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                    Leah Card

                           M.A. Conservation Biology, 2010

Leah_Card.jpgAssessing 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.