Redução do forrageio do iguana-negro-de-cauda-espinhosa, Ctenosaura similis (Sauria: Iguanidae), na presença de estímulos do predador

The presence of a predator may have direct and indirect effects on the behavior of the prey. Although altered behavior may help prey avoid predators, it also can have a potential impact on critical activities such as foraging. Predator-prey interactions are routinely studied in laboratory-based experiments owing to the perceived difficulties of conducting such experiments in natural settings. We conducted an experimental study under field conditions in Palo Verde National Park in northwestern Costa Rica to assess behavioral responses of Black Spiny-tailed Iguanas (Ctenosaura similis) to the presence of predators and predator cues. Free-roaming iguanas were offered mango in designated areas in the presence of a predator (Boa constrictor), a predator cue (B. constrictor feces), and a control (no predator or predator cue). Results indicate that iguanas reduced their foraging efforts in the presence of both a predator and its cue.A presença de um predador pode exercer efeitos diretos e indiretos sobre o comportamento da presa. Embora a alteração do comportamento possa ajudar a presa a evitar predadores, pode também ter um impacto potencial sobre atividades críticas, como o forrageio. As interações predador-presa são comumente estudadas em experimentos de laboratório devido às dificuldades em conduzir experimentos sob condições naturais. Conduzimos um estudo experimental em campo no Parque Nacional Palo Verde, no noroeste da Costa Rica, para avaliar as respostas dos iguanas-negros-de-cauda-espinhosa (Ctenosaura similis) à presença de predadores e de seus estímulos. Oferecemos manga a iguanas livres em áreas pré-estabelecidas na presença de um predador (Boa constrictor), de um estímulo do predador (fezes de B. constrictor) e em uma áreacontrole (sem predador ou estímulo). Os resultados indicam que os iguanas reduziram seus esforços de forrageio tanto na presença do predador como de seu estímulo

Predation and the Maintenance of Color Polymorphism in a Habitat Specialist Squamate

Multiple studies have addressed the mechanisms maintaining polymorphism within a population. However, several examples exist where species inhabiting diverse habitats exhibit local population-specific polymorphism. Numerous explanations have been proposed for the maintenance of geographic variation in color patterns. For example, spatial variation in patterns of selection or limited gene flow can cause entire populations to become fixed for a single morph, resulting in separate populations of the same species exhibiting separate and distinct color morphs. The mottled rock rattlesnake (Crotalus lepidus lepidus) is a montane species that exhibits among-population color polymorphism that correlates with substrate color. Habitat substrate in the eastern part of its range is composed primarily of light colored limestone and snakes have light dorsal coloration, whereas in the western region the substrate is primarily dark and snakes exhibit dark dorsal coloration. We hypothesized that predation on high contrast color and blotched patterns maintain these distinct color morphs. To test this we performed a predation experiment in the wild by deploying model snakes at 12 sites evenly distributed within each of the two regions where the different morphs are found. We employed a 2×2 factorial design that included two color and two blotched treatments. Our results showed that models contrasting with substrate coloration suffered significantly more avian attacks relative to models mimicking substrates. Predation attempts on blotched models were similar in each substrate type. These results support the hypothesis that color pattern is maintained by selective predation

The Bogert Effect Revisited: Salamander Regulatory Behaviors are Differently Constrained by Time and Space

© 2018 The Authors. Ecology and Evolution published by John Wiley & Sons Ltd. The use of behavior to buffer extreme environmental variation is expected to enable species to (a) extend the breadth of environments they inhabit beyond that predicted from climatic data and (b) diminish the negative effects of broad scale and chronic disturbances such as climate change. The term Bogert effect refers to behavioral compensation entailing microhabitat selection to maintain performance across a gradient of environmental conditions resulting in evolutionary inertia of physiological traits. Here, we compare microhabitats used by plethodontid salamanders distributed along an elevational gradient to determine whether there is behavioral compensation that buffers them from deleterious temperatures and moisture levels. Overall, salamanders preferred cooler and more mesic environments and occupied microhabitats that maintained constant moisture conditions at both high- and low-elevation sites. Our results suggest that salamanders use microhabitats to regulate temperature and moisture levels, which is consistent with the Bogert effect. Maintenance of more moist conditions may help buffer these species from rising temperatures but only in suitable high-elevation environments that are likely to disappear over the next century. We conclude that behavioral regulation of temperature and moisture is a potential mechanism for the Bogert effect in plethodontid salamanders

Modified range map of <i>Crotalus lepidus lepidus</i> and a photo of two specimens from the two races.

<p>(A) Map of southwestern Texas showing the ranges of the Stockton-Edward Plateau (Eastern) and Davis Mountains-Big Bend (Western) morphs described by Vincent (1982). The single hatched section represents the eastern morphs range in Texas and the double hatched section represents the western morphs range in Texas. Western field sites for the predation experiment are indicated by red dots and eastern field sites are indicated by blue dots. Note: this map does not illustrate the entire species range, but solely where the morphs were designated as being most prominent by Vincent (1982). (B) A side by side comparison of two live <i>Crotalus l. lepidus</i>. The dark colored snake on the left is from Brewster County in the western portion of their range. The light colored snake on the left is from Edwards County in the eastern portion of their range. Both specimens are part of the collection maintained by Michael Price at the San Angelo Nature Center, located in San Angelo, Texas.</p

Examples of damage to model <i>Crotalus l. lepidus</i> during the course of the model predation study.

<p>All photos show damage on the dorsal surface of models. (A) An example of a decapitated model, note the decapitated head in the bottom right hand corner which has a single peck mark in the center. Typically models found with breaks were either decapitated or broken in several locations. (B) An example of a model showing a peck mark. Peck marks include single circular and triangular marks such as the one shown in this photo and also pairs of triangle shaped pecks indicating an open beak. (C) An example of a model showing bite marks. Bites were either full round chunks removed from the model or the impression of teeth marks left in the model. (D) An example of a model showing a questionable mark. In this case it is clear that a Barbary sheep, <i>Ammotragus lervia</i>, had stepped on the model. However, other questionable attacks include potential arthropod damage and incidences where it was unclear if an avian or non-predator attack occurred.</p

Model selection results from the avian attack and non-predator disturbance analysis.

<p>Only the significant models (<i>P</i><0.05) which demonstrated some level of potential importance according to the number of parameters (K), log likelihood (LL), Akaiki Information Criteria corrected for small sample size (AIC_c), evidence ratio, and AIC_c weight (<i>w_i</i>) are presented. In the column presenting the models an asterisk (*) indicates that parameters are crossed and brackets ([…]) indicate that the preceding parameter is nested within the bracketed parameter. The model containing Color+Region+Region*Color appears to be favored for avian attacks, while the model containing Blotching is favored for non-predator disturbances.</p

Mean achromatic and chromatic contrast values for model snake used in on predation study on limestone and volcanic rock.

<p>Contrast values given in just noticeable differences (JND) for comparisons of limestone and volcanic rocks to the two base model colors of our study (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0030316#pone-0030316-g002" target="_blank">Figure 2</a>). Model type is listed on the x-axis with Eastern Model referring to the model color mimicking snakes from the eastern region in areas of limestone, while Western Model refers to the model color mimicking snakes from the western region on volcanic rock. Different letters above bars indicate significant differences between contrast values for limestone and volcanic rock for the individual model types.</p

Data from: The Bogert effect revisited: salamander regulatory behaviors are differently constrained by time and space

The use of behavior to buffer extreme environmental variation is expected to enable species to a) extend the breadth of environments they inhabit beyond that predicted from climatic data, and b) diminish the negative effects of broad-scale and chronic disturbances such as climate change. The term Bogert effect refers to behavioral compensation entailing microhabitat selection to maintain performance across a gradient of environmental conditions resulting in evolutionary inertia of physiological traits. Here we compare microhabitats used by plethodontid salamanders distributed along an elevational gradient to determine whether there is behavioral compensation that buffers them from deleterious temperatures and moisture levels. Overall, salamanders preferred cooler and more mesic environments and occupied microhabitats that maintained constant moisture conditions at both high and low elevation sites. Our results suggest that salamanders use microhabitats to regulate temperature and moisture levels, which is consistent with the Bogert effect. Maintenance of more moist conditions may help buffer these species from rising temperatures, but only in suitable high-elevation environments that are likely to disappear over the next century. We conclude that behavioral regulation of temperature and moisture is a potential mechanism for the Bogert effect in plethodontid salamanders

Proportion of avian attacks and non-predator disturbances of artificial snake models.

<p>Models were placed in the eastern region on limestone rocks and western region on volcanic rocks (refer to <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0030316#pone-0030316-g001" target="_blank">Figure 1A</a>) during the course of the predation study. The upper graph (A) is showing the proportion of attacks on models that mimicked the coloration of <i>Crotalus l. lepidus</i> from the eastern region. The lower graph (B) is showing the proportion of attacks on models that mimicked the coloration of <i>C. l. lepidus</i> from the western region. The x-axis indicates the type of damage the models sustained as either avian attacks or non-predator disturbances.</p