Differences in growth and foraging behavior of native and introduced populations of an invasive crayfish

The competitive displacement of native by introduced species has often been attributed to differences in growth and behavior of the invader with its competitors. However, is the contribution of these traits to invasion success due to different competitor species between the native and introduced ranges or to differences among populations of the invader? Here we compared the growth and foraging behavior of the rusty crayfish (Orconectes rusticus) from its native and introduced ranges when competing with congeners from both ranges (O. cristavarius and O. propinquus, respectively). Our results indicated that O. rusticus from the introduced range grew significantly more than native O. rusticus and that there was no effect of competitor species on the growth of O. rusticus. Thus, the contribution of higher growth rates to the invasion success of O. rusticus was a result of population differences of O. rusticus in contrast to differences between congeners across both ranges. Foraging activity and recruitment to bait were higher in introduced versus native populations of O. rusticus when competing with O. cristavarius, but, not when competing with O. propinquus. Rather, O. propinquus significantly recruited to bait first when competing with either population of O. rusticus. However, 57% of the time that O. propinquus was first to find the bait, introduced O. rusticus aggressively pirated the bait from O. propinquus. In contrast, native O. rusticus were never observed pirating bait from O. propinquus. We suggest that this behavior may, in part, explain the higher growth observed in introduced populations of O. rusticus. The differences in behavior between O. rusticus populations depending on the competitor species may be due to behavioral flexibility that may drive higher growth rates in introduced populations of this species.     

Differences in aggression,activity and boldness between native and introduced populations of an invasive crayfish

Aggressiveness, along with foraging voracity and boldness, are key behavioral mechanisms underlying the competitive displacement and invasion success of exotic species. However, do aggressiveness, voracity and boldness of the invader depend on the presence of an ecologically similar native competitor in the invaded community? We conducted four behavioral assays to compare aggression, foraging voracity, threat response and boldness to forage under predation risk of multiple populations of exotic signal crayfish Pacifastacus leniusculus across its native and invaded range with and without a native congener, the Shasta crayfish P. fortis. We predicted that signal crayfish from the invaded range and sympatric with a native congener (IRS) should be more aggressive to outcompete a close competitor than populations from the native range (NR) or invaded range and allopatric to a native congener (IRA). Furthermore, we predicted that IRS populations of signal crayfish should be more voracious, but less bold to forage under predation risk since native predators and prey likely possess appropriate behavioral responses to the invader. Contrary to our predictions, results indicated that IRA signal crayfish were more aggressive towards conspecifics and more voracious and active foragers, yet also bolder to forage under predation risk in comparison to NR and IRS populations, which did not differ in behavior. Higher aggression/voracity/boldness was positively correlated with prey consumption rates, and hence potential impacts on prey. We suggest that the positive correlations between aggression/voracity/boldness are the result of an overall aggression syndrome. Results of stream surveys indicated that IRA streams have significantly lower prey biomass than in IRS streams, which may drive invading signal crayfish to be more aggressive/voracious/bold to acquire resources to establish a population.     

Contrasting effects of an invasive ant on a native and an invasive plant

When invasive species establish in new environments, they may disrupt existing or create new interactions with resident species. Understanding of the functioning of invaded ecosystems will benefit from careful investigation of resulting species-level interactions. We manipulated ant visitation to compare how invasive ant mutualisms affect two common plants, one native and one invasive, on a sub-tropical Indian Ocean island. Technomyrmex albipes, an introduced species, was the most common and abundant ant visitor to the plants. T. albipes were attracted to extrafloral nectaries on the invasive tree (Leucaena leucocephala) and deterred the plant’s primary herbivore, the Leucaena psyllid (Heteropsylla cubana). Ant exclusion from L. leucocephala resulted in decreased plant growth and seed production by 22% and 35%, respectively. In contrast, on the native shrub (Scaevola taccada), T. albipes frequently tended sap-sucking hemipterans, and ant exclusion resulted in 30% and 23% increases in growth and fruit production, respectively. Stable isotope analysis confirmed the more predacious and herbivorous diets of T. albipes on the invasive and native plants, respectively. Thus the ants’ interactions protect the invasive plant from its main herbivore while also exacerbating the effects of herbivores on the native plant. Ultimately, the negative effects on the native plant and positive effects on the invasive plant may work in concert to facilitate invasion by the invasive plant. Our findings underscore the importance of investigating facilitative interactions in a community context and the multiple and diverse interactions shaping novel ecosystems.     

Ecologically heterogeneous populations of the invasive ant Wasmannia auropunctata within its native and introduced ranges

Abstract 1. The biology of most invasive species in their native geographical areas remains largely unknown. Such studies are, however, crucial in shedding light on the ecological and evolutionary processes underlying biological invasions. 2. The present study focuses on the little fire ant Wasmannia auropunctata, a species native to Central and South America that has been widely introduced and which has become invasive throughout the tropics. We characterise and compare several ecological traits of native populations in French Guiana with those in one of its introduced ranges, New Caledonia. 3. We found ecologically heterogeneous populations of W. auropunctata coexisting in the species’ native geographical area. First, we found populations restricted to naturally perturbed areas (particularly floodplains) within the primary forest, and absent from the surrounding forest areas. These populations were characterised by low nest and worker densities. Second, we found dominant populations in recent anthropogenic areas (e.g. secondary forest or forest edge along road) characterised by high nest and worker densities, and associated with low ant species richness. The local dominance of W. auropunctata in such areas can be due to the displacement of other species (cause) or the filling‐up of empty habitats unsuitable to other ants (effect). With respect to their demographic features and ant species richness, the populations of native anthropogenic habitats were to a large extent similar to the invasive populations introduced into remote areas. 4. The results point to the need for greater research efforts to better understand the ecological and demographic features of invasive species within their native ranges.     

两种入侵植物与三种本地植物根系特征的比较研究

以菊科2种入侵植物飞机草(Chromolaena odorata (L.)R. M. King & H. Rob)和紫茎泽兰( Eupatorium adenophorum Speng)以及生活型相似的3种本地植物异叶泽兰(Eupatorium heterophyllum DC.)、佩兰(Eupa-torium for...     

Relationships among native and introduced populations of the Argentine ant (Linepithema humile) and the source of introduced populations

The Argentine ant (Linepithema humile) is a damaging invasive species that has become established in many Mediterranean-type ecosystems worldwide. To identify likely sources of introduced populations we examined the relationships among native Linepithema populations from Argentina and Brazil and introduced populations of L. humile using mitochondrial cytochrome b sequence data and nuclear microsatellite allele frequencies. The mitochondrial phylogeny revealed that the populations in Brazil were only distantly related to both the introduced populations and the native populations in Argentina, and confirmed that populations in Brazil, previously identified as L. humile, are likely a different species. The microsatellite-based analysis provided resolution among native and introduced populations of L. humile that could not be resolved using the mitochondrial sequences. In the native range, colonies that were geographically close to one another tended to be genetically similar, whereas more distant colonies were genetically different. Most samples from the introduced range were genetically similar, although some exceptions were noted. Most introduced populations were similar to native populations from the southern Rio Parana and were particularly similar to a population from Rosario, Argentina. These findings implicate populations from the southern Rio Parana as the most likely source of introduced populations. Moreover, these data suggest that current efforts to identify natural enemies of the Argentine ant for biological control should focus on native populations in the southern Rio Parana watershed.     

Recent behavioural and population genetic divergence of an invasive ant in a novel environment

Aim Invasive species frequently exhibit high temporal and spatial variation in abundance. Although ecological aspects undoubtedly affect this variation, genetic factors may also play a part. The invasive unicolonial yellow crazy ant Anoplolepis gracilipes exhibits considerable variation in abundance throughout its extensive distribution in Australia’s Northern Territory, where it was first detected in the 1980s. First, we aimed to determine whether A. gracilipes variation in abundance was associated with behavioural and genetic differentiation of the population and to determine whether one or more introductions occurred. Second, we investigated whether the A. gracilipes population was genetically and behaviourally heterogeneous to determine whether population divergence has occurred since introduction. Location Tropical monsoonal savanna in Arnhem Land, Northern Territory, Australia. Methods Ant abundances were assessed at 13 sites throughout the study region. We used mitochondrial DNA sequences and microsatellite molecular markers to determine population genetic structure, which we correlated with abundance. Behavioural differentiation was assayed using aggression trials and analysed together with genetic data to investigate population divergence. Results Although we found considerable variation in abundance, we found no association between population structure and differences in abundance. Our analyses suggest that A. gracilipes ants in Arnhem Land resulted from a single introduction. The population is not homogeneous, however, as aggression scores varied over both genetic and geographic distance. We also found a positive relationship between genetic and geographic distance. Main conclusions The variation in abundance in the Arnhem Land population of A. gracilipes is clearly not owing to invasion by ants from different sources. The genetic and behavioural differentiation we observed is suggestive of incipient genetic and behavioural divergence, which may be expected over time when an invasive species enters in a new environment.     

飞机草入侵种群与原产地种群生长性状的差异

飞机草(Chromolaena odorata)是我国热带地区危害严重的外来入侵植物,为揭示适应进化对其成功入侵的贡献,在同质种植园中,比较研究了飞机草10个入侵地种群与12个原产地种群生长性状的差异,为排除奠基者效应的可能影响,进一步比较了飞机草10个入侵地种群与其原产地可能的祖先种群间的差异。结果表明,飞机草10个入侵地种群的基茎、株高、分枝数、生物量和比叶面积均显著高于12个原产地种群;与可能的祖先种群相比,飞机草10个入侵种群的生物量、分枝数和比叶面积仍更高。这些结果表明,在长期的入侵过程中飞机草通过进化提高了资源向生长的分配,支持增强竞争能力的进化假说。     

Asexual reproduction in introduced and native populations of the ant Cerapachys biroi

Asexual reproduction is particularly common among introduced species, probably because it helps to overcome the negative effects associated with low population densities during colonization. The ant Cerapachys biroi has been introduced to tropical and subtropical islands around the world since the beginning of the last century. In this species, workers can reproduce via thelytokous parthenogenesis. Here, we use genetic markers to reconstruct the history of anthropogenic introductions of C. biroi, and to address the prevalence of female parthenogenesis in introduced and native populations. We show that at least four genetically distinct lineages have been introduced from continental Asia and have led to the species' circumtropical establishment. Our analyses demonstrate that asexual reproduction dominates in the introduced range and is also common in the native range. Given that C. biroi is the only dorylomorph ant that has successfully become established outside of its native range, this unusual mode of reproduction probably facilitated the species' worldwide spread. On the other hand, the rare occurrence of haploid males and at least one clear case of sexual recombination in the introduced range show that C. biroi has not lost the potential for sex. Finally, we show that thelytoky in C. biroi probably has a genetic rather than an infectious origin, and that automixis with central fusion is the most likely underlying cytological mechanism. This is in accordance with what is known for other thelytokous eusocial Hymenoptera.     

Behavioral interactions of the invasive Argentine ant with native ant species

Summary: The Argentine ant, Linepithema humile, has invaded many areas of the world, displacing native ants. Its behavior may contribute to its competitive success. Staged and natural encounters were observed at food resources in the field, between Argentine ants and eight ant species native to northern California. There was no relation between the frequency of aggression by any ant species and the outcome of encounters, though Argentine ants were more likely than ants of native species to behave aggressively. When an ant of one species initiated an encounter of any kind with an ant of another species, the ant that did not initiate was likely to retreat. This was true of all species studied. Most encounters between ants were initiated by Argentine ants. Thus the native species tended to retreat more frequently than Argentine ants. Interactions between Argentine ants and native species at food resources, causing ants of native species to retreat, may help Argentine ants to displace native species from invaded areas.     

Initial behavior in colony fragments of an introduced population of the invasive ant Wasmannia auropunctata

We investigated in the laboratory the initial behavior of propagules of the invasive ant Wasmannia auropunctata in Cameroon where it has been introduced. Both workers and queens at first feigned death (thanatosis), and then the workers slowly moved around the experimental arena; the queens did the same about 10seconds later. Each queen antennated selected workers that then aggregated together by grasping the hind leg of another ant with their mandibles. When encountering the queen again, the lead worker climbed up the queen's hind leg and onto her back, followed by some other individuals. The remaining workers followed the queen to a location in the experimental arena. When brood was present, the workers transferred it to this location. Orphaned workers did not aggregate, but gathered the brood together and took care of it. By permitting propagules to survive, these behaviors likely contribute to the success of W.?auropunctata as an invader.     

Predatory abilities favour the success of the invasive ant Pheidole megacephala in an introduced area

Abstract:  The invasive African big-headed ant, Pheidole megacephala , is a dominant species in the many areas it has invaded. We examined whether one potential reason for its ecological success might be its predatory efficiency. We compared the density of termite nests in an area of Mexico invaded by P. megacephala with an adjacent area where P. megacephala is not present. We also compared the success of P. megacephala in preying on termites with that of 13 native ant species. We found that termite nest density was significantly lower in areas invaded by P. megacephala (0.33 vs. 1.05 nests per 30 m transect). In field trials, we established that P. megacephala workers were significantly more successful at capturing termite workers from termite nest fragments than even the most successful native ant species, Dorymyrmex pyramicus . For both P. megacephala and D. pyramicus , single scouts could trigger the mass recruitment of nestmates, but P. megacephala was able to recruit greater numbers of nestmates. Combined with their aggressiveness towards other ant species, their highly efficient predatory capacities help explain the ecological success of P. megacephala and demonstrate how it can be a major threat to invertebrate biodiversity in the areas it invades.     

Impact of an introduced ant on native rain forest invertebrates: Pheidole megacephala in monsoonal Australia

Pheidole megacephala is an exotic ant species that has severely affected native invertebrate biodiversity throughout the tropics. Its impacts have been documented extensively in relatively depauperate invertebrate communities, but not in species-rich habitats such as tropical rain forests. Here we describe the local distribution of P. megacephala and its impacts on native invertebrate assemblages in and around a rain forest patch at Howard Springs, in Australia's monsoonal tropics. P. megacephala was found to be confined to a single area of approximately 25 ha, with its distribution centered on drainage lines and the rain forest. Significant but weak correlations were found between its abundance and vegetative canopy cover (positive) and distance from the rain forest (negative). In the most heavily infested area within the rain forest, the abundance of P. megacephala was 37–110 times that of total native ant abundance found within uninfested plots, as measured by pitfall traps. The abundance and richness of native ants and other invertebrates were significantly reduced in litter samples, pitfall catches and foliage beats where P. megacephala was present, inversely relative to the abundance of P. megacephala. Only two individuals of a single native ant species were found within the most infested plot, with native ant richness being reduced to about half in the least infested plot. The most persistent functional groups of native ants in infested plots were Cryptic species, which forage primarily within soil and leaf litter, and Opportunists, which exhibit highly generalised foraging behaviour. The highest abundance of P. megacephala corresponded with a 42–85% decrease in the abundance of other native invertebrates. Insect larvae were totally absent from foliage beats collected at the most heavily infested plot. P. megacephala was found overall to be expanding its range, averaging 12 m range expansion in the dry season and contracting 7 m in the wet season. It is able to spread into surrounding savanna habitats by occupying relatively sheltered microsites, such as beneath logs and at the bases of trees. However, it is unlikely to attain high population densities in open savanna habitats because of its relative intolerance of desiccation, and the prevalence of behaviourally dominant native ant species. Howard Springs is currently the only rain forest patch in monsoonal Australia known to be infested by P. megacephala, but clearly this ant is a serious potential threat to the region's rain forest invertebrate fauna. Received: 19 August 1998 / Accepted: 12 May 1999     

Unadapted behaviour of native,dominant ant species during the colonization of an aggressive,invasive ant

Among the factors driving the invasive success of non-indigenous species, the “escape opportunity” or “enemy release” hypothesis argues that an invader’s success may result partly from less resistance from the new competitors found in its introduced range. In this study, we examined competitive interactions between the little fire ant Wasmannia auropunctata (Roger) and ant species of the genus Pheidole in places where both are native (French Guiana) and in places where only species of Pheidole are native (New Caledonia). The experimental introduction of W. auropunctata at food resources monopolized by the Pheidole species induced the recruitment of major workers only for the Guianian Pheidole species, which were very effective at killing Wasmannia competitors. In contrast, an overall decrease in the number of Pheidole workers and no recruitment of major workers were observed for the New Caledonian species, although the latter were the only ones able to kill the Wasmannia workers. These results emphasize the inappropriate response of native dominant New Caledonian species to W. auropunctata and, thus, the importance of enemy recognition and specification in the organization of ant communities. This factor could explain how invasive animal species, particularly ants, may be able to successfully invade species-rich communities.     

Biogeographic comparisons of the traits and abundance of an invasive crab throughout its native and invasive ranges

High abundances of non-native species in the invaded range may be linked to changes in fitness related traits. However, few studies have compared differences in both life-history traits and abundances of introduced species between their native and invaded ranges. We determined differences in 12 morphological traits, an important fitness related trait (body size), and the abundance of the porcelain crab, Petrolisthes elongatus, in its native (New Zealand) and invasive (Tasmania, Australia) ranges. P. elongatus was more abundant in the introduced range; however, changes in abundance depended on tidal height, with higher abundances only at mid and low tidal zones. The biomass of male crabs was higher in the invaded range compared to the native range, but there was no difference in female biomass between ranges. Despite increases in male biomass, sex ratios between native and invasive populations did not differ. In addition, principal components analysis showed no differences in overall morphology between Tasmania and New Zealand. Our study indicates that increased abundance in the invaded range of P. elongatus may be linked to high values of an important trait (greater biomass) in the invaded range. Importantly, changes in biomass and abundance may be due to P. elongatus being able to utilise mid/low zones more in the invaded range. Furthermore, our findings indicate that understanding how sex specific changes in biomass interact with the recipient environment (biotic and abiotic) in the introduced range will be important for determining the mechanisms underpinning the establishment and spread of P. elongatus.     

The distribution and evolutionary history of Wolbachia infection in native and introduced populations of the invasive argentine ant (Linepithema humile)

Wolbachia pipientis is a maternally transmitted bacterium that often alters the life history of its insect host to maximize transmission to subsequent generations. Here we report on the frequency and distribution of Wolbachia infection in a widespread invasive species, the Argentine ant (Linepithema humile). We screened 1175 individual Argentine ants from 89 nests on five continents and several islands, including numerous locations in both the native (South American) and introduced ranges. We detected Wolbachia in four of 11 native populations, but only one of 21 introduced populations was infected. In the Argentine ant's native range, the distribution of Wolbachia supergroups A and B was nonoverlapping. By coupling infection frequency data with behaviourally defined colony boundaries, we show that infected and uninfected colonies are often adjacent to one another, supporting the proposition that little female-mediated gene flow occurs among Argentine ant colonies. We also conduct a phylogenetic analysis, and show that the Wolbachia infecting both native and introduced populations of Argentine ants belong to two lineages that appear to be specialized on infecting New World ants. One other lineage of Wolbachia has undergone frequent, recent episodes of horizontal transmission between distantly related, introduced insect hosts.