The influence of anthropogenic edge effects on primate populations and their habitat in a fragmented rainforest in Costa Rica

Abstract

When a forest is fragmented, this increases the amount of forest edge relative to the interior. Edge effects can lead to loss of animal and plant species and decreased plant biomass near forest edges. We examined the influence of an anthropogenic forest edge comprising cattle pasture, coconut plantations, and human settlement on the mantled howler (Alouatta palliata), white-faced capuchin (Cebus capucinus), Central American spider monkey (Ateles geoffroyi), and plant populations at La Suerte Biological Research Station (LSBRS), Costa Rica. We predicted that there would be lower monkey encounter rate, mean tree species richness, and diameter at breast height (DBH) in forest edge versus interior, and that monkeys would show species-specific responses to edge based on diet, body size, and canopy height preferences. Specifically, we predicted that howler monkeys would show positive or neutral edge effects due to their flexible folivorous diet, large body size, and preference for high canopy, capuchins would show positive edge effects due to their diverse diet, small body size, and preference for low to middle canopy, and spider monkeys would show negative edge effects due their reliance on ripe fruit, large body size, and preference for high upper canopy. We conducted population and vegetation surveys along edge and interior transects at LSBRS. Contrary to predictions, total monkey encounter rate did not vary between the forest edge and forest interior. Furthermore, all three species showed neutral edge effects with no significant differences in encounter rate between forest edge and interior. Interior transects had significantly higher mean tree species richness than edge transects, and interior trees had greater DBH than edge trees, although this difference was not significant. These results suggest that forest edges negatively impact plant populations at La Suerte but that the monkeys are able to withstand these differences in vegetation.

Howling on the edge: Mantled howler monkey (Alouatta palliata) howling behaviour and anthropogenic edge effects in a fragmented tropical rainforest in Costa Rica

“…Howl sampling conducted at other times of year, including during the dry season, may yield different results for howling rate and bout characteristics at LSBRS. However, because seasonal variation is not expected to impact range use or food item selection in the mantled howler monkey (Bolt et al, ; Chapman, ), we would not necessarily expect it to influence the edge vs. interior spatial patterns of howling in our study.…”

“…Mantled howler monkey density has been suggested to relate to inter‐group aggression in some populations, with higher monkey density in some areas leading to increased aggression (Kitchen et al, ) and howling rate. However, at LSBRS, howler monkey groups were encountered equally in anthropogenic edge and interior (Bolt et al, ), suggesting no difference in monkey group density between forest zones.…”

“…Each survey transect was 50 × 5 m; we aimed to distribute them evenly throughout the Large and Small Forests and camp. Overall, we conducted 17 edge and 12 interior transects (described in detail in Bolt et al, ). Along each transect and within 2.5 m on either side of the transect line, we recorded all trees with circumferences at breast height >10 cm and identified tree species when possible.…”

High density of white‐faced capuchins (Cebus capucinus) and habitat quality in the Taboga Forest of Costa Rica

“…By contrast, capuchin and howler monkeys are often abundant in fragmented tropical dry forests. Capuchins, as behaviorally flexible omnivores, can opportunistically exploit a broad array of plants and animals (Ford & Davis, 1992; Panger et al, 2002; Perry, 2012; Rose, 1994) and can adapt to anthropogenic disturbances that threaten many other species (i.e., showing neutral or even positive edge effects: Bolt et al, 2018 ( C. capucinus ); surviving in fragmented habitats: Lins & Ferreira, 2019 ( Sapajus flavius ); and Cunha, Vieira, & Grelle, 2006 ( Cebus sp.)). The factors that limit capuchin densities are mainly anthropogenic (e.g., human hunting, poaching, and the pet trade (Williams‐Guillén et al, 2013)) or limited access to water.…”

“…For example, in dry forests, where rainfall is scarce for months at a time, capuchins appear to be constrained by access to reliable above‐ground water sources (Fedigan & Jack, 2001). Howler monkeys, in contrast, are perhaps less reliant on above‐ground water sources (Glander, 1978) and more capable of tolerating fragmented habitats due to their leaf‐based diet (Williams‐Guillén et al, 2013; i.e., showing neutral or positive edge effects: Bolt et al, 2018 ( A. palliata ); Lenz, Jack, & Spironello, 2014 ( A. macconelli ); surviving in fragmented habitats: Asensio, Arroyo‐Rodríguez, Dunn, & Cristóbal‐Azkarate, 2009 ( A. palliata mexicana ); Boyle & Smith, 2010 ( A. macconelli )). Nevertheless, when forest fragmentation is accompanied by other factors (e.g., fewer large trees, increased hunting pressure, etc.)…”