Data from: Effects of chronic anthropogenic disturbance and rainfall on the specialization of ant-plant mutualistic networks in the Caatinga, a Brazilian dry forest

1. Anthropogenic disturbance and climate change might negatively affect
the ecosystem services provided by mutualistic networks. However, the
effects of such forces remain poorly characterized. They may be especially
important in dry forests, which (1) experience chronic anthropogenic
disturbances (CADs) as human populations exploit forest resources and (2)
are predicted to face a 22% decline in rainfall under climate change. 2.
In this study, we investigated the separate and combined effects of CADs
and rainfall levels on the specialization of mutualistic networks in the
Caatinga, a seasonally dry tropical forest typical of northeastern Brazil.
More specifically, we examined interactions between plants bearing
extrafloral nectaries (EFNs) and ants. We analyzed whether differences in
network specialization could arise from environmentally mediated variation
in the species composition, namely via the replacement of specialist by
generalist species. 3. We characterized these ant-plant networks in 15
plots (20 x 20 m) that varied in CAD intensity and mean annual rainfall.
We quantified CAD intensity by calculating three indices related to the
main sources of disturbance in the Caatinga: livestock grazing (LG), wood
extraction (WE), and miscellaneous resource use (MU). We determined the
degree of ant-plant network specialization using four metrics: generality,
vulnerability, interaction evenness, and H2’. 4. Our results indicate that
CADs differentially influenced network specialization: we observed
positive, negative, and neutral responses along LG, MU, and WE gradients,
respectively. The pattern was most pronounced with LG. Rainfall also
shaped network specialization, markedly increasing it. While LG and
rainfall were associated with changes in network species composition, this
trend was not related to the degree of species specialization. This result
suggests that shifts in network specialization might be related to changes
in species behavior, not species composition. 5. Our study highlights the
vulnerability of such dry forest ant-plant networks to climate change.
Moreover, dry forests experience highly heterogeneous anthropogenic
disturbances, creating a geographic mosaic of selective forces that may
shape the coevolution of interactions between ants and EFN-bearing plants.