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: 9.92). 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, Aug 28, 2015
    • "Despite recognition that the environment shapes animal social behaviour (Krause & Ruxton, 2002; Korb & Heinze, 2008), studies exploring how and why the incidence of animal sociality varies across broad geographical and taxonomic scales are still scarce. Our study, which uses comprehensive environmental data at two spatial scales to tests specific hypotheses about the distribution of spider social systems, joins a few comparative studies (Jetz & Rubenstein, 2011; Purcell, 2011; Majer et al., 2013) that seek to uncover the ecological factors underlying broad geographical patterns of animal sociality. "
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    ABSTRACT: AimTo evaluate the relative importance of environmental factors relevant to specific hypotheses that have been proposed to explain the distribution of social and subsocial Anelosimus spiders in the American continent and Ecuador. For social species, we test the seasonality and prey size hypotheses, which posit that species forming long-lived multifemale colonies require aseasonal conditions and warm and productive environments in which large insects can develop. For subsocial species, we test the rain intensity and predation risk hypotheses, which posit that species whose colonies contain a single female and her offspring cannot occupy areas where strong rains cause frequent damage to their webs and where warm temperatures and high productivity promote greater predation.LocationAmerica, Ecuador.Methods Using generalized linear models, hierarchical variance partitioning, Maxent distribution modelling and phylogenetically controlled regressions, we analysed the relative importance of environmental variables that either directly or indirectly relate to these non-exclusive hypotheses – temperature and precipitation seasonality (seasonality hypothesis), annual temperature and net primary productivity (insect size and predation hypotheses) and rain intensity (rain intensity hypothesis).ResultsTemperature seasonality, followed by annual temperature and rain intensity, were the most important predictors of the distribution of spider sociality across America, whereas temperature and rain intensity predominated in the largely aseasonal Ecuador. In general, social species were associated with lower temperature seasonality, warmer temperatures and higher rain intensity than subsocial species.Main conclusionThe association of social Anelosimus with warm and wet areas in the tropics is consistent with both the seasonality and prey size hypotheses, i.e. both aseasonal conditions and warm temperatures, which allow large insects to develop, are needed for large social colonies to form. That subsocial Anelosimus drop-out from tropical areas with warm temperatures and high rain intensity is consistent with the hypotheses that high predation risk and disturbance by strong rains exclude subsocial Anelosimus from the lowland rain forest.
    08/2015; DOI:10.1111/geb.12342
    • "On the other hand, in subtropical and tropical regions, higher environmental variability might select for cooperative breeding (Rubenstein and Lovette 2007, Jetz and Rubenstein 2011, but see Gonzalez et al. 2013), which might lead to less male-biased SSD due to high intra-sexual competition in females (Clutton-Brock et al. 2006). In accordance with this hypothesis, cooperative breeding is particularly prevalent in subtropical and tropical areas (Jetz and Rubenstein 2011). Th e zoogeographical regions compared in this study represent not only discrete geographical regions, but also phylogenetic clusters (Holt et al. 2013). "
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    ABSTRACT: Sexual size dimorphism (SSD) is widespread among animals, and is a common indication of differential selection among males and females. Sexual selection theory predicts that SSD should increase as one sex competes more fiercely for access to mates, but it is unclear what effect spatial variation in ecology may have on this behavioral process and SSD. Here, we examine SSD across the class Aves in a spatial and phylogenetic framework, and test several a priori hypotheses regarding its relationship with climate. We mapped the global distribution of SSD from published descriptions of body size, distribution, and phylogenetic relationships across 2581 species of birds. We examined correlations between SSD and nine predictor variables representing a priori models of physical geography, climate, and climate variability. Our results show some support for a global latitudinal trend in SSD based on a weak prevalence of species with low or female-biased SSD in the north, but substantial spatial heterogeneity. While several stronger relationships were observed between SSD and climate predictors within zoogeographical regions, no global relationship emerged that was consistent across multiple methods of analysis. The strong phylogenetic signal and conspicuous lack of support from phylogenetically corrected analyses suggests that any such relationship in birds is likely obscured by the idiosyncratic histories of different lineages. In this manner, our results agree with previous studies in other clades, leading us to conclude that the relationship between climate and SSD is at best complex. This suggests that SSD, and the behavioral dynamics underlying it, may be largely independent of environmental conditions at a global scale.
    Ecography 04/2015; DOI:10.1111/ecog.01531 · 4.21 Impact Factor
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    • "Our preliminary results not presented here indicate that discrepancies between the traditional and new classification of social breeding systems are substantial. For example, our classification significantly alters observed associations between social system and environmental unpredictability in terms of environmental dependency of cooperative breeding, extending and greatly clarifying earlier analyses (e.g., Jetz and Rubenstein 2011). Our analyses indicate that merging together nonfamily and family breeders erroneously associates 2 very different strategies, and in terms of environmental sensitivity, family breeders are more similar to cooperative breeders (Griesser et al. 2014). "
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    ABSTRACT: Cooperative breeding occurs in several major animal phyla, predominantly in arthropods and chordates. A number of comparative analyses have focused on understanding the evolution of cooperative breeding, yielding mixed, inconclusive, and often phyla-specific findings. We argue that much of this ambiguity results from an erroneous classification of social systems into noncooperatively and cooperatively breeding species. The shortcomings of this assumption are apparent among birds where noncooperative species constitute a heterogeneous group: some species are clearly non–family living, with offspring dispersing at or shortly after nutritional independency, whereas other species form persistent family groups through offspring delaying their dispersal substantially beyond independency. Here, we propose an objective, life history–based criterion classifying noncooperative bird species into non–family living and family living species. We demonstrate that by using the family time (the time offspring remain with its parent/s beyond independence) and body size–scaled reproductive investment, we are able to differentiate 2 groups with contrasting life histories. Our classification matches seasonal environmental variation experienced by different species: family living species postpone dispersal beyond the onset of less favorable autumn conditions. We discuss the consequences of this new social system classification for evolutionary and ecological research, potentially allowing solutions to some of the most intriguing riddles in the evolutionary history of birds—and cooperative behavior itself.
    Behavioral Ecology 03/2015; 26(3). DOI:10.1093/beheco/arv015 · 3.16 Impact Factor
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