Habitat openness and predator abundance determine predation risk of warningly colored longhorn beetles (Cerambycidae) in temperate forest

Abstract

Organisms have evolved different defense mechanisms, such as crypsis and mimicry, to avoid detection and recognition by predators. A prominent example is Batesian mimicry, where palatable species mimic unpalatable or toxic ones, such as Clytini (Coleoptera: Cerambycidae) that mimic wasps. However, scientific evidence for the effectiveness of Batesian mimicry in Cerambycids in natural habitats is scarce. We investigated predation of warningly and nonwarningly colored Cerambycids by birds in a temperate forest using beetle dummies. Dummies mimicking Tetropium castaneum, Leptura aethiops, Clytus arietis, and Leptura quadrifasciata were exposed on standing and laying deadwood and monitored predation events by birds over one season. The 20 surveyed plots differed in their structural complexity and canopy openness due to different postdisturbance logging strategies. A total of 88 predation events on warningly colored beetle dummies and 89 predation events on nonwarningly colored beetle dummies did not reveal the difference in predation risk by birds. However, predation risk increased with canopy openness, bird abundance, and exposure time, which peaked in July. This suggests that environmental factors have a higher importance in determining predation risk of warningly and nonwarningly colored Cerambycidae than the actual coloration of the beetles. Our study showed that canopy openness might be important in determining the predation risk of beetles by birds regardless of beetles' warning coloration. Different forest management strategies that often modify canopy openness may thus alter predator-prey interactions.

Keywords: Batesian mimicry; beetle dummies; management intensification; natural disturbance.

1. We investigated predation of different warningly and nonwarningly colored Cerambycids by birds in a temperate forest using beetle dummies. 2. We found no difference in predation risk by birds between warningly colored and nonwarningly colored beetle dummies. However, predation risk increased with canopy openness, bird abundance, and exposure time. 3. Canopy openness plays a crucial role in determining the predation risk of beetles by birds. Different forest management strategies modify canopy openness that can alter predator–prey interactions.

Fig. 1.

Distribution of 5 study plots in Steigerwald forest (Germany) across naturally disturbed forests with various postdisturbance management (intact forest, disturbed, partially logged, and intensively logged). Top right shows hacking beak marks on a Leptura quadrifasciata dummy.

Fig. 2.

Warningly and nonwarningly colored beetle dummies: a) Clytus arietis, b) Leptura quadrifasciata, c) Tetropium castaneum, d) Leptura aethiops.

Fig. 3.

Effect of warning coloration, complexity, canopy openness, exposure time, bird abundance, and Hymenoptera abundance on predation risk based on generalized additive models. Vertical lines indicate range of nonsignificant values (−1.96 < t-value < 1.96).

Fig. 4.

Partial effect of predation risk on beetle dummies by birds across season, modeled by generalized linear mixed models. The gray-shaded area indicates the confidence interval.