Leah
Card
M.A. Conservation
Biology, 2010
Assessing fruit
availability for
a generalist frugivore, the blue monkey (Cercopithecus mitis), in the Kakamega Forest, Kenya
Many studies
have aimed to estimate fruit availability per individual tree and
across a habitat to better understand the foraging ecology of
frugivores. In this study, I evaluated various methods commonly used to
estimate fruit availability by comparing assessments within single
species based on fruit biomass estimates (g of fruit/ tree), DBH of the
trunk, and estimated crown volume for each of 11 tree species that are
important food resources for a frugivorous primate, the blue monkey (Cercopithecus mitis).
I conducted transect surveys throughout each of four monkey home ranges
to compare food tree density, diversity, and size structure. Using the
11 focal species to index available food resources for the monkeys, I
compared the total fruit biomass, crown volume, basal area, and food
availability index, which combined basal area and monthly phenological
data, among the four home ranges. I found that the fruit biomass
estimation was related to the DBH measurement for 2 species and to the
crown volume measurement for 3 species out of the total 11 species,
which suggests that proxy measures used to estimate fruit production do
not correlate consistently across species. The four home ranges shared
similar size structure, species richness, species-area curves, and
species diversity; however, the differences in species composition,
tree abundance, and basal area led to differences in total estimated
fruit production and home range quality. However, when Croton megalocarpus,
a species that has high fruit production, is less preferred by the
monkeys, and varied in abundance among the home ranges, was removed
from the calculations of total estimated fruit production and home
range quality, all four measures agreed in identifying the top two home
ranges in terms of fruit production; however the rank order of the two
lower ranking home ranges was not consistent. When used to combine
estimations across multiple species, size measurements such as DBH and
crown volume do not account for differences in fruit density and
biomass among species. The fruit biomass estimation can account for
these differences and is probably the best method to use despite some
potential for error. However, as it is difficult to estimate fruit
biomass, the use of easier measures such as DBH and crown volume will
continue in studies of food availability.