Recording animal-view videos of the natural world using a novel camera system and software package.

Plants, animals, and fungi display a rich tapestry of colors. Animals, in particular, use colors in dynamic displays performed in spatially complex environments. Although current approaches for studying colors are objective and repeatable, they miss the temporal variation of color signals entirely. Here, we introduce hardware and software that provide ecologists and filmmakers the ability to accurately record animal-perceived colors in motion. Specifically, our Python codes transform photos or videos into perceivable units (quantum catches) for animals of known photoreceptor sensitivity. The plans and codes necessary for end-users to capture animal-view videos are all open source and publicly available to encourage continual community development. The camera system and the associated software package will allow ecologists to investigate how animals use colors in dynamic behavioral displays, the ways natural illumination alters perceived colors, and other questions that remained unaddressed until now due to a lack of suitable tools. Finally, it provides scientists and filmmakers with a new, empirically grounded approach for depicting the perceptual worlds of nonhuman animals.

The ecological and evolutionary stability of interspecific territoriality.

Interspecific territoriality may play an important role in structuring ecological communities, but the causes of this widespread form of interference competition remain poorly understood. Here, we investigate the phenotypic, ecological and phylogenetic correlates of interspecific territoriality in wood warblers (Parulidae). Interspecifically territorial species have more recent common ancestors and are more similar phenotypically, and are more likely to hybridise, than sympatric, non-interspecifically territorial species. After phylogenetic corrections, however, similarity in plumage and territorial song are the only significant predictors of interspecific territoriality besides syntopy (fine-scale geographic overlap). Our results do not support the long-standing hypothesis that interspecific territoriality occurs only under circumstances in which niche divergence is restricted, which combined with the high incidence of interspecific territoriality in wood warblers (39% of species), suggests that this interspecific interaction is more stable, ecologically and evolutionarily, than commonly assumed.

The evolutionary consequences of interspecific aggression.

Competition has always been a cornerstone of evolutionary biology, and aggression is the predominant form of direct competition in animals, but the evolutionary effects of aggression between species are curiously understudied. Only in the past few years, existing theoretical frameworks have been extended to include interspecific aggression, and significant empirical advances have been made. After arguing that agonistic character displacement (ACD) theory provides the most suitable theoretical framework, we review new empirical evidence for ACD and the results of mathematical models of the process. We consider how ACD can be distinguished empirically from ecological and reproductive character displacement and the additional challenges posed by developmental plasticity. We also provide the first taxonomically broad review of theoretical and empirical work on the effects of interspecific aggression on species coexistence and range limits. We conclude by highlighting promising directions for future research on the evolutionary effects of interspecific aggression.

Inferring predator behavior from attack rates on prey-replicas that differ in conspicuousness.

Behavioral ecologists and evolutionary biologists have long studied how predators respond to prey items novel in color and pattern. Because a predatory response is influenced by both the predator's ability to detect the prey and a post-detection behavioral response, variation among prey types in conspicuousness may confound inference about post-prey-detection predator behavior. That is, a relatively high attack rate on a given prey type may result primarily from enhanced conspicuousness and not predators' direct preference for that prey. Few studies, however, account for such variation in conspicuousness. In a field experiment, we measured predation rates on clay replicas of two aposematic forms of the poison dart frog Dendrobates pumilio, one novel and one familiar, and two cryptic controls. To ask whether predators prefer or avoid a novel aposematic prey form independently of conspicuousness differences among replicas, we first modeled the visual system of a typical avian predator. Then, we used this model to estimate replica contrast against a leaf litter background to test whether variation in contrast alone could explain variation in predator attack rate. We found that absolute predation rates did not differ among color forms. Predation rates relative to conspicuousness did, however, deviate significantly from expectation, suggesting that predators do make post-detection decisions to avoid or attack a given prey type. The direction of this deviation from expectation, though, depended on assumptions we made about how avian predators discriminate objects from the visual background. Our results show that it is important to account for prey conspicuousness when investigating predator behavior and also that existing models of predator visual systems need to be refined.

Climatic niche shift predicts thermal trait response in one but not both introductions of the Puerto Rican lizard Anolis cristatellus to Miami, Florida, USA.

Global change is predicted to alter environmental conditions for populations in numerous ways; for example, invasive species often experience substantial shifts in climatic conditions during introduction from their native to non-native ranges. Whether these shifts elicit a phenotypic response, and how adaptation and phenotypic plasticity contribute to phenotypic change, are key issues for understanding biological invasions and how populations may respond to local climate change. We combined modeling, field data, and a laboratory experiment to test for changing thermal tolerances during the introduction of the tropical lizard Anolis cristatellus from Puerto Rico to Miami, Florida. Species distribution models and bioclimatic data analyses showed lower minimum temperatures, and greater seasonal and annual variation in temperature for Miami compared to Puerto Rico. Two separate introductions of A. cristatellus occurred in Miami about 12 km apart, one in South Miami and the other on Key Biscayne, an offshore island. As predicted from the shift in the thermal climate and the thermal tolerances of other Anolis species in Miami, laboratory acclimation and field acclimatization showed that the introduced South Miami population of A. cristatellus has diverged from its native-range source population by acquiring low-temperature acclimation ability. By contrast, the introduced Key Biscayne population showed little change compared to its source. Our analyses predicted an adaptive response for introduced populations, but our comparisons to native-range sources provided evidence for thermal plasticity in one introduced population but not the other. The rapid acquisition of thermal plasticity by A. cristatellus in South Miami may be advantageous for its long-term persistence there and expansion of its non-native range. Our results also suggest that the common assumption of no trait variation when modeling non-native species distributions is invalid.

Vocal and anatomical evidence for two-voiced sound production in the greater sage-grouse Centrocercus urophasianus.

Greater sage-grouse, Centrocercus urophasianus, have been a model system in studies of sexual selection and lek evolution. Mate choice in this species depends on acoustic displays during courtship, yet we know little about how males produce these sounds. Here we present evidence for previously undescribed two-voiced sound production in the sage-grouse. We detected this ;double whistle' (DW) using multi-channel audio recordings combined with video recordings of male behavior. Of 28 males examined, all males produced at least one DW during observation; variation in DW production did not correlate with observed male mating success. We examined recordings from six additional populations throughout the species' range and found evidence of DW in all six populations, suggesting that the DW is widespread. To examine the possible mechanism of DW production, we dissected two male and female sage-grouse; the syrinx in both sexes differed noticeably from that of the domestic fowl, and notably had two sound sources where the bronchi join the syrinx. Additionally, we found males possess a region of pliable rings at the base of the trachea, as well as a prominent syringeal muscle that is much reduced or absent in females. Experiments with a live phonating bird will be necessary to determine how the syrinx functions to produce the whistle, and whether the DW might be the result of biphonation of a single sound source. We conclude that undiscovered morphological and behavioral complexity may exist even within well-studied species, and that integrative research approaches may aid in the understanding of this type of complexity.

The role of interspecific interference competition in character displacement and the evolution of competitor recognition.

The extent to which interspecific interference competition has contributed to character evolution is one of the most neglected problems in evolutionary biology. When formerly allopatric species come into secondary contact, aggressive interactions between the species can cause selection on traits that affect interspecific encounter rates (e.g. habitat preferences, activity schedules), competitor recognition (e.g. colouration, song), and fighting ability (e.g. weaponry, body size). We define agonistic character displacement (ACD) as the process of phenotypic evolution in a population caused by interference competition with one or more sympatric species and which results in shifts in traits that affect the rate, intensity or outcome of interspecific aggression. After clarifying the relationships between ACD and other evolutionary processes that may occur when species come into secondary contact, we develop an individual-based, quantitative genetic model to examine how traits involved in competitor recognition would be expected to evolve under different secondary contact scenarios. Our simulation results show that both divergence and convergence are possible outcomes, depending on the intensity of interspecific exploitative competition, the costs associated with mutual versus unilateral recognition, and the extent of phenotypic differences prior to secondary contact. We then devise a set of eight criteria for evaluating putative examples of ACD and review the empirical literature to assess the strength of existing evidence and to identify promising avenues for future research. Our literature search revealed 33 putative examples of ACD across insects, fishes, bats, birds, lizards, and amphibians (15 divergence examples; 18 convergence examples). Only one example satisfies all eight criteria for demonstrating ACD, but most case studies satisfy four or more criteria. The current state of the evidence for ACD is similar to the state of the evidence for ecological character displacement just 10 years ago. We conclude by offering suggestions for further theoretical and empirical research on ACD.