DOI: 10.5061/dryad.mgqnk991f
title: Data from: What need for speed? Lizards from islands missing predators sprint slower

description: Here we test the hypothesis that island species that have evolved in
 predator-poor environments have reduced locomotor abilities. More than 60%
 of recent recorded extinctions are from islands 1, and island taxa are
 often susceptible to invasive predators typically because of the loss of
 ancestral antipredator behaviors. While locomotor abilities are critical
 for escaping predation, little is known on how the presence of different
 types of native predators influences these abilities by maintaining
 selective pressure. To fill this gap, we documented sprint speed in the
 Aegean wall lizard (Podarcis erhardii) from Aegean islands (Greece) with
 varying levels of predation pressure. We show that on islands where
 mammalian predators were present, lizards sprinted fastest. Lizards
 sprinted at an intermediate speed where predators other than mammals were
 present, and lizards sprinted slowest on islands where no predators were
 present. These results indicate that lizards from the lowest-predation
 islands are most vulnerable and preventing the introduction of invasive
 predators should be prioritized for these island systems.
description: <strong>Study
 system</strong> The Cyclades
 archipelago is a cluster of land-bridge islands located in the central
 Aegean Sea (Greece). Since
 the end of the last glacial maximum approximately 18,000 years ago, rising
 sea levels have fragmented former mainland coastal regions.
 As Holocene sea level rise separated the area, populations of plants and
 animals also became increasingly isolated, thus setting the stage for the
 evolution of locally adapted island phenotypes. The study area
 has warm, long, dry summers and mild, rainy winters as is typical of
 Mediterranean region climates. Humans have inhabited the region for
 thousands of years, altering the vegetation through agriculture and animal
 grazing. Today island habitats consist typically of agricultural fields
 edged by dry-stone walls and embedded in a matrix of spiny,
 summer-deciduous, low-growing woody vegetation known
 as <em>phrygana</em>. The Aegean wall
 lizard (<em>Podarcis erhardii</em>, Lacertidae) is a
 medium-sized lizard, typically ranging in size from 48-78 mm from snout to
 vent.  <em>P. erhardii</em> is found throughout the southern
 Balkans, mainland Greece, and many Aegean islands, and is common
 throughout the Cyclades island group. The species has – with the exception
 of closed canopy forests – broad habitat preferences and can be found in
 particularly high densities in areas where appropriate refugia, like
 dry-stone walls are present. The diet of <em>P. erhardii</em>
 consists predominately of arthropods, although it occasionally includes
 vegetation and fruit. Aegean wall lizards are poor overwater dispersers
 and genetic studies confirm that each population has evolved in response
 to locally prevailing conditions since isolated by rising sea levels. More
 than 25 island subspecies are recognized reflecting the broad
 morphological and genetic variation found in the different Aegean islands
 and pronounced adaptation to local environments. <strong>Island
 Characteristics</strong> Study sites
 (N=22 see Fig. 1, Table 1) were selected to include a range of island
 sizes and ages (i.e. periods of isolation), as well as predation
 environments.  Using methods described more fully in Brock et al. and
 Pafilis et al., we assessed predator presence on an island by combining
 published information with field surveys for any direct (live or dead
 individuals) or indirect (burrows, fecal matter, tracks) evidence of
 predators. Predator species were grouped into six categories: rats (R),
 predatory mammals (M), raptorial birds (B), vipers (V), sand boas (SB),
 and other snakes (OS). Each predator category is characterized by distinct
 hunting strategies, which likely results in different antipredator
 behaviors. Rats (<em>Rattus rattus</em>), for example, are
 considered in a category distinct from “mammals” because in the Cyclades
 the rats are small, opportunistic predators that do not prey on lizards to
 the same effective capacity as feral cats (<em>Felis
 catus</em>) and stone martens (<em>Martes foina</em>)
 which use burst speed to capture prey. Snakes are separated into three
 categories based on hunting strategies. Vipers (<em>Vipera
 ammodytes</em>) are sit-and-wait predators that ambush and
 envenomate prey. Sand boas (<em>Eryx jaculus</em>) are
 constrictors that will prey on adult and juvenile lizards, but mostly feed
 on lizard eggs. ‘Other snakes’ includes several diurnal colubrid taxa
 (e.g. <em>Natrix natrix, Elaphe quatuorlineata, Dolichophis
 caspius</em>) that actively search for prey. Lizard
 population density measurements were taken along one 100 m-long, 5 m-wide
 transect within each study site.  Following established protocols, lizards
 seen or heard were counted by an observer (SS) while walking along the
 transect during peak hours of lizard activity (09:00-11:00, and
 15:00-17:00) and under optimal environmental conditions (20-25<sup>
 o</sup>C; sunny; windspeeds&lt;2Bf). Previous research has
 suggested that habitat openness is an important determinant of sprint
 speed. At each location, we measured habitat openness along a 100 m long
 transect randomly laid out within the habitat occupied by <em>P.
 erhardii</em> at that location. Substrate type, vegetation type and
 height above the ground were recorded at 1 m intervals along the transect.
 Areas with vegetation &lt;5cm high were categorized as open habitat
 amenable to rapid running. <strong>Animal Methods and
 Morphology</strong> Lizards were
 caught by noosing or baiting with mealworms (<em>Tenebrio
 </em>sp. larvae) during early summer (May-early July) 2016. A sample
 of 18-34 lizards were taken from each location. Each lizard was given a
 unique, temporary number on the back using a non-toxic marker. While in
 captivity, lizards were held in 60cm x 41.6cm x 33.7cm terraria, and were
 provided with water <em>ad libitum</em>, and fed mealworms
 once a day. Morphometric data, including snout to vent length (SVL), front
 and hind limb length, and hindleg span (hindspan) were measured using
 digital slide calipers.<sup> </sup>Lizards were sexed and body
 mass measurements were collected using a spring-loaded scale, (Pesola
 10020). Lizards were returned to the place of capture after all
 morphological and performance measurements were recorded. <strong>Sprint
 Trials</strong> Sprint speed was
 measured using a 230 cm long and 40 cm wide wooden racetrack. Every lizard
 ran 3 sprint trials to ensure that at least one good measure of sprint
 speed was obtained. Before each sprint trial, lizards were allowed to
 thermoregulate for at least an hour in a temperature gradient.
 Temperatures were taken by cloacal thermometer immediately after each
 trial. Trials were spaced at least 1 hour apart to allow the lizards time
 to recover. Using a video camera (GoPro; Hero Black 4; 1280 x 720 px),
 video of each trial was recorded at 240 frames per second; the camera was
 positioned 1.5 m above the racetrack, so that a clear dorsal view of the
 running lizard was visible for at least one full meter of the racetrack.
 Using the video analysis tool SAVRA (code: https://github.com/bkazez/savra) custom-built for Donihue, a measurement of the distance travelled between every 5 frame sequence was calculated, and fit with a quintic spline using the SPAPI function in MatLab (MathWorks Inc. 20) as described in Donihue in order to calculate velocity of the lizard in m/sec. The fastest of the three trials for each lizard was selected for use in analyses. Gravid females were excluded from the analysis, as were trials where individual lizards did not run normally. Stamina and sprint trials were run more than 12 hours apart to allow the lizards time to recover between measurements. <strong>Stamina Trials</strong> In addition to sprint trials, a subset of 20 lizards was randomly selected from each island sample to participate in stamina trials. Gravid females were further excluded from the analysis. Lizards were allowed to thermoregulate for an hour before each trial and temperatures were recorded by cloacal thermometer immediately before the start of each trial. Lizards were placed in a circular track, 2.71 m in circumference, with the bottom covered with sand. Researchers worked in pairs, the animal handler encouraged the lizard to run for as long as possible and the observer used a stopwatch to record the length of each trial to the nearest second. Lizards were encouraged to run along the track by light tapping on the base of the tail. A trial ended when an animal did not start running after ten tail taps and was unable right itself when flipped on its back. Three stamina trials were performed on each lizard, with at least 90 minutes between trials to allow for recovery. <strong>Statistical Analysis</strong> Performance (sprint speed and stamina), and most morphological values (SVL, hindlimb length, and hindspan length) and island characterics (island age, island area, and lizard density) were Log<sub>10</sub>-transformed to ensure normality of residuals. Visual inspection and heterogeneity tests confirmed that error variation was approximately Gaussian and uniformly distributed in all analyses. Pearson correlations were used to explore relationships between locomotor performance and morphological characteristics, as well as island characteristics (island age, island area, % open habitat, lizard density, and number of predator categories). We used a linear mixed model approach to analyze how sprint speed and stamina were influenced by different ecological drivers. Different predation variables were included in different models. All models included sex, lizard body size (snout-vent length), and lizard body temperature to control for these factors that are known to affect lizard running performance. Snout-vent length is typically used as a measure of body size, which is linked to stride length and sprint speed, and body temperature has also been broadly linked to sprint speed. Previous research in this study system suggested island age was important to other antipredator defenses, so it was included in the linear mixed model analysis for further examination.             We compared 8 <em>a priori</em> models to identify which predator types were most important in shaping sprint speed and stamina. Models looked at the presence or absence of any predators, total predation, and individual predator types. The binary “Zero Predation” model separated islands with no predators present from islands with any type of predator. The “Sum Predation” model summed all the predator types found on each island, assuming each predator type added equal predation pressure to the system as described in Brock et al. Alternatively, another model estimated an effect of each predator type individually and simultaneously (R+SB+V+B+OS+M). This model considers the fact that predator types are not the same and might each affect sprint speed or stamina in unique ways. Based on <em>a priori</em> knowledge, the other five models emphasized mammals (M) and predatory birds (B) as the predators most likely to affect locomotor performance. In order to catch prey, mammals stalk and chase prey, often capturing an animal after a burst of speed. Predatory birds utilize a similar approach: after locating prey from above they swoop down to capture an animal. Models of birds, mammals, and birds and mammals combined were calculated with and without separating the zero predation islands. Including zero predation has the effect of calculating whether other predators beyond mammals and/or birds had an impact on sprint speed. In order to, determine whether time of isolation influenced sprint speed and stamina, island age (Log<sub>10</sub>-transformed) was added as another fixed effect to the 8 models stated above. Models were then compared using Akaike Information Criteria, using AICc values and the associated Akaike weights. Finally, we examined a potential trade-off between stamina and sprint speed, after controlling for other potentially confounding factors. In a general linear model, stamina for each individual was predicted by the combined effects of maximum sprint speed, individual sex, snout vent length, and trial temperature.
description: The three main files used in the analyses were the Dataset 1,2,
 and 3 files. These files were used for sprint speed analysis, stamina
 analysis, and island averages respectively. However,
 there is a lot of additional data from video analysis. Every sprint video
 is available and is labeled as the island name and the number of the video
 (eg. Amorgos1.mp4) the can be found in the zip file for each location
 (i.e. Amorgos.zip). Video files were analyzed using the program SAVRA (see
 the link in the methods below), values from this program were then saved
 into an Excel file that was labeled with the island name (eg.
 Amorgos5.xlsx). These files were then used in Matlab to calculate velocity
 (code is in files: get_quintic_spline_and_max_va.m and
 run_for_all_the_lizards.m). Using this code we obtained velocity (sprint
 speed) values, that were then saved into Microsoft word documents (eg.
 amorgosvalues.docx). These values were then matched to the appropriate
 video, lizard, and trial. This information is available in the file
 (SemegenetAl Sprint Speed Trial Numbers.xlsx) some trials have more that
 one video listed because the quality of the video was poor or the lizard
 failed to run the full distance on camera. These values were then input
 into the Dataset 1 sprint speed file. Some trials were thrown out because
 values were significantly off. This data was then input into the main
 files used for analyses. Correlation tables are in the file labeled
 “SemegenetAl Pearson Correlations.” Results and syntax of mixed models are
 in the files labled “Sprint Mixed Model Outputs Log10 SemegenetAl” and
 (Stamina Mixed Model Outputs Log10 SemegenetAl”. A detailed methodology is
 included in the Methods section above.