Shade-grown cacao supports a self-sustaining population of two-toed but not three-toed sloths.
Abstract
The development of shade-grown agro-ecosystems has increasingly been identified as a strategy for conserving tropical biodiversity. While biodiversity tends to be higher in agro-ecosystems than in monocultures, the extent to which shade-grown crops support viable populations of sensitive and specialized tropical species has not been assessed. We conducted a comparative demographic study between Hoffmann's two-toed sloth Choloepus hoffmanni and the brown-throated three-toed sloth Bradypus variegatus in a shade-grown cacao farm in Costa Rica. Choloepus hoffmanni bred year-round, whereas B. variegatus bred seasonally, with females giving birth to young over a 6-month period peaking in late February. Relatively short time to offspring independence allowed B. variegatus females to breed annually, but longer periods of maternal care prevented C. hoffmanni from doing so. Annual survival rates for adult males of both species derived from radiomarking and known fates models were high (>0.90). Most adult mortality was the result of predation by domestic dogs Canis lupus familiaris and coyotes Canis latrans. Estimates of population growth rates derived from a matrix population model indicated that the abundance of C. hoffmanni, but not B. variegatus, was stable in the absence of immigration. However, genetic parentage methods indicated that significant immigration of B. variegatus into the study area occurred and that the local population may be stable. Synthesis and applications. Our results suggest that shade-grown crops embedded within an agro-ecosystem can support viable populations of some specialized tropical animals; other species, however, may require immigration from surrounding forests to maintain stable populations. More broadly, the value of human-modified landscapes for biodiversity may be overestimated when some species are dependent on immigration from intact habitats. Our results suggest that shade-grown crops embedded within an agro-ecosystem can support viable populations of some specialized tropical animals; other species, however, may require immigration from surrounding forests to maintain stable populations. More broadly, the value of human-modified landscapes for biodiversity may be overestimated when some species are dependent on immigration from intact habitats.