Interactions between invading benthivorous fish and native whitefish in subarctic lakes

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The introduced signal crayfish and native noble crayfish have different effects on sublittoral macroinvertebrate assemblages in boreal lakes

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Multi‐faceted impacts of native and invasive alien decapod species on freshwater biodiversity and ecosystem functioning

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Stable resource polymorphism along the benthic littoral–pelagic axis in an invasive crayfish

Although intraspecific variability is now widely recognized as affecting evolutionary and ecological processes, our knowledge on the importance of intraspecific variability within invasive species is still limited. This is despite the fact that understanding the linkage between within‐population morphological divergences and the use of different trophic or spatial resources (i.e., resource polymorphism) can help to better predict their ecological impacts on recipient ecosystems. Here, we quantified the extent of resource polymorphism within populations of a worldwide invasive crayfish species, Procambarus clarkii, in 16 lake populations by comparing their trophic (estimated using stable isotope analyses) and morphological characteristics between individuals from the littoral and pelagic habitats. Our results first demonstrated that crayfish occured in both littoral and pelagic habitats of seven lakes and that the use of pelagic habitat was associated with increased abundance of littoral crayfish. We then found morphological (i.e., body and chelae shapes) and trophic divergence (i.e., reliance on littoral carbon) among individuals from littoral and pelagic habitats, highlighting the existence of resource polymorphism in invasive populations. There was no genetic differentiation between individuals from the two habitats, implying that this resource polymorphism was stable (i.e., high gene flow between individuals). Finally, we demonstrated that a divergent adaptive process was responsible for the morphological divergence in body and chela shapes between habitats while difference in littoral reliance neutrally evolved under genetic drift. These findings demonstrated that invasive P. clarkii can display strong within‐population phenotypic variability in recent populations, and this could lead to contrasting ecological impacts between littoral and pelagic individuals.     

An invasive species may be better than none: invasive signal and native noble crayfish have similar community effects

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Infection with a trematode parasite differentially alters competitive interactions and antipredator behaviour in native and invasive crayfish

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Effects of an invasive crayfish on trophic relationships in north‐temperate lake food webs

1. The introduction of invasive species is one of the main threats to global biodiversity, ecosystem structure and ecosystem processes. In freshwaters, invasive crayfish alter macroinvertebrate community structure and destroy macrophyte beds. There is limited knowledge on how such invasive species‐driven changes affect consumers at higher trophic levels. 2. In this study, we explore how the invasive rusty crayfish Orconectes rusticus, a benthic omnivore, affects benthic macroinvertebrates, as well as the broader consequences for ecosystem‐level trophic flows in terms of fish benthivory and trophic position (TP). We expected crayfish to decrease abundance of benthic macroinvertebrates, making most fish species less reliant on benthic resources. We expected crayfish specialists (e.g. Lepomis sp. and Micropterus sp.) to increase their benthic dependence. 3. In 10 northern Wisconsin lakes, we measured rusty crayfish relative abundance (catch per unit effort, CPUE), macroinvertebrate abundance, and C and N stable isotope ratios of 11 littoral fish species. We used stable isotope data and mixing models to characterise the trophic pathways supporting each fish species, and related trophic structure to crayfish relative abundance, fish body size and abiotic predictors using hierarchical Bayesian models. 4. Benthic invertebrate abundance was negatively correlated with rusty crayfish relative abundance. Fish benthivory increased with crayfish CPUE for all 11 fish species; posterior probabilities of a positive effect were >95%. TP also increased slightly with crayfish CPUE for some species, particularly smallmouth bass, largemouth bass, rock bass and Johnny darter. Moreover, both fish body size and lake abiotic variables explained variation in TP, while their effects on benthivory were small. 5. Rusty crayfish abundance explained relatively little of the overall variation in fish benthivory and TP. Although rusty crayfish appear to have strong effects on abundances of benthic macroinvertebrates, energy flow pathways and trophic niches of lentic fishes were not strongly influenced by invasive rusty crayfish.     

Niche differentiation among invasive crayfish and their impacts on ecosystem structure and functioning

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The role of alien fish (the centrarchid Micropterus salmoides) in lake food webs highlighted by stable isotope analysis

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Distribution and community-level effects of the Chinese mystery snail (Bellamya chinensis) in northern Wisconsin lakes

Managing invasive species requires information about their distributions and potential effects, but community-level impacts of invasive animals remain poorly understood. The Chinese mystery snail (Bellamya chinensis) is a large invasive gastropod that achieves high densities in waters across North America, yet little is known about its ecological significance in invaded systems. We surveyed 44 lakes to describe the patterns and determinants of B. chinensis distributions in northern Wisconsin, USA, and to assess the likelihood of effects on native snail communities in the invaded systems. B. chinensis was widespread among surveyed lakes (21 of 42 lakes with snails) and its occurrence was correlated with indicators of lake productivity and anthropogenic dispersal vectors (boat landings, distance to population centers, shoreline housing density). Some native snail species tended not to occur at sites where B. chinensis was abundant; among these was Lymnaea stagnalis, which suffered reduced survival in the presence of B. chinensis in a recently published mesocosm study. However, there was no difference in overall snail assemblage structure at either the site or lake level as a function of B. chinensis presence or abundance. Lake occurrences of many snail species have apparently been lost over time, but a comparison to a 1930s survey showed that there was no increased likelihood of species loss in lakes invaded by B. chinensis (or by the invasive crayfish Orconectes rusticus). Although B. chinensis is widespread and sometimes abundant in northern Wisconsin lakes, it does not appear to have strong systematic impacts on native snail assemblages.     

Homogenization of fish assemblages in different lake depth strata at local and regional scales

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Feeding behaviour,predatory functional responses and trophic interactions of the invasive Chinese mitten crab (Eriocheir sinensis) and signal crayfish (Pacifastacus leniusculus)

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Comparison of trophic function between the globally invasive crayfishes <Emphasis Type="Italic">Pacifastacus leniusculus</Emphasis> and <Emphasis Type="Italic">Procambarus clarkii</Emphasis>

Impacts of invasive species may manifest most strongly if these organisms are highly distinct functionally from the native species they often replace. Yet, should we expect functional differences between native and invasive species of generalist organisms like freshwater crayfish? Some existing evidence has pointed to native and invasive crayfish species as ecologically equivalent. We contribute to this literature by comparing the trophic niches of the globally invasive crayfishes Pacifastacus leniusculus and Procambarus clarkii, by applying carbon and nitrogen stable isotope analyses to replicated allopatric (alone) and sympatric (together) lake populations in western Washington State, USA, where P. clarkii has been recently introduced and P. leniusculus is presumed native. Our study corrected for potential inherent differences in lake food webs as a consequence of lake abiotic or biotic characteristics using random effects in linear mixed effects models. We found that although overall trophic niche size or area of these species was not significantly different, P. leniusculus was significantly higher in trophic position than P. clarkii when also accounting for the effects of body size, sex, and lakes as random effects. This pattern of increased trophic position of P. leniusculus over P. clarkii was conserved over time in one sympatric lake for which we had data over multiple years. Cumulatively, our findings point to trophic differences between the globally cosmopolitan crayfishes P. leniusculus and P. clarkii, particularly when accounting for the ways that ecosystem context can affect food web structure of communities and the trophic resources available to these consumers.     

Reliance of brown trout on terrestrial prey varies with season but not fish density

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An invasive fish promotes invasive plants in Minnesota lakes

1. Biological invasions can greatly alter ecological communities, affecting not only the diversity and abundance but also composition of invaded assemblages. This is because invaders’ impacts are mediated by characteristics of resident species: some may be highly sensitive to invader impacts while others are unaffected or even facilitated. In some cases, this can result in invasive species promoting further invasions; in particular, herbivory by introduced animals has been shown to disproportionately harm native plants, which can indirectly benefit non-native plants. Here, we investigated whether such patterns emerged through the effects of an invasive fish species on lake plant communities.
2. Specifically, we tested whether invasion of Minnesota (U.S.A.) lakes by Cyprinus carpio (common carp), an omnivorous, benthivorous fish known to reduce abundance and richness of aquatic plants, differentially affected native versus non-native plant species. We applied statistical models to a large, long-term monitoring dataset (206 macrophyte taxa recorded in 913 lakes over a 20-year time period) to test whether carp altered community composition, to identify which macrophyte species were most sensitive to carp and determine whether species characteristics predicted carp sensitivity, and to characterise consequences of carp invasion on lake-level vegetation attributes.
3. We found that carp exerted strong selective pressure on community composition. Native macrophytes, those with a more aquatic growth form, and those considered less tolerant of disturbance (i.e. higher coefficients of conservatism) were more sensitive to carp. Conversely, no introduced macrophytes exhibited sensitivity to carp and all had higher probabilities of occurrence as carp abundance increased. The net effect of carp invasion was a shift toward less species-rich plant communities characterised by more non-native and disturbance-tolerant species.
4. These results have several implications for conservation and management. First, they reinforce the need to prevent further spread of carp outside of their native range. Where carp have already established, their control should be incorporated into efforts to restore aquatic vegetation; this may be an essential step for recovering particular plant species of high conservation importance. Furthermore, reducing carp abundance could have ancillary benefits of reducing dominance by invasive plant species. Lastly, where carp cannot be eliminated, managers should target native macrophytes that are relatively tolerant of carp in shoreline plantings and other revegetation efforts.

     

A trematode parasite alters growth,feeding behavior,and demographic success of invasive rusty crayfish (Orconectes rusticus)

Nonindigenous species can cause major changes to community interactions and ecosystem processes. The strong impacts of these species are often attributed to their high demographic success. While the importance of enemy release in facilitating invasions has often been emphasized, few studies have addressed the role of parasites in the invasive range in controlling demographic success of potential invaders. Here we examine whether a trematode parasite (Microphallus spp.) can contribute to previously documented alternate states in the abundance of invasive rusty crayfish (Orconectes rusticus) in north temperate lakes in Wisconsin, USA. Microphallus infect O. rusticus after emerging from their first intermediate host, a hydrobiid snail. As previously documented, O. rusticus reduce densities of hydrobiid snails through direct predation and destruction of macrophyte habitat. Therefore, if Microphallus substantially reduce O. rusticus fitness, these parasites may reinforce a state of low crayfish abundance, and, at the other extreme, abundant crayfish may repress these parasites, reinforcing a state of high crayfish abundance. From samples collected from 109 sites in 16 lakes, we discovered (1) a positive relationship between crayfish infection intensity and hydrobiid snail abundance, (2) a negative relationship between parasite prevalence and crayfish abundance, and (3) a negative relationship between parasite prevalence and crayfish population growth. With experiments, we found that infection with Microphallus reduced foraging behavior and growth in O. rusticus, which may be the mechanisms responsible for the population reductions we observed. Overall results are consistent with the hypothesis that Microphallus contributes to alternate states in the abundance and impacts of O. rusticus.     

Optimising control of invasive crayfish using life‐history information

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Interactions among invaders: community and ecosystem effects of multiple invasive species in an experimental aquatic system

With ecosystems increasingly supporting multiple invasive species, interactions among invaders could magnify or ameliorate the undesired consequences for native communities and ecosystems. We evaluated the individual and combined effects of rusty crayfish (Orconectes rusticus) and Chinese mystery snails [Bellamya (=Cipangopaludina) chinensis] on native snail communities (Physa, Helisoma and Lymnaea sp.) and ecosystem attributes (algal chlorophyll a and nutrient concentrations). Both invaders are widespread in the USA and commonly co-occur within northern temperate lakes, underscoring the importance of understanding their singular and joint effects. An outdoor mesocosm experiment revealed that while the two invaders had only weakly negative effects upon one another, both negatively affected the abundance and biomass of native snails, and their combined presence drove one native species to extinction and reduced a second by >95%. Owing to its larger size and thicker shell, adult Bellamya were protected from crayfish attack relative to native species (especially Physa and Lymnaea), suggesting the co-occurrence of these invaders in nature could have elevated consequences for native communities. The per capita impacts of Orconectes (a snail predator) on native snails were substantially greater than those of Bellamya (a snail competitor). Crayfish predation also had a cascading effect by reducing native snail biomass, leading to increased periphyton growth. Bellamya, in contrast, reduced periphyton biomass, likely causing a reduction in growth by native lymnaeid snails. Bellamya also increased water column N:P ratio, possibly because of a low P excretion rate relative to native snail species. Together, these findings highlight the importance of understanding interactions among invasive species, which can have significant community- and ecosystem-level effects.     

Trophic flexibility by roach Rutilus rutilus in novel habitats facilitates rapid growth and invasion success

Stable isotope and gut content analyses, in conjunction with backcalculated length‐at‐age estimates of growth, were employed to examine the relationship between trophic ecology and growth rate of a successful invader, Rutilus rutilus, in eight lakes in Ireland. The data revealed that R. rutilus was a trophic generalist in Irish lakes. It utilized a greater proportion of pelagic resources in mesotrophic lakes than in eutrophic lakes, potentially due to a greater density of benthic macroinvertebrates in eutrophic systems. The species was characterized by a large dietary and isotopic niche width and high temporal and spatial variations in diet. Growth rates were typical of those found in the native range of the species and were unrelated to either lake productivity or fish's diet. A generalist trophic ecology confers significant advantages on an invasive species, allowing it to exploit a variety of novel resources and fluctuations in prey availability.