August, Peter V. (1981) Population and Community Ecology of Small Mammals in Northern Venezuela.
Population and community Ecology of Small Mammals in Northern Venezuela
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PETER V: AUGUST
Boston University Graduate School, 1981
Major Professor: Thomas H. Kunz, Associate Professor of Biology
Small mammals were studied in two research areas in northern Venezuela for two years. The first study site was in premontane tropical forest located in Parque Nacional Guatopo. The objective of this aspect of the srudy was to estimate population density, monitor movements, and test for microhabitat selection in mammals within a 160 g to 5000g size range. Mammals of this size are difficult to study using traditional grid methods; therefore, I used a transect-assessment line configuration of large National live traps. The second site was located in the llanos of Venezuela. The objective of this portion of the study was to evaluate the effects of seasonal environment and a patchy distribution of habitats on small mammal population ecology and mammalian community structure.
In 11 months of censusing on transect and assessment trap lines in the Guatopo study area, I collected sufficient data on three species of mammals (Didelphis marsupialis, Sciurus granatensis, and Proechimys semispinosus) to estimate population size. The densities derived were 0.37 Didelphis/ha, 0.13 Sciurus/ha, and 0.45 Proechimys/ha. These values compare favorably with reported densities for these species in other habitats, however, they were consistently on the low extreme. This may result from biases inherent in using large live traps set on the ground as well as the tendency for other studies using grid configurations of traps to overestimate density.
Movement patterns were most affected by the geometry of trap placement and less affected by age, sex, and breeding condition of each species.
Didelphis was found to be a habitat specialist and preferred streamside environments. Proechimys was a habitat generalist.
Sciurus showed a weak preference for hillside habitat. The community matrix of these taxa showed no evidence of interspecific competition.
In the Llanos censusing, 38.329 trap nights yielded 387 captures of 197 individuals. Small mammal density and species richness varied among grids and temporally within grids. Marmosa robinsoni and Zygodontomys brevicauda capture rates varied seasonally; Marmosa captures rates declined in the wet season and Zygodontomys captures increased at the onset of the rainy season. Reproductive activity in Marmosa was greatest at the end of the dry season and start of the wet season. Zygodontomys and Heteromys anomalus showed no distinct seasonal patterns in reproduction. Movement patterns and home range size for Marmosa and Zygontomys were associated with the dispersion of preferred habitat. As optimal habitat became patchily distributed, movements and home range size increased. There was little overlap in home range of male Marmosa and this suggests a territorial spacing system, however, captures were insufficient to documents this with certainty. Habitat selection in Marmosa and Zygodontomys was also associated with the distribution of preferred habitat. When favored habitat was continuous, there was no evidence of habitat selection. When favored habitat was patchy in distribution, habitat selection was apparent.
The Venezuelan Llanos contains a depauparate small mammal fauna. This is likely due to historical and environmental reasons. Habitat complexity and habitat heterogeneity were poorly correlated with small mammal diversity, density and biomass. Total mammal species richness (exclusive of bats) was strongly correlated with measures of habitat complexity and less so with heterogeneity. Complex habitats had larger mammal faunas due to the expansion of existing ecological guilds rather than guild addition. Llanos mammal communities were highly structured; the relative abundance of mammals in foraging and locomotor classes was relatively constant among study areas regardless of species density.