Elschot, K. (2007) Effects of poaching on seed-predatory interactions of a Neotropical palm. Master's Thesis / Essay, Biology.
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Abstract
Hunting and poaching have become a major problem in tropical forest conservation (Redford 1992). Many forests have lost most if not all large bird and mammal species and more species may disappear in the future, if human activities like hunting and habitat fragmentation don't decrease (Hughes eta!. 1997, Thiollay 1999). Because most of the large-bodied species have important ecological functions such as dispersal and predation, their decrease may have major effects on other species present in the same food web. The impact of these effects depends on the complexity of the food web; complex food webs are more stable and will have other species in the same functional group to compensate, while simple food webs might not have this option. A reduction in one species can result in shifts in population sizes of the other species in the same web (Christianou & Ebenman 2004, Borrvall et aI.2000). Predators form an important functional group in food webs, because they prevent their prey species from gaining dominance. In tropical forests, seed predators cause the density-dependent mortality that is thought to maintain high tree diversity (Janzen 1970, Connell 1971). The aim of this study was to assess the effects of mammal poaching on seed predatory interactions in the palm species Astrocaryum standleyanum. The web involves one resource, one frugivore and four seed-predators. I determined (1) the functioning of this food web, (2) how reduced mammal abundance affected the interactions within the food web, and (3) how reduced mammal abundance affected the total level of density-dependent seed mortality caused by the seed predators. In the Neotropical forest in Panama, I compared interactions at 3 high and 3 low palm density plots at each of two sites, one without poaching and one with high poaching intensity. Besides indirect interactions among seed predators via the shared resource, I found complex direct interactions among the frugivore and the seed predators in the food web.Reduction in mammal abundance changed the infestation rates of three other seed predators. The infestation rate of one predator, a bruchid beetle, increased, while infestation rates of two other predators, scolytid beetles and fungi, decreased. Seed survival increased, as the bruchid beetle did not compensate for the reduction in seed predation by mammals due to poaching. Evidence was found for density-dependent mortality due to a higher seed viability, but could not be lead back to the three nonmammalian seed predators. Thus, hunting indirectly relieved seed predation and reduced density-dependence of seed mortality in this palm species. Enhanced seedling recruitment could lead to an increase in population size of this palm at the cost of other species, and result in a decrease in biodiversity.
| Item Type: | Thesis (Master's Thesis / Essay) |
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| Degree programme: | Biology |
| Thesis type: | Master's Thesis / Essay |
| Language: | English |
| Date Deposited: | 15 Feb 2018 07:31 |
| Last Modified: | 15 Feb 2018 07:31 |
| URI: | https://fse.studenttheses.ub.rug.nl/id/eprint/9111 |
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