Quantifying predation to insects: An experimental approach

Overview & Synopsis

Predation can affect biodiversity and ecosystem processes considerably. However, its effects on threatened insects is poorly understood as predation is usually studied from the predators’ rather than the preys’ perspective. Human activities can severely alter predator occurrence, e.g. by livestock grazing that may attract predators. We conducted two field experiments using (1) camera traps with insect baits to identify main predators and (2) reflecting foils to investigate insect survival in relation to grazing frequency and predator presence. Our target species was the critically endangered Crau plain grasshopper (Prionotropis rhodanica) which has been suggested to be potentially threatened by expanding predators, such as cattle egrets (Bubulcus ibis), crows and lesser kestrel (Falco naumanni). The first experiment identified mainly crows, particularly rooks (Corvus frugilegus), as predators. The second experiment showed that crows and cattle egrets were positively related to grazing and negatively to insect survival (which was notably affected by crow presence). Crows and cattle egrets peaked during the early reproduction period of the Crau plain grasshopper, suggesting a potential impact on its population. Our results show that the simultaneous colonization and increase of synanthropic predator species represents a plausible threat for the grasshopper. Our novel experimental approach considering the preys’ perspective should therefore encourage similar studies to quantify predation risk for threatened invertebrates. While direct effects of habitat deterioration on insect populations are well known and easy to study, secondary effects of changing predator communities should receive more attention in insect conservation.