Temporal shifts in dung beetle community structure within a protected area of tropical wet forest: a 35-year study and its implications for long-term conservation

1. Throughout much of the tropics, habitat loss is increasing and intensifying on the unprotected land surrounding conservation areas. The influence of these land-use changes on biodiversity is poorly understood. This study used data on dung beetles, a taxonomic group widely acknowledged to be an effective ecological indicator of anthropogenic disturbance, to evaluate temporal changes in diversity inside a natural protected area. 2. Using data from quantitative sampling events over the last 35 years along with an exhaustive review of the information available in museums and the literature, we present evidence suggesting that the dung beetles community structure has shifted dramatically over time at La Selva Biological Station, Costa Rica. 3. To date, 50 dung beetle species have been reported from La Selva. Of these, 10 (20%) were consistently collected within the study timeframe while 21 species (42%) were uncommon. Our results indicate a tendency toward decreasing species richness and changes in species composition over time. 4. Analysis of the community structure revealed a decrease in diversity (H'), an increase in dominance (D) and a decrease in evenness (J) over the 35-year period; all of which can be linked to an increase in the dominance of one species (Onthophagus acuminatus). These changes were also reflected in the proportional abundance of major species guilds. 5. Synthesis and applications. Despite the relatively low human impact within La Selva, this study suggests that the dung beetle community has changed as result of habitat loss in the surrounding landscape and the progressive increasing isolation of the reserve over the last 35 years. Our findings, together with studies of other biota in the reserve, indicate a worrying decline in the conservation value of La Selva in recent decades. This shift in the diversity and composition of native forest biota needs to be taken into account in future studies that continue to rely on La Selva as providing an intact baseline for comparative research. More importantly, we suggest that the size of the reserve may need to be increased if its ecological integrity is to be restored. This study provides further evidence that isolated protected areas may often fail to safeguard biodiversity in the long term, and that to be viable, conservation strategies urgently need to adopt a wider landscape perspective.