Nursery Roosts and Community Diversity of Nearctic Bats

Abstract

The hypothesis is presented that, because roosts are of survival value and bats have various adaptations for coloniality, the distribution and abundance of colonial Nearctic bats is determined largely by the availability of suitable roosts. Nearctic bat faunal size is correlated with the presence or absence of structures used for roosting. Both faunal size and community diversity vary in a geographically patchy rather than clinal fashion, implying little correlation with length of the growing season or diversity of insect communities. High bat diversity characterizes areas where all types of roost structures occur, whereas some kinds of roosts are missing in places of low bat diversity. A species' “contribution to diversity” (H′n) shows in which parts of its range it is an important contributor to its community. Each species uses particular sorts of roosts, and in summer a roost typically contains only one species. High survival rates, strong site attachment, and low natality rates are striking demographic adaptations of the more colonial species. Probably the key benefits of roosts are physiological advantages ensuring optimal growth of embryos and young and successful overwintering. Possible physiological and behavioral adaptations that may enable bats to take full advantage of roosts are suggested. I anticipate that the interaction of physiological requirements with the opportunities provided by summer and winter roosts will dominate future explanations of the distribution and relative abundances of temperate zone bats. The importance of roosts indicates that roosts should be managed as a key feature of the habitat of bats whose populations are in need of protection.