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Invasive predators are often hypothesized to negatively affect native invertebrates, but impacts have not been measured for most invaders. We quantified the effects of Solenopsis papuana, an invasive thief ant that is widespread in Hawaiʻi, on invertebrate communities via an experimental manipulation study. We established six pairs of plots in the Waiʻanae Mountains of Oʻahu, suppressed S. papuana in half of the plots, and measured the responses of invertebrates 6 months and 1 year later. Leaf litter and pitfall sampling revealed that ground-dwelling invertebrate communities were highly invaded, with native species comprising 24% of the taxa and only ~ 1–2% of the individuals captured. Relatively few taxonomic groups increased significantly in abundance following suppression of S. papuana, and responses were generally inconsistent between the two sampling periods. Significant increases in species richness in ant-suppressed plots were more common, particularly in pitfall samples. Most of the significant changes involved non-native species, but several native species also appear to be impacted by S. papuana. Although statistically significant responses were relatively uncommon, nearly all taxonomic groups exhibited non-significant increases in abundance and species richness in response to S. papuana suppression, and there were no significant decreases in either abundance or species richness for any taxonomic group. This suggests that in their current highly invaded states, mesic forest ground-dwelling invertebrate communities are broadly but relatively weakly affected by S. papuana. This conclusion may be tempered by the difficulty of accurately measuring effects on rare species, many of which may now be absent from these communities.

The lepidopteran herbivore Secusio extensa (Erebidae: Arctiinae) was purposefully released in Hawaii in 2013 to control Madagascar fireweed, Senecio madagascariensis (Asteraceae: Senecioneae), an invasive weed of rangelands and other open areas. In conjunction with this biocontrol effort, we conducted pre- and post-release monitoring of S. madagascariensis in field plots, and post-release monitoring of non-target plants. Secusio extensa successfully established on the two islands where it was released, dispersed widely, and even colonized a neighboring island. However, in the first three years after release, S. extensa could only be found sporadically and in low abundances on its target host. In contrast, it underwent population outbreaks on the related, alternative host, Cape ivy (Delairea odorata, Asteraceae: Senecioneae), which is also a noxious weed in Hawaii. In addition to D. odorata, we observed S. extensa to feed on only two other related non-target plants in the tribe Senecioneae, among 24 species monitored. In several microsites supporting higher densities of S. extensa on S. madagascariensis, larval abundances peaked during a short period in the spring, but were insufficiently high to cause substantial damage to affected plants. The causes for low larval densities of S. extensa on its target host are unclear. We found no strong evidence for parasitism or predation of S. extensa larvae. However, females preferred to oviposit on D. odorata over S. madagascariensis, and larvae exhibited a marginally significant preference for feeding on D. odorata over S. madagascariensis. This preference, along with lower nutritional quality of S. madagascariensis relative to D. odorata, may explain why S. extensa has been unable to build large populations on its intended target, but has done so on an alternate host. Clarifying the roles of these mechanisms may help predict the continuing performance of S. extensa in controlling S. madagascariensis.

As the most remote archipelago in the world, the Hawaiian Islands are home to a highly endemic and disharmonic biota that has fascinated biologists for centuries. Forests are the dominant terrestrial biome in Hawai‘i, spanning complex, heterogeneous climates across substrates that vary tremendously in age, soil structure, and nutrient availability. Species richness is low in Hawaiian forests compared to other tropical forests, as a consequence of dispersal limitation from continents and adaptive radiations in only some lineages, and forests are dominated by the widespread Metrosideros species complex. Low species richness provides a relatively tractable model system for studies of community assembly, local adaptation, and species interactions. Moreover, Hawaiian forests provide insights into predicted patterns of evolution on islands, revealing that while some evidence supports “island syndromes,” there are exceptions to them all. For example, Hawaiian plants are not as a whole less defended against herbivores, less dispersible, more conservative in resource use, or more slow-growing than their continental relatives. Clearly, more work is needed to understand the drivers, sources, and constraints on phenotypic variation among Hawaiian species, including both widespread and rare species, and to understand the role of this variation for ecological and evolutionary processes, which will further contribute to conservation of this unique biota. Today, Hawaiian forests are among the most threatened globally. Resource management failures – the proliferation of non-native species in particular – have led to devastating declines in native taxa and resulted in dominance by novel species assemblages. Conservation and restoration of Hawaiian forests now rely on managing threats including climate change, ongoing species introductions, novel pathogens, lost mutualists, and altered ecosystem dynamics through the use of diverse tools and strategies grounded in basic ecological, evolutionary, and biocultural principles. The future of Hawaiian forests thus depends on the synthesis of ecological and evolutionary research, which will continue to inform future conservation and restoration practices.

Threats to endangered insect species that act independently of those associated with habitat loss are often suspected, but are rarely confirmed or quantified. This may hinder the development of the most effective recovery strategies, which are increasingly needed for listed insects. Since 2006, 14 species of flies within the large, showy Hawaiian picture-winged Drosophila group have been added to the US threatened and endangered species list. Many of these species are thought to be limited by host plant rarity, but also by predation on immature stages by invasive ants. We tested the latter hypothesis with a field experiment involving Drosophila crucigera, a more common surrogate for sympatric endangered species, and the invasive ant Solenopsis papuana, on the island of Oʻahu. We established ant suppression and control plots across three forest sites. Within each plot we placed a host plant branch piece, into which lab-reared flies had oviposited, and subsequently tracked weekly emergence of adults. Numbers of flies that emerged were 2.4 times higher in ant-suppressed plots than in control plots; this 58% reduction in survival from egg to adult in the presence of ants was similar across all three sites. Among plots, numbers of emerged flies exhibited a pattern suggesting that the detrimental effect of ants is density dependent. These results confirm that S. papuana, and possibly other invasive ant species, can strongly impact the reproductive success of Hawaiian picture-winged Drosophila. They also point to several management actions, beyond habitat restoration, that may improve the recovery of these imperiled flies.

Invasive ants can influence abundance and diversity of insect pollinators, and this effect may be expected to be especially strong on oceanic islands. We examined abundance of native Hylaeus bees and patterns of flower visitation to three native Hawaiian plant species (Leptecophylla tameiameiae, Santalum haleakalae, and Geranium cuneatum) in presence and absence of invasive Argentine ants (Linepithema humile) in the subalpine shrubland of Haleakalā volcano. Native bees, nonnative honeybees, and microlepidoptera were responsible for the majority of visits to flowers of the three plant species. Ants visited flowers of S. haleakalae and G. cuneatum relatively commonly in ant-invaded zones but were less common or absent on flowers of L. tameiameiae in the same zones. Zones with ants had fewer Hylaeus bees in yellow pan traps than the zone without ants, and overall flower visitation rates to one plant species, G. cuneatum, were six times lower in sites containing ants. In one of two observation years...

Invasive ants can have strong ecological effects on native arthropods, but most information on this topic comes from studies of a handful of ant species. The ecological impacts of the many additional introduced ‘tramp’ ant species are largely unknown. In mesic upland forests of O‘ahu, Hawai‘i, ten species of introduced ants were found on four species of understory trees. However, these ants were generally uncommon and occurred at relatively low densities in this habitat type. The most common and abundant ant was Plagiolepis alluaudi, which favored the native tree Pipturus albidus. Ecological effects of ants on arthropods were found to be modest, with overall arthropod community composition not significantly different between ant-occupied and ant-free trees. Most taxonomic groups were similar in abundance and richness between ant-occupied and ant-free trees, except adventive Coleoptera, adventive Hemiptera, and Lepidoptera were less abundant on ant-occupied trees, and adventive Coleoptera and adventive Hemiptera also had lower richness on ant-occupied trees. Among Lepidoptera, caterpillars of two endemic groups had significantly lower incidences on trees with higher ant abundances, while other caterpillars did not. Arthropod trophic structure was largely unaffected, except that chewing herbivores comprised a smaller fraction of biomass on ant-occupied trees. While overall ecological effects were weak in comparison to prior results involving other ant species in Hawai‘i, some of the impacts suggest that higher densities of these introduced ant species could result in similar interactions with arthropods as those of the better-studied invasive ant species.

Hawaii is home to over 60 ant species, including five of the six most damaging invasive ants. Although there have been many surveys of ants in Hawaii, the last island-wide hand-collection survey of ants on Oahu was conducted in 1988–1994. In 2012, a timed hand-collection of ants was made at 44 sites in a systematic, roadside survey throughout Oahu. Ants were identified and species distribution in relation to elevation, precipitation and soil type was analyzed. To assess possible convenience sampling bias, 15 additional sites were sampled further from roads to compare with the samples near roads. Twenty-four species of ants were found and mapped; Pheidole megacephala (F.), Ochetellus glaber (Mayr), and Technomyrmex difficilis Forel were the most frequently encountered ants. For six ant species, a logistic regression was performed with elevation, average annual precipitation, and soil order as explanatory variables. O. glaber was found in areas with lower precipitation around Oahu. Paratrechina longicornis (Latrielle) and Tetramorium simillimum (Smith, F.) were found more often in lower elevations and in areas with the Mollisol soil order. Elevation, precipitation, and soil type were not significant sources of variation for P. megacephala, Plagiolepis alluaudi Emery, and T. difficilis. P. megacephala was associated with fewer mean numbers of ants where it occurred. Ant assemblages near and far from roads did not significantly differ. Many species of ants remain established on Oahu, and recent invaders are spreading throughout the island. Mapping ant distributions contributes to continued documentation and understanding of these pests.

Termites are economically-important structural pests, costing residents of Hawaii over $100 million annually. On Oahu, the last published termite swarming survey occurred from 1969 to 1971, and the last termite hand-collection survey occurred from 1998 to 2000. To contribute data on termite occurrences on Oahu, a light-trap survey took place from February 2011 to September 2012, and a hand-collection survey occurred from September to November 2012. Formosan subterranean termite, Coptotermes formosanus Shiraki, swarming was compared over the duration of the study, finding peak swarming in May 2011. C. formosanus alate activity density was regressed with environmental factors, finding a negative correlation with average wind speed and a positive correlation with average rainfall. Coptotermes gestroi (Wasmann) alates were observed in April, June, and July 2011 and in June 2012. Four species of termites were found in the hand-collection survey of 44 sites: Incisitermes immigrans (Snyder) (n = 8/44), C. formosanus (n = 2/44), Cryptotermes cynocephalus Light (n = 1/44), and Neotermes sp. (n = 1/44). This study contributes to distribution data for termite species on Oahu and records alate activity for two important termite pests.

The diets of sympatric rodents partially define their realized niches. Identifying items in stomachs of introduced rodents helps determine rodents' trophic positions and species most at risk of consumption. In the Hawaiian Islands, which lacked rodents prior to human arrival, three rodents (Rattus rattus or black rat, R. exulans or Pacific rat, Mus musculus or house mouse) commonly coexist in native habitats where they consume a wide range of plants and animals. These three rodent species were trapped in montane forest for 2.5 years; their stomach contents were analyzed to determine short-term diets (n = 12-95 indiv. per species), and isotopic fractions of d 15 N and d 13 C in their bone collagen were analyzed to further estimate their trophic positions (n = 11-20 indiv. per species). For all three species, (75 % of individuals had plants and (90 % had arthropods in their stomachs, and significant differences in mean relative abundances were found for food items in stomachs among all three rodents. Rodents may be dispersing some native and non-native seeds, includ- ing the highly invasive Clidemia hirta. Most identi- fiable arthropods in rodent stomachs were non-native, and no stomachs contained birds, snails, or lizards. The d 15 N and d 13 C signatures were consistent with trophic feeding differences revealed from stomach contents. Dietary niche differentiation by coexisting rodent species is evident in this forest, with Pacific rats being intermediate between the mostly carnivorous house mouse and the mostly herbivorous black rat; such findings can help forecast rodent impacts and direct management efforts in ecosystems where these invasive animals coexist.

Because invasive species threaten the integrity of natural ecosystems, a major goal in ecology is to develop predictive models to determine which species may become widespread and where they may invade. Indeed, considerable progress has been made in understanding the factors that influence the local pattern of spread for specific invaders and the factors that are correlated with the number of introduced species that have become established in a given region. However, few studies have examined the relative importance of multiple drivers of invasion success for widespread species at global scales. Here, we use a dataset of >5,000 presence/absence records to examine the interplay between climatic suitability, biotic resistance by native taxa, human-aided dispersal, and human modification of habitats, in shaping the distribution of one of the world's most notorious invasive species, the Argentine ant (Linepithema humile). Climatic suitability and the extent of human modification of habitats are primarily responsible for the distribution of this global invader. However, we also found some evidence for biotic resistance by native communities. Somewhat surprisingly, and despite the often cited importance of propagule pressure as a crucial driver of invasions, metrics of the magnitude of international traded commodities among countries were not related to global distribution patterns. Together, our analyses on the global-scale distribution of this invasive species provide strong evidence for the interplay of biotic and abiotic determinants of spread and also highlight the challenges of limiting the spread and subsequent impact of highly invasive species We acknowledge financial support from the Centre of Excellence for Invasion Biology (N.R.-P. and D.M.R.), from the Catalan Agency for Management of University and Research Grants (Generalitat de Catalunya) through Beatriu de Pinós Postdoctoral Grants 2006 BP-A 10124 and 2008 BP-B 00042 (to N.R.-P.), from the Hans Sigrist Foundation (to D.M.R.), from the Spanish Ministry of Science and Innovation Grant CGL2007-64080-C02-02/BOS (to C.G. and N.R.-P.), from the Spanish Ministry of Science and Innovation and the European Regional Development Fund Grant CGL2007-64080-C02-01/BOS (to X.E.), from the Blue Skies Programme of the National Research Foundation (to C.H.), from the Danish National Research Foundation (to J.S.P.), from Department of Energy–Program for Ecosystem Research Grant DE-FG02-08ER64510 (to N. J.S.), from National Science Foundation Grant DEB 0716966 (to A.V.S.), and from the New Zealand Foundation for Research, Science, and Technology Grant C09X0507 (to D.W.)

Invasive species are causing population declines and extinctions of native species worldwide. Correlates of species vulnerability, which help identify at-risk taxa, are not well developed for arthropods, particularly with respect to threats from invasive species. At five sites undergoing invasion by ants in the Hawaiian Islands, we assessed body size, population density, trophic role and provenance (introduced or endemic to the Hawaiian Islands) as potential correlates of vulnerability for 300 arthropod species. Among rare species, prove- nance was the most important factor associated with absence from invaded plots, with endemic species much more commonly absent. Trophic role was also important, but only when interacting with provenance: endemic carnivores were by far the most vulnerable group, followed by endemic detritivores. For non-rare species, Hawaii endemics were sig- nificantly more reduced in invaded plots compared to introduced species. In addition, species that occurred at lower population densities were more vulnerable than those occurring at higher densities. Body size did not correlate with vulnerability for either rare or non-rare species. Despite these trends, there was relatively high variability in responses to invasion among species in many taxonomic orders, as well as among populations of particular species at different sites. While the consideration of additional intrinsic traits might increase pre- dictive ability to some degree (e.g., intrinsic traits only explained 21% of the variation in impact among non-rare species), community-specific extrinsic factors appear to play a large role in influencing outcomes for many species, making prediction substantially more difficult.

Mechanistic models for predicting species' distribution patterns present particular advantages and challenges relative to models developed from statistical correlations between distribution and climate. They can be especially useful for predicting the range of invasive species whose distribution has not yet reached equilibrium. Here, we illustrate how a physiological model of development for the invasive Argentine ant can be connected to differences in micro-site suitability, population dynamics and climatic gradients; processes operating at quite different spatial scales. Our study is located in the subalpine shrubland of Haleakala National Park, Hawaii, where the spread of Argentine ants Linepithema humile has been documented for the past twenty-five years. We report four main results. First, at a microsite level, the accumulation of degree-days recorded in potential ant nest sites under bare ground or rocks was significantly greater than under a groundcover of grassy vegetation. Second, annual degree-days measured where population boundaries have not expanded (456-521 degree-days), were just above the developmental requirements identified from earlier laboratory studies (445 degree-days above 15.9°C). Third, rates of population expansion showed a strong linear relationship with annual degree-days. Finally, an empirical relationship between soil degree-days and climate variables mapped at a broader scale predicts the potential for future range expansion of Argentine ants at Haleakala, particularly to the west of the lower colony and the east of the upper colony. Variation in the availability of suitable microsites, driven by changes in vegetation cover and ultimately climate, provide a hierarchical understanding of the distribution of Argentine ants close to their cold-wet limit of climatic tolerances. We conclude that the integration of physiology, population dynamics and climate mapping holds much promise for making more robust predictions about the potential spread of invasive species.

Measuring the impacts of invasive species on recipient biotic communities can be challenging because standard ecological field experiments may be impossible, undesirable or inaccurate due to limita- tions of scale. Many studies therefore rely on a com- parative observational approach, in which invaded areas are compared to similar nearby uninvaded areas, but this approach suffers from reduced inferential power because of the inability to randomly assign treatments. When possible, the best solution may be to incorporate comparative sampling over time, from before and after invasion, as a means of validating comparisons across space. We used this approach to assess the impacts of Argentine and big-headed ants on arthropod communities at two natural area sites in the Hawaiian Islands. Two sampling events, separated by 2 years, indicated that invaded plots at each site were significantly different from uninvaded plots in terms of overall community composition and distributions of certain indicator species. This compositional change associated with ant invasion was accompanied by a significant decrease in arthropod species richness at one site, but not at the second site. Changes in arthropod communities from before invasion to after invasion in separate before-after plots at each site were qualitatively consistent with the aforementioned changes measured across the invasion boundaries, but were smaller in magnitude because the invasion processes were still in early stages. Together, these findings support the inference that carefully planned studies of biological invasions that use a comparative observational approach can provide an accurate picture of resultant community level changes, and illustrate an effective method for validating such studies.

There is a general consensus that the diversity of a biotic community can have an influence on its stability, but the strength, ubiquity, and relative importance of this effect is less clear. In the context of biological invasions, diversity has usually been studied in terms of its effect on a community's invasibility, but diversity may also influence stability by affecting the magnitude of compositional or functional changes experienced by a community upon invasion. We examined the impacts of invasive ants on arthropod communities at five natural area sites in the Hawaiian Islands, and assessed whether differences among sites in community diversity and density variables were related to measures of stability. Ant invasion was usually associated with significant changes in overall community composition, as measured by Bray-Curtis distances, particularly among endemic subsets of the communities. Changes in mean species richness were also strong at three of the five sites. Among sites, diversity was negatively related to stability as measured by resistance to overall compositional change, but this effect could not be separated from the strong negative effect of invasive ant density on compositional stability. When compositional stability was measured as proportional change in richness, the best predictor of stability among endemic community subsets was endemic richness, with richer communities losing proportionately more species than species-poor communities. This effect was highly significant even after controlling for differences in invasive ant density and suggested that communities that had already lost many endemic species were resistant to further species loss upon ant invasion, while more intact communities remained vulnerable to species loss. Communities underwent strong but idiosyncratic functional shifts in association with ant invasion, both in terms of trophic structure and total arthropod biomass. There were no apparent relationships, however, between functional stability and community diversity or density measures. Instead, invasive ant density was the best among-site predictor of the magnitude of functional change. Overall, diversity appeared to be a poor predictor of stability in the face of ant invasion in these communities, possibly because any actual diversity effects were overshadowed by community-specific factors and variation in the magnitude of the ant-mediated perturbation.

The Hawaiian Islands support a speciose radiation of native Mecyclothorax beetles (Coleoptera: Carabidae). This lineage has undergone a classical island radiation resulting in extensive ecological specialization, flight-wing loss, and 100% single-island endemism. We report on the sympatric occurrence of several Mecyclothorax species endemic to Haleakala volcano, East Maui with the newly arrived, adventive Trechus obtusus (Coleoptera: Carabidae), a tramp species originally from Europe. Arrival of T. obtusus in afforested, non-native gymnosperm plantation forest near Polipoli, Maui was associated with subsequent decreased abundance of native Mecyclothorax beetles. Since discovery of T. obtusus on Haleakala, their populations have been transformed through subsequent increase in frequency of brachypterous individuals. Consequences of this transformation to flight-wing dimorphic populations may simultaneously include enhanced reproductive capacity of brachypterous individuals, increased local adaptation of populations, and enhanced metapopulational dynamics ultimately permitting range expansion and occupation far beyond anything observed for the monomorphically brachypterous native Mecyclothorax. Trechus obtusus and several Mecyclothorax species occur sympatrically with Argentine ant, Linepithema humile (Hymenoptera: Formicidae) in subalpine shrublands on Haleakala. Recent sampling corroborates earlier findings that localized presence of Argentine ant is associated with significantly decreased abundance of native Mecyclothorax. Conversely, abundance of the continental T. obtusus is not significantly affected by ant presence.

Analysis of long-term patterns of invasion can reveal the importance of abiotic factors in influencing invasion dynamics, and can help predict future patterns of spread. In the case of the invasive Argentine ant ( Linepithema humile ), most prior studies have investigated this species’ limitations in hot and dry climates. However, spatial and temporal patterns of spread involving two ant populations over the course of 30 years at a high elevation site in Hawaii suggest that cold and wet conditions have influenced both the ant’s distribution and its rate of invasion. In Haleakala National Park on Maui, we found that a population invading at lower elevation is limited by increasing rainfall and presumably by associated decreasing temperatures. A second, higher elevation population has spread outward in all directions, but rates of spread in different directions appear to have been strongly influenced by differences in elevation and temperature. Patterns of foraging activity were strongly tied to soil temperatures, supporting the hypothesis that variation in temperature can influence rates of spread. Based on past patterns of spread, we predicted a total potential range that covers nearly 50% of the park and 75% of the park’s subalpine habitats. We compared this rough estimate with point predictions derived from a degree-day model for Argentine ant colony reproduction, and found that the two independent predictions match closely when soil temperatures are used in the model. The cold, wet conditions that have influenced Argentine ant invasion at this site are likely to be influential at other locations in this species’ current and future worldwide distribution.

Recent biotic surveys in subalpine shrubland on Haleakalā Volcano, Maui, Hawai‘i, have resulted in rediscovery of several species of carabid beetles previously known only from their nineteenth-century type specimens. Blackburnia lenta (Sharp), described from specimens collected just below Haleakalā summit in 1894, was found at lower elevational sites ranging from 2,400 to 2,750 m. Mecyclothorax rusticus Sharp, last seen in 1896, and M. nubicola (Blackburn), collected only in 1878, were also rediscovered in that vicinity. Recent collections of B. lenta contradict the U.S. Fish and Wildlife Service's previous classification of this species as one likely to be extinct. Nevertheless, B. lenta's known distribution comprises only 145 ha within an elevational zone that is bounded above and below by unicolonial populations of the invasive alien Argentine ant, Linepithema humile (Mayr). The known recent collections of M. rusticus and M. nubicola also occurred outside the distributional range of the Argent...

Limiting dispersal is a fundamental strategy in the control of invasive species, and in certain situations containment of incipient populations may be an important management technique. To test the feasibility of slowing the rapid spread of two Argentine ant (Linepithema humile) supercolonies in Haleakala National Park, Hawaii, we applied ant bait and toxicant within an experimental plot situated along a supercolony boundary. The 120 × 260 m plot simulated a small section of what could potentially be a 120 m wide treatment encompassing the entire expanding boundaries of both supercolonies. Foraging ant numbers at baited monitoring stations decreased sharply within two weeks after treatment, and ant spread was completely halted within the plot for at least one year. In contrast, an adjacent untreated colony boundary advanced an average of 65.2 m over the course of 1 year. Most of this spread took place in the summer and fall, at the time of highest ant abundance at bait monitoring stations, while no outward dispersal occurred during the spring and early summer. These patterns are consistent with the hypothesis that local budding dispersal in this unicolonial species stems from density dependent pressure rather than inherent founding behavior associated with mating. Based on results from this experiment, we are investigating the effectiveness of annual boundary treatments in slowing the Argentine ant invasion at Haleakala National Park. The goals of this program are to protect populations of native arthropods and to keep options open for eventual attempts at eradication.

The Argentine ant, Linepithema humile (Mayr), has proven to be a threat to native arthropod species in Haleakala National Park, Maui, HI, and is also a potential threat to the park's native flora. As it continues to expand its range, an effort has been undertaken to eradicate it, or at the least, control its spread. The 1st part of this effort focused on finding a bait carrier for subsequent toxicant-based control tests. A year-long bait preference test was implemented at each of the ant's 2 infestation sites in Haleakala National Park, in which 6 solid baits and 2 liquid baits were assessed for attractiveness and feasibility for large scale control. At both sites, a toxicant-free formulation of Maxforce, a protein-based granular bait made from ground silkworm, Bombyx mori (L.), pupae, and a 25% sugar water solution were the most attractive baits. Ants took more Maxforce (without toxicant) and sugar water than all other baits, including honey granules and a fish protein bait. Sugar water, however, is difficult to distribute over large natural areas. Maxforce was therefore concluded to be the best bait carrier for toxicant-based control at Haleakala National Park because of its attractiveness and its ease for large scale broadcast dispersal.

In an effort to develop a chemical control strategy for the invasive Argentine ant, Linepithema humile (Mayr), in Haleakala National Park, Maxforce, which is formulated with 0.9% hydramethylnon, was used in test plots to determine the efficacy of the ant bait in the field. Initially, Maxforce was tested at 2 application rates: broadcast at 2.25 kg/ha (2 lb/acre) and 4.5 kg/ha (4 lb/acre). Later, the following treatments were also tested: a Maxforce and honey granule mix, Maxforce with 0.5% hydramethylnon, Maxforce with a different solvent, Maxforce distributed in exposed piles, and Maxforce distributed in covered piles. Although there were significant differences in the magnitude of ant reduction among the various treatments, all yielded the same general result. Foraging ant numbers at monitoring bait stations declined an average maximum of 97.0% in the test plots, with no plots achieving 100% reduction. At 2 mo after treatment the mean number of foraging ants was reduced by 92.1%. Nest survival in the plots appeared to be affected to a lesser degree, but could not be monitored accurately over the longer term because of the phenomenon of nest movement. A 2nd identical application 1 mo after the initial application in plots treated with Maxforce at 2.25 and 4.5 kg/ha did not result in eradication. Bait molding, quick mortality, and toxicant breakdown from UV radiation created a short exposure time to the bait and toxicant, which may have been the main obstacle to achieving eradication.

Biological invasions represent communities in flux. Although stasis is never the rule in nature, biological interactions in communities usually occur within a framework of shared ecological and evolutionary history. Consequently, biological invasions represent unique opportunities to study dynamics that can otherwise be difficult to observe (Elton 1958). Invasive ants are excellent organisms with which to pursue this goal, in part because ants as a group play a variety of important ecological roles within biological communities (Holldobler and Wilson 1990). Ant invasions hold much potential for improving an understanding of ecological processes in general, as well as of interactions more specific to myrmecology. For instance, the dynamics that exist during ant invasions may reveal the traits that promote behavioural or ecological dominance. Furthermore, highly successful invasive ant species are often less conspicuous in their native ranges, so identification of the factors responsible for their greater prominence in introduced areas can provide insight into the more typical workings of ant communities, may highlight intrinsic differences between communities that have formed in separate biogeographic regions, and may suggest possible methods of control. Understanding ant invasion processes and causes of success thus has both basic and applied relevance. Human activities have introduced many ant species to new biogeographic regions (McGlynn 1999b; Chapter 13). While most introduced ant species have limited success in spreading away from the human-modified habitats in which they usually first arrive, a subset can invade nearby, or even distant, undisturbed natural habitats. This distinction is not always hard and fast, as virtually all species exhibit different degrees of invasiveness and ecological dominance in different locales, and sometimes even under similar conditions in the same locale (e.g. Abbott et al. 2007). Notwithstanding, the following species are the most consistent in their ability to penetrate natural ecosystems and affect the composition or abundance of native species within them (Holway et al. 2002a): the Argentine ant (Linepithema humile), the red imported fire ant (Solenopsis invicta), the tropical fire ant (S. geminata), the big-headed ant (Pheidole megacephala), the little fire ant (Wasmannia auropunctata), and the yellow crazy ant (Anoplolepis gracilipes) (see Plate 14). We focus on these species because of their pronounced invasive tendencies, and also because they have been studied the most intensively, especially with regard to the factors that control spread and underlie dominance. In fact, the majority of our knowledge on these topics comes from studies on just two species: S. invicta and L. humile. This represents both a major weakness and a clear avenue for progress in the field, pointing to a need for more complete information on the ecologies of other invasive ant species, as well as their close relatives that fail to become invasive (Chapter 13; see also Section 14.4). This limitation must be acknowledged at the outset, as it impinges on our under

Sampling of arthropods in ground and woody vegetation habitats in highland areas on the islands of Hawaii and Maui revealed six species of psocids of the genus Liposcelis. Three are new and are here described. L. maunakea sp. n. and L. volcanorum sp. n. are closely related and form a small species complex together with L. nasus Sommerman and L. deltachi Sommerman from southwestern United States and northern Mexico. A key to the species of this complex is included. The third new species, L. kipukae sp. n., is a member of group II-C with only 5 ommatidia in the eye. A key to the known species of group II-C with fewer than 7 ommatidia in the eye is included. First Hawaiian records are presented for L. bostrychophila Badonnel, L. deltachi, and L. rufa Broadhead. The first known males of L. bostrychophila are reported and described. This species is very widespread, but generally parthenogenetic.

Detailed assessments of species responses to climate change are uncommon, owing to the limited nature of most ecological and local climate data sets. Exceptions, such as the case of the Haleakalā silversword, can provide important insights into the complexity of biological responses to changing climate conditions. We present a time series of decadal population censuses, combined with a pair of early population projections, which together span the past 80 years of demographic history for this alpine plant. The time series suggests a strong population recovery from the 1930s through the 1980s, likely owing at least in part to management actions taken on its behalf. In contrast, the population is estimated to have suffered a decline of approximately 60 % since the early 1990s. Fine-scale estimates of rainfall within silversword habitat are strongly correlated with these decadal-scale population changes over the past 50 years, with rainfall estimated to be substantially lower on average during the two most recent inter-census periods (after 1991). The reversal in the silversword population trajectory, and declines in rainfall in silversword habitat, coincide with an abrupt increase in the frequency of occurrence of the trade wind inversion (TWI) in Hawaiʻi around 1990. The shift in TWI incidence, which is linked to stronger subsidence in the Hadley circulation, has led to drier conditions in high elevation ecosystems in Hawaiʻi and appears to be eliciting ecological responses. Other regions influenced by the TWI could be similarly affected. The silversword case study reveals additional unexpected outcomes, such as the likely initial retraction from wetter, rather than drier, portions of the range in response to drying conditions. This pattern may stem in part from variation in drought tolerance across the range, highlighting the importance of detailed ecological and climatic information for making accurate predictions about climate change responses.