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Behavioral Limitation of Round‐Tailed Ground Squirrel Density

Behavioral Limitation of Round‐Tailed Ground Squirrel Density The two principal hypotheses of behavioral population regulation–territorial limitation and social stress–were tested in a 4—yr study of a high density, free—living population of round—tailed ground squirrels, Spermophilus tereticaudus, in Arizona. After couplation in early March, 22 to 31% of the adult squirrels, predominatly ♂ ♂, seemed to disperse. In late June, 29 to 45% of the juveniles, predominantly ♂ ♂ again, seemed to disperse. During the 2 yr of intensive study, these dispersal episodes were the major losses from the population, and they were correlated with the onsets of territorial behavior among adults in March and among juveniles in June. This correlation supports the hypothesis that territorial behavior limits population density. However, intensive observation and 2 field experiments involving removal and introduction of juveniles and provision of supplemental food indicate that dispersal was not statistically related to local density, food availability, or aggression. Territorial aggression did not cause emigration of adults or native—born juveniles, though it probably prevented immigration of foreign—born juveniles, during the summer months. Dispersal was not sufficient to limit population density increase. There appeared to be an innate sex difference in juvenile dispersal tendency, perhaps including a differential response to food availibility and litter size. In 1 yr, spring density was unusually high, and many squirrels were wouned in February and March. The population subsequently showed classical symptoms of physiological stress, including reduced reproduction and poor survival. This episode supports the hypothesis that high density leads to socially induced physiological stress, which eventually reduces density. However, the stress did not prevent the squirrel density from reaching a much higher level in the following spring. There were relatively few wounds and no sign of stress at the higher density. Physiological stress was not predictably related to density and was not sufficient to limit density increase. In summary, behavioral factors were not sufficient to limit squirre density when food was abundant and predation rate was low. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Ecology Wiley

Behavioral Limitation of Round‐Tailed Ground Squirrel Density

Dunford, Christopher
Ecology , Volume 58 (6) – Nov 1, 1977
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References (38)

Publisher
Wiley
Copyright
© Society for Community Research and Action
ISSN
0012-9658
eISSN
1939-9170
DOI
10.2307/1935079
Publisher site
See Article on Publisher Site

Abstract

The two principal hypotheses of behavioral population regulation–territorial limitation and social stress–were tested in a 4—yr study of a high density, free—living population of round—tailed ground squirrels, Spermophilus tereticaudus, in Arizona. After couplation in early March, 22 to 31% of the adult squirrels, predominatly ♂ ♂, seemed to disperse. In late June, 29 to 45% of the juveniles, predominantly ♂ ♂ again, seemed to disperse. During the 2 yr of intensive study, these dispersal episodes were the major losses from the population, and they were correlated with the onsets of territorial behavior among adults in March and among juveniles in June. This correlation supports the hypothesis that territorial behavior limits population density. However, intensive observation and 2 field experiments involving removal and introduction of juveniles and provision of supplemental food indicate that dispersal was not statistically related to local density, food availability, or aggression. Territorial aggression did not cause emigration of adults or native—born juveniles, though it probably prevented immigration of foreign—born juveniles, during the summer months. Dispersal was not sufficient to limit population density increase. There appeared to be an innate sex difference in juvenile dispersal tendency, perhaps including a differential response to food availibility and litter size. In 1 yr, spring density was unusually high, and many squirrels were wouned in February and March. The population subsequently showed classical symptoms of physiological stress, including reduced reproduction and poor survival. This episode supports the hypothesis that high density leads to socially induced physiological stress, which eventually reduces density. However, the stress did not prevent the squirrel density from reaching a much higher level in the following spring. There were relatively few wounds and no sign of stress at the higher density. Physiological stress was not predictably related to density and was not sufficient to limit density increase. In summary, behavioral factors were not sufficient to limit squirre density when food was abundant and predation rate was low.

Journal

Ecology – Wiley

Published: Nov 1, 1977

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