Predator-prey role reversals, juvenile experience and adult antipredator behaviour

Abstract

Although biologists routinely label animals as predators and prey, the ecological role of individuals is often far from clear. There are many examples of role reversals in predators and prey, where adult prey attack vulnerable young predators. This implies that juvenile prey that escape from predation and become adult can kill juvenile predators. We show that such an exposure of juvenile prey to adult predators results in behavioural changes later in life: after becoming adult, these prey killed juvenile predators at a faster rate than prey that had not been exposed. The attacks were specifically aimed at predators of the species to which they had been exposed. This suggests that prey recognize the species of predator to which they were exposed during their juvenile stage. Our results show that juvenile experience affects adult behaviour after a role reversal.

Figure 1. Predation of juvenile predators by adult prey that were exposed to adult predators during their development.

Shown is survivorship of groups of ten (A) juvenile predators (N. cucumeris) and (B) juveniles of another predator species (A. swirskii) when exposed to adult female prey (I. degenerans) that had either been exposed to adult predators (N. cucumeris) when juvenile (Exposed, black symbols, n = 22) or not (Control, white symbols, n = 22). Control selected (grey symbols) concerns a subset of the Control group consisting of the 15 individuals that killed most juvenile predators. Shown are the Kaplan-Meier estimates and the standard errors based on the Greenwood formula for the variance (Crawley 2007). Mortality of juvenile predators of both species was due to killing by the adult prey (I. degenerans). As almost all juvenile predators of both species were killed within 24 h, survival after 24 h is not shown in this graph, yet these data were included in the statistical analysis.

Figure 2. Predation of juvenile predators by adult prey that were exposed to adult predators during the first days of the adult prey stage.

Shown is survivorship of groups of ten juvenile predators exposed to adult female prey that had either been exposed to adult predators when adult (Exposed, closed symbols, n = 14) or not (Control, open symbols, n = 14). See legend to Fig. 1 for further explanation.

Figure 3. Killing juvenile predators protects prey offspring.

Shown is survival of juvenile prey and eggs laid by an adult female predator on an arena with dead juvenile predators (black, n = 13) or without (Control, white, n = 13). Shown is the fraction (mean + s.e.m.) of juvenile prey surviving on the entire arena and the fraction (mean + s.e.m.) of eggs laid on the patch on which the juvenile prey were released. **: P < 0.01; *: P < 0.05.