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Predation, Cover, and Food Manipulations During a Spring Decline of Microtus townsendii

Mary J. Taitt and C. J. Krebs
Journal of Animal Ecology
Vol. 52, No. 3 (Oct., 1983), pp. 837-848
DOI: 10.2307/4458
Stable URL: http://www.jstor.org/stable/4458
Page Count: 12
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Predation, Cover, and Food Manipulations During a Spring Decline of Microtus townsendii
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Abstract

(1) We manipulated, in combination, predation, cover, and food for populations of Microtus townsendii during spring 1981. (2) We suspended fish net over grassland to reduce heron predation, cut the grass to increase predation and decrease cover, spread straw to increase cover, and provided whole oats as extra food. (3) In the first 6 weeks of spring, high precipitation caused flooding, natural cover was poor, and peak numbers of herons were present. In the following 4 weeks there was no flooding, natural vegetation was improving, and few predators were present. (4) Populations protected from predation had higher immigration, survival, and density than unprotected populations in the 6-week period, while populations with extra cover and food increased in number. Voles with food were heavier and reproduced earlier than voles on all other grids. (5) All populations, irrespective of treatment, exhibited compensatory loss in the later 4-week period. In this period, males moved more and had more wounds, while females were lactating and had shorter movements than in the early spring. (6) We conclude that the first 6-week period of the 1981 spring decline was the result of predation, and the last 4-weeks of the decline was the result of density-dependent dispersal, possibly induced by interactions with mature females.

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