Few data exist on the long-term dynamics of tropical populations, particularly for some of the most threatened species, which include numerous mammals. The Tropical Ecology Assessment and Monitoring Network (TEAM) recently published the first standardized assessment for tropical mammal occupancy trends based on in situ camera trap data from tropical forest protected areas worldwide. Occupancy declined in 21% of the 393 monitored mammal populations, increased in 18% and exhibited no change in 23%, while 38% of mammal populations were detected too infrequently to assess occupancy change. Here, we asked, what were the drivers of these occupancy trends? We evaluated autecological properties, such as species’ body size, dietary guild, natal dispersal distances and dietary breadth, as well as synecological properties, such as predator-prey interactions and competition between species. Specifically, we quantified trophic interactions through a directed network and calculated the graph strength of each species within its local mammal food web. We conducted ordinal regression models using occupancy trend (increasing, decreasing, etc.) as the response variable and performed AIC model selection to determine the most parsimonious model with the greatest explanatory power for the estimated occupancy trends. Finally, we calculated McFadden's R squared to assess model fit.
The best explanatory model of tropical mammal occupancy trends included trophic interaction strength, hunting status and dietary breadth (McFadden’s R2 = 0.14; NB values of 0.2 - 0.4 are considered indicative of excellent model fit). Specifically, populations with higher trophic interaction strength and broader diets (i.e. dietary generalists) were more likely to increase in occupancy during the 3–8 year study period. Conversely, populations with fewer trophic connections within the food web and with more specialized diets were more likely to decline in occupancy or have too few observations for their occupancy trend to be estimated. These results highlight the importance of food web connectance for maintaining populations of tropical mammals and the potential vulnerability of specialists to population decline.