Complex competition interactions between Egyptian fruit bats and black rats in the real world.

Background: Interspecific interactions, including competition and predation, are key drivers of ecological systems. Understanding these interactions remains challenging in the wild as it requires quantifying their effects, particularly the non-consumptive effects (NCEs) driven by predation risk. We conducted a 7-month study in a semi-natural open bat colony, monitoring interactions between Egyptian fruit bats (Rousettus aegyptiacus) and black rats (Rattus rattus) competing for food, where rats also pose a potential predation risk to the bats.

Results: Video analysis revealed that bat responses to rats were fundamentally different from responses to conspecifics. The primary response was avoidance, with bat landings near food decreasing significantly when rats were present. For the 789 landings that did occur, bats showed increased vigilance and reduced foraging success, demonstrating clear NCEs. Crucially, bat foraging strategies were highly context-dependent, shifting with seasonal resource availability and rat abundance. During winter when rats were uncommon, the bats primarily employed predation risk-averse strategies (avoidance and vigilance). In spring, when rats were frequent, although there was clear temporal partitioning between the bat and the rat populations, some of the bats shifted to heterospecific interference competition, and occasionally attacked the rats to gain access to food-a behavior inconsistent with simple risk-aversion models.

Conclusions: Our findings demonstrate that the bat-rat interactions are dynamically modulated by resource availability, which alters rat presence and thereby the context-dependent interplay between interference competition and NCEs. This study provides rare quantitative evidence of how behaviorally flexible animals strategically manage interference competition and predation risk based on seasonal ecological conditions.