Comparative feeding rates of native and invasive ascidians

Ascidians have a recent history of species introductions globally, often with strong ecological impacts. Comparisons of per capita effects of invaders and comparable natives are useful to assess such impacts. Here, we explore ingestion rates (IR) and clearance rates (CR) of Ciona intestinalis and Ciona robusta, co-occurring native and non-native ascidians, respectively, from Brittany, France. IR was positively related to food concentration, with the invader responding more strongly to increasing food concentration. CR also differed by species, with the invader demonstrating higher values. C. robusta exhibited a higher functional response (Type I) than did C. intestinalis (Type II). Relative impact measured using seasonal abundance and IR revealed that C. robusta has a much greater impact than C. intestinalis at all food concentrations tested, though the former has a constrained distribution which limits its regional impact. Nevertheless, when abundant, we expect C. robusta to exert a greater impact on algal foods

Competitive exclusion of pulmonate landsnails in an invasion context

Invasive species are non-native organisms that become established in an ecologically naive environment to the detriment of the local environment and/or economy. However, some species become established but fail to expand their range or have a significant impact. The European native grove snail Cepaea nemoralis has been widely introduced to new areas through human activities, and now occurs in a wide variety of locations owing to its ecological generalism and broad native distribution. The species occurs in SW Essex County, where it is abundant in urbanized and disturbed areas of Windsor but scarce in native woodlands. We hypothesize that the native forest-inhabiting, similarly-sized, and fellow detritivorous Mesodon thyroidus competitively excludes the grove snail from this habitat type. In order to test this, a functional response (FR) or feeding rate framework was applied to individual snails collected from urban areas of Windsor (C. nemoralis) and from Kopegaron Conservation Area (C. nemoralis and M. thyroidus). Feeding trials were conducted under controlled conditions, whereby identically sized leaf squares, analogous to \u27prey items\u27 in traditional FR methods, were consumed over a fixed time period of 24 hours. Statistical analyses of FR curves (feeding rate as a function of food supplied) and their derived parameters were conducted in \u27R\u27, using maximum likelihood model fitting of nonlinear FR curves. Results showed significantly greater resource acquisition parameters for the native M. thyroidus in comparison to the non-native C. nemoralis, indicating that the native snail competitively excludes the invasive from the forest interior. FR methods can be used to test all aspects of invasion biology, but this study represents the first time that FR has been used to test the competitive exclusion of terrestrial invertebrates in an invasion ecology scenario

Odour detection times

Odour detection times for individuals of each species (Mesodon thyroidus and Cepaea nemoralis) across different food levels and food treatments

Data from: 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 SW Ontario, one native (Mesodon thyroidus) and one non-indigenous (Cepaea nemoralis) 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 SW 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

Joint foraging consumption data

Consumption data of Mesodon thyroidus and Cepaea nemoralis in joint foraging scenarios. 'Density' represents the total number of food items supplied in each replicate

Functional response (consumption data) of Mesodon thyroidus

Raw consumption data of M. thyroidus individuals used for generating functional response curves and analyzing 'a' and 'h' parameters

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

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