Ecological Impact Of Invasive Species Research Articles

Functional responses of male and female European green crabs suggest potential sex-specific impacts of invasion.

Predicting the impacts of predatory invasive species is important for prioritising conservation interventions. Functional response experiments, which examine consumption by predators in relation to prey density, are a useful way to assess the potential strength of novel predator-prey relationships. However, such experiments are often conducted without consideration of sex or only with males to reduce invasion risk. Here, we compared the functional responses of male and female European green crabs (Carcinus maenas), a global invader, feeding on varnish clams (Nuttallia obscurata) to test whether the two sexes have similar potential for impact. We also examined potential correlates of predation behaviour by measuring sex-specific movement and prey choice. Both sexes displayed a Type II hyperbolic functional response, which can destabilise prey populations at low prey densities. However, males and females exhibited some differences in foraging behaviour. Female green crabs had slightly lower attack rates, which were not linked to sex differences in movement, and slightly longer handling times, which were not linked to sex differences in prey choice. These small, non-significant differences nevertheless translated into significantly greater functional response ratios, which are used to predict the ecological impact of invasive species, for males than females. There was no difference in the proportion of clams consumed between males and females with similar crusher claw heights, but females have smaller crusher claws on average, hence they consumed a smaller proportion of clams. Repeated surveys of four populations of European green crabs established in British Columbia, Canada, showed that sex ratio is highly variable. Taken together, these results and population-level modelling suggest that trying to evaluate the potential impact of European green crabs on clam populations by sampling only males could result in overestimation, even in populations that have male-biased sex-ratios. Consumer sex might generally be an important feature to consider when using functional response experiments to forecast the impact of new invasive species, especially those with marked sexual dimorphism that affect foraging.

Adding insult to injury: anthropogenic noise intensifies predation risk by an invasive freshwater fish species

The ecological impact of invasive species is likely to be modulated by human-induced alterations in habitats, which represents another driver of biodiversity loss. We tested the effect of soundscape degradation on predation by the round goby Neogobius melanostomus, one of Europe’s “worst invasive species”. For this, we compared the relationship between per capita predation rate and prey density (i.e., the functional response) in the presence or absence of motorboat sounds. Unexpectedly, fish displayed a stronger functional response with additional noise, which could be explained by a higher mobility promoting encounters with prey. Our results suggest that anthropogenic noise is likely to exacerbate the impact of invasive species.

Impact of native and invasive cyclopoid predators in relation to the diversity of the zooplankton community

Abstract The ecological impact of invasive species may be less in communities with high species diversity. We hypothesized that the feeding rates of an invasive copepod would be unaffected by high species diversity of prey in the medium as compared with a native species which would have reduced feeding rates under similar conditions. The biotic resistance to prey consumption was evaluated by testing consumption rate of the invasive species: Mesocyclops pehpeiensis and the native species: Mesocyclops longisetus curvatus, Acanthocyclops americanus, Eucyclops sp. and Microcyclops dubitabilis separately exposed to two treatments: high diversity with 13 prey species (rotifers and microcrustaceans) and low diversity with three prey species (determined on the basis of previous studies on zooplankton diversity in Mexican water bodies). We also tested the prey preference index of M. pehpeiensis in the absence and presence of the native copepod M. longisetus curvatus. M. pehpeiensis consumed the same number of prey in both treatments, regardless of high or low diversity conditions, whereas the four native species consumed less prey in the high diversity than the low diversity treatments. High community diversity may not represent an obstacle to the successful establishment of the invasive exotic copepod M. pehpeiensis.

Invasive populations of Spiraea tomentosa (Rosaceae) are genetically diverse but decline during succession in forest habitats

Population genetic and ecological data may help to control invasive plants, which are considered to be a major threat to natural habitats. In contrast to expected bottleneck events, genetic diversity of such invasive populations may be high due to extensive propagule pressure or admixture. The ecological impact of invasive species has been broadly evaluated in the field, however, long term-studies on the fate of invasive plants are scarce. We analysed genetic diversity and structure in invasive Spiraea tomentosa populations in eastern Germany and western Poland by using an Amplified Fragment Length Polymorphism approach. Potential hybridisation between co-occurring diploid Sp.tomentosa and tetraploid Sp. douglasii was investigated using Flow Cytometry. The genetic analyses were complemented by data from a thirteen-year vegetation study in an area invaded by both Spiraea species. We found no evidence for spontaneous hybridisation between Spiraea species. In populations of Sp.tomentosa genetic diversity (He=0.26) and genetic structure (ΦPT=0.27) were high and comparable to other outcrossing woody plants. Low levels of clonality, the presence of seedlings and of new patches in sites that had been colonised over the last 13 years imply that populations also increase and spread via sexual reproduction. In all habitat types, species diversity declined following Sp.tomentosa invasion. However, detailed aerial mapping of a forest reserve with ongoing succession revealed that Spiraea spp. populations declined over a ten year period following invasion. Despite its potential dispersal ability and its negative effects on plant communities, invasive Spiraea populations may be controlled by increasing canopy cover in forest habitats.

Community composition influences the population growth and ecological impact of invasive species in response to climate change.

Predicting long-term impacts of introduced species is challenging, since stressors related to global change can influence species-community interactions by affecting both demographic rates of invasive species and the structure of the invaded ecosystems. Invasive species can alter ecosystem structure over time, further complicating interactions between invasive species and invaded communities in response to additional stressors. Few studies have considered how cumulative impacts of species invasion and global change on the structure of invaded ecosystems may influence persistence and population growth of introduced species. Here, we present an empirically based population model for an invasive epiphytic bryozoan that can dramatically alter the structure of its invaded kelp bed ecosystems. We use this model to predict the response of invasive species to climate change and associated changes in the invaded community. Population growth of the bryozoan increased under near-future projections of increasing ocean temperature; however, the magnitude of population growth depended on the community composition of invaded kelp beds. Our results suggest that, in some cases, indirect effects of climate change mediated through changes to the structure of the invaded habitat can modulate direct effects of climate change on invasive species, with consequences for their long-term ecological impact. Our findings have important implications for management of invasive species, as modifying invaded habitats at local to regional scales may be more logistically feasible than addressing stressors related to global climate change.

Predicting predatory impact of juvenile invasive lionfish (Pterois volitans) on a crustacean prey using functional response analysis: effects of temperature, habitat complexity and light regimes

The ecological implications of biotic interactions, such as predator-prey relationships, are often context-dependent. Comparative functional responses analysis can be used under different abiotic contexts to improve understanding and prediction of the ecological impact of invasive species. Pterois volitans (Lionfish) [Linnaeus 1758] is an established invasive species in the Caribbean and Gulf of Mexico, with a more recent invasion into the Mediterranean. Lionfish are generalist predators that impact a wide range of commercial and non-commercial species. Functional response analysis was employed to quantify interaction strength between lionfish and a generic prey species, the shrimp (Paleomonetes varians) [Leach 1814], under the contexts of differing temperature, habitat complexity and light wavelength. Lionfish have prey population destabilising Type II functional responses under all contexts examined. Significantly more prey were consumed at 26 °C than at 22 °C. Habitat complexity did not significantly alter the functional response parameters. Significantly more prey were consumed under white light and blue light than under red light. Attack rate was significantly higher under white light than under blue or red light. Light wavelength did not significantly change handling times. The impacts on prey populations through feeding rates may increase with concomitant temperature increase. As attack rates are very high at low habitat complexity this may elucidate the cause of high impact upon degraded reef ecosystems with low-density prey populations, although there was little protection conferred through habitat complexity. Only red light (i.e. dark) afforded any reduction in predation pressure. Management initiatives should account for these environmental factors when planning mitigation and prevention strategies.

The ecological impact of invasive cane toads on tropical snakes: Field data do not support laboratory-based predictions

Predicting which species will be affected by an invasive taxon is critical to developing conservation priorities, but this is a difficult task. A previous study on the impact of invasive cane toads (Bufo marinus) on Australian snakes attempted to predict vulnerability a priori based on the assumptions that any snake species that eats frogs, and is vulnerable to toad toxins, may be at risk from the toad invasion. We used time-series analyses to evaluate the accuracy of that prediction, based on >3600 standardized nocturnal surveys over a 138-month period on 12 species of snakes and lizards on a floodplain in the Australian wet-dry tropics, bracketing the arrival of cane toads at this site. Contrary to prediction, encounter rates with most species were unaffected by toad arrival, and some taxa predicted to be vulnerable to toads increased rather than declined (e.g., death adder Acanthophis praelongus; Children's python Antaresia childreni). Indirect positive effects of toad invasion (perhaps mediated by toad-induced mortality of predatory varanid lizards) and stochastic weather events outweighed effects of toad invasion for most snake species. Our study casts doubt on the ability of a priori desktop studies, or short-term field surveys, to predict or document the ecological impact of invasive species.

Impacts of eggs and tadpoles of the invasive cane toad (Bufo marinus) on aquatic predators in tropical Australia

Invasive species affect native ecosystems in a variety of ways, and the magnitude of impact may depend upon many factors. In an invading species such as the cane toad (Bufo marinus), the multiphasic life history creates a potential for impact to differ between life history stages. Previous research on the impact of cane toads in Australia has focused on fatal poisoning of predators that ingest terrestrial stages of the toad, but aquatic stages (eggs, larvae) are toxic also. We exposed nine native Australian fish species and one native Australian turtle species to the eggs and larvae of toads. Strong species differences were evident, both in palatability (propensity to attack the egg or larva), and in subsequent responses (e.g. taste and reject the item, vs. ingest it). Toad eggs were less likely than toad tadpoles to be attacked, but also less likely to be rejected before ingestion (probably because the non-toxic jelly coat masks the presence of toxins in the ovum). As a result, predators were far more likely to be killed by ingesting toad eggs than toad tadpoles. Fortuitously, the spatial and temporal availability of toad egg masses restricts encounter rates with predators, so that overall ecological impact may be low despite the high vulnerability of a fish or turtle that encounters such an egg mass. Understanding such ontogenetic shifts in the nature of interactions and magnitude of impact is crucial if we are to understand the overall ecological impact of invasive species.

Biological invasions and phenotypic evolution: a quantitative genetic perspective

Among the many different components of global environmental change, biological invasions represent the one with the most long-term ecological and evolutionary consequences, as effects are irreversible. Although the ecological impact of invasive species has been under great scrutiny, its evolutionary aspects and consequences have remained less explored. Once established, an important part of the success of an invasive species will depend on the presence of genetic variation in populations at the geographic boundaries upon which natural selection can act. This information is integrated in G, the matrix of additive genetic variances and covariances for a suite of traits. The G-matrix shows the restrictions and potentialities of adaptive evolution and, together with natural selection determine the direction and rate of phenotypic evolution. Here I propose that a geographic analysis of G in populations of the introduced and native range becomes essential to understand critical evolutionary issues associated with invasion success.

Mass mortality of native anuran tadpoles in tropical Australia due to the invasive cane toad ( Bufo marinus)

Specific pathways of the ecological impact of invasive species remain poorly known. Although the spread of toxic cane toads ( Bufo marinus) through tropical Australia is widely believed to have caused extensive mortality of native reptiles and mammals, effects of toad ingestion on native anurans have been virtually ignored. Our studies on the Adelaide River floodplain show that the most numerous vertebrate victims of toad invasion are native tadpoles that die when they attempt to consume toad eggs. We documented 11 episodes of mass mortality, totalling >1300 tadpoles of 10 species, in five waterbodies within a single wet-season shortly after the toads invaded. A causal link between toad breeding and tadpole mortality is supported by observations that: (1) in at least 9 of the 11 waterbodies involved, toads bred immediately prior to mortality events; (2) water quality was indistinguishable from that of control ponds, and tadpoles placed in that water remained healthy; (3) dead tadpoles showed no sign of disease; and (4) laboratory trials showed rapid, 100% mortality in native tadpoles exposed to freshly-laid toad eggs. Despite these high mortality rates, toad invasion does not appear to threaten the viability of anuran populations because frogs often breed in ponds not used by toads, and because density-dependent growth and survival within tadpole communities mean that additional mortality may not reduce the total effective recruitment of metamorph frogs from a waterbody.