Food selection by a hyperdense population of red howler monkeys (Alouatta seniculus)
We studied diet choice by a generalist herbivore, the red howler monkey (Alouatta seniculus) under conditions of high and normal population density. Densities equivalent to 800–1000 km−2 (roughly 20–40 times normal) occurred in populations trapped on small, predator-free islands in Lago Guri, Venezuela. For three successive years, we studied one such population, a group of six animals living on a 0.6-ha island and compared its feeding ecology to that of two groups living at normal densities on a 190-ha island. The 0.6-ha island supported a total of 351 trees >10 cm dbh of 46 species, whereas >100 species probably occurred within the 16- and 23-ha home ranges of the two large-island howler troops. Small-island howlers were thus predicted to consume fewer resources, in particular less fruit, and to be less selective in diet choice than large-island howlers. As predicted, small-island howlers consumed fewer resources and obtained a smaller fraction of their intake from rare tree species (those contributing <1% of basal area). Small-island howlers consumed less fruit (2% of feeding time vs. 22%) and more foliage (73% vs. 55%) than the large-island groups. Diet breadth of small-island howlers was markedly less than that of their large-island counterparts. Tree species not present on the small island contributed [greater-than-or-equal]60% of leaf consumption by large-island howlers. Foliage sources preferred by large-island howlers were different in each of 3 years, whereas foliage of the same species of tree consistently ranked first on the small island. Long-term persistence (17 y) of self-perpetuating howler groups on Lago Guri islets at >20 times normal density strongly suggests that food availability does not limit mainland populations.(Accepted December 15 2004)
Key Words: food selectivity; forest fragments; Lago Guri; land-bridge island; population density; population regulation; red howler monkey; Venezuela.
c1 Corresponding author.