BONACCORSO: A PANAMANIAN BAT COMMUNITY


tides it can efficiently find and handle. The weight that a bat can carry
in flight without seriously impeding maneuverability probably sets
the upper limit on food particle size for these animals. In fact, A.
jamaicensis selects F. insipida fruits that are 1.7 times larger than the
average weight of available fruits (Morrison 1978, this study). The
largest figs are left because they are too heavy for effective flight.
 The distribution of mean body weights for each bat species on BCI
by guild is plotted in Figure 16. The species within the groundstory
frugivore, canopy frugivore, and piscivore guilds increase in body
weights by a geometric progression of 1.3 to 1.8, with one exception in
the canopy frugivore guild. The relationship between body size and
food size may also be important as a means of resource partitioning
within other guilds: the two species of Pteronotus differ in mean
weight by a factor of 1.4, the three species of Mycronycteris differ by a
factor of 1.5, the males of the sexually dimorphic emballonurids differ
by a factor of 1.2 to 1.5. Unfortunately adequate data on food particle
selection exists only for the three largest canopy frugivores in this
study and for the emballonurid insect-eaters studied by Bradbury and
Vehrencamp (1976), all of which roughly select food particles in direct
proportion to body weight. However, the circumstantial evidence of
strictly adherable increments in body weight within a guild suggest
that food particle size is an important mechanism of food partitioning
and a selective factor controlling body size within the above mentioned
guilds.

FORAGING AND REPRODUCTIVE STRATEGIES
CANOPY FRUGIVORES
 Many fruits preferred by bats have attributes of color, odor, taste,
 etc. that reduce their availability to, or preference by, most other kinds
 of fruit-eating animals (Humphrey and Bonaccorso 1978). Hence,
 many of the competitive interactions any bat species encounters over
 fruit resources, either in ecological or recent evolutionary time, are
 with other species of bats of its own feeding guild or other individuals
 of its own species. However, competition between fruit bats and other
 frugivorous animals does occur. Morrison (1978) calculated that black
 howler monkeys (Aloutata palliata) and the Jamaican fruit bat (Ar-
 tibeus jamaicensis) roughly consume 9% and 7% of the annual BCI fig
 crop respectively. The howlers prefer unripened figs (Hladik and
 Hladik 1969), while Artibeus and other bats will eat only mature
 fruits. Thus, howlers reduce the total fig crop that can become
 available to fruit bats. Fruits preferred by canopy frugivore bats seem
 to be unimportant food items for birds.