| Density-dependent mortality of dominant plants caused by host-specific plant pathogens may help prevent competitive exclusion and maintain high tree species diversity in the tropics. Additionally, natural and anthropogenic changes in forest structure that affect microclimate may alter plant disease development and the ecological impacts of disease.I investigated the impacts of pathogens on seed and seedling mortality and the maintenance of seedling diversity in the lowland tropical moist forest of Los Tuxtlas Biosphere Reserve, Mexico. First, I found that seedling diversity was greater in control plots than when soil-borne pathogens were excluded by treatment with fungicide, as predicted if pathogens help reduce competitive exclusion and enhance community diversity during the seed-to-seedling transition. However, community evenness did not differ between control and fungicide plots, and more common species were not more likely than rare species to benefit from the removal of pathogens. In contrast to previous studies, I found a no significant difference between seedling diversity and the diversity of the seed rain. Second, I used fungicide applications to assess the impacts of pathogens on seed germination of nine plant species across forest understory sites, light-gaps, and fragments, and compared the impact of pathogens on shade-tolerant vs. pioneer species. Fungicide treatment significantly increased seed germination across species. Disease pressure varied among species, but contrary to previous results, pressure was greater for the more shade-tolerant species. Spatial variation in microclimate was not associated with variation in pressure from soil-borne pathogens. These results suggest that plant pathogens may play some role in maintaining the diversity of tropical trees, but disease impacts vary greatly across tree species, time, and space.Finally, I examined the perceptions of scientists and practitioners on the use of scientific ecological knowledge in the management practices of Los Tuxtlas Biosphere Reserve to identify novel approaches to integrate ecological theory into conservation strategies. Little scientific ecological knowledge is being used to inform specific management actions in the reserve. The lack of institutional capacity, inadequate infrastructure, small budgets, and lack of time prevent managers from seeking ecological information, while the demand to publish in academic journals and the lack of funding opportunities limit scientists to engaging in applied activities. Formal, long-term collaborations between institutions could help to close the existing gap between conservation scientists and practitioners, and ultimately enhance knowledge transfer. |
