Complex impacts of an invasive omnivore and native consumers on stream communities in California and Hawaii

The effects of invasive species on native communities often depend on the characteristics of the recipient community and on the food habits of the invasive species, becoming complicated when the invader is omnivorous. In field enclosure experiments, we assessed the direct and interactive effects of an invasive omnivorous crayfish (Procambarus clarkii) and either native herbivorous snails (Physella gyrina) or shrimp (Atyoida bisulcata) on stream communities in California and Hawaii, respectively. Based on literature data and the characteristics of each study site, we predicted that crayfish would affect primarily algal-based trophic linkages in an open California stream but detritus-based trophic linkages in a shaded Hawaiian stream, with trophic cascades mediated through crayfish effects on primary consumers being observed in both systems. As predicted, crayfish in California directly reduced periphyton, filamentous algae, sediment, and snail levels, but generated a cascade by decreasing snail densities and increasing periphyton biomass. Contrary to prediction, crayfish did not reduce total invertebrate biomass. As predicted, crayfish in Hawaii reduced leaf litter, filamentous algae, and benthic invertebrate biomass. Contrary to our predictions, however, a trophic cascade was not observed because shrimp did not affect periphyton levels, crayfish did not reduce shrimp abundance, and crayfish had greater negative impacts on filamentous algae than did shrimp. Our findings highlight that the same invasive species can generate different effects on disparate systems, probably as mediated through the availability of different food types, flexibility in the invasive species’ food habits, and complex pathways of trophic interaction.     

Experimental Test of Preferences for an Invasive Prey by an Endangered Predator: Implications for Conservation

Identifying impacts of exotic species on native populations is central to ecology and conservation. Although the effects of exotic predators on native prey have received much attention, the role of exotic prey on native predators is poorly understood. Determining if native predators actively prefer invasive prey over native prey has implications for interpreting invasion impacts, identifying the presence of evolutionary traps, and predator persistence. One of the world’s most invasive species, Pomacea maculata, has recently established in portions of the endangered Everglade snail kite’s (Rostrhamus sociabilis plumbeus) geographic range. Although these exotic snails could provide additional prey resources, they are typically much larger than the native snail, which can lead to lower foraging success and the potential for diminished energetic benefits in comparison to native snails. Nonetheless, snail kites frequently forage on exotic snails. We used choice experiments to evaluate snail kite foraging preference in relation to exotic species and snail size. We found that snail kites do not show a preference for native or exotic snails. Rather, snail kites generally showed a preference for medium-sized snails, the sizes reflective of large native snails. These results suggest that while snail kites frequently forage on exotic snails in the wild, this behavior is likely driven simply by the abundance of exotic snails rather than snail kites preferring exotics. This lack of preference offers insights to hypotheses regarding effects of exotic species, guidance regarding habitat and invasive species management, and illustrates how native-exotic relationships can be misleading in the absence of experimental tests of such interactions.     

Two for one: inadvertent introduction of <Emphasis Type="Italic">Euglandina</Emphasis> species during failed bio-control efforts in Hawaii

The introduction of the predatory land snail, Euglandina rosea (Férrusac, 1821) from Florida to Hawaii to control the giant African snail, Lissachatina fulica (Bowdich, 1822) is among the most publicized biological control cases gone awry. Following preliminary genetic analyses that revealed a second, possibly undescribed Euglandina species was probably introduced to Hawaii, we used an integrative systematic approach combining both genetic and morphological assessments to examine the taxonomic status of the snail referred to as E. rosea in Hawaii. Genetic and morphological analyses support the interpretation that two Euglandina species were introduced to and have become established in Hawaii and can be readily distinguished based on morphological differences. This finding has significant ramifications for understanding both historical and contemporary biocontrol as it suggests that: (1) other species may have been inadvertently introduced through bio-control programs, (2) inadequate understanding of the taxonomy of bio-control agents has obscured our ability to effectively study their ecological impacts, and (3) while the US has no comprehensive regulatory framework for importing biological control agents, one is urgently needed. This also has wide-ranging implications for conservation efforts throughout the tropics because Euglandina from Oahu, Hawaii were released on other Hawaiian Islands, New Guinea, Okinawa, Palau Islands, Philippines, India, Bonin Islands and Bermuda for use in biological control programs that led to catastrophic loss of endemic land snail diversity.     

Extinct even before scientific recognition: a remarkable radiation of helicinid snails (Helicinidae) on the Gambier Islands, French Polynesia

Recent literature abounds with reports of the decline and extinction of the endemic species of Achatinellidae and Partulidae in the Hawaiian and Society Islands, respectively, resulting from the introduction of the predatory snail Euglandina rosea. Here, we describe a previously unrecognised radiation of helicinid land snails from the Gambier Islands of French Polynesia, with up to seven species co-occurring in a single locality and up to eight species on a single island. This radiation had already become extinct (nine of ten species) several decades before the expansion of E. rosea in the Pacific, and even before the species were collected for scientific study. The Gambier Islands case study shows that massive extinctions of endemic land snails had already taken place in the nineteenth century, but have remained largely unrecognised and undocumented. Nine of the ten species are new to science and are described here almost entirely based on empty shells collected from the shell bank of the soil after the extinction had already taken place. This helicinid radiation alone increases the number of documented global mollusc extinctions by almost 2 %. Most of the species are minute and, at 1.5 mm, rank among the smallest, if not the smallest, species in the family. Several have apertural barriers and one has opercular apophyses—character states not previously documented in Pacific helicinids. Whereas the only surviving Gambier species belongs anatomically to the genus Sturanya, representative helicinid species from the Austral, Society and Cook Islands are not congeneric with it, and the generic name Nesiocina is here established for the latter taxa. It is hypothesised that the extinct Gambier species were also Nesiocina.     

Complex interactions among fish, snails and macrophytes: implications for biological control of an invasive snail

The golden apple snail (Pomacea canaliculata), a native of freshwater wetlands of South America, has invaded many Asian countries and grazed heavily in agricultural and wild areas. Common carp (Cyprinus carpio) has been proposed as a biological control agent against this snail, but little is known about its impact on non-target aquatic plants and animals. In a 8-week enclosure experiment, we quantified the impact of common carp on three species of aquatic macrophytes and nine species of snails, including the apple snail, in a shallow pond. The results showed that the apple snail or carp alone significantly reduced the plant biomass, although the apple snail had a stronger overall herbivorous effect than the carp. The carp completely removed juvenile apple snails, but had only a weak predatory effect on larger apple snails and no effect on the adults’ oviposition frequency. Furthermore, the carp significantly reduced the populations of most species of other snails that occurred naturally in the pond. Our results thus indicate that common carp can be an effective biological control agent against the invasive apple snail, but caution should be taken about its potential to reduce wetland floral and faunal diversity.     

Parasites reduce food web robustness because they are sensitive to secondary extinction as illustrated by an invasive estuarine snail

A robust food web is one in which few secondary extinctions occur after removing species. We investigated how parasites affected the robustness of the Carpinteria Salt Marsh food web by conducting random species removals and a hypothetical, but plausible, species invasion. Parasites were much more likely than free-living species to suffer secondary extinctions following the removal of a free-living species from the food web. For this reason, the food web was less robust with the inclusion of parasites. Removal of the horn snail, Cerithidea californica, resulted in a disproportionate number of secondary parasite extinctions. The exotic Japanese mud snail, Batillaria attramentaria, is the ecological analogue of the native California horn snail and can completely replace it following invasion. Owing to the similarities between the two snail species, the invasion had no effect on predator–prey interactions. However, because the native snail is host for 17 host-specific parasites, and the invader is host to only one, comparison of a food web that includes parasites showed significant effects of invasion on the native community. The hypothetical invasion also significantly reduced the connectance of the web because the loss of 17 native trematode species eliminated many links.     

Trait-based plant mortality and preference for native versus non-native seedlings by invasive slug and snail herbivores in Hawaii

Non-native herbivores may alter plant communities through their preferential consumption of seedlings of different species. We assessed seedling herbivory by two invasive gastropod species in Hawaii, the giant African snail (Achatina fulica) and the Cuban brown slug (Veronicella cubensis). We hypothesized that six native species would suffer greater gastropod herbivory than four non-native species, and that species with short stature, thin leaves, and lacking physical defenses would suffer the greatest mortality from gastropods. Herbivory was measured during 13-day preference trials using enclosures that each contained four different woody species (two native, two non-native) and were assigned to one of three treatments: giant African snail, Cuban brown slug, or control (no gastropod). Discriminant function analysis was used to predict gastropod-induced seedling mortality from a suite of seedling characteristics. Native species did not always experience greater herbivory than non-natives species, and seedling mortality was 0–100 %. Native Pipturus albidus and Clermontia parviflora suffered 100 % mortality from V. cubensis herbivory, and P. albidus, Psychotria hawaiiensis, and Myrsine lessertiana suffered ≥80 % mortality from A. fulica. Two non-natives (Fraxinus uhdei, Clidemia hirta), and two natives (Metrosideros polymorpha, Diospyros sandwicensis), suffered little damage and no mortality. Non-native Ardisia elliptica suffered 10–30 % gastropod mortality, and non-native Psidium cattleianum mortality was 0–50 %. Leaf thickness best predicted species mortality caused by slugs and snails; some thicker-leaved species suffered most. Invasive snails and slugs threaten some native and non-native seedlings by directly consuming them. Current and future plant community structure in Hawaii may in part reflect the feeding preferences of invasive gastropods.     

New evidence of ectomycorrhizal fungi in the Hawaiian Islands associated with the endemic host Pisonia sandwicensis (Nyctaginaceae)

Ectomycorrhizal plants and fungi are ubiquitous in mainland forests, but because of dispersal limitations are predicted to be less common on isolated islands. For instance, no native ectomycorrhizal plants or fungi have ever been reported from Hawaii, one of the most remote archipelagos on Earth. Members of the plant tribe Pisonieae are common on many islands, and prior evidence shows that some species associate with ectomycorrhizal fungi. However, until now, the Pisonieae species of Hawaii had yet to be examined for their mycorrhizal status. Here we sampled roots from members of the genus Pisonia growing on the Hawaiian islands of Oahu, Maui and Hawaii. We used molecular and microscopic techniques to categorize trees with respect to their mycorrhizal associations. We report that the Hawaiian endemic Pisonia sandwicensis forms ectomycorrhizas with at least five fungal operational taxonomic units (corresponding closely to species) belonging to four genera. We also report that this tree species is monophyletic with other ectomycorrhizal Pisonia species. We suggest that in light of the newly discovered Hawaiian ectomycorrhizal fungal community and other island ectomycorrhizal communities, dispersal limitations do not prevent the colonization of remote islands by at least some ectomycorrhizal fungi.     

Patterns of introduction of non-indigenous non-marine snails and slugs in the Hawaiian Islands

The native snails of the Hawaiian Islands are disappearing. One cause is predation by introduced carnivorous snails. Habitat destruction/modification is also important, facilitating the spread of other non-indigenous snails and slugs. Eighty-one species of snails and slugs are recorded as having been introduced. Thirty-three are established: 12 freshwater, 21 terrestrial. Two or three species arrived before western discovery of the islands (1778). During the nineteenth century about one species per decade, on average, was introduced. The rate rose to about four per decade during the twentieth century, with the exception of an especially large number introduced in the 1950s as putative biocontrol agents against the giant African snail, Achatina fulica. The geographical origins of these introductions reflect changing patterns of commerce and travel. Early arrivals were generally Pacific or Pacific rim species. Increasing trade and tourism with the USA, following its annexation of Hawaii, led to an increasing proportion of American species. More general facilitation of travel and commerce later in the twentieth century led to a significant number of European species being introduced. African species dominated the 1950s biological control introductions. The process continues and is just part of the homogenization of the unique faunas of tropical Pacific islands.     

A tale of three seas: consistency of natural history traits in a Caribbean–Atlantic barnacle introduced to Hawaii

Predictive models in invasion biology rely on knowledge of the life history and ecological role of invading species. However, species may change in key traits as they invade a new region, making prediction difficult. For marine invertebrate invaders there have been too few comparative studies to determine whether change in key traits is the exception or the rule. Here we examined populations of the intertidal barnacle Chthamalus proteus in three locations in its native range in the Caribbean and Atlantic, and in the Hawaiian Islands, where it has recently invaded, as a model system for such comparative studies. We measured body size, fecundity, population density and vertical distribution, compared habitat use and investigated aspects of the barnacle’s ecological role in Curaçao, Panama and Brazil and the main Hawaiian Islands. In terms of these measures, the barnacle has undergone little change in its invasion of Hawaii. Thus, if this barnacle had been studied in its native range, predictions about its spread in Hawaii could have been made. As little was known about this barnacle in either its native range or Hawaii, we also carried out studies of its larval life history, fecundity, growth, and mortality. Based on this work, we predict that this barnacle will continue to spread, aided by vessel traffic, throughout the Hawaiian Islands and elsewhere in the Pacific.     

Evaluating the efficacy of land snail survey techniques in Hawaii: implications for conservation throughout the Pacific

Terrestrial micromolluscs (snails with an adult maximum shell dimension <5 mm) constitute a considerable proportion of the land snail fauna of the Pacific. However, micromolluscs are often underestimated in biological surveys because of size bias. It has been argued that visual searches are preferable on Pacific islands because: (1) size biases are limited based on the understanding that most native Pacific island land snails are very small, and (2) amount of labor is less than other methods such as soil surveys and adequate for inventory purposes (though not for abundance assessments). To test whether visual surveys and soil surveys were accurately recording all taxa, land snail inventories were completed in three forest reserves (5 sampling sites in each) on the island of Oahu, Hawaii. Visual surveys involved 30-min visual search in a 10 m² site; soil surveys involved sieving leaf litter and topsoil from four 0.3 m² quadrats and extracting snails with the aid of a microscope. The data indicate a size and microhabitat bias associated with both techniques. Visual surveys consistently collected large arboreal and litter-dwelling species but missed a significant portion of micromolluscs, while soil surveys collected micromolluscs but missed larger snails. Because of such biases, employing both methods is critical for collecting all taxa at a survey location. As such, we recommend that future land snail surveys on Pacific Islands incorporate both survey techniques. Obtaining a complete inventory is critical if we are to understand species distributions and patterns of diversity and make well-informed conservation recommendations.     

A reptilian smoking gun: first record of invasive Jackson’s chameleon (<Emphasis Type="Italic">Chamaeleo jacksonii</Emphasis>) predation on native Hawaiian species

Here we report the first conclusive evidence of an introduced reptile (Chamaeleo jacksonii) feeding on Hawaiian taxa, including 11 snails in four endemic genera from two families, including four individuals of an endangered species (Achatinella mustelina), and native insects in five genera. Native Hawaiian invertebrates were discovered in the dissected stomachs of wild caught Jackson’s chameleons collected from June to November 2009 on the island of Oahu. Although Jackson’s chameleons were introduced to the Hawaiian Islands in the early 1970s, ecological impacts have never been documented. Of particular concern is the fact that chameleons have previously only rarely been found in native Hawaiian habitat, although 12 were recently collected in a mid-elevation native forest, an area that is not likely to be suitable for their long-term persistence, but that is adjacent to higher elevation pristine forest where endemic prey are abundant and favorable climatic conditions exist for chameleon persistence. One concern is that Jacksons’s chameleons may be undergoing a range expansion into upper elevation pristine forests. If chameleons reach and establish populations in these areas, devastating impacts to the native ecosystem are possible. A thorough understanding of the impacts of chameleons on Hawaiian fauna will require additional evaluation and sampling, but dissemination of this discovery in a timely fashion is important as it provides new information regarding this threat. Monitoring and collection of chameleons is ongoing, particularly in native Hawaiian forest habitats at mid and upper elevations (600–1,300 m).     

Po'ouli landscape bioinformatics models predict energetics, behavior, diets, and distribution on Maui

This study uses a spatially explicit microclimate/biophysicalapproach to examine the potential distribution of the Po'oulion Maui to find either new habitats to search for existenceor refine search efforts in previously occupied areas. We usedspecific physiological and behavioral ecology bird data, andPo'ouli morphological and spectral data obtained from museumspecimens to address ecological and conservation-related questionsabout the Po'ouli that are otherwise very difficult to quantify.Laboratory and field tested microclimate and biophysical—behavioralanimal computer models were integrated with remote sensing technologies.To show that the generic microclimate and endotherm models canpredict metabolic and water loss requirements of Hawaiian Honeycreepers,we used the 2 species with known physiological properties, theHawaiian Amakihi, Hemignathus virens, and the Hawaiian Anianiau,Hemignathus parvus. Predictions were within experimental measurementerror of the laboratory measurements. Then using field ratherthan laboratory conditions as input data, we predict the fielddistribution of the Amakihi on Maui as the first spatial testof the models applied to birds. Results are consistent withAmakihi field distribution data. Fossils show that the Po'oulionce lived on Maui at low elevations in dry/mesic habitats ona likely diet of native tree snails and insects. The arrivalof lethal mosquito-borne avian malaria in Hawaii exterminatedlow elevation Po'ouli forcing a population shift to mountainrainforests and possibly a snail diet instead of insects. Toexplore the maximum consequences of such a diet shift we assumedexclusive diets of snails versus insects at both low and highelevations. Snail diets require     

Prey preference and gregarious attacks by the invasive flatworm Platydemus manokwari

The flatworm Platydemus manokwari (Tricladida: Rhynchodemidae) preys on various species of land snail, and its introduction to areas outside of its native range is thought to have caused the extinction of native land snails on several Pacific islands. Platydemus manokwari occurs in areas where land snails have been absent since its invasion, suggesting that the flatworm can prey on animals other than land snails. To identify the alternative prey and prey preferences of P. manokwari, I examined the feeding ecology of P. manokwari under field and laboratory conditions. Individuals were observed attacking live earthworms in a forest where land snails are already extinct, on Chichijima, Ogasawara (Bonin) Islands, Japan. I also observed them attacking earthworms and a species of isopod and land snail in the lab. To prey on the worm, similar to other earthworm-eating flatworms, P. manokwari wrapped itself around the prey and fed on it by inserting its pharynx into the earthworm’s body. Large earthworms were able to escape P. manokwari attacks by autotomy, but the autotomized body parts were eaten. Several P. manokwari individuals together attacked earthworms that were larger than themselves. The laboratory experiments showed that such gregarious attacks increased predation success on both large earthworms and land snails. The flatworms also attacked the isopods, although the predation rate was low. These results demonstrate that P. manokwari is a polyphagous predator of slow-moving soil invertebrates (land snails, slugs, earthworms, and isopods) and that invasion by P. manokwari may directly and indirectly impact native soil fauna.     

Impact of invasive apple snails on the functioning and services of natural and managed wetlands

At least 14 species of apple snail (Ampullariidae) have been released to water bodies outside their native ranges; however, less than half of these species have become widespread or caused appreciable impacts. We review evidence for the impact of apple snails on natural and managed wetlands focusing on those studies that have elucidated impact mechanisms. Significant changes in wetland ecosystems have been noted in regions where the snails are established: Two species in particular (Pomacea canaliculata and Pomacea maculata) have become major pests of aquatic crops, including rice, and caused enormous increases in molluscicide use. Invasive apple snails have also altered macrophyte community structure in natural and managed wetlands through selective herbivory and certain apple snail species can potentially shift the balance of freshwater ecosystems from clear water (macrophyte dominated) to turbid (plankton dominated) states by depleting densities of native aquatic plants. Furthermore, the introductions of some apple snail species have altered benthic community structure either directly, through predation, or indirectly, through exploitation competition or as a result of management actions. To date much of the evidence for these impacts has been based on correlations, with few manipulative field or mesocosm experiments. Greater attention to impact monitoring is required, and, for Asia in particular, a landscape approach to impact management that includes both natural and managed-rice wetlands is recommended.     

A tale of two snails: is the cure worse than the disease?

The giant African snail, Achatina fulica, has been introduced to many parts of Asia as well as to numerous islands in the Indian and Pacific Ocean, and has recently reached the West Indies. It has been widely decried as a disaster to agricultural economies and a threat to human health, leading to a clamor for the introduction of biological control agents. In fact, the lasting impact on agriculture may not be severe, and the human health risk is probably minor. This snail can be an aesthetic atrocity and a nuisance in other ways, however. Wherever A. fulica has achieved high densities, it has subsequently undergone a striking decline. Although this decline has been attributed to introduced predators, there is little evidence for this hypothesis; instead, epizootic disease seems to be at least part of the cause. However, the introduced predators, especially a New World snail, Euglandina rosea, have wrought havoc with the native land snails of many islands. They have already caused many extinctions and will almost certainly cause others. This predator was introduced by government agencies in many areas despite warnings from competent biologists that the effects could be disastrous. Pressures for such actions may become overwhelming in the face of a highly visible invasion, despite policies that should mandate extreme caution.     

Native and introduced gastropods in laurel forests on Tenerife,Canary Islands

The introduction of non-native gastropods on islands has repetitively been related to a decline of the endemic fauna. So far, no quantitative information is available even for the native gastropod fauna from the laurel forests (the so-called Laurisilva) of the Canary Islands. Much of the original laurel forest has been logged in recent centuries. Based on vegetation studies, we hypothesized that densities and the number of introduced species decline with the age of the regrowth forests. We sampled 27 sites from which we collected thirty native and seven introduced species. Two introduced species, Milax nigricans and Oxychilus alliarius, were previously not reported from the Canary Islands. Assemblage composition was mainly structured by disturbance history and altitude. Overall species richness was correlated with slope inclination, prevalence of rocky outcrops, amounts of woody debris and leaf litter depth. Densities were correlated with the depth of the litter layer and the extent of herb layer cover and laurel canopy cover. Introduced species occurred in 22 sites but were neither related to native species richness nor to the time that elapsed since forest regrowth. One introduced slug, Lehmannia valentiana, is already wide-spread, with densities strongly related to herb cover. Overall species richness seemed to be the outcome of invasibility, thus factors enhancing species richness likely also enhance invasibility. Although at present introduced species contribute to diversity, the potential competition between introduced slugs and the rich native semi-slug fauna, and the effects of introduced predatory snails (Oxychilus spp. and Testacella maugei) warrant further monitoring.     

Diversity and phylogenetic relationships of Wolbachia in Drosophila and other native Hawaiian insects

Wolbachia is a genus of parasitic alphaproteobacteria found in arthropods and nematodes, and represents on of the most common, widespread endosymbionts known. Wolbachia affects a variety of reproductive functions in its host (e.g., male killing, cytoplasmic incompatibility, parthenogenesis), which have the potential to dramatically impact host evolution and species formation. Here, we present the first broad-scale study to screen natural populations of native Hawaiian insects for Wolbachia, focusing on the endemic Diptera. Results indicate that Wolbachia infects native Hawaiian taxa, with alleles spanning phylogenetic supergroups, A and B. The overall frequency of Wolbachia incidene in Hawaiian insects was 14%. The incidence of infection in native Hawaiian Diptera was 11% for individuals and 12% for all species screened. Wolbachia was not detected in two large, widespread Hawaiian dipteran families—Dolichopodidae (44 spp screened) and Limoniidae (12 spp screened). Incidence of infection within endemic Hawaiian lineages that carry Wolbachia was 18% in Drosophilidae species, 25% in Caliphoridae species, > 90% in Nesophrosyne species, 20% in Drosophila dasycnemia and 100% in Nesophrosyne craterigena. Twenty unique alleles were recovered in this study, of which 18 are newly recorded. Screening of endemic populations of D. dasycnemia across Hawaii Island revealed 4 unique alleles. Phylogenetic relationships and allele diversity provide evidence for horizontal transfer of Wolbachia among Hawaiian arthropod lineages.     

Modeling the Habitat Retreat of the Rediscovered Endemic Hawaiian Moth Omiodes continuatalis Wallengren (Lepidoptera: Crambidae)

Survey data over the last 100 years indicate that populations of the endemic Hawaiian leafroller moth, Omiodes continuatalis (Wallengren) (Lepidoptera: Crambidae), have declined, and the species is extirpated from large portions of its original range. Declines have been attributed largely to the invasion of non-native parasitoid species into Hawaiian ecosystems. To quantify changes in O. continuatalis distribution, we applied the maximum entropy modeling approach using Maxent. The model referenced historical (1892–1967) and current (2004–2008) survey data, to create predictive habitat suitability maps which illustrate the probability of occurrence of O. continuatalis based on historical data as contrasted with recent survey results. Probability of occurrence is predicted based on the association of biotic (vegetation) and abiotic (proxy of precipitation, proxy of temperature, elevation) environmental factors with 141 recent and historic survey locations, 38 of which O. continuatalis were collected from. Models built from the historical and recent surveys suggest habitat suitable for O. continuatalis has changed significantly over time, decreasing both in quantity and quality. We reference these data to examine the potential effects of non-native parasitoids as a factor in changing habitat suitability and range contraction for O. continuatalis. Synthesis and applications: Our results suggest that the range of O. continuatalis, an endemic Hawaiian species of conservation concern, has shrunk as its environment has degraded. Although few range shifts have been previously demonstrated in insects, such contractions caused by pressure from introduced species may be important factors in insect extinctions.     

Distribution,movement, and microhabitat use of the introduced predatory snail Euglandina rosea in Hawaii: implications for management

The purposeful introduction of the land snail Euglandina rosea, which feeds exclusively on snails and slugs, has been implicated as a major factor in the decline of diverse Pacific island land snail faunas. We report on the distribution, movement patterns, and microhabitat preferences of E. rosea in a gulch in the Waianae Mountains, Oahu, Hawaii, because such data will help focus management actions at a local scale to protect native snail populations in areas where E. rosea is established. The Waianae Mountains harbor many endangered or threatened snails, most currently found in isolated habitat patches near the ridges. Conversely, most living individuals (28/29) and shells (46/56) of E. rosea were collected within the gulch, which supported higher densities of other native and non‐native snails, and was cooler and more moist than the ridges. Thirteen individuals of E. rosea were tracked (eight directly using a bobbin and thread method, and five indirectly by mark–recapture); most (10/13) moved on average <2.5 m per week (range 0.1–25.21 m), and all stayed within the gulch. Members of E. rosea preferred leaf litter over open, fern/shrub, or wood microhabitats. There were large differences in the population density of E. rosea over small spatial scales, indicating that there may be places where native snail populations could persist even in areas where populations of E. rosea are established. Identifying areas with differing population densities of E. rosea is critical for not only understanding why some native snail species may be more vulnerable to extinction, but also to locate areas where predation pressure is low and conservation efforts will be most likely to succeed.