Impacts of hunting on tree and vertebrate communities in French Guiana

Abstract

Vertebrates are hunted throughout the tropics, resulting in severe declines of their populations. These vertebrates play crucial roles in shaping tropical forests, through processes such as seed dispersal, seed predation and browsing, which affect the survival chances of seeds and tree recruits (i.e. seedlings and saplings). The loss of vertebrates is therefore thought to affect the composition of recruit communities, eventually resulting in compositional changes in adult tree communities. In the long-term this might affect the forest biodiversity, carbon sequestration and nutrient cycling. Hunting is non-random, as vertebrates with a large body mass are the favored game species. Therefore hunting particularly affects populations of large vertebrate species. Body mass and other vertebrate functional traits, as well as functional traits of fruits, seeds and leaves, drive the interactions that lead to seed dispersal, seed predation and browsing. Therefore, hunting likely decreases survival changes for particular tree species, while increase them for others, depending on their functional traits. Consequently, hunting hypothetically affects the fruit, seed and leaf composition of tree recruit communities. How hunting affects tropical forests remained largely unclear, and the aim of this research was to better this. Due to the importance functional traits in vertebrate – fruit and vertebrate – leaf interactions, the focus of this research lied mainly on functional traits and functional composition. First the research focused on looking at how hunting affects the functional composition of vertebrate assemblages, by comparing hunted and non-hunted assemblages across French Guiana. Next, the question was which vertebrate and fruit traits were important for vertebrate – fruit interactions, and if these relationships were different between hunted and non-hunted species. For this a large dataset was compiled, through a literature search, of fruit traits, vertebrate traits and vertebrate – fruit interactions. Finally, differences in functional composition of tree recruit communities in relation to the levels of hunting-induced defaunation were tested, for which data of eight tree recruit and adult communities across French Guiana were collected, each with its own level of defaunation. This study showed that hunting affects the functional composition of vertebrate communities, and that hunted vertebrates interact with different fruits compared to non-hunted vertebrates. Furthermore, hunting-induced defaunation was found to be related to the functional composition of the tree recruit communities. However, these relationships were with leaf traits rather than with fruit and seed traits, suggesting that hunting strongly affects browsing. As browsing has so far received little attention in the context of hunting, this finding is a particularly important new insight. The findings of this research provide new tools for nature managers and policy makers to formulate strategies for the conservation of tree communities of tropical forests.