In the Light of Evolution Volume V: Cooperation and Conflict (2011) / Chapter Skim
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4 Spatiotemporal Environmental Variation, Risk Aversion, and the Evolution of Cooperative Breeding as a Bet-Hedging Strategy--DUSTIN R. RUBENSTEIN
4 Spatiotemporal Environmental Variation, Risk Aversion, and the Evolution of Cooperative Breeding as a Bet-Hedging Strategy--DUSTIN R. RUBENSTEIN
Pages 69-86
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From page 69... ...
Cooperative breeding behavior could therefore be a risk-averse strategy to maximize fitness by reducing environmentally induced fecundity variance. Such a within-generation bet-hedging hypothesis for social evolution predicts that (i)
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From page 70... ...
To understand the adaptive value of cooperative breeding behavior in variable environments, research ers must consider both mean and environmentally induced variance in fecundity. Determining how spatiotemporal environmental variation drives risk-averse strategies may provide insights into the evolution of complex social behavior.
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From page 71... ...
are not the only form of environmental variation that can influence cooperative breeding behavior. Environmental variation in time can also influence social behavior, including dispersal decisions and the adoption of different breeding roles.
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From page 72... ...
] may shed light on the evolution of cooperative breeding behavior, particularly as it relates to spatiotemporal environmental variation.
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From page 73... ...
Here, I will study the effects of spatial and temporal environmental variation on fecundity variance in an avian cooperative breeder. Specifically, I will examine how mean and variance in group reproductive success change with increasing potential for cooperation, and how the potential for cooperation relates to environmental varia tion.
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From page 74... ...
RESULTS To integrate spatial and temporal environmental variation into a framework for understanding the evolution of complex animal societies, I examined the environmental correlates of reproductive success in the cooperatively breeding superb starling using data from a 10-year field study representing 20 breeding seasons; birds typically breed twice a year during both the long and short rains. Superb starlings are endemic to the savanna of East Africa, which like most semiarid ecosystems is a spatially and temporally variable environment (Rubenstein, 2009)
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From page 75... ...
Peaks in rainfall were trimodal, highlighting the long and short rainy seasons, as well as a third peak in July and August. White bars indicate the primary breeding months, whereas graybars indicate the primary dry season months.
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From page 76... ...
standardized variance in repro ductive success was negatively related to breeding rainfall. Thus, fecundity variance decreased with increasing environmental quality or conditions.
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From page 77... ...
standardized variance in reproductive success was negatively related to percentage vegetation cover. Thus, fecundity variance decreased with increasing territory quality.
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From page 78... ...
. However, just as many reproductive behaviors and components of superb starling physiology are influenced by rainfall in the prebreeding period leading up to the long rains breeding season (Rubenstein, 2007a,b; Rubenstein et al., 2008)
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From page 79... ...
Thus, cooperative breeding and the formation of large, complex family groups in superb starlings may be related directly to environmental variation. If cooperative breeding behavior within these large family groups is indeed a within-generation bet-hedging strategy to maximize fitness by reducing fecundity variance in spatially heterogeneous or temporally unpredictable environments, then variance in reproductive success should also be related to environmental variation in space and/ or time.
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From page 80... ...
If cooperative breeding is a strategy to reduce risk in variable envi ronments, do spatially and temporally variable environments influence social behavior in similar ways, as has been proposed previously (Emlen, 1982a,b) , or do the mechanisms underlying group formation differ in the different types of environments?
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From page 81... ...
may differ in temporally and spatially variable environments. Although the data presented here are consistent with the hypothesis that spatiotemporal environmental variation promotes cooperative breeding as a risk-averse behavioral coping strategy, it is not the only pos sible explanation.
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From page 82... ...
In superb starlings and other birds, cooperative breeding may be a riskaverse strategy to maximize fitness in a range of environmental conditions by reducing fecundity variance. In particular, when mean reproductive success does not differ between high- and low-quality territories, or between good and bad years, selection on variance may be important.
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From page 83... ...
Active nests were checked every 1–3 days throughout the study during the hatching and nestling stages. Group reproductive success was quantified as the proportion of eggs laid that fledged young in each nest for each group in each breeding season.
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From page 84... ...
. This period represents the primary dry season and the 3 months with the greatest coefficients of variation in mean monthly rainfall (Fig.
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From page 85... ...
, the American Museum of Natural History Chapman Fund, the American Ornithologists' Union, the Wilson Ornithological Society, the Society for Integrative and Comparative Biology, the Ani mal Behaviour Society, the Harvard Travellers Club, the Society of Sigma Xi, Cornell University, the Cornell Laboratory of Ornithology Benning Fund, and Cornell Sigma Xi.
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