Intraspecific variation in group size in the blackbuck antelope: the roles of habitat structure and forage at different spatial scales |
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Authors: | Kavita Isvaran |
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Institution: | (1) Department of Zoology, University of Florida, 223 Bartram Hall, Gainesville, FL 32611, USA;(2) Centre for Ecological Sciences, Indian Institute of Science, Bangalore, 560 012, India |
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Abstract: | The main ecological factors that are hypothesized to explain the striking variation in the size of social groups among large
herbivores are habitat structure, predation, and forage abundance and distribution; however, their relative roles in wild
populations are not well understood. I combined analyses of ecological correlates of spatial variation in group size with
analyses of individual behaviour in groups of different sizes to investigate factors maintaining variation in group size in
an Indian antelope, the blackbuck Antilope cervicapra. I measured group size, habitat structure, forage, and the occurrence of predators in ten blackbuck populations, and, at
a smaller spatial scale, within an intensively studied population. To examine the processes by which these ecological factors
influence group size, I used behavioural observations and an experiment to estimate the shape of the relationship between
group size and potential costs and benefits to individuals. Group size varied extensively both among and within populations.
Analyses of spatial variation in group size suggested that both forage and habitat structure influence group size: large-scale,
among-population variation in group size was primarily related to habitat structure, while small-scale, within-population
variation was most closely related to forage abundance. Analyses of individual behaviour suggested that larger groups incur
greater travel costs while foraging. However, individuals in larger groups appeared to experience greater benefits, namely
the earlier detection of a “predator”, a reduction in vigilance, and an increase in the time spent feeding. Overall, these
findings suggest that individuals in groups experience a trade-off between predation-related benefits and costs arising from
feeding competition. Habitat structure and forage likely influence the nature of this trade-off; thus, variation in these
ecological factors may maintain variation in group size. The role of predation pressure and other factors in explaining the
remaining variation needs further exploration.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. |
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Keywords: | Antilope cervicapra Intraspecific variation Group living Habitat structure Forage |
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