Seasonal variability in tropical agroecological communities: How shifting precipitation regimes may affect predation rates of a globally important coffee pest
Coffee is particularly susceptible to variations in temperature and precipitation predicted in climate change forecasts for coffee growing regions. However, the effects of climate change on production are not limited to direct effects on the coffee plant. Seasonal variations will also affect pest and predator populations that may indirectly affect coffee production. The coffee berry borer is among the most damaging global coffee pests. The adults directly damage the fruit by boring into the coffee fruit thus rendering it unsuitable for production and harvest. Ants are thought to be the primary predators of the coffee berry borer, but the seasonal dynamics of their prey consumption has not yet been studied. We examined the effect of limiting rainfall on the predation of the coffee berry borer by ground-foraging ants. We first performed a prey removal experiment in the dry and rainy seasons and then followed this initial experiment with a large rainfall exclusion experiment. To assess the affect of limited rainfall on predation rates we established 20 paired sites (rainfall exclusion and control plots) across two coffee farms and performed the same prey removal experiment six times over the course of eight months.
Our results from the initial prey removal experiment performed in both seasons indicated a substantially higher rate of predation during the dry season relative to the rainy season. And our following rainfall exclusion experiment did not differ significantly from the controls in light, air temperature, soil temperature or humidity. The exclusion experiment, however, provided unexpected results. For the first three experiments, prior to large accumulations of rainfall (and in contrast to the findings from the initial experiment), prey removal rates were significantly lower in the rainfall exclusion plots. For the latter experiments, the results changed again, suggesting an interaction between rainfall accumulation and predation rates. While the results are not conclusive, this research provides necessary insight into how the predicted altered precipitation regimes associated with global climate change may affect important species interactions.