A North Temperate Bat Community: Structure and Prey Populations

Abstract

Food habits and food partitioning were investigated in a North Temperate insectivorous bat community. Analysis of fecal material showed a differential utilization of moths and beetles—the two groups of insects that generally contribute the greatest to diets of insectivorous bats. Based on several criteria, most bats could be classified as either moth or beetle strategists. Most species of bats were in the 5 to 10-gram weight class. The abundance of species in this weight class is hypothesized to be a reflection of the abundance of insects in the 6 to 10-millimeter length class. Various mechanisms for partitioning prey are discussed and a model of habitat partitioning is presented. Various parameters of the potential prey population were investigated. Moths appear to be the most abundant and predictable and, in terms of size, the most diversified nocturnal insect group. Coleoptera are second in diversity of size followed by Hymenoptera, Diptera, Homoptera, and Hemiptera. Insects in the 6 to 10-millimeter length class were the most abundant. At certain localities in the southwestern United States as many as 18 species of insectivorous bats may be captured with mist nets placed over water surfaces (Jones, 1965, 1966). All species known to occur in an area are rarely captured on a given night, but capture of 8 to 10 species is not unlikely. Diversity of species in the genus Myotis is especially high—4 to 7 species are often captured. A question which follows from these observations is: To what extent is coexistence of these bats related to partitioning of food resources? I began a study in March 1970, which sought answers to this question by an investigation of the food habits of the bats at one of these localities. Answers were sought also to the following questions: What is the nature of food partitioning, if it occurs? What is the structure of the bat community? What is the structure of the prey community?