Arboreal mammals may be tolerant, neutral, or intolerant of anthropogenically-created forest edges. Habitat and diet preferences frequently influence a mammal’s response to these edges. However, responses to edges created by natural disturbances and the factors involved in such responses are less known. As climate change alters natural disturbance regimes, it grows increasingly urgent to understand the similarities (or differences) between anthropogenic edge effects and natural disturbance and how arboreal mammals respond to the latter. Andranobe Forest, Masoala National Park, Madagascar offers an ideal location to study this relationship because frequent cyclones create abundant tree-fall canopy gaps there. Moreover, it is home to two day-active arboreal mammals with different habitat and diet preferences, red ruffed (Varecia rubra) and white-fronted brown (Eulemur albifrons) lemurs. We asked whether these species were tolerant, neutral, or intolerant of tree-fall gaps. Using instantaneous focal animal sampling, we observed V. rubra for 308 hours and E. albifrons for 280 hours from September 2017 through February 2018, recording their locations at five-minute intervals. Returning to these locations, we measured the distance to and size of the nearest gap. We recorded the distance to and size of the nearest gap for 383 transect trees to use as a control.
Results/Conclusions
Using a generalized linear mixed model (GLMM), we tested for the contribution of tree type (visited by V. rubra, visited by E. albifrons, or transect) to variation in distance to the nearest gap. We included week as a random effect. Trees visited by V. rubra were further away from gaps (mean = 4.9 m, SD = 6.5 m) than transect trees (4.3 m, SD = 5.1 m) or trees visited by E. albifrons (4.0 m, SD = 5.3m; p <0.01). However, the mean distance to the nearest gap of V. rubra decreased over time. These data suggest that E. albifrons is somewhat edge tolerant while V. rubra is less so, at least during the seasons of study. Despite extraordinary habitat loss and fragmentation in Madagascar over the past 50 years, no lemur species have gone extinct during this time period. Adaptations to natural disturbance such as tree-fall canopy gaps may proffer some resiliency to anthropogenic disturbance. Understanding the effect of small-scale disturbance on different species will allow us to more accurately estimate carrying capacity and project population growth rates. These metrics are increasingly needed for conservation management as anthropogenic habitat conversion and climate change place many species at extinction risk.