Biogeographic differences between native and non-native populations of crayfish alter species coexistence and trophic interactions in mesocosms

Biogeographical comparisons of native and non-native populations allow researchers to understand the degree to which traits contributing to invasion success are intrinsic or change during the invasion process. Here, we investigate whether traits underlying interspecific competition change following invasion and whether these alter the impacts of two crayfish congeners that have invaded into each other’s native ranges. Specifically, we compared native and non-native populations of rusty (Faxonius rusticus) and virile crayfish (F. virilis). We compared native and non-native populations of each species using laboratory assays to examine aggression and large mesocosms with the congeners in sympatry to examine growth and survival as well as impacts on lower trophic levels. We found that non-native virile crayfish were more aggressive in response to a threat than native virile crayfish and exhibited greater growth and survival in sympatry with rusty crayfish. These intraspecific differences were large enough to alter coexistence between species in the mesocosm experiment, which is consistent with patterns of coexistence between these species in the field. We did not observe differences in traits between native and non-native rusty crayfish, but rusty crayfish were consistently competitively dominant over virile crayfish in paired laboratory assays. Non-native populations of both species had greater impacts on lower trophic levels than native populations. Taken together, these findings provide new evidence that trait changes during invasions may enhance ecological impacts of invasive animals and their ability to compete with closely related native species.     

Intensive trapping and increased fish predation cause massive population decline of an invasive crayfish

1. Invasive species frequently have adverse impacts on native communities and ecosystems. Management options are often limited. Our goal is to evaluate the effect of intensive trapping and fish predation on the population dynamics of an invasive crayfish. 2. From 2001 to 2005, we removed invasive rusty crayfish (Orconectes rusticus) by trapping in Sparkling Lake in northern WI. In addition, the Wisconsin Department of Natural Resources restricted harvest of fish species known to consume crayfish, thereby increasing predation on crayfish that are too small to trap. 3. After an initial increase, catch rates of rusty crayfish declined by approximately 95%, from 11 crayfish per trap per day in 2002 to 0.65 in 2004. The catch rate in 2005 remained low at 0.5 crayfish per trap. Females comprised nearly 50% of the catch from 2002 to 2004. Unlike rusty crayfish in Sparkling Lake, catch rates of O. rusticus and Orconectes propinquus in three nearby lakes increased or remained relatively constant over the 5‐year removal period. 4. We also examined the influence of habitat and temperature on crayfish catch rates. Catch rates were highest at water temperatures between 20 and 25 °C and on cobble, log or macrophyte habitats that may serve as refuge from fish predation. 5. Five summers of intensive trapping and fisheries management practices reduced abundances, but did not extirpate rusty crayfish in Sparkling Lake. To determine the potential of trapping as a management option for invasive crayfishes, these methods must be tested in other systems.     

Predation on invasive zebra mussel, Dreissena polymorpha, by pumpkinseed sunfish, rusty crayfish, and round goby

The enemy release hypothesis states that invasive species are successful in their new environment because native species are not adapted to utilize the invasive. If true for predators, native predators should have lower feeding rates on the invasive species than a predator from the native range of the invasive species. We tested this hypothesis for zebra mussel (Dreissena polymorpha) by comparing handling time and predation rate on zebra mussels in the laboratory by two North American species (pumpkinseed, Lepomis gibbosus, and rusty crayfish, Orconectes rusticus) and one predator with a long evolutionary history with zebra mussels (round goby, Neogobius melanostomus). Handling time per mussel (7 mm shell length) ranged from 25 to >70 s for the three predator species. Feeding rates on attached zebra mussels were higher for round goby than the two native predators. Medium and large gobies consumed 50–67 zebra mussels attached to stones in 24 h, whereas pumpkinseed and rusty crayfish consumed <11. This supports the hypothesis that the rapid spread of zebra mussels in North America was facilitated by low predation rates from the existing native predators. At these predation rates and realistic goby abundance estimates, round goby could affect zebra mussel abundance in some lakes.     

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.     

Effects of an invasive crayfish on the littoral macroinvertebrates of large boreal lakes are habitat specific

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Divergent responses of exposed and naive Pacific tree frog tadpoles to invasive predatory crayfish

Invasive predators can devastate native species and ecosystems. However, native species may be able to coexist with invasive predators through a variety of mechanisms, such as changes in morphology or behavior due to a plastic response or selection on fixed anti-predator traits. We examined whether exposed and naive populations of Pacific tree frog tadpoles (Pseudacris regilla) display divergent morphological and behavioral traits in response to the invasive predatory red swamp crayfish (Procambarus clarkii). Tadpoles were collected from three study streams with and three without crayfish, in the Santa Monica Mountains of Southern California. We analyzed tadpole morphology and tested anti-predator behavior and survival in the laboratory. Tadpoles from streams with crayfish had shallower, narrower tails than tadpoles from streams without crayfish. Tadpoles from streams with and without crayfish were less active after exposure to crayfish chemical cues. The divergent morphology of naive and exposed tadpoles is consistent with tadpoles exhibiting a plastic response to crayfish or undergoing selection from crayfish predation. In laboratory predation experiments, we found no difference in survival between tadpoles from streams with and without crayfish but tadpoles that survived predation had deeper tail muscles than those that were killed or injured. Our results suggest that deeper tails are advantageous in the presence of crayfish, yet tadpoles from crayfish streams had shallower tails than those from crayfish-free streams. Shallower tails may have an alternative unmeasured advantage or there may be a physiological constraint to developing deeper tails in the wild. These results highlight the ability of a native frog to respond to an invasive predatory crayfish, potentially allowing for coexistence.     

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.     

Reciprocal Relationships Between Exotic Rusty Crayfish,Macrophytes, and <Emphasis Type="Italic">Lepomis</Emphasis> Species in Northern Wisconsin Lakes

Abstract The non-native rusty crayfish (Orconectes rusticus) has invaded many lakes of northern Wisconsin, profoundly changing littoral zones in the process. There are other lakes that have been invaded, but do not exhibit these changes. We hypothesized that endogenous feedbacks could form involving rusty crayfish, the macrophytes they destroy, and Lepomis species whose abundance is positively related to macrophyte abundance and also consume juvenile crayfish. We assessed this proposal with long-term data from one lake, a regional comparative study, and a case study of Lepomis predation on crayfish. Through time and across lakes, abundances of rusty crayfish, littoral macrophytes and species of the genus Lepomis were related in a fashion that indicated a set of feedbacks that regulate the abundance of all three. Intense predation on juvenile crayfish by abundant Lepomis is capable of maintaining some crayfish populations at low abundance. Thus, some lakes display profound ecological changes where crayfish achieve high abundance, and others sustain crayfish at low abundance. Consequently, lakes invaded by rusty crayfish may take on the appearance of alternative ecological regimes. Direct experimentation is necessary to determine if, and under what conditions, a lake can exist in either regime. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Between‐lake variation in the trophic ecology of an invasive crayfish

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Coupling long-term studies with meta-analysis to investigate impacts of non-native crayfish on zoobenthic communities

1. Biological invasions are widely recognised as a significant component of human‐caused environmental change and a primary threat to native biodiversity. The negative impacts of species invasions are particularly evident for freshwater crayfish faunas. 2. This study provides novel insight into the ecological effects of native and non‐native crayfish on zoobenthic communities (with emphasis on the non‐native rusty crayfish, Orconectes rusticus) across broad scales by combining a meta‐analysis of small‐scale experimental studies with a long‐term observational study conducted over a 24 year period in Sparkling Lake, Wisconsin, U.S.A. (46°00′N, 89°42′W). 3. The meta‐analysis summarised quantitatively the results of cage experiments for seven species of crayfish spanning four continents. We found that total zoobenthos densities (primarily Gastropoda and Diptera) were significantly lower in treatments containing crayfish relative to controls; a result that was significant for non‐native crayfish but not for crayfish in their native range, perhaps owing to a small sample size. In contrast to other species, rusty crayfish were also negatively associated with Ephemeroptera. 4. Results from the time series analysis comparing temporal trends in rusty crayfish and invertebrate abundances from Sparkling Lake were consistent with the findings from the meta‐analysis. Rusty crayfish were negatively correlated with the abundance of total zoobenthos, Diptera, Ephemeroptera and Odonata, as well as families of Trichoptera. 5. By coupling the results from short and long‐term research, our study offers greater insight into the nature of crayfish‐invertebrate interactions in aquatic systems, revealing consistent effects of invasive crayfish on native fauna. The control and management of invasive species is facilitated by the knowledge that well executed small‐scale studies may be extrapolated to understand larger‐scale ecological interactions.     

Effects of crayfish on leaf litter breakdown and shredder prey: are native and introduced species functionally redundant?

Recent increases in biological invasions frequency may have important consequences on native communities. However, functional redundancy between invasive and native species could reduce non-native species effects on native ecosystems. Despite this, even small differences in functional traits between these species may still have unpredictable effects on colonized ecosystems. Invasive crayfish, as ecosystem engineers, potentially have wide and complex effects on recipient ecosystems, even when replacing a native counterpart. We used laboratory microcosms to test whether native (Astacus astacus) and invasive crayfish species (Orconectes limosus, Pacifastacus leniusculus and Procambarus clarkii) are actually functionally redundant in their effects on prey/shredder density and leaf litter breakdown. Results show that crayfish strongly influenced macroinvertebrate numbers and leaf litter breakdown and indicate that differences in direct (prey and leaf litter consumption) and indirect (prey habitat use and leaf litter breakdown) effects between crayfish species do exist. While the replacement of A. astacus by O. limosus may have induced only minor changes in freshwater ecosystems, invasions by the larger and more aggressive P. clarkii and P. leniusculus will likely have strong effects on invaded ecosystem. Overall, there seems to be no functional redundancy between these four species and outcomes of crayfish invasion will likely be species specific.     

Testing the differential predation hypothesis for the invasion of rusty crayfish in a stream community: laboratory and field experiments

1. We tested the hypothesis that the non‐native rusty crayfish (Orconectes rusticus) is less vulnerable to predators than two native species (O. propinquus and O. obscurus) it is replacing in streams of the upper Susquehanna River catchment (New York, U.S.A.). 2. We used laboratory experiments to compare species‐specific predation rates by smallmouth bass (Micropterus dolomieu) on crayfish of equal size and field tethering experiments to compare relative predation rates between native O. propinquus and non‐native O. rusticus by the suite of crayfish predators in our system. We predicted that crayfish size would affect predation rate but that predation rates would be equal among species when size was controlled. 3. We also tested for two potential artefacts of tethering. We tethered crayfish in cages to test whether the ability to escape from tethers is size specific, and we tested whether tethering alters differential predation among crayfish species by the smallmouth bass. 4. In the laboratory, smallmouth bass predation on rusty crayfish was lower than on either of the native species. In the field, predation risk for tethered crayfish was inversely related to size but did not differ among species when size was taken into account. Because rusty crayfish in the field experiment were slightly larger than the native species, as in nature, mortality was overall lower for the rusty crayfish. 5. In cages, smaller crayfish were more probably to escape from tethers than larger ones, an artefact that may partially confound results from our tethering experiments. Unexpectedly, tethering nearly eliminated predation by smallmouth bass. This artefact prevented us from testing for an interaction of tethering with differential predation and means that the results of field tethering experiments do not include any contribution from smallmouth bass predation. 6. Our experiments highlight the importance of explicitly considering potential artefacts that could confound results. 7. Our results indicate that differential predation contributes to the rusty crayfish's invasion of a stream community. In our study system, predation rates on rusty crayfish are lower than for native species mostly because of selection by predators for smaller crayfish; species‐specific characteristics such as behaviour that further reduce predation may also contribute, especially where smallmouth bass predation is important.     

Over-invasion in a freshwater ecosystem: newly introduced virile crayfish (Orconectes virilis) outcompete established invasive signal crayfish (Pacifastacus leniusculus)

Biological invasions are a key threat to freshwater biodiversity, and identifying determinants of invasion success is a global conservation priority. The establishment of introduced species is predicted to be hindered by pre-existing, functionally similar invasive species. Over a five-year period we, however, find that in the River Lee (UK), recently introduced non-native virile crayfish (Orconectes virilis) increased in range and abundance, despite the presence of established alien signal crayfish (Pacifastacus leniusculus). In regions of sympatry, virile crayfish had a detrimental effect on signal crayfish abundance but not vice versa. Competition experiments revealed that virile crayfish were more aggressive than signal crayfish and outcompeted them for shelter. Together, these results provide early evidence for the potential over-invasion of signal crayfish by competitively dominant virile crayfish. Based on our results and the limited distribution of virile crayfish in Europe, we recommend that efforts to contain them within the Lee catchment be implemented immediately.     

The rapid spread of rusty crayfish (Orconectes rusticus) with observations on native crayfish declines in Wisconsin (U.S.A.) over the past 130 years

The rusty crayfish, Orconectes rusticus, is one of America’s best-known non-indigenous crayfishes, having been identified as extirpating native crayfishes and disrupting local aquatic ecosystems. Over the past 40–50 years, rusty crayfish have spread from its historical range in the Ohio River drainage (U.S.A.), to waters throughout much of Illinois, Michigan, Wisconsin, and Minnesota and parts of 11 other states, Ontario (Canada) and the Laurentian Great Lakes. Using a comprehensive dataset based on all known historical records and extensive present-day surveys (n = 2775) this study reports on the invasion history of rusty crayfish, with observations on concomitant declines of native crayfishes in Wisconsin over the past 130 years (1870–2004). We found that rusty crayfish occurrences have increased from 7% of all crayfish records collected during the first 20 years of their invasion (1965–1984) to 36% of all records during the last 20 years, and that rusty crayfish have replaced the northern clearwater crayfish (O. propinquus) and virile crayfish (O. virilis) as the most dominant member of the contemporary crayfish fauna. In light of our results we discuss the introduction, establishment and integration phases of the rusty crayfish invasion and provide preliminary predictions of the potential distribution of rusty crayfish in Wisconsin lakes based on critical environmental requirements.     

Differences Found in the Macroinvertebrate Community Composition in the Presence or Absence of the Invasive Alien Crayfish,Orconectes hylas

Introductions of alien species into aquatic ecosystems have been well documented, including invasions of crayfish species; however, little is known about the effects of these introductions on macroinvertebrate communities. The woodland crayfish (Orconectes hylas (Faxon)) has been introduced into the St. Francis River watershed in southeast Missouri and has displaced populations of native crayfish. The effects of O. hylas on macroinvertebrate community composition were investigated in a fourth-order Ozark stream at two locations, one with the presence of O. hylas and one without. Significant differences between sites and across four sampling periods and two habitats were found in five categories of benthic macroinvertebrate metrics: species richness, percent/composition, dominance/diversity, functional feeding groups, and biotic indices. In most seasons and habitat combinations, the invaded site had significantly higher relative abundance of riffle beetles (Coleoptera: Elmidae), and significantly lower Missouri biotic index values, total taxa richness, and both richness and relative abundance of midges (Diptera: Chironomidae). Overall study results indicate that some macroinvertebrate community differences due to the O. hylas invasion were not consistent between seasons and habitats, suggesting that further research on spatial and temporal habitat use and feeding ecology of Ozark crayfish species is needed to improve our understanding of the effects of these invasions on aquatic communities.     

Niche partitioning and stochastic processes shape community structure following whitefly invasions

One of the most detrimental impacts of invasive species is the exclusion of native species, which reduces biodiversity and can alter community structure. Coexistence between invaders and native species across large scales, however, might be promoted by niche partitioning and/or stochastic processes, even when one species is excluded in some habitats. Here, we examined the effects of species traits, stochastic processes, and niche partitioning on coexistence of two morphocryptic whitefly species in the Bemisia tabaci complex: the invasive Mediterranean (MED) species and the native Middle East-Asia Minor 1 (MEAM1) species. These species engage in intense reproductive interference, which can result in the exclusion of one species or the other in shared habitats. Both species, however, have coexisted in sympatry in Israel for many years, where MED is invasive and MEAM1 is native. Using a spatially explicit model, we show that both stochastic processes and niche partitioning can promote coexistence between MEAM1 and MED, although predicted community structure differs drastically in each scenario. Comparison of field observations with model results indicated that variation in habitat use leading to niche partitioning was a primary factor driving coexistence between MEAM1 and MED across landscapes, although stochastic processes affected the establishment of rare species within habitats. In many systems, combining models with field surveys can be used to isolate and test mechanisms underlying patterns of community structure following invasions.     

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

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Behavioural and growth differences between experienced and naïve populations of a native crayfish in the presence of invasive rusty crayfish

1. Species invasions are a leading threat to native species and ecosystems. How populations of native species respond to the presence of invasive species will ultimately determine their long-term persistence.
2. In this study, we capitalise on a unique opportunity to compare the behaviour and growth of naïve and experienced virile crayfish ( Orconectes virilis Hagen) populations in the presence of invasive rusty crayfish ( O. rusticus Girard ) . In behavioural trials, experienced O. virilis (coexisted with O. rusticus for >30 years) showed more aggressive behaviour than their naïve counterparts. Naïve O . virilis retreated from aggressive interactions with O. rusticus 38% more often than experienced O . virilis. Experienced O. virilis spent 39% more time occupying shelter than naïve O. virilis.
3. There were also differences in O. rusticus behaviour: O. rusticus spent 24% more time occupying shelter with naïve O. virilis relative to experienced O. virilis .
4. In field mesocosm experiments with O. rusticus , naïve O . virilis declined in body mass by 1% while experienced O. virilis' body mass increased by 6%, thus highlighting the potential population-level implications of the previously observed behavioural effects.
5. Our work demonstrates significant behaviour and growth differences between naïve and experienced O. virilis in the presence of invasive O. rusticus. Whether this difference is the result of phenotypic plasticity or evolution by natural selection remains to be determined. Either way, this area of inquiry has implications for managing native populations and species in an increasingly invaded world.     

Habitat-specific effects of particle size, current velocity, water depth, and predation risk on size-dependent crayfish distribution

This study assessed effects of abiotic (current velocity, water depth, particle size) and biotic (predation risk for crayfish, size distribution and densities of predatory fish) variables on habitat- and size-specific distribution patterns of lotic crayfish (Orconectes obscurus) using field surveys and tethering experiments. Additionally, particle size manipulations were used with predation assays to assess habitat-specific interactions since the average particle size increased from deep pools to shallow pools to riffles. Large crayfish had the highest densities in deep pools and were associated with increased water depth, whereas small and medium crayfish had the highest densities in shallow pools and were strongly associated with increased particle size and decreased water depth. Regardless of size, crayfish in deep pools had significantly lower survival than in shallow pools and riffles. However, only small crayfish showed consistent differences in predation risk by habitat type and were significantly more vulnerable to predation than larger crayfish. Additionally, large rocky refugia resulted in significantly higher survival of small crayfish in the combined particle manipulation/tethering experiment. Overall, predation appears to be a key mechanism structuring habitat-specific distribution patterns for only small O. obscurus. Large substrates may be particularly important in habitats where both small crayfish density and predation risk are high.