PARENT SESSION
Session #18: Mechanisms underlying the maintenance of diversity and mode of regeneration in tropical forests: tests of alternative hypotheses. Organized by: W.P. Carson, C. Gehring, and T. Theimer.
Wednesday, August 8, 2001. Madison Ballroom B
Ground-dwelling vertebrates, mycorrhizal fungi and seedling diversity in an Australian tropical rain forest.
Gehring, Catherine1,2, Theimer, Tad1,2, 1 2
ABSTRACT- The role of vertebrates in maintaining tropical tree diversity is a question of critical importance given the increasing anthropogenic impacts on tropical systems and their native vertebrate populations. Although interactions between selected vertebrate and tree species have been studied repeatedly, experimental tests of the community level effects of vertebrates are relatively rare. We excluded ground-dwelling vertebrates from 14 6 x 7.5 m plots in an Australian tropical rainforest for 3 years and monitored seedling recruitment, survival and growth, as well as mycorrhizal innoculum potential. Vertebrate exclusion resulted in significantly higher seedling recruitment and seedling survival, leading to significantly greater seedling abundance and species richness. Differences in seedling survival were significant only for new recruits during the first 6-12 months after recruitment. Vertebrate exclusion also resulted in significantly reduced mycorrhizal innoculum potential based on bioassays using both corn and a native rainforest tree. In corn, these differences in mycorrhizal colonization led to significant differences in growth. However, for rainforest seedlings, increased mycorrhizal innoculm potential apparently did not overcome the negative effects of vertebrates, as growth on exclosure plots was significantly higher than on controls. The major effect of ground-dwelling vertebrates in this system was to reduce the overall abundance of seedlings. Although this reduction resulted in lower species richness, diversity did not differ between treatments, in part because the increase in species richness in the absence of vertebrates was offset by a decrease in evenness.
KEY WORDS: rain forest, diversity, mycorrhiza, seedling dynamics