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The Evolution of Coloniality in White-tailed and Black-tailed Prairie Dogs (Sciuridae: Cynomys Leucurus and C. Ludovicianus)

John L. Hoogland
Ecology
Vol. 62, No. 1 (Feb., 1981), pp. 252-272
Published by: Wiley
DOI: 10.2307/1936685
Stable URL: http://www.jstor.org/stable/1936685
Page Count: 21
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The Evolution of Coloniality in White-tailed and Black-tailed Prairie Dogs (Sciuridae: Cynomys Leucurus and C. Ludovicianus)
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Abstract

In a 6-yr study, I investigated possible selective bases for coloniality in two species of squirrels (Sciuridae): loosely colonial White-tailed Prairie Dogs (Cynomys leucurus) and densely colonial Black-tailed Prairie Dogs (C. ludovicianus). White-tail study sites were in Wyoming and Colorado, USA; Black-tail study sites were in Colorado and South Dakota. I examined three hypotheses that might explain the evolution of coloniality: (a) shortage of suitable habitat, (b) social facilitation of foraging, and (c) reduced predation. The apparent surplus of unused suitable habitat and the absence of isolated individuals both indicated that prairie dogs are not forced to live together because of habitat shortages. An analysis of prairie dog foraging patterns indicated that there is no social facilitation of foraging in terms of either (a) group hunting of either large or elusive prey, (b) the location of large, scattered food supplies, (c) modification of the soil in order to effect the growth of vegetation that is more favorable or more abundant than that which would otherwise result, or (d) group defense of foraging grounds. Three lines of evidence indicate that reduced predation may be the most important benefit of prairie dog coloniality. First, simulated predatory attacks by badgers (Taxidea taxus) indicated that individuals in large wards (subcolonies) detect predators more quickly than do individuals in smaller wards; further, Black-tails detect predators more quickly than do White-tails. Second, individuals in large wards devote proportionately less time to alertness (i.e., scanning for predators) than do individuals in smaller wards, and Black-tails are less vigilant than are White-tails. Third, breeding synchronization and center-edge differences in individual alertness both indicate the possible importance of self herd effects. Interspecific differences in ward size and ward density may ultimately result because White-tail habitats contain significantly more protective cover than do Black-tail habitats.

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