Document: JOD-3-52-52

Mechanisms of coexistence in Philippine bats.

SEDLOCK, J.L.*

University of Illinois at Chicago, Chicago, IL 60607, U.S.A. ¹

Abstract:
Within the framework of optimal foraging theory, I consider three mechanisms of coexistence that may contribute to the diversity of insectivorous bat communities. In the first, structural complexity among habitats provides the axis of environmental heterogeneity. Species can coexist along this axis if there is a trade-off in foraging efficiency among habitats. The second and third mechanisms involve the partitioning of the temporal and spatial variation in nightly insect abundance through a trade-off in maintenance and foraging efficiencies, and one in flight speed and foraging efficiencies. I tested these mechanisms in a Philippine insectivorous bat community within the Makiling Forest Reserve on Luzon Island. I monitored bat and insect activity along transects in three distinct and adjacent habitat types (forest, agro-forest and creek), during three time intervals over the course of 63 nights. I monitored bat activity with an AnabatII bat detector. Rhinolophids and Vespertilionds separated along an axis of habitat complexity, the former biasing its activity to more closed habitats and the latter in less cluttered habitats. Among the Vespertilionds, Myotis horsfieldii seemed to coexist with Myotis muricola and Pipistrellus javanicus by partitioning the spatial variance in insect abundance. The former foraged at higher elevations where insect abundance was lower, and the others coexisted at the rich patches through a trade-off in interference ability and foraging efficiency along a temporal axis of insect abundance. Among the Rhinolophids in the forest, R. arcuatus and R. subrufus coexist via microhabitat selection, the former selecting perches in the cluttered understory and the latter selecting subcanopy perches. The mechanism of coexistence approach has proven successful in elucidating bat community structure. By recognizing only the most salient environmental attributes that may promote coexistence, one can identify the structure in even the most complex bat communities. A further strength of this approach lies in its generality. These mechanisms may provide insights into the structure of not only other bat communities, but other taxa which are volant predators of a temporally and spatially dynamic prey.

Keywords: bats, mechanism of coexistence, optimal foraging, Philippines

This abstract is being presented at: 11:45 AM in session:
Oral Session #21: Small Mammal Population Ecology.