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Creators/Authors contains: "Pollock, Henry S."

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  1. Abstract

    The climate variability hypothesis posits that an organism's exposure to temperature variability determines the breadth of its thermal tolerance and has become an important framework for understanding variation in species' susceptibilities to climate change. For example, ectotherms from more thermally stable environments tend to have narrower thermal tolerances and greater sensitivity to projected climate warming. Among endotherms, however, the relationship between climate variability and thermal physiology is less clear, particularly with regard to microclimate variation—small‐scale differences within or between habitats. To address this gap, we explored associations between two sources of temperature variation (habitat type and vertical forest stratum) and (1) thermal physiological traits and (2) temperature sensitivity metrics within a diverse assemblage of Neotropical birds (n = 89 species). We used long‐term temperature data to establish that daily temperature regimes in open habitats and forest canopy were both hotter and more variable than those in the forest interior and forest understory, respectively. Despite these differences in temperature regime, however, we found little evidence that species' thermal physiological traits or temperature sensitivity varied in association with either habitat type or vertical stratum. Our findings provide two novel and important insights. First, and in contrast to the supporting empirical evidence from ectotherms, the thermal physiology of birds at our study site appears to be largely decoupled from local temperature variation, providing equivocal support for the climate variability hypothesis in endotherms. Second, we found no evidence that the thermal physiology of understory forest birds differed from that of canopy or open‐habitat species—an oft‐invoked, yet previously untested, mechanism for why these species are so vulnerable to environmental change.

     
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  2. Abstract

    Species interactions link animal behaviour to community structure and macroecological patterns of biodiversity. One common type of trophic species interaction is disturbance foraging—the act of obtaining food at a disturbance created by another organism. Disturbance foraging is widespread across the animal kingdom, especially among birds, yet previous research has been largely anecdotal and we still lack a synthetic understanding of how this behaviour varies geographically, phylogenetically and ecologically. To address these gaps, we conducted a comprehensive literature review to test focal hypotheses about disturbance foraging behaviour in birds. We found that avian disturbance foraging was geographically ubiquitous, occurring in both aquatic and terrestrial habitats across six continents and four oceans. Consistent with predictions based on established species diversity gradients in different habitat types, the majority of terrestrial observations occurred at tropical latitudes, whereas aquatic observations took place most frequently in temperate marine waters. Although disturbance foraging was widespread across the avian phylogeny, contrary to our prediction, the behaviour was also conserved phylogenetically (Pagel'sλ = 0.7) and clustered within suboscine landbirds in terrestrial environments and seabirds in aquatic environments. Similarly, although disturbers were taxonomically diverse as we predicted, interactions were unexpectedly dominated by swarm‐raiding ants in terrestrial environments and cetaceans in aquatic environments. Diet and body mass were also important predictors of disturbance foraging associations: Responders followed disturbers with similar diets and larger body sizes. Overall, our hypothesis‐testing framework provides insight into the importance of geography, phylogeny and ecology as predictors of disturbance foraging behaviour. We anticipate that this comprehensive assessment of disturbance foraging will serve to generate additional hypotheses and spark future research and management considerations about this fascinating but poorly studied suite of species interactions, especially as biotic interactions face unprecedented risks in our rapidly changing world.

     
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  3. Abstract

    Personality, or repeatable variation in behavior, may impact an animal's survival or reproduction. Parental aggression is one such personality trait with potentially direct implications for fitness, as it can improve offspring survival during vulnerable early life stages. We took advantage of a long‐term nest box and fledgling survival monitoring project to explore the potential fitness consequences of both repeatability and variation in parental aggression in breeding pairs of a locally endangered passerine species (Såli: Micronesian starling,Aplonis opaca) in the presence of an invasive predator, the brown treesnake (Boiga irregularis), on the island of Guam. To do so, we tested for associations between aggressive offspring defense throughout the nesting cycle and three fitness measures: hatching success, fledging success, and post‐fledging survival. Aggression varied greatly among breeding pairs and was repeatable within pairs (R = .47), providing evidence of a personality trait. Consistent with parental investment theory, nest stage was the best predictor of parental aggression, which increased with offspring age. Aggression was positively correlated with hatching success during the egg stage, but not nestling or post‐fledging survival. We propose that parental aggression was decoupled from nestling and fledgling survival because parents were unable to defend young from nocturnal, invasive brown treesnakes. More broadly, our findings demonstrate that repeatable variation in personality traits may not necessarily confer fitness benefits, particularly in the presence of invasive predators.

     
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