Long-term impacts of oil spill pollution on the insectivorous bat community in the hyper-arid Evrona Nature Reserve, Israel

Vachellia (known as Acacia) trees are key species for various taxa in desert ecosystems, and highly important foraging sites for insectivorous bat species. Bats are one of the largest groups of mammals in desert habitats and potentially exercise top-down control of insects in natural and agricultural desert ecosystems. In both 1974 and 2014, large-scale oil spills contaminated the hyper-arid Evrona Nature Reserve in the southern Arava Valley, Israel. The reserve is a unique ecosystem and hosts a high density of Vachellia trees and wildlife. Following the 2014 spill, a biodiversity program was launched in 2016 and lasted five years, during which I used acoustic monitoring to compare bat diversity in the polluted and unpolluted areas. I tracked the changes in bat species richness, foraging and feeding activity, bat community structure, and the activity of gleaner bats, which generally prey on ground-dwelling arthropods. I predicted that these variables would be negatively impacted by the oil spill due to the contamination's direct and indirect effects. The results partially supported my predictions. The oil contamination had a significant negative effect on bat richness, feeding activity, and gleaner bat activity, but total bat activity and community structure were not affected by the oil spill. These negative impacts occurred at the beginning of the monitoring period and were less pronounced as time passed since the initial spill. The increase in feeding activity and species richness over the years reflects a decrease in the negative effects on the bats from the oil spill, possibly due to increase in resource availability and reduction in the contamination's direct effects. This trend enabled the recovery of the foraging behavior of different assemblages of bat species in Evrona Nature Reserve and may indicate how these top nocturnal insect predators react over time to terrestrial oil spill events in other desert ecosystems.