Variation in dietary breadth among groups of black howler monkeys is not associated with the vegetation attributes of forest fragments.

Habitat disturbance alters vegetation structure and composition. For example, in forest fragments, the rate of secondary plant species recruitment and mortality in species typical of old-growth forests are higher. For many arboreal primates, movement between fragments is infrequent and difficult, thus the dietary breadth of herbivorous primates that live in fragments is expected to change. It is likely that the ability of howler monkeys (Alouatta spp.) to live in a large array of habitat types is related to their ability to exploit a broad set of both difficult to digest and high energy resources. However, if small fragments have fewer trees and plant species, food selection by howler monkeys could be limited, which would undermine their persistence. To address this question, we compared the dietary breadth of 14 groups of Yucatán black howler monkeys (Alouatta pigra) living in different fragments, and hypothesized that dietary breadth should be associated to the vegetation attributes of the habitat. We characterized the vegetation structure and composition in each fragment and collected a total of 3,747 focal hr on the feeding behavior of 60 adult individuals. Dietary diversity, both in terms of the rate of plant species used as food sources (plant species used per unit of time) and percentage of ingested food from the top five plant species with overall highest ingestion rate, was not related to vegetation attributes but rather associated with the degree of folivory, such that higher folivory led to more diverse diets. Groups living in fragments with higher tree density used a larger number of trees as food sources. Therefore, black howler monkeys living in small fragments with disturbed vegetation continued to preserve diet diversity, confirming that dietary diversification is an important goal in the foraging strategy of howler monkeys.