Occurrence of blood-feeding terrestrial leeches (Haemadipsidae) in a degraded forest ecosystem and their potential as ecological indicators

Blood-feeding invertebrates are emerging model taxa in biodiversity assessments, both as indicators of mammal abundance and also as sources of mammal DNA for identification. Among these, terrestrial leeches arguably offer the greatest promise; they are abundant and widespread in the humid tropics, and their blood meals can be easily assayed to establish diet. Unfortunately, terrestrial leeches are understudied, with little known about their ecology and behavior. Such information is needed to evaluate their utility as ecological indicators and to account for potential sampling biases that might arise from habitat preferences. By combining occupancy modeling and thermal tolerance assays, we determined the factors affecting species occurrence in the related terrestrial brown (Haemadipsa sumatrana) and tiger leech (Haemadipsa picta), both of which are widespread in tropical forests in Southeast Asia. We sampled both species across a degraded forest landscape in Sabah, Borneo, in wet and dry seasons, associating occurrence with habitat-level metrics. We found that, for both species, detection probability increased with canopy height regardless of season. Additionally, increased vegetation heterogeneity had a strong negative influence on brown leech occurrence in the dry season, implying an interaction between vegetation structure and climate. However, we found no difference in physiological thermal tolerance (CT_MAX) between the two species. Finally, using a reduced dataset, we found a small improvement in brown leech model fit when including mammal abundance. Our results suggest that the presence of terrestrial leeches may act as useful ecological indicators of habitat quality and potentially mammalian abundance. Abstract in Indonesia is available with online material.