Plant protection services mediated by extrafloral nectaries decline with aridity but are not influenced by chronic anthropogenic disturbance in Brazilian Caatinga

1. Most terrestrial species occur in human-modified landscapes that are experiencing climate change. In addition to direct impacts on species, both anthropogenic disturbance and climate change can have important effects through changes in species interactions, including the disruption of ecological services provided by them.

2. Here we investigate how chronic anthropogenic disturbance (CAD) and aridity affect the effectiveness of plant protection services provided by ants to plants bearing extrafloral nectaries (EFNs).

3. The study was conducted across 13 01-ha plots distributed along CAD and aridity gradients in Caatinga vegetation of northeastern Brazil. We focused on Pityrocarpa moniliformis, the most abundant and widely distributed EFN-bearing tree species occurring in our study area, and used experimental attack rates on termites as a measure of effectiveness of ant protection services. We investigated the relative roles of nectar production (volume and concentration) and ant...