Joshua R. King

Ants as bioindicators of habitat disturbance: validation of the functional group model for Australia's humid tropics

A functional group model of ant community composition has been widely used in Australia to analyse biogeographical patterns of ant community structure and the responses of ant communities to disturbance. The model has provided valuable support to the widespread use of ant communities as bioindicators of ecological change. However, the model was developed from studies of arid-zone faunas, and its applicability to the World Heritage rainforests of Queenslands humid tropics has not yet been validated. Here we test predictions based on the functional group model for ant communities in Queenslands humid rainforests, by documenting ant community composition and its responses to disturbance on the Atherton Tablelands. Five sites were studied, comprising two relatively undisturbed reference sites representing contrasting rainforest types, and three previously cleared sites, two of which were undergoing revegetation. A variety of sampling techniques were employed, including pitfall trapping, litter extractions, baiting, and general searching. A total of 50 ant species from 29 genera were collected. Site species richness was highest at the reference sites, and lowest at the unvegetated disturbed site, and overall was negatively related to mean ground temperature. As predicted by the functional group model, behaviorally dominant dolichoderines were uncommon or absent at the reference sites, and the most common ants were Generalized myrmicines and Opportunists. Also as predicted, habitat disturbance favored Opportunists, and, as the disturbance involved canopy clearance, this led to colonization by Iridomyrmex and other Dominant dolichoderines. Opportunists represented about 40% of total ants in traps at the reference sites, compared with 80–95% at the disturbed sites. Except one species, Tropical Climate Specialists and Specialist Predators were absent from disturbed sites.In conclusion, patterns of ant composition in relation to disturbance on the Atherton Tablelands conform to the functional group model that has been widely applied to ant faunas elsewhere in Australia. The model may therefore play an important role in the use of ants as bioindicators of ecological change in the World Heritage rainforests of this region.

Experimental evidence that human impacts drive fire ant invasions and ecological change

Biological invasions are often closely associated with human impacts and it is difficult to determine whether either or both are responsible for the negative impacts on native communities. Here, we show that human activity, not biological invasion, is the primary driver of negative effects on native communities and of the process of invasion itself. In a large-scale experiment, we combined additions of the exotic fire ant, Solenopsis invicta, with 2 disturbance treatments, mowing and plowing, in a fully crossed factorial design. Results indicate that plowing, in the absence of fire ants, greatly diminished total native ant abundance and diversity, whereas fire ants, even in the absence of disturbance, diminished some, but not all, native ant abundance and diversity. Transplanted fire ant colonies were favored by disturbance. In the absence of disturbance and on their own, fire ants do not invade the forest habitats of native ants. Our results demonstrate that fire ants are “passengers” rather than “drivers” of ecological change. We propose that fire ants may be representative of other invasive species that would be better described as disturbance specialists. Current pest management and conservation strategies should be reassessed to better account for the central role of human impacts in the process of biological invasion.

Evaluation of Sampling Methods and Species Richness Estimators for Ants in Upland Ecosystems in Florida

Abstract The growing emphasis on including invertebrates in global biodiversity conservation efforts has prompted an increase in the study of invertebrate assemblages. Invertebrate sampling designs and the bias of individual methods, nevertheless, remain poorly understood for a variety of habitats. We used a structured inventory approach to sampling ants in five upland ecosystems in Florida. We evaluated the efficiency of quantitative and nonquantitative methods for sampling ants. We also evaluated the performance of four species richness estimators. A total of 3,774 species occurrences were distributed among 1,732 samples that contained 94 species from 31 genera. Twenty unique species and 10 duplicate species were collected. Compared with a comprehensive species list for Florida, sampling captured ≈66% of the regional fauna and ≈70–90% of species within the ecosystems studied. Combinations of sampling methods were much more effective for assessing species richness. Individual methods were complementary and sampled only part of the entire assemblage. Nonparametric estimators (an incidence-based coverage estimator [ICE] and a jackknife estimator [Jack2]) performed better than lognormal fitting, and Michaelis-Menten curve extrapolation. However, none of the estimators was stable, and their estimates should be viewed with skepticism. The results of this study provide support for the use of the Ants of the Leaf Litter (ALL) protocol for thoroughly sampling ant assemblages in temperate and subtropical ecosystems. Furthermore, our results indicate that even in relatively species-poor (compared with the tropics) temperate and subtropical regions, a large sampling effort that includes multiple sampling methods is the most effective manner of thoroughly sampling an ant assemblage. Therefore, we suggest that structured inventory should be adopted for a wider variety of terrestrial invertebrate studies.

Host Location Behavior in a Parasitoid of Imported Fire Ants

Female parasitoids use a hierarchy of cues to locate suitable hosts. We conducted a series of field observations and experiments to examine host location behavior in Pseudacteon tricuspis Borgmeier, a phorid parasitoid of Solenopsis invicta Buren worker ants. The parasitoids were frequently attracted to host workers at disturbed colonies, but were almost never attracted to host workers foraging at baits. When conspecific nonnestmate workers were introduced to baits, resulting in aggressive interactions, parasitoids appeared at the majority of baits. Moreover, larger numbers of parasitoids appeared at baits to which greater numbers of nonnestmate workers had been added. Addition of nonnestmate workers to disturbed colonies resulted in increased numbers of parasitoids attracted. Pseudacteon tricuspis did not display a pattern of uniform distribution at disturbed colonies but often was very abundant at some colony locations while absent or rare at nearby colony locations. Solenopsis invicta workers release alarm pheromones in aggressive interactions with nonnestmates, and this substance is likely an important chemical cue that attracts P. tricuspis flies to host workers from a distance.

Social insects dominate eastern US temperate hardwood forest macroinvertebrate communities in warmer regions.

Earthworms, termites, and ants are common macroinvertebrates in terrestrial environments, although for most ecosystems data on their abundance and biomass is sparse. Quantifying their areal abundance is a critical first step in understanding their functional importance. We intensively sampled dead wood, litter, and soil in eastern US temperate hardwood forests at four sites, which span much of the latitudinal range of this ecosystem, to estimate the abundance and biomass m−2 of individuals in macroinvertebrate communities. Macroinvertebrates, other than ants and termites, differed only slightly among sites in total abundance and biomass and they were similar in ordinal composition. Termites and ants were the most abundant macroinvertebrates in dead wood, and ants were the most abundant in litter and soil. Ant abundance and biomass m−2 in the southernmost site (Florida) were among the highest values recorded for ants in any ecosystem. Ant and termite biomass and abundance varied greatly across the range, from <1% of the total macroinvertebrate abundance (in the northern sites) to >95% in the southern sites. Our data reveal a pronounced shift to eusocial insect dominance with decreasing latitude in a temperate ecosystem. The extraordinarily high social insect relative abundance outside of the tropics lends support to existing data suggesting that ants, along with termites, are globally the most abundant soil macroinvertebrates, and surpass the majority of other terrestrial animal (vertebrate and invertebrate) groups in biomass m−2. Our results provide a foundation for improving our understanding of the functional role of social insects in regulating ecosystem processes in temperate forest.

A case study of human exacerbation of the invasive species problem: transport and establishment of polygyne fire ants in Tallahassee, Florida, USA

Understanding how exotic invasive species are spread is fundamental for ecology and conservation biology. Human transport has become one of the primary modes of dispersal for exotic species. We examined how the multiple queen, or polygyne, social form of the fire ant Solenopsis invicta is spread along roadsides in Tallahassee, Florida, USA. We then determined the likely source of this expanding population, which was a central soil depot. A survey of road maintenance practices in counties of several southeastern states and Texas revealed that the use of a central soil depot is a common practice. Road maintenance therefore may be the primary source for the establishment of new polygyne fire ant populations in this region and elsewhere. Control efforts focused on the soil depots will help to limit further spread of polygyne fire ants and perhaps other invasive organisms, particularly invasive weeds.

Temperate forest termites: ecology, biogeography, and ecosystem impacts

1. Wood decomposition in temperate forests is dominated by termites, fungi, and some species of ants and beetles. Outside of urban areas, temperate termite ecology is largely unknown, particularly when compared to tropical termites and other temperate organisms in the functional guild of wood‐decomposing animals.

Experimental evidence for weak effects of fire ants in a naturally invaded pine-savanna ecosystem in north Florida.

1. Fire ants naturally invade some undisturbed ecosystems of high conservation value and may negatively impact co‐occurring ants.

Ant distribution in relation to ground water in north Florida pine flatwoods

Abstract Longleaf pine savannas are one of the most threatened ecosystems in the world, yet are understudied. Ants are a functionally important and diverse group of insects in these ecosystems. It is largely unknown how local patterns of species diversity and composition are determined through the interaction of this dominant animal group with abiotic features of longleaf pine ecosystems. Here we describe how an important abiotic variable, depth to water table, relates to ant species distributions at local scales. Pitfall trapping studies across habitat gradients in the Florida coastal plains longleaf pine flatwoods showed that the ant community changed with mild differences in habitat. In this undulating landscape, elevation differences were less than 2 m, and the depth to the water table ranged from < 20 cm to 1.2 m. The plant species composing the ground cover were zoned in response to depth to water, and shading by canopy trees increased over deeper water tables. Of the 27 ant species that were analyzed, depending on the statistical test, seven or eight were significantly more abundant over a deep water table, eight to ten over a shallow one, and nine to eleven were not significantly patterned with respect to depth to water. Ant species preferring sites with shallow groundwater also preferred the shadier parts of the sites, while those preferring sites with deeper groundwater preferred the sunnier parts of the sites. This suggests that one group of species prefers hot-dry conditions, and the other cooler-moist. Factor analysis and abundance-weighted mean site characteristics generally confirmed these results. These results show that ant communities in this region respond to subtle differences in habitat, but whether these differences arise from founding preferences, survival, competition, or some combination of these is not known.

The ant, Aphaenogaster picea, benefits from plant elaiosomes when insect prey is scarce.

ABSTRACT Myrmecochory is a facultative, mutualistic interaction in which ants receive a proteinrich food reward (elaiosome) in return for dispersing plant seeds. In North American northeastern hardwood forests, Aphaenogaster ants are the primary genus dispersing myrmecochorous plants. In these forests, myrmecochores occur in plant guilds of understory spring ephemerals or seasonal greens. This mutualism has been demonstrated tor Aphaenogaster rudis (Emery) and individual plant species, but it has not been demonstrated for other Aphaenogaster species or guilds of myrmecochores as they naturally occur. Aphaenogaster picea (Wheeler) colonies were fed three treatments over 5 mo: 1) a mixture of only elaiosomes from an entire plant guild, 2) a diet of only insect protein and 3) a combination diet of both elaiosomes and insect protein. This experiment investigated two potential hypotheses through which elaiosomes can benefit ants: 1) elaiosome proteins can substitute for protein nutritional requirements when ants are prey-limited, and 2) elaiosome nutrition can supplement insect protein when prey is ample. First, a mixture of elaiosomes from four myrmecochorous plant species provided to A. picea colonies was sufficient to maintain worker production, larval growth, and fat stores when no other food was available. A. picea colonies consuming elaiosomes as their only protein source could be sustained for a growing season (5 mo). Second, colonies fed both elaiosomes and protein did not yield more productive colonies than a control diet of just insect protein. These results support the hypothesis that myrmecochory is indeed a facultative mutualism in which ants take advantage of the protein content of elaiosomes when it is favorable, but when they are not limited by insect prey they do not gain any additional benefit from elaiosomes.