Fragmentation and Alteration of Seed Dispersal Processes: An Initial Evaluation of Dung Beetles, Seed Fate, and Seedling Diversity1

Given current accelerated trends of tropical land conversion, forest fragments are being incorporated into many conservation programs. For investing in fragments to be a viable conservation strategy, forest fragments must maintain their ecological integrity over the long term. Based on fieldwork in 22 forest fragments in the crater lakes region of western Uganda and in the continuous forest of Kibale National Park, we examined (1) seed predation on experimentally dispersed seeds, (2) abundance and composition of the dung beetle community that may play a major role in removing seeds from sites of high seed predation, and (3) compared the fragments’ seedling community composition to adult tree community composition and the seedling community in continuous forest. First, the rate of seed removal at experimental stations was lower in forest fragments (85% remaining after 1 day) than at stations in the continuous forest (79% remaining) and the probability of stations being discovered by seed predators was lower in fragments (23%) than in the intact forest (41%). Second, there was a 62 percent decline in fragment dung beetle abundance. The magnitude of this decline varied among dung beetle guilds that process dung and seeds in different fashions. The abundance of large rollers that move large seeds away from sites of defecation did not differ, but medium and smaller rollers and burying beetles that process small and medium-sized seeds were less common in the fragments than in the intact forest. Finally, we compared the seedling community composition relative to adult tree community composition by identifying all adult trees in each fragment and by sampling the composition of the seedling community. We found some evidence to suggest that there was movement of seeds among forest fragments by large-bodied dispersers, particularly chimpanzees (Pan eoghdytes) and hornbills (Ceratogymna subcylindricus). Key word: Dung beetks; jagmentation; ki‘bak National Park; regeneration; rodents; seed dispersal; UganL. HUMAN MODIFICATION OF ECOSYSTEMS IS THREATENING BIODIVERSITY ON A GLOBAL SCALE (Laurance 1999, Nepstad et al. 1999, Chapman & Peres 2001). Modifications to tropical forests do not just result in forest being uniformly reduced in size; they also result in forest being fragmented. It is critical that we understand the conservation value of these fragments because less than 5 percent of tropical forests are legally protected (Oates 1996) and national parks and reserves, even if effectively protected, will fail to conserve species for which Received 14 November 2002; revision accepted 16 June 2003. ranges do not fall within a protected area. As a result, conservation of many tropical forest species will depend on the capacity of fragmented forests to support their populations. For fragmented forest to have an important conservation value, they must maintain their ecological integrity sufficiently to maintain target species over the long term. This requires that ( 1 ) fragments are not further degraded by human activities and (2) ecological processes operating in fragments are maintained. With respect to the first requirement, unfortunately much of the previous work on fragmented habitats has involved the study of fragments in protected areas and has largely ignored