PARENT SESSION
Oral Session #105: Conservation Ecology: Biodiversity.
Presiding: L. Alonso
Friday, August 9. 9:00 AM to 12:00 PM. Grand Ballroom Central, Radisson.
Ecological consequences of the selective mammalian defaunation in tropical rain forests.
Mendoza, Eduardo*,1, Dirzo, Rodolfo1, 1 Instituto de Ecología, Universidad Nacional Autónoma de México, México, D.F., México
ABSTRACT- Studies of the conservation of rain forest mammals indicate that medium/large species are particularly prone to extinction due to anthropogenic perturbation. Small mammals may be unaffected or even benefited. Nevertheless, information on the effects on ecological processes is very limited. The aim of this study was to explore such effects by means of field surveys and experiments in three comparative Mexican rainforest sites along a perturbation gradient. Standardized linear transects were carried out to assess the conservation status of the medium-large sized mammalian fauna through diurnal and nocturnal sightings and track detection. To test if small mammal populations may undergo an ecological release in the absence of medium-large mammals (predators and competitors) trapping was carried out at the same sites. Additional experiments were carried out in the most conserved site to explore the effects of selective defaunation on seed predation/dispersal. We predicted that the absence of medium/large mammals and abundance of rodents would increase predation of small seeds. Experiments tested: a) dietary preferences of small rodents in laboratory cages, b) small-rodent seed removal using field exclosures, c) seed removal rates and fate in free-access plots and in plots with access only to small rodents. Experiments were carried out in a paired design using seeds of plant species (taxonomic family) of contrasting seed masses. While medium/large were very sensitive to human perturbation, small rodents were able to withstand perturbation. Experiments of dietary preference and removal showed a consistent preference of rodents for small versus larger seeds. Seed removal rates were faster for small seeds although most of the seeds (small and large) were removed in a lapse of a few days. This study suggest that selective defaunation may affect plant recruitment patterns and tropical forest diversity.
KEY WORDS: defauntation, tropical conservation, seed predation, plant recruitment