DOI: 10.5061/dryad.3tx95x6mn
title: Nectar robbing effects over a key nectar source plant (Tecoma fulva, Bignoniaceae) in a dry tropical Andean valley

description: Zoophilous flowering plants have features to attract their pollinators,
 which may also be used by exploiters like nectar robbers. Nectar robbers
 access nectar by probing flower corollas (primary robbing) or using
 existing holes (secondary robbing). Nectar robbing can negatively impact a
 plant’s fitness directly by damaging the reproductive structures of the
 flower or indirectly by modifying the visitation patterns of pollinators.
 We tested the hypothesis that the robbed flowers are less visited by
 legitimate pollinators by comparing floral visitors and visitation
 frequency in primary-, secondary- and un-robbed flowers of Tecoma fulva
 spp. altoandina, a native shrub species that is an important
 nectar source for nectarivores in the dry valleys of the Bolivian Andes
 (Bignoniaceae). The Giant Hummingbird, Patagona gigas (Trochilidae), was
 the main visitor of T. fulva, and visited more frequently un-robbed
 flowers, followed by secondary robbed and primary robbed flowers. The
 variation in visitation frequency may result in less pollen transport to
 robbed flowers, which may have negative consequences for biological
 fitness, probably manifested in decreased seed production.
description: We conducted the study in the municipality of Mecapaca
 (16.639818º S and 68.015356º W; see Figure S1) near La Paz city, at ~2900
 m asl in the Andean dry valley region of Bolivia (Beck et al., 2015). The
 average annual temperature is ~15 ºC and annual precipitation is ~400 mm
 (SENAMHI 2017). According to Schmida (1985) this region comprises a
 semiarid area. The dominant vegetation is scrub, with shrubs, herbaceous
 plants, and columnar cacti (López, 2003). Cacti such as
 <em>Corryocactus</em> <em>melanotrichus</em> and
 <em>Trichocereus bridgessi</em>, thorny shrubs such as
 <em>Colletia spinossisima</em>, micro-foliated and/or thorny
 trees, and shrubs such as<em> Neltuma alba</em>,
 <em>Vachelia acuminate,</em> and <em>Schinus
 areira</em> are common (Beck et al., 2015; names were actualized
 according to Catalogue of Bolivia from Tropicos:
 http://legacy.tropicos.org/Project/BC). Sunrise was between 6:30 - 6:45 h
 and sunset was between 18:00 - 18:15 h.
 <em>Tecoma fulva</em> spp.
 <em>altoandina</em> (Bignoniaceae), <em>T.
 fulva</em> hereafter, has a disjunct distribution between 2200 and
 3600 m asl, from southern Peru in the Huancavelica and Apurimac valleys,
 and northern Bolivia in the provinces of Camacho (Sorata locality) and
 Murillo (municipalities of Nuestra Señora de La Paz, Mecapaca and Luribay)
 (Wood, 2008; see Figure S1 its distribution in Bolivia). It is the only
 subspecies present at elevations of &gt;2700 m. It is a shrubby plant
 but can become arborescent (Beck and Zenteno-Ruiz, 2015). Its
 funnel-shaped flowers have relatively long corollas (up to 8 cm long) and
 a red-orange color (Wood, 2008), typical of flowers pollinated by
 hummingbirds and also used by nectar robbers (Rojas-Nossa et al., 2016;
 Wilson et al., 2004). The stamens are slightly exserted, with the most
 exposed pair longer than the inner pair. Its flowers have styles longer
 than the stamen filaments and the corolla is longer than in the other
 subspecies (Wood, 2008), suggesting a low probability of autogamy
 (Biernaskie and Cartar, 2004). An individual plant can produce &gt;
 100 flowers in a year, depending on its size, which can reach 3 m in
 height (Beck et al., 2015). It presents flowers asynchronously throughout
 the year, with flowering peaks between March and May, as well as August to
 September in some years (Pacheco et al., 2015, and unpublished
 data). <em>Tecoma fulva </em>in our study
 area show flowers with diurnal anthesis, moderate nectar volume
 (mean±<em>SD</em>: 8.16 ± 2.78 µl) and moderate nectar
 concentration (26.9 ± 3.07 ºBx), with peaks at the end of the afternoon
 (Figure S2 shows nectar volume and concentration during the day), typical
 nectar features in ornithophilous flowers (Faegri and Van der Pjil, 1979;
 Fenster et al., 2004; Wilson et al., 2004). These nectar features are also
 common in flowers subject to bird- and bee-mediated nectar robbing (Genini
 et al., 2010; Rojas-Nossa et al., 2016, Pelayo et al., 2017, Tie et al.,
 2023). 2.2. Sampling design
 Sampling was conducted between May and August 2018, focusing on
 approximately 50 <em>T. fulva</em> individuals occupying an
 area of ~2 ha, although not all of them were in bloom. The site was at the
 edge of a rough road with almost no vehicular traffic.
 In May, we selected 20 adult plants between 1.5 and 3 m tall,
 with at least 30 flowers each, for observations of floral visitors. Type
 of visit (legitimate - anther and stigma contact, primary robbing,
 secondary robbing, pollen collection, corolla contact, stigma contact, and
 antagonists visits; Figure 1) and the number of visits were quantified,
 both per plant (considering all available flowers per plant) and per
 marked flower of different types (unrobbed, primary robbed and secondary
 robbed). Assuming the possibility of nectar replenishment after nectar
 removal by pollinators or nectar robbers (Ordano and Ornelas 2004, Lou et
 al. 2014), we established marked flowers of the second day of anthesis
 with different types as starting flowers for our observations. Assignment
 of flowers to different types (unrobbed, primary robbed, and secondary
 robbed) was done before sunrise (5:30-6:30 am). Visits to flowers were
 recorded in 30-minute periods, every two hours, from 7:00 to 18:00 h, on
 five flowers per type of flower of 20 individual plants (300 flowers
 observed), making a total of 3.5 h of observation per day and an overall
 total of 70 hours in 10 days. The records were made by direct observation,
 at approximately 10 m from the observed plant, using
 binoculars.    Marked flowers from different
 inflorescences were examined to determine whether they were unrobbed,
 primary robbed, or secondary robbed; with five flowers per type of flower.
 Flowers categorized as primary robbed already had a hole or cut at the
 base of the flower, either in the bract or corolla. Secondary robbed
 flowers also had a hole as a result of primary robbing, but secondary
 robbing was simulated by removing as much of the remaining nectar as
 possible with a medical syringe, avoiding damage to the flower structure.
 Unrobbed flowers did not show any of the features of primary or secondary
 robbed flowers and, to ensure that they were not robbed throughout the
 day, they were checked periodically for nectar robbing holes. Occasionally
 some flowers changed from unrobbed to robbed flowers or from primary to
 secondary theft, as some robbers visited them. These flowers with their
 new status were excluded from their respective flower type for analysis,
 but this only occurred in some plants. To evaluate the effects of robbing
 on nectar production, 60 flowers were marked on their first day of
 anthesis with (28 flowers) and without natural nectar robbing (30 flowers)
 at the end of the day (17:00-18:00 h). On the morning of the following day
 (7:00-9:00 h), nectar was extracted from these marked flowers to quantify
 the volume of nectar available under natural conditions (unbagged
 flowers). 2.3. Data analysis The
 flower number of visits at the plant level was analyzed using Generalized
 Linear Models to evaluate differences in visitation rates to flowers
 between visiting species and time of the day. For this analysis, residuals
 were adjusted to a negative binomial distribution with a “log” link. We
 did not divide the number of visits by flower number and time of
 observation to obtain visit rates as response variable; instead, the
 number of observed flowers and time of observation were assigned as offset
 variables in the models, as the former varied between plants and
 observation time was restricted to 0.5 h every 2 h (Reitan and Nielsen,
 2016). The indirect effects of nectar robbing were
 evaluated in two ways. First, the difference in nectar volume between
 robbed and unrobbed flowers was analyzed with a linear model, considering
 flowers as replicates. Second, indirect effects of nectar robbing on the
 number of visits by different types of visitors (legitimate, primary
 robbers, secondary robbers, and pollen collectors) were evaluated with
 generalized linear mixed-models with Poisson error distribution and the
 alternative square root link (Buckley, 2001, Bolker, 2015). Individual
 plants were considered as random factors. The pooled number of visits per
 flower category (unrobbed, primary robbed, and secondary robbed) was used
 as the response variable, with 20 replicates per category (i.e., Kohl and
 Steffan-Dewenter, 2022). In addition, we also evaluated pooled visits to
 compare unrobbed vs robbed flowers (all primary and secondary robbed
 flowers). The pooled number of visits was not divided by flower number and
 time of observation to obtain a visit rate as a response variable;
 instead, the number of observed flowers and time of observation were
 assigned as offset variables in the models, as the former varied between
 flower types and observation time was restricted to 3.5 h (Reitan and
 Nielsen, 2016). As we found differences among legitimate visitors, we also
 conducted separate analyses for each legitimate visitor, using a similar
 approximation. In all cases, residuals were tested to verify normality. To
 test for overdispersion in the residuals, we calculated the dispersion
 parameter (residual deviance/degrees of freedom) and considered values
 less than 1.5 as indicating no overdispersion (Carruthers et al.,
 2008). All models were selected by comparing the Akaike
 Information Criterion value for small samples between submodels (Delta
 AICc&lt;2). When the difference between the AICc values of the best
 and null models was small, the Likelihood Ratio Test (LRT) was used to
 verify differences (Anderson et al., 2008). Models that accounted for
 random effects were also compared against null models with random effects.
 Paired comparisons between factor levels were done using Tukey
 <em>post-hoc </em>tests, based on the best models without
 random effects. Analyses were carried out in the R platform (version
 4.2.2; R Core Team, 2022) using packages “lme4” to build GLMMs (Bates et
 al., 2015), “MuMIn” for model selection (Barton, 2018), “MASS” to build
 GLMs with a negative binomial distribution (Venables, 2002), and “emeans”
 for the <em>post-hoc</em> analysis (Lenth et al.,
 2019).
description: # Nectar robbing effects over a key nectar source plant (*Tecoma fulva*,
 Bignoniaceae) in a dry tropical Andean valley
 [https://doi.org/10.5061/dryad.3tx95x6mn](https://doi.org/10.5061/dryad.3tx95x6mn) The dataset contains information on observed flower visits at two levels: at the plant level, considering all available flowers, and at the level of marked flowers of different types (unrobbed, primary robbed, and secondary robbed). The data also includes information on visitors’ species identity for all types of visitors, including pollinators, nectar robbers, pollen collectors, and those who only contacted the corolla. Additionally, there is information on the nectar volume of robbed and unrobbed flowers. The data was analyzed to identify and quantify flower visitors to flowers of a key nectar source shrub, *Tecoma fulva* spp. *altoandina*. The analysis revealed that the principal visitors are hummingbirds as pollinators, followed by nectar robbers and pollen collectors. Interestingly, hummingbirds visit robbed flowers less frequently than unrobbed flowers. ## Description of the data and file structure The data consists of three tables. Each Excel file contains the following information on the first sheet and a description of the variables and units on the second sheet. * **Flower_visits_plantlevel:** In the following order, this table contains the plant ID (plant_id), number of flowers for each plant (f_number), number of visits to all available flowers at the plant level (n_visits), which was recorded for every visitor (species), which also were categorized according to their behavior (type_visitor). Number of visits was recorded in each 30 min (t_obs) every 2 hours (hour). * **Flower_visits_markedflowers:** In the following order, this table contains the plant ID (plant_id), species identity (species), type of visitor (type_visit), pooled number of visits (n_visits) to marked flowers by flower type (flower_type: primary robbed, secondary robbed and unrobbed), flower type of unrobbed and robbed flowers (flower_type_pooled), number of observed marked flowers (n_flowers) and number of damaged flowers (n_flowers_damaged). Pooled number of visits represents the sum of the number of visits to marked flowers for each type of flower, during the total of 3.5 hours of observation (t_obs) in a day. * **Nectar_unrobbed_vs_robbed flowers**: This table contains information on nectar volume in microliters. Nectar was collected from different flowers (flower_id) of different plants (plant_id), flowers showed a hole in the corolla or not as evidence of nectar robbing (flower_type: unrobbed or robbed).