Predation risk between cannibalistic aeshnid dragonflies influences their functional response on a larval salamander prey

Comparative feeding behaviour of native and introduced terrestrial snails tracks their ecological impacts

A developing body of theory and empirical evidence suggest that feeding behaviour as measured by the functional response (FR) can assist researchers in assessing the relative potential, ecological impacts and competitive abilities of native and introduced species. Here, we explored the FRs of two land snails that occur in south-western Ontario, one native (Mesodonthyroidus) and one non-indigenous (Cepaeanemoralis) to Canada. The non-indigenous species appears to have low ecological impact and inferior competitive abilities. Consistent with theory, while both species conformed to Type II functional responses, the native species had a significantly higher attack rate (5.30 vs 0.41, respectively) and slightly lower handling time (0.020 vs 0.023), and hence a higher maximum feeding rate (50.0 vs 43.5). The non-indigenous species exhibited a significantly longer time to contact for a variety of food types, and appeared less discriminating of paper that was offered as a non-food type. The non-indigenous species also ate significantly less food when in mixed species trials with the native snail. These feeding patterns match the known low ecological impact of the introduced snail and are consistent with the view that it is an inferior competitor relative to the native species. However, field experimentation is required to clarify whether the largely microallopatric distributions of the two species in south-western Ontario reflect competitive dominance by the native species or other factors such as habitat preference, feeding preferences or predator avoidance. The relative patterns of feeding behaviour and ecological impact are, however, fully in line with recent functional response theory and application.

When Predators Avoid Predation by Their Con- and Heterospecific Competitors: Non-consumptive Effects Mediate Foraging Behavior and Prey Handling Time of Predators

Aphids show highly aggregated distributions, and thus their predators tend to aggregate as well, creating conditions optimal to consumptive and non-consumptive (N-CEs) effects among competing predators, both conspecific and heterospecific. If predatory larvae are themselves potential prey for other predators, they may be also sensitive to N-CEs imposed by their con- or heterospecifics. A partitioned Petri-dish that permitted the passage of visual and chemical signals was used to examine the N-CEs of predator on foraging behavior of other predators, as prey themselves. Functional responses of second-instar Chrysoperla carnea Stephens (Chrysopidae: Neuroptera) and third-instar Coccinella undecimpunctata L. (Coccinellidae: Coleoptera) to Aphis craccivora Koch. (Aphididae: Hemiptera) in the absence and presence of predation threat were derived. Both predators responded to presence of competitor signals with declined consumption, but lower attack rate and longer handling time were evident for C. undecimpunctata. The functional response type of second-instar C. carnea did not alter, even in the presence of larger heterospecifics, remaining a type 2 functional response in all treatments, but that of third-instar C. undecimpunctata did under the predation risk of third-instar C. carnea. Therefore, the third-instar C. undecimpunctata appeared to have suffered foraging costs (longer handling time and lower attack rate) under predation risk of C. carnea, but second-instar C. carnea did not. If predatory larvae of both species are synchronized in the same aphid patch, C. undecimpunctata might leave the patch to minimize its own risk of being preyed upon, or at least search at reduced rates. Thus, N-CEs may signify be biologically significant.