Abstract
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.
Highlights
Introduction of non-indigenous species (NIS) is largely a consequence of unintentional and intentional human-mediated mechanisms
Each food class was represented five times. Both snail species conformed to a Type II functional response, though C. nemoralis has not reached the curve’s asymptote and M. thyroidus individuals exhibited a significantly greater feeding ability with increasing food levels (Fig. 1)
Species Density Treatment Species*Density Species*Treatment Density*Treatment Species*Density*Treatment Residuals df Application of comparative functional responses has allowed researchers to discriminate between invader species with high and low ecological impact (e.g. Dick et al 2014, 2017a; Xu et al 2016b), and may elucidate relative competitive ability (Tilman 1977; Dick et al 2017b)
Summary
Introduction of non-indigenous species (NIS) is largely a consequence of unintentional and intentional human-mediated mechanisms. Some NIS adversely affect native species and alter the communities in which they establish Elton (1958) proposed that characteristics of a native community could be important in providing resistance by native species against successful establishment of NIS. A large literature subsequently demonstrated that interactions (largely predation and competition) by native species could impair or prevent establishment of NIS Levine et al 2004; Cobián-Rojas et al 2018). Cases in which a native species competitively excludes a potential invader are interesting, as they may provide valuable insights into context-specific factors that permit the native species to resist invasion (Paini et al 2008; Zenni and Nuñez 2013). In many other cases, colonizing species may suppress native ones or limit their distributions (e.g. Petren and Case 1996)
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