Paul D. Krushelnycky

COMPOSITIONAL AND FUNCTIONAL STABILITY OF ARTHROPOD COMMUNITIES IN THE FACE OF ANT INVASIONS

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 communitys 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.

Limiting Spread of a Unicolonial Invasive Insect and Characterization of Seasonal Patterns of Range Expansion

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.

Correlates of vulnerability among arthropod species threatened by invasive ants

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, provenance 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 significantly 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 predictive 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.

Unfortunate encounters? Novel interactions of native Mecyclothorax, alien Trechus obtusus (Coleoptera: Carabidae), and Argentine ant (Linepithema humile, Hymenoptera: Formicidae) across a Hawaiian landscape

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.

Rediscovery and Uncertain Future of High-Elevation Haleakala Carabid Beetles (Coleoptera)

ABSTRACT 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 Services previous classification of this species as one likely to be extinct. Nevertheless, B. lentas 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 Argentine ant. Mature eggs held in the lateral oviducts of B. lenta females averaged 1.4× the volume of the largest eggs previously reported among 13 species of Blackburnia. We hypothesize that the giant eggs of B. lenta result from selective forces favoring large, well-nourished developing and hatched first-instar larvae, consistent with a patchy distribution of suitable microhabitat and prey in the subalpine Haleakalā landscape. The specialized life history of B. lenta, and coincidence of distributional limits of the three rediscovered carabid species with range limits of the Argentine ant populations suggest that all would be jeopardized by future distributional expansion of Argentine ant. These intersecting phenomena compel us to conclude that B. lenta, M. nubicola, and M. rusticus are appropriate candidates for I.U.C.N. threatened species designation, pending further studies of their geographic ranges and historical trends in abundance.

Ecology of some lesser-studied introduced ant species in Hawaiian forests

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.

Mecyclothorax palikea sp.n. from the Waianae Range, Oahu, and the biogeographical history of Hawaii's M. flavomarginatus species group (Coleoptera: Carabidae: Moriomorphini)

Mecyclothorax palikea, sp.n. is described from the vicinity of Palikea, southern Waianae Range, Oahu, HI, USA and is assigned to Brittons Mecyclothorax flavomarginatus species group. Cladistic analysis, based on 20 morphological characters and including several outgroup taxa, places Mecyclothorax impunctatus Liebherr of Molokai as adelphotaxon to the other eight species of the group, with subsequent speciation events successively isolating M. sharpi Britton of West Maui versus a clade of seven Oahu species. Phylogenetic relationships among the Oahu clade species posit three historical speciation events vicariating ancestors on the western Waianae and eastern Koolau Ranges. Mecyclothorax palikea is placed as adelphotaxon to M. carteri (Perkins), a species allopatrically distributed to the north in the Waianae, corroborating existence of southern and northern areas of endemism within the Waianae Range. Relative ages of the respective volcanoes housing M. flavomarginatus group species — Waianae (3.7 million years ago), Koolau (2.6 million years ago), Eastern Molokai (1.8 million years ago), West Maui (1.3 million years ago)—imply that ancestral occupation of Oahu by this group occurred subsequent to completion of the shield building phases of Oahus two volcanoes, Waianae and Koolau. Diversification within the group on Oahu was associated with vicariance events that occurred within a terrestrial environment. Whereas all four species of the M. flavomarginatus group occupying Waianae Range habitats have been observed recently in nature, collection of M. flavomarginatus in 1906 represents the most recent record for any M. flavomarginatus group species in the Koolau Range, indicating the importance of conserving appropriate Waianae Range habitats in order to preserve representative biodiversity in this species group.

Compilation of climate data from heterogeneous networks across the Hawaiian Islands

Long-term, accurate observations of atmospheric phenomena are essential for a myriad of applications, including historic and future climate assessments, resource management, and infrastructure planning. In Hawai‘i, climate data are available from individual researchers, local, State, and Federal agencies, and from large electronic repositories such as the National Centers for Environmental Information (NCEI). Researchers attempting to make use of available data are faced with a series of challenges that include: (1) identifying potential data sources; (2) acquiring data; (3) establishing data quality assurance and quality control (QA/QC) protocols; and (4) implementing robust gap filling techniques. This paper addresses these challenges by providing: (1) a summary of the available climate data in Hawai‘i including a detailed description of the various meteorological observation networks and data accessibility, and (2) a quality controlled meteorological dataset across the Hawaiian Islands for the 25-year period 1990-2014. The dataset draws on observations from 471 climate stations and includes rainfall, maximum and minimum surface air temperature, relative humidity, wind speed, downward shortwave and longwave radiation data.

Patterns of Floral Visitation to Native Hawaiian Plants in Presence and Absence of Invasive Argentine Ants

Abstract: 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, flower visitation to L. tameiameiae was also reduced in sites containing ants. Results suggest that Argentine ants may cause a reduction of native Hylaeus bee abundances; however, other factors correlated with elevation cannot be ruled out as the cause of differences in Hylaeus abundances across our sites.