Title

Effects of forest fragmentation on populations of a common canopy tree in eastern Brazilian Amazonia

Date of Award

2002

Availability

Article

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Biology

First Committee Member

Theodore H. Fleming, Committee Chair

Abstract

This study investigated the effects on populations of a common canopy tree of the loss of potential seed dispersers due to forest fragmentation in eastern Brazilian Amazonia. Populations of Eschweilera coriacea (Lecythidaceae) were sampled and compared at three sites, including a 200-ha forest fragment missing a number of frugivorous mammals and two 3500-ha forest patches with apparently intact mammal faunas. Recent generations were expected to be more aggregated at the site missing mammals, and also less abundant because of decreasing seed/early seedling survival in proximity to parent trees. The size structure, density and dispersion patterns of the populations were examined in two 1-ha plots per site. The reproductive phenology of adults was monitored monthly, individual fruit crops were measured and adults were observed to identify seed predators and potential dispersers. New cohorts of seeds/seedlings were monitored monthly in transects (4400 m 2 per site) to evaluate seed dispersal, predation, germination and survival. The Janzen-Connell model of seed survival and seedling recruitment, and density-dependent effects on recruitment were examined. Differences in juvenile dispersion patterns among sites could not be related to the loss of seed dispersers, and seed dispersal was actually greater at the site missing mammals. Fragmentation could thus have been neutral or even beneficial to the dispersal of E. coriacea at this site. Although population densities varied up to fourfold, regeneration seemed adequate for the maintenance of populations at all sites. Juveniles were clumped, while adults were randomly distributed. A negative effect of adult density on juveniles was found, whereas seed/seedling survival was positively related to fruiting tree density. Differential mortality close to adults supported the Janzen-Connell model. Flowering peaked at the beginning of the wet season, and fruiting extended over the second half of the wet season. Seed production was synchronized. Increased seed/seedling survival during a high production season suggested predator swamping and led to greater seedling recruitment. Less variation in seed production between years was observed in the smallest fragment, which may have been a consequence of fragmentation if, for example, pollination processes were disrupted, leading to a decline in seed production during "favorable years."

Keywords

Biology, Botany; Biology, Ecology; Environmental Sciences

Link to Full Text

http://access.library.miami.edu/login?url=http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3071289