Impacts of hunting on seed dispersal in a Central African tropical forest.

摘要

Throughout the tropics, mammalian seed dispersers are being hunted to local extinction, generating concern not only about the loss of these species, but also about the consequences for plants they disperse. In this dissertation, I compare two rainforest sites in Cameroon---one with heavy hunting pressure and one protected from hunting---to appraise the loss of mammalian seed dispersers and to assess the impact of this loss on (1) hornbills in genera Ceratogymna and Bycanistes (which compete with mammals for fruits), and (2) Antrocaryon klaineanum (Anacardiaceae), a tree which relies on mammals for seed dispersal.;Surveys of arboreal frugivores indicate that three of the five monkey species, as well as chimpanzee and gorilla, have been extirpated from the hunted forest. However, hornbills seem to be thriving, with higher diversity, relative abundance, and diet species richness than in protected forest. I found evidence that they consume fruits of 50 species of tree and liana, disperse 26 species to their nest sites, and seedling plot surveys at nests confirmed that hornbill activity influences seedling composition in both protected and disturbed forests.;Although hornbill-diet species are receiving dispersal services, mammal-dispersed species (such as A. klaineanum) may be in peril. Diaspore counts underneath A. klaineanum adults indicate that seed removal is severely reduced in the hunted forest. Furthermore, genetic exclusion analysis of maternally-inherited endocarp tissue from diaspores collected under the canopies revealed that seed dispersal in the hunted forest is also greatly reduced. Far fewer seeds had an origin other than the putative "mother" above in the hunted than the protected forest (2% vs 48%) and far fewer seeds were dispersed away from conspecific canopies (4% vs. 88%). This results in an effective genetic neighborhood (Ne) that 55% smaller in the hunted forest (3.49 vs. 7.83) and an effective neighborhood area that is less than one-sixth that in the protected forest (0.42 vs 3.09 km2).;This study provides strong evidence that loss of dispersal agents can lead to reduced seed dispersal and drastically reduced genetic neighborhoods, disrupting the dispersal loop and creating an acute risk of loss of genetic variability.