The invasive predatory snail Oxychilus alliarius is established in many locations around the world including the Hawaiian Islands. Anecdotal evidence suggests that it negatively impacts indigenous snail species where it has been introduced, although such impacts have not been quantified. On the Hawaiian island of Oahu, we tested the hypothesis that indigenous snails, especially small ones (<3 mm in maximum dimension), would be less abundant where O. alliarius had established populations. Fifty-six sites at four locations were repeatedly surveyed for snails between July 2010 and April 2011. The composition of the snail fauna differed in relation to O. alliarius abundance, as well as location. Notably, the abundance of the native Succineidae was negatively related with that of O. alliarius. The abundance of the native Tornatellidinae was significantly related to O. alliarius abundance but this relationship differed among locations, negative at one site and positive at the other three; these snails do not appear to be negatively impacted by O. alliarius. We also monitored the rate of expansion of a newly introduced O. alliarius population along a transect through a bog on the summit of Oahu’s highest mountain, Mt. Kaala. The population’s range expanded linearly between 2008 and 2011 by approximately 300 m (mean c. 113 m/year). This is the first attempt to quantify the impacts of O. alliarius on threatened native island snail faunas. While the results are complex, its high abundance, rapid rate of population expansion and probable negative impacts on certain species caution vigilance in preventing its introduction and spread to as yet uninvaded islands and locations.
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Plants critical for Hawaiian land snail conservation: arboreal snail plant preferences in Puʻu Kukui Watershed, Maui
Abstract The Hawaiian archipelago was formerly home to one of the most species-rich land snail faunas (> 752 species), with levels of endemism > 99%. Many native Hawaiian land snail species are now extinct, and the remaining fauna is vulnerable. Unfortunately, lack of information on critical habitat requirements for Hawaiian land snails limits the development of effective conservation strategies. The purpose of this study was to examine the plant host preferences of native arboreal land snails in Puʻu Kukui Watershed, West Maui, Hawaiʻi, and compare these patterns to those from similar studies on the islands of Oʻahu and Hawaiʻi. Concordant with studies on other islands, we found that four species from three diverse families of snails in Puʻu Kukui Watershed had preferences for a few species of understorey plants. These were not the most abundant canopy or mid canopy species, indicating that forests without key understorey plants may not support the few remaining lineages of native snails. Preference for Broussaisia arguta among various island endemic snails across all studies indicates that this species is important for restoration to improve snail habitat. As studies examining host plant preferences are often incongruent with studies examining snail feeding, we suggest that we are in the infancy of defining what constitutes critical habitat for most Hawaiian arboreal snails. However, our results indicate that preserving diverse native plant assemblages, particularly understorey plant species, which facilitate key interactions, is critical to the goal of conserving the remaining threatened snail fauna.
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- NSF-PAR ID:
- 10281644
- Date Published:
- Journal Name:
- Oryx
- ISSN:
- 0030-6053
- Page Range / eLocation ID:
- 1 to 6
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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null (Ed.)Abstract Since 1955 snails of the Euglandina rosea species complex and Platydemus manokwari flatworms were widely introduced in attempted biological control of giant African snails ( Lissachatina fulica ) but have been implicated in the mass extinction of Pacific island snails. We review the histories of the 60 introductions and their impacts on L. fulica and native snails. Since 1993 there have been unofficial releases of Euglandina within island groups. Only three official P. manokwari releases took place, but new populations are being recorded at an increasing rate, probably because of accidental introduction. Claims that these predators controlled L. fulica cannot be substantiated; in some cases pest snail declines coincided with predator arrival but concomitant declines occurred elsewhere in the absence of the predator and the declines in some cases were only temporary. In the Hawaiian Islands, although there had been some earlier declines of native snails, the Euglandina impacts on native snails are clear with rapid decline of many endemic Hawaiian Achatinellinae following predator arrival. In the Society Islands, Partulidae tree snail populations remained stable until Euglandina introduction, when declines were extremely rapid with an exact correspondence between predator arrival and tree snail decline. Platydemus manokwari invasion coincides with native snail declines on some islands, notably the Ogasawara Islands of Japan, and its invasion of Florida has led to mass mortality of Liguus spp. tree snails. We conclude that Euglandina and P. manokwari are not effective biocontrol agents, but do have major negative effects on native snail faunas. These predatory snails and flatworms are generalist predators and as such are not suitable for biological control.more » « less
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Abstract Ecological restoration is beneficial to ecological communities in this era of large‐scale landscape change and ecological disruption. However, restoration outcomes are notoriously variable, which makes fine‐scale decision‐making challenging. This is true for restoration efforts that follow large fires, which are increasingly common as the climate changes.
Post‐fire restoration efforts, like tree planting and seeding have shown mixed success, though the causes of the variation in restoration outcomes remain unclear. Abiotic factors such as elevation and fire severity, as well as biotic factors, such as residual canopy cover and abundance of competitive understorey grasses, can vary across a burned area and may all influence the success of restoration efforts to re‐establish trees following forest fires.
We examined the effect of these factors on the early seedling establishment of a tree species—māmane (
Sophora chrysophylla )—in a subtropical montane woodland in Hawaiʻi. Following a human‐caused wildfire, we sowed seeds of māmane as part of a restoration effort. We co‐designed a project to examine māmane seedling establishment.We found that elevation was of overriding importance, structuring total levels of plant establishment, with fewer seedlings establishing at higher elevations. Residual canopy cover was positively correlated with seedling establishment, while cover by invasive, competitive understorey grasses very weakly positively correlated with increased seedling establishment.
Our results point to specific factors structuring plant establishment following a large fire and suggest additional targeted restoration actions within this subtropical system. For example, if greater native woody recruitment is a management goal, then actions could include targeted seed placement at lower elevations where establishment is more likely, increased seeding densities at high elevation where recruitment rates are lower, and/or invasive grass removal prior to seeding. Such actions may result in faster native ecosystem recovery, which is a goal of local land managers.
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Abstract Non‐native freshwater snails can play important roles as consumers, hosts, and prey. Despite their potential ecological importance, global patterns in non‐native snail taxonomy, geography, and ecology have not been documented. Our objectives were to use a semi‐quantitative systematic review to describe non‐native freshwater snail global diversity, distribution, mechanisms of introduction, and interactions with natural enemies, including parasites and predators.
Based on 506 relevant publications, we recorded 95 non‐native freshwater snail species from 16 families. Six taxonomic families, and pulmonate snails as a group, were over‐represented relative to the number of species expected by chance. Eight snail species represented 63% of the research records. A few snail taxa (15%) were widespread global invaders, reported from four or more continents, while most invasions were limited to a single continent. Australia and the Pacific Islands were the largest ‘sink’ for non‐native snails, with the greatest difference in the number of non‐native taxa relative to native taxa that had spread to other continents.
Aquarium hobby sales were implicated as the most common mechanism of introduction (41% of species), followed by “hitchhiking” on aquatic vegetation, human consumption, use for biocontrol, transportation in canals, commercial shipping, and outdoor recreation. A search of internet sales posts indicated that four of the six over‐represented snail families were readily available for purchase online.
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1017/S0030605320000873
