Observations of the sloths allowed the scientists to estimate female reproductive timing and frequency. Researchers estimated sloth survival rates using information from radio collared adult males over a two-year period. These data were then used to estimate the population growth rates for each of the species. Lastly, the team employed an innovative genetic kinship approach to estimate the degree to which immigrants contributed to the population growth of each species.
Not surprisingly, their findings indicated that both species avoided monocultures and human development, preferring intact tropical forest patches instead. The two-toed sloth used some pastures, while the three-toed sloth avoided pastures altogether. Both species also slightly avoided or showed neutrality toward the shade-grown cocoa crops.
In general, the Hoffman's two-toed sloth used a greater variety of tree species than that of the brown-throated three-toed sloth. A dietary generalist, the two-toed sloth consumed some fruit and animal matter in addition to a variety of tree leaves. In contrast, the three-toed sloth exhibited a much stronger dependence on intact tropical forest, and fed only on two tree species within the agro-ecosystem.
Peery and Pauli concluded that the two-toed sloths in their study area constituted a stable population, and even demonstrated positive population growth. However, the population of three-toed sloths did not fare nearly as well and relied on immigration from adjacent, intact ecosystems.
The greater adaptability of the two-toed sloth in its use of habitat and resources explains its better success among shade-grown crops, according to the researchers. On the other hand, the three-toed sloth's more specialized diet and habitat requirements meant the species couldn't survive solely in shade grown cocoa plantations.
In a broader sense, these conclusions contribute to our understanding of how other Neotropical arboreal mammals, such as primates, may fare in modified habitats. As Peery and Pauli explain, "our results indicate that some generalists are more resilient to the conversion of tropical forests to shade-grown agricultural systems than specialists."
Therefore, while shade-grown agro-ecosystems, such as the cocoa plantation in Costa Rica, support more animal species than monoculture systems, they may be inadequate for habitat specialists like the three-toed sloth.
The researcher's findings imply that shade-grown agro-ecosystems are not the magic answer to biodiversity loss. Rather, they are a positive alternative to be used with other conservation strategies.
Read more: http://news.mongabay.com/2015/0422-widmayer-sloths.html#ixzz3YQVGhk3q