Article

Environmental Uncertainty and the Global Biogeography of Cooperative Breeding in Birds

Department of Ecology and Evolutionary Biology, Yale University, 165 Prospect Street, New Haven, CT 06520, USA.
Current biology: CB (Impact Factor: 9.57). 03/2011; 21(1):72-8. DOI: 10.1016/j.cub.2010.11.075
Source: PubMed

ABSTRACT

Understanding why organisms as different as amoebas, ants, and birds cooperate remains an important question in evolutionary biology. Although ecology can influence cooperation and conflict within animal societies and has been implicated in species differences in sociality, the environmental predictors of sociality across broad geographic and taxonomic scales remain poorly understood. In particular, the importance of temporal variation in selection pressure has been underestimated in most evolutionary studies. Environmental uncertainty resulting from climatic variation is likely to be an important driver of temporal variation in selection pressure and therefore is expected to impact the evolution of behavioral, morphological, and physiological traits, including cooperation. Using a data set of over 95% of the world's birds, we examine the global geography and environmental, biotic, and historical biogeographic predictors of avian social behavior. We find dramatic spatial variation in social behavior for which environmental and biotic factors--namely, among-year environmental variability in precipitation--are important predictors. Although the clear global biogeographic structure in avian social behavior carries a strong signal of evolutionary history, environmental uncertainty plays an additional key role in explaining the incidence and distribution of avian cooperative breeding behavior.

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Available from: Dustin R. Rubenstein
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    • "These findings demonstrate that individual differences in sensitivity to ecological conditions, and the knock-on effects this has on the composition of animal groups, can influence selection on social behaviors such as cooperative care. Our findings support suggestions that more variable ecological conditions promote helping behavior (Rubenstein and Lovette 2007; Jetz and Rubenstein 2011; Rubenstein 2011), but do not support the mechanism that Rubenstein (2011) hypothesized produced this pattern. He suggested subordinates were increasing their helping effort in variable conditions as a bet-hedging strategy to reduce their fecundity variance and avoid zero reproductive output. "
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    ABSTRACT: Ecological conditions are expected to have an important influence on individuals’ investment in cooperative care. However, the nature of their effects is unclear: both favorable and unfavorable conditions have been found to promote helping behavior. Recent studies provide a possible explanation for these conflicting results by suggesting that increased ecological variability, rather than changes in mean conditions, promote cooperative care. However, no study has tested whether increased ecological variability promotes individual-level helping behavior or the mechanisms involved. We test this hypothesis in a long-term study population of the cooperatively breeding banded mongoose, Mungos mungo, using 14 years of behavioral and meteorological data to explore how the mean and variability of ecological conditions influence individual behavior, body condition, and survival. Female body condition was more sensitive to changes in rainfall leading to poorer female survival and pronounced male-biased group compositions after periods of high rainfall variability. After such periods, older males invested more in helping behavior, potentially because they had fewer mating opportunities. These results provide the first empirical evidence for increased individual helping effort in more variable ecological conditions and suggest this arises because of individual differences in the effect of ecological conditions on body condition and survival, and the knock-on effect on social group composition. Individual differences in sensitivity to environmental variability, and the impacts this has on the internal structure and composition of animal groups, can exert a strong influence on the evolution and maintenance of social behaviors, such as cooperative care.
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    • "Nowadays, differences of perspective more obviously reflect the important taxonomic difference in the nature of cooperative behaviors: investigating direct direct fitness and cost/benefit issues are important where no permanent caste division occurs, while genetic considerations become more important in species in which the allocation to a particular caste is permanent. Thus, vertebrate " helpers, " capable of breeding, typically characterize the former, while studies of social insects have tended to focus on the highly eusocial species that characterize the latter (e.g., Jetz and Rubenstein, 2011; Bourke, 2014). Nevertheless, the similarities between cooperatively breeding vertebrates and the primitively social bees and wasps often remain overlooked, despite the successful application of reproductive skew models (see Nonacs and Hager, 2011) as a shared conceptual framework. "

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    • "In this way , cooperative traits in social spiders appear to be driven by environmental constraints similarly to social mammals or birds ( Emlen , 1982 ; Faulkes et al . , 1997 ; Jetz and Rubenstein , 2011 ) . "
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