BONACCORSO: A PANAMANIAN BAT COMMUNITY


however, the very narrow niche breadths of the other specialists seem
to be the result of small samples in calculating niche breadths. There is
a significant positive correlation between sample size and the number
of plant species in Table 4 (r = 0.865).
 Niche overlap in food species is compared in Table 5. The highest
values of overlap occur between species most similar in size. A.
phaeotis overlaps little with all the fig specialists, except for V. helleri,
which is similar in size to A. phaeotis. The high values of overlap be-
tween many of the fig specialist species indicate that some mechanism
other than selection of food species must reduce behavioral in-
terference and/or interspecific competition for food in this guild if food
is a limiting factor.
 Several types of evidence suggest that, at least during some parts
of the year, food is a limiting factor for fruit bats on BCI. The biomass
of fruit and the number of species of fruiting trees fluctuate quite
drastically on a seasonal basis (see Phenology section). During the late
wet season fruit availability is low, and an increased proportion of cap-
tured fruit bats have empty stomachs (83% in Oct-Nov) as compared
to times of fruit abundance (71% in Mar-Apr). Also in the late wet
season various other frugivorous mammals come to the laboratory
clearing with increased frequency to seek food (Foster 1973). By the
late wet season several species of fruit bats have temporarily moved
out of the study area in response to low food levels (Bonaccorso and
Humphrey, in prep.). Even when fruit is very abundant in terms of
total biomass, many types are concentrated in a limited amount of
space, the few trees fruiting at any moment, and may still be a limiting
factor for population size.
 VERTICAL STRATIFICATION..-Handley (1967) and Harrison (1962)

TABLE 5.-FEEDING NICHE OVERLAPS (C) AMONG SPECIES OF CANOPY FRUGIVORES.
 LOWER DIAGONAL INDICATES OVERLAP BETWEEN FIG SPECIALISTS MOST
 SIMILAR IN SIZE.



 0 5



 A. phaeotis .215 .345 .615 .241 .465 .485 .518
 V. pusilla .968 .452 .796 .679 .272 .152
 C trinitatum .893 .743 .644 .209 .412
 V. helleri .798 .886 .852 .452
 C. villosum .727 .200 .310
 V. caraccioloi .994 .962
 A. jamaicensis .983


1979