Marine subsidies change short‐term foraging activity and habitat utilization of terrestrial lizards

Resource pulses are brief periods of unusually high resource abundance. While population and community responses to resource pulses have been relatively well studied, how individual consumers respond to resource pulses has received less attention. Local consumers are often the first to respond to a resource pulse, and the form and timing of individual responses may influence how the effects of the pulse are transmitted throughout the community. Previous studies in Bahamian food webs have shown that detritivores associated with pulses of seaweed wrack provide an alternative prey source for lizards. When seaweed is abundant, lizards (Anolis sagrei) shift to consuming more marine‐derived prey and increase in density, which has important consequences for other components of the food web. We hypothesized that the diet shift requires individuals to alter their habitat use and foraging activity and that such responses may happen very rapidly. In this study, we used recorded video observations to investigate the immediate responses of lizards to an experimental seaweed pulse. We added seaweed to five treatment plots for comparison with five control plots. Immediately after seaweed addition, lizards decreased average perch height and increased movement rate, but these effects persisted for only 2 days. To explore the short‐term nature of the response, we used our field data to parametrize heuristic Markov chain models of perch height as a function of foraging state. These models suggest a “Synchronized‐satiation Hypothesis,” whereby lizards respond synchronously and feed quickly to satiation in the presence of a subsidy (causing an initial decrease in average perch height) and then return to the relative safety of higher perches. We suggest that the immediate responses of individual consumers to resource pulse events can provide insight into the mechanisms by which these consumers ultimately influence community‐level processes.     

Climate warming: a loss of variation in populations can accompany reproductive shifts

The most documented response of organisms to climate warming is a change in the average timing of seasonal activities (phenology). Although we know that these average changes can differ among species and populations, we do not know whether climate warming impacts within‐population variation in phenology. Using data from five study sites collected during a 13‐year survey, we found that the increase in spring temperatures is associated with a reproductive advance of 10 days in natural populations of common lizards (Zootoca vivipara). Interestingly, we show a correlated loss of variation in reproductive dates within populations. As illustrated by a model, this shortening of the reproductive period can have significant negative effects on population dynamics. Consequently, we encourage tests in other species to assess the generality of decreased variation in phenological responses to climate change.     

Experimental studies of adaptive differentiation in Bahamian Anolis lizards

Populations of the lizards Anolis carolinensis and A. sagrei were experimentally introduced onto small islands in the Bahamas. Less than 15 years after introduction, we investigated whether the populations had diverged and, if so, whether differentiation was related to island vegetational characteristics or propagule size. No effect of founding population size was evident, but differentiation of A. sagrei appears to have been adaptive, a direct relationship existed between how vegetationally different an experimental island was from the source island and how much the experimental population on that island had diverged morphologically. Populations of A. carolinensis had also diverged, but were too few for quantitative comparisons. A parallel exists between the divergence of experimental populations of A. sagrei and the adaptive radiation of Anolis lizards in the Greater Antilles; in both cases, relative hindlimb length and perch diameter are strongly correlated. This differentiation could have resulted from genetic change or environmentally-driven phenotypic plasticity. Laboratory studies on A. sagrei from a population in Florida indicate that hindlimb length exhibits adaptive phenotypic plasticity. Further studies are required to determine if the observed differences among the experimental populations are the result of such plasticity. Regardless of whether the differences result from plasticity, genetic change, or both, the observation that anole populations differentiate rapidly and adaptively when exposed to novel environmental conditions has important implications for understanding the adaptive radiation of Caribbean anoles.     

Miami heat: Urban heat islands influence the thermal suitability of habitats for ectotherms

The urban heat island effect, where urban areas exhibit higher temperatures than less‐developed suburban and natural habitats, occurs in cities across the globe and is well understood from a physical perspective and at broad spatial scales. However, very little is known about how thermal variation caused by urbanization influences the ability of organisms to live in cities. Ectotherms are sensitive to environmental changes that affect thermal conditions, and therefore, increased urban temperatures may pose significant challenges to thermoregulation and alter temperature‐dependent activity. To evaluate whether these changes to the thermal environment affect the persistence and dispersal of ectothermic species in urban areas, we studied two species of Anolis lizards (Anolis cristatellus and Anolis sagrei) introduced to Miami‐Dade County, FL, USA, where they occur in both urban and natural habitats. We calculated canopy openness and measured operative temperature (T_e), which estimates the distribution of body temperatures in a non‐thermoregulating population, in four urban and four natural sites. We also captured lizards throughout the day and recorded their internal body temperature (T_b). We found that urban areas had more open canopies and higher T_e compared to natural habitats. Laboratory trials showed that A. cristatellus preferred lower temperatures than A. sagrei. Urban sites currently occupied by each species appear to lower thermoregulatory costs for both species, but only A. sagreihad field T_b that were more often within their preferred temperature range in urban habitats compared to natural areas. Furthermore, based on available T_e within each species' preferred temperature range, urban sites with only A. sagrei appear less suitable for A. cristatellus, whereas natural sites with only A. cristatellus are less suitable for A. sagrei. These results highlight how the thermal properties of urban areas contribute to patterns of persistence and dispersal, particularly relevant for studying species invasions worldwide.     

Urbanization and biological invasion shape animal personalities

Novel selective pressures derived from human activities challenge the persistence of animal populations worldwide. Behavior is expected to be a major factor driving animals’ responses to global change because it largely determines how animals interact with the environment. However, the role of individual variation in behavior to facilitate the persistence of animals in changing environments remains poorly understood. Here, we adopted an animal personality approach to investigate whether different behavioral traits allow animals to deal with two major components of global change: urbanization and biological invasions. By studying six populations of Anolis sagrei lizards, we found for the first time that anoles vary consistently in their behavior across different times and contexts. Importantly, these animal personalities were consistent in the wild and in captivity. We investigated whether behavioral traits are pulled in different directions by different components of global change. On the one hand, we found that lizards from urban areas differ from nearby forest lizards in that they were more tolerant of humans, less aggressive, bolder after a simulated predator attack, and they spent more time exploring new environments. Several of these risk‐taking behaviors constituted a behavioral syndrome that significantly differed between urban and forest populations. On the other hand, the behavior of urban A. sagrei coexisting with the invasive predatory lizard Leiocephalus carinatus was associated with dramatic changes in their foraging niche. Overall, we provide evidence that differences in animal personalities facilitate the persistence of animals under novel selective regimes by producing adaptive behaviors relevant to their ecology such as predator avoidance. Our results suggest that natural selection can favor certain behaviors over others when animals are confronted with different ecological challenges posed by global change. Therefore, we underscore the need to incorporate behavioral ecology into the study of how animals adaptively respond to human‐induced environmental changes.     

Display Behavior and Habitat Use in Single and Mixed Populations of Anolis carolinensis and Anolis sagrei Lizards

Introduced species can have a variety of effects on the behavior and ecology of native species. We compared display behavior and habitat use of introduced Anolis sagrei and native Anolis carolinensis lizards across three sites in Southern Louisiana. The chosen sites were similar in that they were all located in urban settings with clumped vegetation. The first site contained only A. sagrei, the second supported sympatric A. sagrei and A. carolinensis populations, and the third site harbored only A. carolinensis. We found that (1) A. carolinensis perched significantly higher when A. sagrei was present, consistent with previous studies, whereas perch height of A. sagrei was not altered by the presence of A. carolinensis; (2) A. carolinensis in single and mixed sites exhibited different proportions of display types, with individuals at the mixed Tulane site performing significantly more C displays than those at the single site; and (3) Anolis sagrei at the Tulane mixed site exhibited less push‐ups than those in the site with A. sagrei alone. These data suggest that the arrival of congeners can affect display behavior of anoles, although such effects are different for the natives and the invaders.     

Comparisons of behavioural and TRPA1 heat sensitivities in three sympatric Cuban Anolis lizards

Thermal tolerances of organisms play a role in defining geographic ranges and occurrence of species. In Cuba, three sympatric species of Anolis lizards (Anolis allogus, Anolis homolechis and Anolis sagrei) inhabit different thermal microhabitats. A previous study found that these species showed distinct gene expression patterns in response to temperature stimuli, suggesting the genetically distinct thermal physiology among species. To investigate whether the Anolis species inhabiting locally distinct thermal habitats diverge their thermal tolerances, we first conducted behavioural experiments to analyse the temperatures at which the three Anolis species escape from heat source. Then, for each of the three species, we isolated cDNA encoding a putative molecular heat sensor, transient receptor potential ion channel ankyrin 1 (TRPA1), which has been suggested to play a role on eliciting behavioural responses to heat stimuli. We performed electrophysiological analysis to quantify activation temperature of Anolis TRPA1 to see whether the pattern of divergence in TRPA1 responses is congruent with that of divergence in behavioural responses. We found that temperatures triggering behavioural and TRPA1 responses were significantly lower for shade‐dwelling species (A. allogus) than for sun‐dwelling species (A. homolechis and A. sagrei). The ambient temperature of shade habitats where A. allogus occurs stays relatively cool compared to that of open habitats where A. homolechis and A. sagrei occur and bask. The high temperature thresholds of A. homolechis and A. sagrei may reflect their heat tolerances that would benefit these species to inhabit the open habitats.     

Time scale matters: genetic analysis does not support adaptation‐by‐time as the mechanism for adaptive seasonal declines in kokanee reproductive life span

Seasonal declines of fitness‐related traits are often attributed to environmental effects or individual‐level decisions about reproductive timing and effort, but genetic variation may also play a role. In populations of Pacific salmon (Oncorhynchus spp.), seasonal declines in reproductive life span have been attributed to adaptation‐by‐time, in which divergent selection for different traits occurs among reproductively isolated temporal components of a population. We evaluated this hypothesis in kokanee (freshwater obligate Oncorhynchus nerka) by testing for temporal genetic structure in neutral and circadian‐linked loci. We detected no genetic differences in presumably neutral loci among kokanee with different arrival and maturation dates within a spawning season. Similarly, we detected no temporal genetic structure in OtsClock1b, Omy1009uw, or OmyFbxw11, candidate loci associated with circadian function. The genetic evidence from this study and others indicates a lack of support for adaptation‐by‐time as an important evolutionary mechanism underlying seasonal declines in reproductive life span and a need for greater consideration of other mechanisms such as time‐dependent, adaptive adjustment of reproductive effort.     

Comparative thermal ecology of two lizards

Summary In a habitat judged to be energetically costly for thermoregulation, mean body temperatures (MBT's) ofAnolis sagrei are significantly higher than those ofA. distichus. As indexed by the slope of the regression of body temperatures (T _b ) on substrate temperature (T _s ),A. sagrei is more dependent upon environmental temperatures thanA. distichus.In a habitat judged to be less costly for thermoregulation and where interspecific competition for perch sites may be less, MBT's ofA. sagrei are significantly higher, proportionally more lizards occupy sunny perches, and the slope of the regression of T _b on T _s is significantly less, than for conspecifics in the costly habitat.As indexed by length-specific fat body weights, well-nourished lizards in the costly habitat have T _b 's which are independent of environmental temperature; T _b 's of poorly-nourished lizards are highly dependent upon environmental temperature. This relationship does not hold for lizards in the low-cost habitat.These results corroborate the hypothesis that energetic costs are important in controlling the extent to which lizards thermoregulate. In high-cost habitats lizards thermoregulate less precisely than in low-cost habitats. Lizards that exploit the habitat as if it were highly productive thermoregulate more precisely than lizards that exploit the environment as if it were of low productivity.     

Predation by an exotic lizard,Anolis sagrei,alters the ant community structure in betelnut palm plantations in southern Taiwan

Abstract 1. Predators can affect prey directly by reducing prey abundance and indirectly by altering behavioural patterns of prey. From previous studies, there is little evidence that ant community structure is affected by vertebrate predation. 2. Researchers tend to consider the interactions between vertebrate predators and ants to be weak. The present study examined the impact of the exotic invasive lizard, Anolis sagrei, on the ant community structure by manipulating the density of lizards within enclosures. The natural density of A. sagrei in the field was surveyed and used as the stocking density rate in the lizard‐present sub‐enclosures. 3. Before the lizard density was manipulated, there was no difference in the ant diversity between sub‐enclosures. After the lizard density manipulation, the ant diversity in sub‐enclosures with A. sagrei present was significantly different from that of enclosures where the lizards were absent, although the overall ant abundance did not differ significantly. 4. The ant diversity difference was generated by a significant reduction of the ant species Pheidole fervens in sub‐enclosures with A. sagrei present. Such an abundance change might be the result of direct predation by the lizards, or it might be generated by a foraging site shift by this ant. 5. The results of this study thus demonstrated that the invasion of an exotic vertebrate can significantly alter the community structure of ants, perhaps through the combined direct and indirect effects of lizards on ants.     

Assessing seasonal demographic covariation to understand environmental‐change impacts on a hibernating mammal

Natural populations are exposed to seasonal variation in environmental factors that simultaneously affect several demographic rates (survival, development and reproduction). The resulting covariation in these rates determines population dynamics, but accounting for its numerous biotic and abiotic drivers is a significant challenge. Here, we use a factor‐analytic approach to capture partially unobserved drivers of seasonal population dynamics. We use 40 years of individual‐based demography from yellow‐bellied marmots (Marmota flaviventer) to fit and project population models that account for seasonal demographic covariation using a latent variable. We show that this latent variable, by producing positive covariation among winter demographic rates, depicts a measure of environmental quality. Simultaneously, negative responses of winter survival and reproductive‐status change to declining environmental quality result in a higher risk of population quasi‐extinction, regardless of summer demography where recruitment takes place. We demonstrate how complex environmental processes can be summarized to understand population persistence in seasonal environments.     

Pulsed seaweed subsidies drive sequential shifts in the effects of lizard predators on island food webs

Most prominent theories of food web dynamics imply the simultaneous action of bottom–up and top–down forces. However, transient bottom‐up effects resulting from resource pulses can lead to sequential shifts in the strength of top–down predator effects. We used a large‐scale field experiment (32 small islands sampled over 5 years) to probe how the frequency and magnitude of pulsed seaweed inputs drives temporal variation in the top–down effects of lizard predators. Short‐term weakening of lizard effects on spiders and plants (the latter via a trophic cascade) were associated with lizard diet shifts, and were more pronounced with larger seaweed inputs. Long‐term strengthening of lizard effects was associated with lizard numerical responses and plant fertilisation. Increased pulse frequency reinforced the strengthening of lizard effects on spiders and plants. These results underscore the temporally variable nature of top–down effects and highlight the role of resource pulses in driving this variation.     

Between‐individual variation drives the seasonal dynamics in the trophic niche of a Neotropical marsupial

The dynamics of population niches result from the variation in resource use within individuals and also from the variation between individuals. The prevalence of one mechanism or the other leads to competing hypotheses about the major mechanisms underlying the empirical observations of the contraction/expansion dynamics of the trophic niche in natural populations. In this study, we investigated how within‐ and between‐individual variation in resource use shapes the food niche dynamics of the woolly mouse opossum, Marmosa paraguayana (Didelphimorphia: Didelphidae), in a remnant of the highly seasonal Cerrado in south‐eastern Brazil. To do so, we analysed the faecal samples of live‐trapped individuals to determine their diets within the wet and dry seasons. In addition to a seasonal shift in the composition of the diet, the population trophic niche was significantly wider during the dry season than the wet season. This expansion resulted from larger between‐individual variation in the dry season that was not related to sex preferences, whereas the individual niche widths did not significantly increase from the wet to the dry seasons. Our findings add to the growing list of animal populations that show individual‐level variation in resource use. Furthermore, these results represent a pattern of individual‐level response to seasonal changes that is different from patterns reported for other organisms. We suggest that a pathway to build more realistic foraging models and produce more accurate predictions on population and community dynamics is to consider between‐individual variation and short‐term niche dynamics.     

Adult survival and reproductive rate are linked to habitat preference in territorial,year‐round resident Song Sparrows Melospiza melodia

Individual animal fitness can be strongly influenced by the ability to recognize habitat features which may be beneficial. Many studies focus on the effects of habitat on annual reproductive rate, even though adult survival is typically a greater influence on fitness and population growth in vertebrate species with intermediate to long lifespans. Understanding the effects of preferred habitat on individuals over the annual cycle is therefore necessary to predict its influences on individual fitness. This is particularly true in species that are resident and territorial year‐round in the temperate zone, which may face potential trade‐offs between habitat that maximizes reproduction and that which maximizes non‐breeding season (‘over‐winter’) survival. We used a 37‐year study of Song Sparrows Melospiza melodia residing territorially year‐round on a small island to examine what habitat features influenced adult over‐winter survival, how site‐specific variation in adult survival vs. annual reproductive rate influenced long‐term habitat preference, and if preferred sites on average conferred higher individual fitness. Habitat features such as area of shrub cover and exposure to intertidal coastline predicted adult over‐winter survival independent of individual age or sex, population size, or winter weather. Long‐term habitat preference (measured as occupation rate) was better predicted by site‐specific annual reproductive rate than by expected over‐winter survival, but preferred sites maximized fitness on average over the entire annual cycle,. Although adult over‐winter survival had a greater influence on population growth (λ) than did reproductive rate, the influence of reproductive rate on λ increased in preferred sites because site‐specific variation in reproductive rate was higher than variation in expected over‐winter survival. Because preferred habitats tended to have higher mean site‐specific reproductive and adult survival rates, territorial birds in this population do not appear to experience seasonal trade‐offs in preferred habitat but are predicted to incur substantial fitness costs of settling in less‐preferred sites.     

Sex‐skewed trophic impacts in ephemeral wetlands

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Prothonotary warbler nestling growth and condition in response to variation in aquatic and terrestrial prey availability

Aquatic prey subsidies entering terrestrial habitats are well documented, but little is known about the degree to which these resources provide fitness benefits to riparian consumers. Riparian species take advantage of seasonal pulses of both terrestrial and aquatic prey, although aquatic resources are often overlooked in studies of how diet influences the reproductive ecology of these organisms. Ideally, the timing of resource pulses should occur at the time of highest reproductive demand. This study investigates the availability of aquatic (mayfly) and terrestrial (caterpillar) prey resources as well as the nestling diet of the prothonotary warbler (Protonotaria citrea) at two sites along the lower James River in Virginia during the 2014 breeding season. We found large differences in availability of prey items between the two sites, with one having significantly higher mayfly availability. Nestling diet was generally reflective of prey availability, and nestlings had faster mean growth rates at the site with higher aquatic prey availability. Terrestrial prey were fed more readily at the site with lower aquatic prey availability, and at this site, nestlings fed mayflies had higher mean growth rates than nestlings fed only terrestrial prey. Our results suggest that aquatic subsidies are an important resource for nestling birds and are crucial to understanding the breeding ecology of riparian species.     

The influence of spatio-temporal resource fluctuations on insular rat population dynamics

Local spatio-temporal resource variations can strongly influence the population dynamics of small mammals. This is particularly true on islands which are bottom-up driven systems, lacking higher order predators and with high variability in resource subsidies. The influence of resource fluctuations on animal survival may be mediated by individual movement among habitat patches, but simultaneously analysing survival, resource availability and habitat selection requires sophisticated analytical methods. We use a Bayesian multi-state capture-recapture model to estimate survival and movement probabilities of non-native black rats (Rattus rattus) across three habitats seasonally varying in resource availability. We find that survival varies most strongly with temporal rainfall patterns, overwhelming minor spatial variation among habitats. Surprisingly for a generalist forager, movement between habitats was rare, suggesting individuals do not opportunistically respond to spatial resource subsidy variations. Climate is probably the main driver of rodent population dynamics on islands, and even substantial habitat and seasonal spatial subsidies are overwhelmed in magnitude by predictable annual patterns in resource pulses. Marked variation in survival and capture has important implications for the timing of rat control.     

Not All Signals are Equal: Male Brown Anole Lizards (Anolis sagrei) Selectively Decrease Pushup Frequency Following a Simulated Predatory Attack

The use of conspicuous communication signals often increases a signaler's risk of predation. Many species communicate with a repertoire of signals that may differ in their conspicuousness to predators. Few studies have examined the ability of prey to selectively decrease the use of individual signals in their displays under heightened predation risk. Here, I examined the behavior of male brown anole lizards (Anolis sagrei) in response to a simulated predatory attack from a model kestrel. This species communicates with three major visual signal types, the head‐bob, pushup, and dewlap extension, which vary in their motion and spectral characteristics. I predicted that lizards would decrease frequencies of the dewlap extension and pushup following the attack, but not the head‐bob. Males modulated their use of individual signals by decreasing pushup rates, but not head‐bob rates. Decreases in dewlap frequency were marginally significant. One explanation for these results is that lizards decrease frequencies of signal types based partly on their conspicuousness. The energetic cost of each signal type may be an equally important factor that determines the signaler's response to predators, particularly if a predatory attack is perceived as imminent.     

Does ecological specialization transcend scale? Habitat partitioning among individuals and species of Anolis lizards

Ecological specialization is common across all levels of biological organization, raising the question of whether the evolution of specialization at one scale in a taxon is linked to specialization at other scales. Anolis lizards have diversified repeatedly along axes of habitat use, but it remains unknown if this diversification into habitat use specialists is underlain by individual specialization. From repeated observations of individuals in a population of Anolis sagrei in Florida, we show that the extent of habitat use specialization among individuals is comparable to the extent of specialization in the same traits among ten sympatric Anolis habitat specialist species in Cuba. However, the adaptive correlations between habitat use and morphology commonly seen across species of Anolis were not observed across individuals in the sampled population. Our results therefore suggest that while patterns of ecological specialization can transcend scale, these parallels are the consequence of distinct ecological processes acting at microevolutionary and macroevolutionary scales.