Effects of Sevin on Small-Mammal Populations in Agricultural and Old-Field Ecosystems

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Abstract
The objective of this investigation was to quantify effects of an insecticide (Sevin) on the population dynamics of meadow voles (Microtus pennsylvanicus) and feral house mice (Mus musculus) contained within agricultural and old-held communities. The study area consisted of eight 0.1-ha plots enclosed by sheets of 20-gauge galvanized steel. Agricultural plots were planted to oats (Avena sativa) then permitted to proceed into secondary succession the following year. Densities of Mus populations in agricultural plots were 50–75% higher in the sprayed plots following treatment as compared to control plots. Conversely, densities of Microtus populations in agricultural plots were significantly lower in sprayed plots following treatment as compared to control values. This difference was attributed to the effect of the insecticide on pregnant female voles which exhibited a delay of 5–6 weeks in an increase in the reproductive rate following treatment. No differences in population densities of Mus or Microtus related to treatment were found in the old-field community at any time. Trapping efficiencies did not differ significantly between treatments for either community type, although Mus was recaptured nearly twice as frequently as Microtus within both community types. Trapping efficiency for both Mus and Microtus was significantly higher in the old-field community than the agricultural community. The agricultural community exhibited higher rates of plant productivity, higher small-mammal reproductive rates, and higher small-mammal carrying capacities, but lower total community stability, than the old-field community.