Forest structure and seasonally inundated grassland shape tropical mammal communities under moderate disturbance

Abstract

Tropical biodiversity is threatened globally by anthropogenic disturbances, particularly forest degradation and overhunting. Where large mammals have been extirpated, smaller bodied “mesomammals” may play an important ecological role (e.g., as seed dispersers). However, these species are disproportionally affected by overhunting for wildlife trade markets and are routinely understudied as they tend to be rare, cryptic, and nocturnal. Few studies have examined spatiotemporal responses to anthropogenic disturbance by mesomammals at the community level, which may identify imbalances within an ecosystem that could threaten species persistence. We deployed camera traps throughout Cat Tien National Park (i.e., Nam Cat Tien area), southern Vietnam, to (1) identify long‐term changes in terrestrial mesomammal richness and (2) evaluate the effects of forest structure and anthropogenic disturbance on an 18‐species mesomammal community within a historically disturbed tropical forest using hierarchical Bayesian community occupancy models. We found that site occupancy was driven by the interaction between distance to seasonally inundated grassland and absolute forest cover (basal area per hectare). This may be due to the combination of intact forest benefits (refuge from predators and hunters, denning sites) and early successional grassland resources (forage quality), as well as high levels of tolerance for disturbed forest among the largely generalist mesomammal community of Nam Cat Tien. We found no negative effects of current anthropogenic factors at the community level. However, we did find that four disturbance‐tolerant small carnivores have been extirpated since the 1990s and continued human presence in the park suggests that hunting and snaring remain an acute threat to native mesomammals. Without continued efforts to address the unsustainable harvest of wildlife, Southeast Asian's remaining mesomammals are at risk of extirpation despite resilience to moderate levels of disturbance.

Estimating arboreality and the effects of forest structure on tropical tree‐dwelling mesomammals using arboreal camera traps

“…In addition, according to the Murphy & Phan (2002) and Polet & Ling (2004) CTNP biodiversity list, our arboreal surveys detected all arboreal and semi‐arboreal mesomammals previously detected in the park with the exception of binturong (which have not been sighted in the park since 2002; Murphy & Phan, 2002). In contrast, we detected only 19 out of 23 (83%) terrestrial mesomammals (for additional details see Masseloux et al ., 2022). In the following analyses, we did not include Elliot's silver langur, Sunda pangolin, pygmy slow loris Nycticebus pygmaeus , and stump‐tailed macaque Macaca arctoides due to the sparsity of detections (naïve occupancy <0.1) leading to model convergence issues.…”

“…Sites were selected at varying proximity to anthropogenic disturbance (urban areas, park edge, roads), with minimum proximity between adjacent sites of 500 m. Cameras were active across three seasons: wet 2019 (June 2019 to October 2019), dry 2020 (November 2019 to April 2020) and wet 2020 (May 2020 to September 2020). Terrestrial cameras were set approximately 30–70 cm off the ground on or near human trails (within 5 m) from June 2019 to January 2020 as part of a larger terrestrial occupancy study (Masseloux et al ., 2022) but were moved off‐trail (within 50 m of the original site) from January to September 2020 due to high theft rates.…”