19.360</strong></td><td><strong>1</strong></td><td><strong>&lt;0.001</strong></td><td>-0.771 ± 0.165</td><td>1.026</td></tr><tr><td>Treatment*pre-exposure</td><td>1.039</td><td>4</td><td>0.904</td><td></td><td></td></tr><tr><td rowspan="3">Exploration</td><td>Treatment</td><td>5.639</td><td>4</td><td>0.228</td><td></td><td></td></tr><tr><td>Pre-exposure period</td><td><strong>24.231</strong></td><td><strong>1</strong></td><td><strong>&lt;0.001</strong></td><td>-0.853 ± 0.142</td><td>28.639</td></tr><tr><td>Treatment*pre-exposure</td><td>4.277</td><td>4</td><td>0.370</td><td></td><td></td></tr><tr><td rowspan="3">Travelled distances</td><td>Treatment</td><td>4.475</td><td>4</td><td>0.345</td><td></td><td></td></tr><tr><td>Pre-exposure period</td><td><strong>9.531</strong></td><td><strong>1</strong></td><td><strong>0.002</strong></td><td>-0.491 ± 0.156</td><td>112.615</td></tr><tr><td>Treatment*pre-exposure</td><td>4.168</td><td>4</td><td>0.384</td><td></td><td></td></tr><tr><td rowspan="3">Average speed</td><td>Treatment</td><td>4.473</td><td>4</td><td>0.346</td><td></td><td></td></tr><tr><td>Pre-exposure period</td><td><strong>9.528</strong></td><td><strong>1</strong></td><td><strong>0.002</strong></td><td>-0.491 ± 0.156</td><td>0.188</td></tr><tr><td>Treatment*pre-exposure</td><td>4.160</td><td>4</td><td>0.384</td><td></td><td></td></tr><tr><td rowspan="3">Proportion time moving</td><td>Treatment</td><td>5.904</td><td>4</td><td>0.206</td><td></td><td></td></tr><tr><td>Pre-exposure period</td><td><strong>19.030</strong></td><td><strong>1</strong></td><td><strong>&lt;0.001</strong></td><td>-0.644 ± 0.139</td><td>0.050</td></tr><tr><td>Treatment*pre-exposure</td><td>1.175</td><td>4</td><td>0.882</td><td></td><td></td></tr></tbody></table>

Five treatments were tested, including plastic frog, water frog, Odonata larvae, red swamp crayfish and African clawed frog. The pre-exposure period indicates the value of the studied behaviour before the predator exposure period (that is, before the introduction of the predator or neutral treatment). Statistics of the likelihood ratio test are addressed with $\chi^2$, $df$ and $P$ value. SD indicates the standard deviation of the three nested random factor replicates, the order of treatment exposure and the day of the test. Significant effects are indicated in boldface ($P < 0.05$). Table 3 shows the post hoc pairwise comparisons among treatment levels when significant. $\beta$ ± SE are indicated for significant variables.

nearest neighbour distance among *Pelophylax* spp. tadpole individuals. These behavioural adjustments could be attributed to antipredator responses (Cooper & Blumstein, 2015; Hammer et al., 2023).

## *Behavioural Responses to Predators*

Antipredator strategies have been previously reported in amphibians that have experienced predation risk (Hossie et al., 2017; Wilson et al., 2018). These responses include modifications in larval activities (Laurila, 2000; Zhang et al., 2015), spatial avoidance of predators (Nunes et al., 2013), the use of refuges (Bleach et al., 2014; D'Amore et al., 2009; Pearl et al., 2003), morphological changes (Melotto et al., 2021) and adjustments in the timing of metamorphosis (Vodrážková et al., 2020).

In particular, our study showed that predators could induce a grouping strategy in tadpoles, thereby reducing their distance to the nearest neighbours. This finding supports previous observations that aggregation is a common reactive strategy of prey to reduce predation risk (Ioannou et al., 2011), including anuran tadpoles (Stav et al., 2007). This aggregative response is relevant to the antipredator behaviour of *Pelophylax* spp. tadpoles, which are not known to be gregarious or social. In our study, the aggregation of *Pelophylax* spp. tadpoles was particularly marked when they were exposed to African clawed frogs and less or not visible when they were exposed to invertebrates (Odonata larvae and crayfish). Despite being a native predator (Teplitsky et al., 2004), Odonata larvae, which is a sit-and-wait predator, elicited the lowest antipredator response in *Pelophylax* spp. tadpoles. Although Odonata larvae are smaller than the other predators used for exposure (crayfish and African clawed frogs), behavioural adjustments were observed upon exposure to Odonata larvae compared with the pre-exposure period, which is similar to a neutral treatment, such as water frogs. This behavioural response indicates that detection was effective. Therefore, the lowest response to Odonata larvae could not be explained by differences in body size among

predators. In addition, variability in the release of chemical cues by predators could affect the reliability of the responses of tadpoles across trials (Fraker, 2008). Other anuran species are present in our wetlands, including the Iberian spiny toad, *Bufo spinosus*, and the European tree frog, *Hyla arborea*, but they are not known to prey upon tadpoles as they are mostly terrestrial. Therefore, their presence does not affect the observed antipredator responses. Moreover, although anuran tadpoles can sometimes react to general anuran chemical cues, our results indicate that the observed responses were predator specific, as tadpoles did not show similar aggregation or avoidance behaviours in the neutral treatment. Thus, measuring cue concentrations at the end of the exposure period could assess the mechanism by which predator activity levels influence variability in behavioural responses.

In addition, the distance of tadpoles from the predator chamber increased in the presence of African clawed frogs, which indicates an escape behaviour for spatial avoidance of the predator. A previous study in California revealed that native anurans were absent from many areas invaded by African clawed frog, although they were never found in their stomachs (Crayon, 2005), indicating the emigration of local amphibians from those threatened areas. This exclusion could result in the local extinction of vulnerable native amphibians, thereby diminishing biodiversity.

Although behavioural responses such as freezing and reduced swimming activity (Hossie et al., 2017) are common antipredator behaviours in many anuran larvae such as common frog, *Rana temporaria* (Laurila, 2000), black-spotted pond frog, *Rana nigromaculata*, terrestrial frog, *Rana limnocharis* (Zhang et al., 2015) and Italian agile frog, *Rana latastei* (Scribano et al., 2020), no significant differences were found in swimming activity, exploration or time spent moving between the neutral and exposed predator treatments. On the one hand, the balance between fleeing and freezing in response to predators could explain this result (Cooper & Blumstein, 2015). Indeed, prey may display active (e.g. flight) or passive (e.g. freezing) responses when faced with a predator. On the other hand, considering the dilution effect or social buffering,
<figure><img src="image_5.png" /><figcaption>**Figure 1.** Effects of predator exposure on (a) the mean interindividual distance (cm), (b) the nearest neighbour distance (cm) and (c) the distance to the predator chamber (cm). Five treatments were proposed, including two neutral treatments with the plastic frog and water frog, *Pelophylax* spp.; three exposures to predators with Odonata larvae, red swamp crayfish, *Procambarus clarkii*, and African clawed frog, *Xenopus laevis*. The values are presented as the difference between the predator exposure minus the pre-exposure period. The box plots indicate the medians (bold line), means (triangles), first and third quartiles, 95% confidence intervals (whiskers) and outliers (open dots). Significant differences are presented in Tables 1 and 2.</figcaption></figure>

the presence of larger groups may reduce individual responses to predators (Peacor, 2003; Van Buskirk et al., 2011). In our study, the increased distance from the predator chamber when African clawed frog was present indicated that *Pelophylax* spp. tadpoles adopted an active response strategy, which explained the stability of their swimming activity. Furthermore, this stable swimming activity allows tadpoles to maintain their foraging ability (Barta et al., 2004; Gazzola et al., 2018). This hypothesis could be tested in the future by comparing the feeding behaviour of tadpoles exposed to African clawed frogs with those exposed to other predators to evaluate the costs and fitness outcomes associated with predation risk. Finally, further studies should also explore the variation in the behavioural responses of tadpoles to predation risk at the light of behavioural syndrome.

## Recognition of IAS as Predators

The behavioural responses observed in our study highlight the ability of *Pelophylax* spp. tadpoles to detect and recognize predators at early developmental stages (30 dph in our study). This result is supported by previous studies showing the precocious ability of embryonic amphibians to detect and recognize predators (Ferrari & Chivers, 2010; Hammond et al., 2024; Hettyey et al., 2012).

Although native prey often shows naivety towards introduced predators (Cox & Lima, 2006; Rehage et al., 2009), our study demonstrated that African clawed frogs elicited strong antipredator behaviours of *Pelophylax* spp. tadpoles. Although the tadpoles had never been exposed to African clawed frogs before, they displayed antipredator responses to the presence of these predators, indicating that they may have developed adaptive behavioural responses. Phillips and Shine (2006) demonstrated that 67 years or 23 generations were sufficient for the Australian black snake, *Pseudechis porphyriacus*, to develop adaptive behavioural and physiological responses to IAS (e.g. the cane toad, *Bufo marinus*). Alternatively, naive (e.g. native) prey can sometimes recognize and respond to novel (e.g. invasive) predators through mechanisms that overcome evolutionary naivety (Carthey & Banks, 2014; Cox & Lima, 2006). First, the predator generalization hypothesis indicates that prey may recognize a general predator archetype and display an antipredator response, particularly if the invasive predator is phylogenetically close to a native predator. Second, the generic response hypothesis assumes that a novel predator may have traits commonly associated with predators (e.g. large size and specific movements), leading to a generic antipredator response from naive prey. In the present study, *Pelophylax* spp. tadpoles adopted the generic antipredator responses of aggregation and cohesion to protect themselves from African clawed frogs. In amphibian tadpoles, larger groups experience more attacks, but they have lower per capita predation rates (Spieler, 2003). Furthermore, previous studies showed that prey use information about conspecific density to adjust their defences (Davenport & Chalcraft, 2014; Guadin et al., 2021). In general, behavioural responses to predation risk are short-term reversible strategies (Relyea, 2001; Turner, 1997), and they often serve as the first line of defence for native species when they are exposed to invasive predators (Sih et al., 2010). Therefore, aggregation could provide an effective generic antipredator strategy for tadpoles in response to invasive African clawed frogs. However, such antipredator behaviour could, in turn, help IAS detect tadpoles because of the increase in group size (Ioannou & Krause, 2008), thereby facilitating predation and contributing to the success of *X. laevis*.

Although escape behaviour is a well-known antipredator response to invasive red swamp crayfish (Marquis et al., 2004; Mathis & Gall, 2010; Nunes et al., 2013; Pearl et al., 2003), tadpoles did not increase their distance from the predator chamber when exposed to this species, which is contrary to our predictions. Considering that red swamp crayfish were introduced in France approximately 100 years ago, similar or more marked antipredator behaviours were expected compared with those displayed in response to the African clawed frog that was introduced more recently. Such an unexpected result has been previously observed in the Iberian water frog, *Pelophylax perezi* (Nunes et al., 2014). Long-term invaded populations consistently presented low activity levels, which serve as an immediate antipredator mechanism (Nicieza, 1999; Toscano, 2017) or modified morphological defences (e.g. deeper tails) as antipredator responses (Nunes et al., 2014). By contrast, they did not show context-dependent antipredator
<caption>**Table 3**</caption>

Post hoc Tukey test examining the effect of predators and contrasting five classes with regard to the difference in mean interindividual distances, nearest neighbour distance and distance to the predator chamber between the predator exposure and pre-exposure periods of *Pelophylax* spp. tadpoles

<table><thead><tr><th rowspan="3">Contrast</th><th colspan="4">Behavioural response variables</th></tr><tr><th colspan="2">Interindividual distances</th><th colspan="2">Nearest neighbour distance</th><th colspan="2">Distance to predator</th></tr><tr><th>Estimate ± SE</th><th>P</th><th>Estimate ± SE</th><th>P</th><th>Estimate ± SE</th><th>P</th></tr></thead><tbody><tr><td>PF-CR</td><td>-0.384 ± 0.423</td><td>0.894</td><td>4.771 ± 3.654</td><td>0.653</td><td>-1.327 ± 0.604</td><td>0.181</td></tr><tr><td>WF-CR</td><td>-0.616 ± 0.454</td><td>0.655</td><td>5.034 ± 3.710</td><td>0.620</td><td>0.823 ± 0.630</td><td>0.687</td></tr><tr><td>OL-CR</td><td>-0.379 ± 0.431</td><td>0.904</td><td>8.027 ± 4.009</td><td>0.233</td><td>0.465 ± 0.638</td><td>0.949</td></tr><tr><td>CF-CR</td><td><strong>-1.815 ± 0.423</strong></td><td><strong>&lt;0.001</strong></td><td>1.504 ± 3.584</td><td>0.992</td><td><strong>3.887 ± 0.593</strong></td><td><strong>&lt;0.001</strong></td></tr><tr><td>WF-PF</td><td>-0.232 ± 0.461</td><td>0.987</td><td>0.262 ± 1.368</td><td>0.999</td><td><strong>2.150 ± 0.600</strong></td><td><strong>0.003</strong></td></tr><tr><td>OL-PF</td><td>0.005 ± 0.435</td><td>1.000</td><td>3.256 ± 2.045</td><td>0.463</td><td>0.862 ± 0.604</td><td>0.610</td></tr><tr><td>CF-PF</td><td><strong>-1.431 ± 0.423</strong></td><td><strong>0.006</strong></td><td><strong>-3.267 ± 0.977</strong></td><td><strong>0.006</strong></td><td><strong>5.214 ± 0.601</strong></td><td><strong>&lt;0.001</strong></td></tr><tr><td>OL-WF</td><td>0.237 ± 0.431</td><td>0.981</td><td>2.994 ± 2.143</td><td>0.593</td><td>-1.289 ± 0.593</td><td>0.190</td></tr><tr><td>CF-WF</td><td>-1.199 ± 0.465</td><td>0.074</td><td><strong>-3.529 ± 1.169</strong></td><td><strong>0.018</strong></td><td>3.064 ± 0.624</td><td><strong>&lt;0.001</strong></td></tr><tr><td>CF-OL</td><td><strong>-1.436 ± 0.436</strong></td><td><strong>0.009</strong></td><td><strong>-6.523 ± 1.918</strong></td><td><strong>0.005</strong></td><td><strong>4.352 ± 0.631</strong></td><td><strong>&lt;0.001</strong></td></tr></tbody></table>

PF: plastic frog, WF: water frog *Pelophylax* spp., CF: African clawed frog *Xenopus laevis*, CR: red swamp crayfish *Procambarus clarkii*, OL: Odonata larvae. Significant effects are shown in boldface (P < 0.05).

behaviour influenced by factors such as developmental stage, social environment and predator cues (that is, aggregation and predator avoidance; Nicieza, 1999), as we observed in response to African clawed frogs.

Overall, although failures of alien predator recognition by native prey are common because of the lack of shared evolutionary history (Sih et al., 2010), our study shows that native prey can recognize and respond to the presence of an IAS approximately 40 years after its introduction, with responses being more pronounced compared with those to native or long-term invasive predators. Conducting further studies is necessary to determine whether the observed responses are more likely to result from rapid adaptive responses (Phillips & Shine, 2006) or from more generic antipredator strategies (Carthey & Banks, 2014; Cox & Lima, 2006).

## Conclusion

In this study, predators, particularly African clawed frogs, induced significant indirect impacts of predation rather than direct effects (Creel & Christianson, 2008). These indirect effects could influence the demographic parameters of populations (Zanette et al., 2011). The significantly negative effects of IAS on the population dynamics of native species have also been revealed, including amphibians, where fitness, survival and reproductive success decline in the presence of IAS (Nunes et al., 2019). The grouping strategies adopted by larval stages exposed to a threat may lead to temporary competition for resources among individuals during a crucial growth period and may affect size at metamorphosis, development and survival (Richter-Boix et al., 2004). The exacerbated responses to IAS are particularly concerning, as they can lead to major disruptions in ecosystems. Furthermore, this study highlights the ability of amphibian tadpoles to adjust their behaviour in the presence of invasive alien predators, thereby shedding light on the significant predation risk posed by alien predators and the remarkable ability of native prey to recognize and respond to these threats over approximately 40 years. The responses observed in tadpoles that had never been exposed to a predator indicate the significant adaptive potential of populations in the face of human-induced rapid environmental changes (Sih et al., 2011). These findings indicate the significant risk effects that IAS can induce and the ecological challenges they pose to native ecosystems.

## Author Contributions

**Manon Bonnet:** Writing – review & editing, Data curation. **Tatiana Colchen:** Writing – review & editing, Writing – original draft, Validation, Supervision, Project administration, Methodology, Investigation, Formal analysis, Data curation, Conceptualization. **Clément Harmange:** Writing – review & editing, Formal analysis. **Eléonore Moreau:** Writing – review & editing, Data curation. **Julien Morin:** Data curation. **Alain Pagano:** Writing – review & editing, Validation, Supervision, Project administration, Methodology, Investigation, Funding acquisition, Conceptualization. **Olivier Pays:** Writing – review & editing, Validation, Supervision, Project administration, Funding acquisition, Formal analysis, Conceptualization.

## Data Availability

A file with the behavioural data and fixed factors used for statistical analyses is available as Supplementary Material.

## Declaration of Interest

The authors declare no conflicts of interest.

## Acknowledgments

We would like to thank Vinci Autoroute for allowing access to the ponds, J. Secondi for providing administrative support for ethical approval procedures and V. Chureau for providing administrative and technical support. We are also grateful to the three anonymous referees for their valuable suggestions.

## Supplementary Material

Supplementary material associated with this article is available at https://doi.org/10.1016/j.anbehav.2025.123255.

## References

Altendorf, K. B., Laundre, J. W., González, C. A. L., & Brown, J. S. (2001). Assessing effects of predation risk on foraging behaviour of mule deer. *Journal of Mammalogy*, 82(2), 430–439. https://doi.org/10.1644/1545-1542(2001)082<0430:AЕОРО>2.0.CO;2
Anson, J. R., & Dickman, C. R. (2013). Behavioral responses of native prey to disparate predators: Naïveté and predator recognition. *Oecologia*, **171**(2), 367–377. https://doi.org/10.1007/s00442-012-2424-7

Balestrieri, A., Gazzola, A., Pellitteri-Rosa, D., & Vallortigara, G. (2019). Discrimination of group numerousness under predation risk in anuran tadpoles. *Animal Cognition*, **22**(2), 223–230. https://doi.org/10.1007/s10071-019-01238-5

Barta, Z., Liker, A., & Mónus, F. (2004). The effects of predation risk on the use of social foraging tactics. *Animal Behaviour*, **67**(2), 301–308. https://doi.org/10.1016/j.anbehav.2003.06.012

Basille, M., Fortin, D., Dussault, C., Bastille-Rousseau, G., Ouellet, J.-P., & Courtois, R. (2015). Plastic response of fearful prey to the spatiotemporal dynamics of predator distribution. *Ecology*, **96**(10), 2622–2631. https://doi.org/10.1890/14-1706.1

Blackburn, T. M., Cassey, P., Duncan, R. P., Evans, K. L., & Gaston, K. J. (2004). Avian extinction and mammal introductions on oceanic islands. *Science*, **305** (5692), 1955–1958. https://doi.org/10.1126/science.1101617

Blackburn, T. M., Pysek, P., Bacher, S., Carlton, J. T., Duncan, R. P., Jarošík, V., Wilson, J. R. U., & Richardson, D. M. (2011). A proposed unified framework for biological invasions. *Trends in Ecology & Evolution*, **26**(7), 333–339. https://doi.org/10.1016/j.tree.2011.03.023

Bland, J. D., & Temple, S. A. (1990). Effects of predation-risk on habitat use by Himalayan Snowcocks. *Oecologia*, **82**(2), 187–191. https://doi.org/10.1007/BF00323534

Bleach, I., Beckmann, C., Brown, G. P., & Shine, R. (2014). Effects of an invasive species on refuge-site selection by native fauna: The impact of cane toads on native frogs in the Australian tropics. *Austral Ecology*, **39**(1), 50–59. https://doi.org/10.1111/aec.12044

Blumstein, D. T., Daniel, J. C., & Springett, B. P. (2004). A test of the multi-predator hypothesis: Rapid loss of antipredator behavior after 130 years of isolation. *Ethology*, **110**(11), 919–934. https://doi.org/10.1111/j.1439-0310.2004.01033.x

Buchanan, A. L., Hermann, S. L., Lund, M., & Szendrei, Z. (2017). A meta-analysis of non-consumptive predator effects in arthropods: The influence of organismal and environmental characteristics. *Oikos*, **126**(9), 1233–1240. https://doi.org/10.1110/oik.04384

Buske, C., & Gerlai, R. (2011). Early embryonic ethanol exposure impairs shoaling and the dopaminergic and serotoninergic systems in adult zebrafish. *Neurotoxicology and Teratology*, **33**(6), 698–707. https://doi.org/10.1016/j.ntt.2011.05.009

Carthey, A. J. R., & Banks, P. B. (2014). Naïveté in novel ecological interactions: Lessons from theory and experimental evidence. *Biological Reviews*, **89**(4), 932–949. https://doi.org/10.1111/brv.12087

Carthey, A. J. R., Bucknall, M. P., Wierucka, K., & Banks, P. B. (2017). Novel predators emit novel cues: A mechanism for prey naivety towards alien predators. *Scientific Reports*, **7**(1), Article 16377. https://doi.org/10.1038/s41598-017-16656-z

Chiara, V., & Kim, S. (2023). AnimalTA: A highly flexible and easy-to-use program for tracking and analysing animal movement in different environments. *Methods in Ecology and Evolution*, **14**(7), 1699–1707. https://doi.org/10.1111/2041-210X.14115

Cooper, J., & Blumstein, D. (2015). Escaping from predators: An Integrative view of escape decisions. https://doi.org/10.1017/CBO9781107447189.

Courant, J., Secondi, J., Vollette, J., Herrel, A., & Thirion, J.-M. (2018). Assessing the impacts of the invasive frog, *Xenopus laevis*, on amphibians in western France. *Amphibia-Reptilia*, **39**(2), 219–227. https://doi.org/10.1163/15685381-17000153

Courant, J., Vogt, S., Marques, R., Measey, J., Secondi, J., Rebelo, R., De Villiers, A., Ihlow, F., De Busschere, C., Backeljau, T., Rödder, D., & Herrel, A. (2017). Are invasive populations characterized by a broader diet than native populations? *PeerJ*, **5**, Article e3250. https://doi.org/10.7717/peerj.3250

Cox, J., & Lima, S. (2006). Naïveté and an aquatic–terrestrial dichotomy in the effects of introduced predators. *Trends in Ecology & Evolution*, **21**(12), 674–680. https://doi.org/10.1016/j.tree.2006.07.011

Crawford, D. A., Conner, L. M., Morris, G., & Cherry, M. J. (2020). Predation risk increases intraspecific heterogeneity in white-tailed deer die activity patterns. *Behavioral Ecology*, **32**(1), 41–48. https://doi.org/10.1093/beheco/araa089

Crayon, J. J. (2005). Family pipidæ. In M. Lannoo (Ed.), *The conservation status of United States species* (pp. 522–526). University of California Press. https://doi.org/10.1525/9780520929432-065.

Creel, S., & Christianson, D. (2008). Relationships between direct predation and risk effects. *Trends in Ecology & Evolution*, **23**(4), 194–201. https://doi.org/10.1016/j.tree.2007.12.004

Creel, S., Schuette, P., & Christianson, D. (2014). Effects of predation risk on group size, vigilance, and foraging behavior in an African ungulate community. *Behavioral Ecology*, **25**(4), 773–784. https://doi.org/10.1093/beheco/aru050

D'Amore, A., Kirby, E., & McNicholas, M. (2009). Invasive species shifts ontogenetic resource partitioning and microhabitat use of a threatened native amphibian. *Aquatic Conservation: Marine and Freshwater Ecosystems*, **19**(5), 534–541. https://doi.org/10.1002/aqc.1026

Davenport, J. M., & Chalcraft, D. R. (2014). Increasing conspecific density weakens the ability of intermediate predators to develop induced morphological defences to top predators. *Freshwater Biology*, **59**(1), 87–99. https://doi.org/10.1111/fwb.12248

Davenport, J. M., King, A. B., Riley, A. W., Hampson, M. E., & Constantinides, P. (2020). The non-consumptive effects of predators and personality on prey growth and mortality. *Ethology*, **126**(3), 363–371. https://doi.org/10.1111/eth.12981

Dittmann, L., & Schausberger, P. (2017). Adaptive aggregation by spider mites under predation risk. *Scientific Reports*, **7**(1), Article 10609. https://doi.org/10.1038/s41598-017-10819-8

Early, R., Bradley, B. A., Dukes, J. S., Lawler, J. J., Olden, J. D., Blumenthal, D. M., Gonzalez, P., Grosholz, E. D., Ibañez, I., Miller, L. P., Sorte, C. J. B., & Tatem, A. J. (2016). Global threats from invasive alien species in the twenty-first century and national response capacities. *Nature Communications*, **7**(1), Article 12485. https://doi.org/10.1038/ncomms12485

Faraway, J. J. (2006). Extending linear model with R: Generalized linear, mixed effects and nonparametric regression. Chapman & Hall/CRC.

Ferrari, M. C. O., & Chivers, D. P. (2010). The ghost of predation future: Threat-sensitive and temporal assessment of risk by embryonic woodfrogs. *Behavioral Ecology and Sociobiology*, **64**(4), 549–555. https://doi.org/10.1007/s00265-009-0870-y

Flores, C. A., Crossland, M. R., Arreortúa, M., & González-Bernal, E. (2024). Responses of showy leopard frog larvae (*Lithobates spectabilis*) to the presence of introduced rainbow trout in Mexico. *Aquatic Conservation: Marine and Freshwater Ecosystems*, **34**(9), Article e4254. https://doi.org/10.1002/aqc.4254

Fouquet, A. (2001). Des clandestins aquatiques. *Zamenis*, **6**, 10–11.

Fraker, M. E. (2008). The dynamics of predation risk assessment: Responses of anuran larvae to chemical cues of predators. *Journal of Animal Ecology*, **77**(4), 638–645. https://doi.org/10.1111/j.1365-2656.2008.01386.x

Fraker, M. E. (2010). Risk assessment and anti-predator behavior of wood frog (*Rana sylvatica*) tadpoles: A comparison with green frog (*Rana clamitans*) tadpoles. *Journal of Herpetology*, **44**(3), 390–398. https://doi.org/10.1670/09-033.1

Gall, B. G., & Mathis, A. (2010). Response of native and introduced fishes to presumed antipredator secretions of Ozark hellbenders (*Cryptobranchus alleganiensis bishoi*). *Behaviour*, **147**(13–14), 1769–1789. https://doi.org/10.1163/000579510X535749

Gazzola, A., Balestrieri, A., Martín, J., & Pellitteri-Rosa, D. (2018). Is it worth the risk? Food Deprivation effects on tadpole anti-predatory responses. *Evolutionary Biology*, **45**(1), 67–74. https://doi.org/10.1007/s11692-017-9430-y

Gentili, R., Schaffner, U., Martinoli, A., & Citterio, S. (2021). Invasive alien species and biodiversity: Impacts and management. *Biodiversity*, **22**(1–2), 1–3. https://doi.org/10.1080/14888386.2021.1929484

Gherardi, F. (2006). Crayfish invading Europe: The case study of *Procambarus clarkii*. *Marine and Freshwater Behaviour and Physiology*, **39**(3), 175–191. https://doi.org/10.1080/10236240600869702

Gliwicz, Z. M. (1994). Relative significance of direct and indirect effects of preda- tion by planktivorous fish on zooplankton. *Hydrobiologia*, **272**(1), 201–210. https://doi.org/10.1007/BF00006521

Guadin, B., Gazzola, A., Balestrieri, A., Scribano, G., Martín, J., & Pellitteri-Rosa, D. (2021). Effects of a group-living experience on the antipredator responses of individual tadpoles. *Animal Behaviour*, **180**, 93–99. https://doi.org/10.1016/j.anbehav.2021.08.009

Hamilton, W. D. (1971). Geometry for the selfish herd. *Journal of Theoretical Biology*, **31**(2), 295–311. https://doi.org/10.1016/0022-5193(71)90189-5

Hammer, T. L., Bize, P., Gineste, B., Robin, J.-P., Groscolas, R., & Viblanc, V. A. (2023). Disentangling the "many-eyes", "dilution effect", "selfish herd", and "distracted prey" hypotheses in shaping alert and flight initiation distance in a colonial seabird. *Behavioural Processes*, **210**(7), Article 104919. https://doi.org/10.1016/j.beproc.2023.104919

Hammond, T. T., Jacobs, L. E., Curtis, M. J., Trotman, E. M., Swaisgood, R. R., & Shier, D. M. (2024). Early life experience with predators impacts development, behavior, and post-translocation outcomes in an endangered amphibian. *Animal Conservation*, **27**(1), 23–36. https://doi.org/10.1111/acv.12880

Hebblewhite, M., Pletscher, D. H., & Paquet, P. C. (2002). Elk population dynamics in areas with and without predation by recolonizing wolves in Banff National Park, Alberta. *Canadian Journal of Zoology*, **80**(5), 789–799. https://doi.org/10.1139/z02-058

Heins, D. C., Knoper, H., & Baker, J. A. (2016). Consumptive and non-consumptive effects of predation by introduced northern pike on life-history traits in threespine stickback. *Evolutionary Ecology Research*, **17**(3), 355–372.

Hermann, S. L., & Landis, D. A. (2017). Scaling up our understanding of non-consumptive effects in insect systems. *Current Opinion in Insect Science*, **20**, 54–60. https://doi.org/10.1016/j.cois.2017.03.010

Hettrey, A., Vågi, B., Török, J., & Hoi, H. (2012). Allocation in reproduction is not tailored to the probable number of matings in common toad (*Bufo bufo*) males. *Behavioral Ecology and Sociobiology*, **66**(2), 201–208. https://doi.org/10.1007/s00265-011-1267-2

Hill, J. M., & Heck, K. L. (2015). Non-consumptive effects of avian predators on fish behavior and cascading indirect interactions in seagrasses. *Oikos*, **124**(6), 750–761. https://doi.org/10.1111/oik.01774

Hossie, T., Landolt, K., & Murray, D. L. (2017). Determinants and co-expression of anti-predator responses in amphibian tadpoles: A meta-analysis. *Oikos*, **126**(2), Article oik.03305. https://doi.org/10.1111/oik.03305

Hothorn, T., Bretz, F., & Westfall, P. (2002). multcomp: Simultaneous inference in general parametric models, 14–25 https://doi.org/10.32614/CRAN/package.multcomp.

Ioannou, C. C., Bartumeus, F., Krause, J., & Ruxton, G. D. (2011). Unified effects of aggregation reveal larger prey groups take longer to find. *Proceedings of the Royal Society B: Biological Sciences*, **278**(1720), 2985–2990. https://doi.org/10.1098/rspb.2011.0003
Ioannou, C. C., & Krause, J. (2008). Searching for prey: The effects of group size and number. *Animal Behaviour, 75*(4), 1383–1388. https://doi.org/10.1016/j.anbehav.2007.09.012

Jarvis, L. E. (2010). Non-consumptive effects of predatory three-spined sticklebacks (*Gasterosteus aculeatus*) on great crested newt (*Triturus cristatus*) embryos. *Herpetological Journal*, 20(4), 271–275.

Kloskowski, J. (2018). Total non-consumptive effects of fish on *Pelobates fuscus* and *Hyla orientalis* tadpoles in pond enclosure experiments. *Zoological Science*, 35 (6), 528. https://doi.org/10.2108/zs180036

Kovacs, E. K., Crowther, M. S., Webb, J. K., & Dickman, C. R. (2012). Population and behavioural responses of native prey to alien predation. *Oecologia*, 168(4), 947–957. https://doi.org/10.1007/s00442-011-2168-9

Landeau, L., & Terborgh, J. (1986). Oddity and the 'confusion effect' in predation. *Animal Behaviour*, 34(5), 1372–1380.

Laurila, A. (2000). Behavioural responses to predator chemical cues and local variation in antipredator performance in *Rana temporaria* tadpoles. *Oikos*, 88 (1), 159–168. https://doi.org/10.1034/j.1600-0706.2000.880118.x

Le Roux, E., Kerley, G. I. H., & Cromsigt, J. P. G. M. (2018). Megaherbivores modify trophic cascades triggered by fear of predation in an African savanna ecosystem. *Current Biology*, 28(15), 2493–2499.e3. https://doi.org/10.1016/j.cub.2018.05.088

Lehtonen, H., Hansson, S., & Winkler, H. (1996). Biology and exploitation of pike-perch, *Stizostedion lucioperca* (L.), in the Baltic Sea area. *Annales Zoologici Fennici*, 33(3), 525–535.

Lima, S. L. (1995). Back to the basics of anti-predatory vigilance: The group-size effect. *Animal Behaviour*, 49(1), 11–20. https://doi.org/10.1016/0003-3472(95) 01049-9

Luedtke, J. A., Chanson, J., Neam, K., Hobin, L., Maciel, A. O., Catenazzi, A., Borzée, A., Hamidy, A., Aowphol, A., Jean, A., Sosa-Bartuano, A., Fong, G. A., De Silva, A., Fouquet, A., Angulo, A., Kidov, A. A., Muñoz Saravia, A., Diesmos, A. C., Tominaga, A., ... Stuart, S. N. (2023). Ongoing declines for the world's amphibians in the face of emerging threats. *Nature*, 622(7982), 308–314. https:// doi.org/10.1038/s41586-023-06578-4

Méndez-Méndez, O., Sánchez-Sánchez, R., Hernández-Luria, J., Smith, G. R., & Lemos-Espinal, J. A. (2023). Behavioural response of *Dryophytes plicatus* tadpoles to the cues of non-native rainbow trout and a native snake. *Amphibia-Reptilia*, 44(4), 517–523.

Marquis, O., Saglio, P., & Neveu, A. (2004). Effects of predators and conspecific chemical cues on the swimming activity of *Rana temporaria* and *Bufo bufo* tadpoles. *Archiv Fur Hydrobiologie*, 160(2), 153–170. https://doi.org/10.1127/ 0003-9136/2004/0160-0153

Mathis, A., & Gall, B. (2010). Response of native and introduced fishes to presumed antipredator secretions of Ozark hellbenders (*Cryptobranchus alleganiensis* bishopi). *Behaviour*, 147(13–14), 1769–1789. https://doi.org/10.1163/ 000579510X535749

Measey, G. J., Rödder, D., Green, S. L., Kobayashi, R., Lillo, F., Lobos, G., Rebelo, R., & Thirion, J.-M. (2012). Ongoing invasions of the African clawed frog, *Xenopus laevis*: A global review. *Biological Invasions*, 14(11), 2255–2270. https://doi.org/ 10.1007/s10530-012-0227-8

Melotto, A., Ficetola, G. F., Pennati, R., Ancona, N., & Manenti, R. (2021). Raised by aliens: Constant exposure to an invasive predator triggers morphological but not behavioural plasticity in a threatened species tadpoles. *Biological Invasions*, 23(12), 3777–3793. https://doi.org/10.1007/s10530-021-02603-7

Mitchell, M. D., & Harborne, A. R. (2020). Non-consumptive effects in fish predator-prey interactions on coral reefs. *Coral Reefs*, 39(4), 867–884. https:// doi.org/10.1007/s00338-020-01920-y

Moll, R. J., Killion, A. K., Montgomery, R. A., Tambling, C. J., & Hayward, M. W. (2016). Spatial patterns of African ungulate aggregation reveal complex but limited risk effects from reintroduced carnivores. *Ecology*, 97(5), 1123–1134. https://doi.org/10.1890/15-0707.1

Moreira, F., Marques, R., Sousa, M., & Rebelo, R. (2017). Breeding in both lotic and lentic habitats explains the invasive potential of the African clawed frog (*Xenopus laevis*) in Portugal. *Aquatic Invasions*, 12(4), 565–574. https://doi.org/ 10.3391/ai.2017.12.412

Nelson, E. H., Matthews, C. E., & Rosenheim, J. A. (2004). Predators reduce prey population growth by inducing changes in prey behaviour. *Ecology*, 85(7), 1853–1858. https://doi.org/10.1890/03-3109

Nicieza, A. G. (1999). Context-dependent aggregation in common frog *Rana temporaria* tadpoles: Influence of developmental stage, predation risk and social environment. *Functional Ecology*, 13(6), 852–858. https://doi.org/10.1046/ j.1365-2435.1999.00375.x

Nunes, A. L., Fill, J. M., Davies, S. J., Louw, M., Rebelo, A. D., Thorp, C. J., Vimercati, G., & Measey, J. (2019). A global meta-analysis of the ecological impacts of alien species on native amphibians. *Proceedings of the Royal Society B: Biological Sciences*, 286(1897), Article 20182528. https://doi.org/10.1098/rspb.2018.2528

Nunes, A. L., Orizaola, G., Laurila, A., & Rebelo, R. (2014). Rapid evolution of constitutive and inducible defenses against an invasive predator. *Ecology*, 95 (6), 1520–1530. https://doi.org/10.1089/13-1380.1

Nunes, A. L., Richter-Boix, A., Laurila, A., & Rebelo, R. (2013). Do anuran larvae respond behaviourally to chemical cues from an invasive crayfish predator? A community-wide study. *Oecologia*, 171(1), 115–127. https://doi.org/10.1007/ s00442-012-2389-6

Pays, O., Blanchard, P., Chamaillé-Jammes, S., Valeix, M., LovPIDGE, A. J., Macdonald, D. W., Périquet, S., Van Der Meer, E., Duncan, P., Mtaré, G., & Fritz, H. (2021). Disentangling the roles of bottom-up and top-down drivers in

the trade-off between food acquisition and safety in prey with multiple predators. *Functional Ecology*, 35(2), 435–449. https://doi.org/10.1111/1365- 2435.13710

Peacor, S. D., Barton, B. T., Kimbro, D. L., Sih, A., & Sheriff, M. J. (2020). A framework and standardized terminology to facilitate the study of predation-risk effects. *Ecology*, 101(12), Article e03152. https://doi.org/10.1002/ecy.3152

Peacor, S. D. (2003). Phenotypic modifications to conspecific density arising from predation risk assessment. *Oikos*, 100(2), 409–415. https://doi.org/10.1034/ j.1600-0706.2003.12043.x

Peacor, S. D., & Werner, E. E. (2001). The contribution of trait-mediated indirect effects to the net effects of a predator. *Proceedings of the National Academy of Sciences*, 98(7), 3904–3908. https://doi.org/10.1073/pnas.071061998

Pearl, C. A., Adams, M. J., Schuytema, G. S., & Nebeker, A. V. (2003). Behavioral responses of anuran larvae to chemical cues of native and introduced predators in the Pacific Northwestern United States. *Journal of Herpetology*, 37(3), 572–576. https://doi.org/10.1670/134-02N

Phillips, B. L., & Shine, R. (2006). An invasive species induces rapid adaptive change in a native predator: Cane toads and black snakes in Australia. *Proceedings of the Royal Society B: Biological Sciences*, 273(1593), 1545–1550. https://doi.org/ 10.1098/rspb.2006.3479

Pinheiro, J., & Bates, D. (2024). *nlme*: Linear and nonlinear mixed effects models (p. 3.1-165). R Core Team. https://doi.org/10.32641/CRAN.packagelme.

Polo-Cavia, N., Gonzalo, A., López, P., & Martín, J. (2010). Predator recognition of native but not invasive turtle predators by naive anuran tadpoles. *Animal Behaviour*, 80(3), 461–466. https://doi.org/10.1016/j.anbehav.2010.06.004

Pujol-Buxó, E., San Sebastián, O., Garriga, N., & Llorente, G. A. (2013). How does the invasive/native nature of species influence tadpoles' plastic responses to predators? *Oikos*, 122(1), 19–29. https://doi.org/10.1111/j.1600-0706.2012.20617.x

Pysek, P., Hulme, P. E., Simberloff, D., Bacher, S., Blackburn, T. M., Carlton, J. T., Dawson, W., Essl, F., Foxcroft, L. C., Genovesi, P., Jeschke, J. M., Kühn, I., Liebhold, A. M., Mandrak, N. E., Meyerson, L. A., Pauchard, A., Pergl, J., Roy, H. E., Seebens, H., ... Richardson, D. M. (2020). Scientists' warning on invasive alien species. *Biological Reviews*, 95(6), 1511–1534. https://doi.org/10.1111/brv.12627

R Core Team. (2022). *R: A language and environment for statistical computing*. R Foundation for Statistical Computing. https://www.R-project.org.

Rehage, J. S., Dunlop, K. L., & Loftus, W. F. (2009). Antipredator responses by native mosquitofish to non-native cichlids: An examination of the role of prey naïveté. *Ethology*, 115(11), 1046–1056. https://doi.org/10.1111/j.1439- 0310.2009.01694.x

Relyea, R. A. (2001). The relationship between predation risk and antipredator responses in larval anurans. *Ecology*, 82(2), 541–554. https://doi.org/10.1890/ 0012-9658(2001)082[0541:TRBPRA]2.0.CO;2

Richter-Boix, A., Llorente, G. A., & Montori, A. (2004). Responses to competition effects of two anuran tadpoles according to life-history traits. *Oikos*, 106(1), 39–50. https://doi.org/10.1111/j.0030-1299.2004.12743.x

Ross, J., Hearn, A. J., Johnson, P. J., & Macdonald, D. W. (2013). Activity patterns and temporal avoidance by prey in response to Sunda clouded leopard predation risk. *Journal of Zoology*, 290(2), 96–106. https://doi.org/10.1111/jzo.12018

Roy, H. E., Pauchard, A., Stoett, P., Renard Truong, T., Bacher, S., Galil, B. S., Hulme, P. E., Ikeda, T., Sankaran, K., McGeoch, M. A., Meyerson, L. A., Nunez, M. A., Ordonez, A., Rahlao, S. J., Schwindt, E., Seebens, H., Sheppard, A. W., & Vandvik, V. (2024). IPBES invasive alien species assessment: Summary for policymakers. *Zenodo*. https://doi.org/10.5281/ZENODO.7430692 (Version 3)

Saidapur, S. K., Veeranagoudar, D. K., Hiragond, N. C., & Shanbhag, B. A. (2009). Mechanism of predator-prey detection and behavioral responses in some anuran tadpoles. *Chemoecology*, 19(1), 21–28. https://doi.org/10.1007/s00049- 009-0004-z

Scribano, G., Balestrieri, A., Gazzola, A., & Pellitteri-Rosa, D. (2020). Strong behavioural defensive responses of endemic *Rana latastei* tadpoles induced by a native predator's odour. *Ethology*, 126(9), 922–930. https://doi.org/10.1111/ eth.13072

Sheriff, M. J., Peacor, S. D., Hawlena, D., & Thaker, M. (2020). Non-consumptive predator effects on prey population size: A dearth of evidence. *Journal of Animal Ecology*, 89(6), 1302–1316. https://doi.org/10.1111/1365-2656.13213

Sih, A. (1994). Predation risk and the evolutionary ecology of reproductive behaviour. *Journal of Fish Biology*, 45(sA), 111–130. https://doi.org/10.1111/j. 1095-8649.1994.tb01087.x

Sih, A., Bolnick, D. I., Luttbeg, B., Orrock, J. L., Peacor, S. D., Pintor, L. M., Preisser, E., Rehage, J. S., & Vonesh, J. R. (2010). Predator-prey naïveté, antipredator behavior, and the ecology of predator invasions. *Oikos*, 119(4), 610–621. https:// doi.org/10.1111/j.1600-0706.2009.18039.x

Sih, A., Ferrari, M. C. O., & Harris, D. J. (2011). Evolution and behavioural responses to human-induced rapid environmental change. *Evolutionary Applications*, 4(2), 367–387. https://doi.org/10.1111/j.1752-4571.2010.00166.x

Sih, A., Hanser, S. F., & McHugh, K. A. (2009). Social network theory: New insights and issues for behavioral ecologists. *Behavioral Ecology and Sociobiology*, 63(7), 975–988. https://doi.org/10.1007/s00265-009-0725-6

Sorato, E., Gullett, P. R., Griffith, S. C., & Russell, A. F. (2012). Effects of predation risk on foraging behaviour and group size: Adaptations in a social cooperative species. *Animal Behaviour*, 84(4), 823–834. https://doi.org/10.1016/j. anbehav.2012.07.003

Spieler, M. (2003). Risk of predation affects aggregation size: A study with tadpoles of *Phrynomantis microps* (Anura: Microhylidae). *Animal Behaviour*, 65(1), 179–184. https://doi.org/10.1006/anbe.2002.2030
Stav, G., Kotler, B. P., & Blaustein, L. (2007). Direct and indirect effects of dragonfly (Anax imperator) nymphs on green toad (Bufo viridis) tadpoles. *Hydrobiologia*, **579**(1), 85-93. https://doi.org/10.1007/s10750-006-0388-5

Stynoski, J., & Noble, V. (2012). To beg or to freeze: Multimodal sensory integration directs behavior in a tadpole. *Behavioral Ecology and Sociobiology*, **66**, https://doi.org/10.1007/s00265-011-1266-3

Teplitsky, C., Plenet, S., & Joly, P. (2004). Hierachical responses of tadpoles to multiple predators. *Ecology*, **85**(10), 2888-2894. https://doi.org/10.1890/03-3043

Thorp, C. J., Vonesh, J. R., & Measey, J. (2019). Cannibalism or congeneric predation? The African clawed frog, *Xenopus laevis* (Daudin), preferentially predates on larvae of Cape platannas, *Xenopus gilli* Rose & Hewitt. *African Journal of Ecology*, **57**(1), 59-65. https://doi.org/10.1111/aje.12577

Toscano, B. J. (2017). Prey behavioural reaction norms: Response to threat predicts susceptibility to predation. *Animal Behaviour*, **132**, 147-153. https://doi.org/10.1016/j.anbehav.2017.08.014

Turner, A. M. (1997). Contrasting short-term and long-term effects of predation risk on consumer habitat use and resources. *Behavioral Ecology*, **8**(2), 120-125. https://doi.org/10.1093/beheco/8.2.120

Van Buskirk, J., Ferrari, M., Kueng, D., Näpflin, K., & Ritter, N. (2011). Prey risk assessment depends on conspecific density. *Oikos*, **120**(8), 1235-1239. https://doi.org/10.1111/j.1600-0706.2010.19311.x

Van Sittert, L., & Measey, G. J. (2016). Historical perspectives on global exports and research of African clawed frogs (*Xenopus laevis*). *Transactions of the Royal Society of South Africa*, **71**(2), 157-166. https://doi.org/10.1080/0035919X.2016.1158747

Verdolin, J. L. (2006). Meta-analysis of foraging and predation risk trade-offs in terrestrial systems. *Behavioral Ecology and Sociobiology*, **60**(4), 457-464. https://doi.org/10.1007/s00265-006-0172-6

Vodrážková, M., Šetlíková, I., & Berec, M. (2020). Chemical cues of an invasive turtle reduce development time and size at metamorphosis in the

common frog. *Scientific Reports*, **10**(1), 7978. https://doi.org/10.1038/s41598-020-64899-0

Werner, E. E., Gilliam, J. F., Hall, D. J., & Mittelbach, G. G. (1983). An experimental test of the effects of predation risk on habitat use in fish. *Ecology*, **64**(6), 1540-1548. https://doi.org/10.2307/1937508

Willems, E. P., & Hill, R. A. (2009). Predator-specific landscapes of fear and resource distribution: Effects on spatial range use. *Ecology*, **90**(2), 546-555. https://doi.org/10.1890/08-0765.1

Wilson, E. A., Dudley, T. L., & Briggs, C. J. (2018). Shared behavioral responses and predation risk of anuran larvae and adults exposed to a novel predator. *Biological Invasions*, **20**(2), 475-485. https://doi.org/10.1007/s10530-017-1550-x

Wilson, N. J., & Williams, C. R. (2014). A critical review of freshwater crayfish as amphibian predators: Capable consumers of toxic prey? *Toxicon*, **82**, 9-17. https://doi.org/10.1016/j.toxicon.2014.02.005

Wittenberg, R. (2005). Invasive alien species—a threat to global biodiversity and opportunities to prevent and manage them. In S. Vidal, U. Kuhlmann, & C. R. Edwards (Eds.), *Western corn rootworm: Ecology and management* (pp. 1-28). CAB International. https://doi.org/10.1079/9780851998176.0001.

Woinarski, J. C. Z., Burbidge, A. A., & Harrison, P. L. (2015). Ongoing unraveling of a continental fauna: Decline and extinction of Australian mammals since European settlement. *Proceedings of the National Academy of Sciences*, **112**(15), 4531-4540. https://doi.org/10.1073/pnas.1417301112

Zanette, L. Y., Clinchy, M., & Suraci, J. P. (2014). Diagnosing predation risk effects on demography: Can measuring physiology provide the means? *Oecologia*, **176**(3), 637-651. https://doi.org/10.1007/s00442-014-3057-9

Zanette, L. Y., White, A. F., Allen, M. C., & Clinchy, M. (2011). Perceived predation risk reduces the number of offspring songbirds produce per year. *Science*, **334** (6061), 1398-1401. https://doi.org/10.1126/science.1210908

Zhang, F., Zhao, J., Zhang, Y., Messenger, K., & Wang, Y. (2015). Antipredator behavioral responses of native and exotic tadpoles to novel predator. *Asian Herpetological Research*, **6**(1), 51-58. https://cstr.cn/32242.14.j.cnki.ahr.140023.