Shade‐grown cacao supports a self‐sustaining population of two‐toed but not three‐toed sloths

Abstract

Summary1. 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 agroecosystems than in monocultures, the extent to which shade-grown crops support viable populations of sensitive and specialized tropical species has not been assessed. 2. 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 shadegrown cacao farm in Costa Rica. 3. 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. 4. Annual survival rates for adult males of both species derived from radiomarking and known fates models were high (>0Á90). Most adult mortality was the result of predation by domestic dogs Canis lupus familiaris and coyotes Canis latrans. 5. 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. 6. 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.

Natal dispersal of tree sloths in a human‐dominated landscape: Implications for tropical biodiversity conservation

“…The natal dispersal movements we observed herein suggest that previous estimates were biased low as a result of emigration that went undetected in the absence of telemetered individuals. Based on the model of Peery and Pauli (), an annual survival rate of 0.550 prior to adulthood is expected to lead to a stable population of three‐toed sloths, and our telemetry‐based survival estimates are thus consistent with a growing population. As a result, the agriculturally dominated landscape at the centre of this study appears to retain the habitat elements needed to sustain sufficiently high juvenile survival, including during natal dispersal, to maintain a viable population of this forest‐obligate species.…”

“…Indeed, survival rates were high for both species: extrapolating from monthly estimates, annual estimates ranged from 0.88 to 1 in the three stages for two‐toed sloths and from 0.68 to 1 for three‐toed sloths. These annual survival estimates were greater than that estimated by Peery and Pauli () using mark–resighting methods for both two‐ (0.726) and especially three‐toed sloths (0.304). The natal dispersal movements we observed herein suggest that previous estimates were biased low as a result of emigration that went undetected in the absence of telemetered individuals.…”

“…We assigned each young sloth into one of the three stage classes based on its association with its mother and space use at the time of each relocation: (1) recently born dependent individuals that were still being carried by their mother; (2) independent individuals that were no longer being carried by their mother, yet remained in their natal home range and (3) dispersing individuals that had left their natal home range. We considered a juvenile to have dispersed if it left its natal home range before it reached adulthood (3 years; Peery & Pauli, and Taube, Keravec, Vié, & Duplantier, ) and its natal home range did not overlap its adult home range. Natal home ranges were defined as the area used by young sloths during the dependent stage, whereas adult home ranges were defined as the area used by adult sloths once they appeared to settle down in a territory following dispersal.…”

“…Next, we removed the season effect given an a priori expectation that this factor was less important than species and stage (model 4) and then evaluated support for a stage‐only model (model 5). Once we selected the most supported model structure for transition probabilities, we repeated the process for survival and also evaluated support for a species by season interaction given that three‐toed sloths time key life‐history events, such as reproduction, to the dry season (Peery & Pauli, ; models 6–12). The probability of recapture was set to 1 in all models because we detected all radio‐tagged sloths in each month that they were alive.…”

A syndrome of mutualism reinforces the lifestyle of a sloth

“…Descending a tree is both risky and energetically costly for any sloth. Indeed, it is the leading cause of mortality for a sloth; more than one-half of all adult sloth mortalities we have documented were depredation events when sloths were at or near the ground [12]. Furthermore, we estimate that the average cost of descending from the canopy to defecate constitutes approximately 8% of a sloth's daily energetic budget (see the electronic supplementary material for details).…”