Is the exotic bumblebee Bombus terrestris really invading Tasmanian native vegetation?

There has been a great deal of disagreement surrounding the capacity of Bombus terrestris to invade Tasmanian native vegetation. This paper reviews the conflicting findings of previous surveys of the invasion of Tasmania by B. terrestris, and presents new data from the 2004–2005 austral summer. From this, it is clear that B. terrestris has extensively invaded Tasmanian native vegetation. The new data provide strong evidence that B. terrestris is breeding in native vegetation in every region of Tasmania. More than 10 bumblebees were seen in one day at 153 locations in native vegetation, including 42 locations within 10 National Parks and 38 locations within the Tasmanian Wilderness World Heritage Area. Nests of B. terrestris were also found within two National Parks. These findings suggest that B. terrestris would also invade native vegetation in non-arid temperate regions of the Australian mainland, if it is introduced there.     

The impact of an exotic social wasp (Vespula germanica) on the native arthropod community of north-west Patagonia, Argentina: an experimental study

Abstract 1. Biological invasions are usually thought to have a negative impact on native communities. However, data supporting this idea are often based on comparative studies between invaded and non‐invaded areas, and are spatially and temporally limited. 2. The present study experimentally assessed the impact of an exotic wasp, Vespula germanica, on the native arthropod community of north‐west Patagonia during 3 years in an area of 80 ha. Vespula germanica is an exotic social vespid that invaded north‐west Patagonia 20 years ago. It has been suggested that its populations affect native arthropods because of its broad diet and also because Patagonia lacks natural enemies and potential competitors for these wasps. 3. Using wasp‐specific toxic baits, V. germanica abundance was reduced in five sites of native woodlands during 3 consecutive years. The abundance, species richness, and composition of arthropods between non‐poisoned (control) and poisoned sites was then compared, both before and after the wasps were poisoned. 4. Wasp abundance represented 6% of the total arthropod catches in non‐poisoned sites and was reduced, on average, by 50% in the treated areas. The abundance, species richness, and composition of the arthropod community (305 species, 24 600 individuals) did not differ between control areas and areas where the abundance of V. germanica was reduced. Significant differences in response variables were found only before wasp poisoning had begun and were related to variations among sites. 5. These results suggest that V. germanica is not affecting the local arthropod assemblages, contradicting past work in other regions. The low relative abundance of wasps in Patagonia, when compared with other invaded regions, might explain the findings. 6. The present study provides further evidence for the importance of large‐scale experimental work with before/after comparisons to fully understand the impact of invaders on natural communities.     

Vulnerability of riparian zones to invasion by exotic vascular plants

We compared the invasibility of riparian plant communities high on river banks with those on floodplain floors for four South African rivers. Analyses of abundant and significant riparian species showed that the floors have 3.1 times more exotic plants than the banks. The percent exotics ranges from 5% to 11% of total species richness for the banks, and from 20% to 30% for the floors. Species richness and percent exotics are negatively correlated for the banks, but not correlated for the floors.Despite great differences in climate, species richness, and landuse history, the percentages of exotic plants in three rivers in the Pacific Northwest of the USA and one river in southwestern France are similar to those in South Africa (24-30% vs. 20-30%, respectively). Furthermore, the high proportions of exotic species in these riparian plant communities are comparable to those reported for vascular plant communities on islands. We conclude that the macro-channel floor regions of the riparian zones of South African rivers are highly vulnerable to invasion by exotic vascular plants.     

Seed removal by small mammals, birds and ants in semi-arid Chile, and comparison with other systems

Aim This study aims to evaluate the relative importance of birds, small mammals, and ants as seed predators at a semi‐arid site in northern Chile. Location Northern Chile, in Parque Nacional Bosque Fray Jorge (30°41′ N, 71°40′ W, c. 80 m elevation). Methods We studied the relative abilities of birds, small mammals, and ants to find and remove millet seeds either singly (i.e. background seed removal) or in bulk. Single seeds were set in shallow depressions in Plexiglas trays which were established in long and arbitrary transects, and were available either to birds (diurnally) or small mammals (nocturnally) or were covered by hardware cloth and therefore available only to ants. Bulk removal was evaluated with seeds in Petri dishes that also were established in long and arbitrary transects, and trays were either open diurnally (birds) or nocturnally (small mammals); a third set of trays was covered with hardware cloth cages to excluded vertebrates, and ants were given access to Petri dishes with twigs that were arranged across the edge of the dishes. All experiments lasted four days and nights, and trays and dishes were checked and replenished as needed in the morning and evening. In the former study vertebrate consumption was determined as the mean number of seeds removed from trays (within a given transect) minus the number removed from ant‐only trays. Because ants were rarely seen in vertebrate access Petri dishes, however, we did not correct consumption there. Treatments were compared using repeated measures mixed model analysis of variance. In addition to evaluating patterns within this community, we compared our results against those obtained in similar studies in various arid regions. Results Diurnal seed consumption was significantly greater than nocturnal seed consumption, which in turn was significantly greater than consumption by ants. Diurnal consumption was highly seasonal, evidently corresponding to the seasonal arrival and departure of migratory birds. In general, South American sites exhibit much lower levels of seed predation than sites in the northern hemisphere, but removal at our site appears to be much greater and more strongly avian‐dominated than at other sites in South America. Our results are consistent with predictions based on a hypothesis relating precipitation to seed predictability. Main conclusions Both birds and small mammals were much more important seed consumers at our site than elsewhere in South America, whereas ants have been relatively unimportant at all South American sites studied to date. Although the dominant seed consumers differ across sites, overall levels of seed removal appear similar in South America and Australia, and substantially lower than reported from sites in the northern hemisphere and Africa.     

Localized invasion of the North American Harris mud crab, Rhithropanopeus harrisii, in the Panama Canal: implications for eradication and spread

As the rate of biological invasions continues to increase, a growing number of aquatic introduced species are becoming globally widespread. Despite this ubiquitous phenomenon, rarely do we discover aquatic invaders early enough to allow the possibility of eradication. Recently, the North American Harris mud crab (Rhithropanopeus harrisii) was found in the waters adjacent to the Panama Canal and herein we provide an assessment of the crab’s distribution in Panama to evaluate the possibility of eradication. Using salinity tolerance experiments, we also evaluate the potential for further spread of this crab within the Canal. Our results suggest that populations of R. harrisii are currently limited to two manmade lagoons which are adjacent to the Panama Canal. Our experiments suggest that both juvenile and adult R. harrisii can survive in salinities found outside its current range in Panama. Although it is difficult to predict the potential for future spread and impacts in Panama, current management strategies could reduce the probability for spread locally as well as elsewhere in the world given the intensity of shipping in this region. The current containment of this invader suggests that a localized eradication may be possible.     

Invasion of exotic earthworms into ecosystems inhabited by native earthworms

The most conspicuous biological invasions in terrestrial ecosystems have been by exotic plants, insects and vertebrates. Invasions by exotic earthworms, although not as well studied, may be increasing with global commerce in agriculture, waste management and bioremediation. A number of cases has documented where invasive earthworms have caused significant changes in soil profiles, nutrient and organic matter dynamics, other soil organisms or plant communities. Most of these cases are in areas that have been disturbed (e.g., agricultural systems) or were previously devoid of earthworms (e.g., north of Pleistocene glacial margins). It is not clear that such effects are common in ecosystems inhabited by native earthworms, especially where soils are undisturbed. We explore the idea that indigenous earthworm fauna and/or characteristics of their native habitats may resist invasion by exotic earthworms and thereby reduce the impact of exotic species on soil processes. We review data and case studies from temperate and tropical regions to test this idea. Specifically, we address the following questions: Is disturbance a prerequisite to invasion by exotic earthworms? What are the mechanisms by which exotic earthworms may succeed or fail to invade habitats occupied by native earthworms? Potential mechanisms could include (1) intensity of propagule pressure (how frequently and at what densities have exotic species been introduced and has there been adequate time for proliferation?); (2) degree of habitat matching (once introduced, are exotic species faced with unsuitable habitat conditions, unavailable resources, or unsuited feeding strategies?); and (3) degree of biotic resistance (after introduction into an otherwise suitable habitat, are exotic species exposed to biological barriers such as predation or parasitism, “unfamiliar” microflora, or competition by resident native species?). Once established, do exotic species co-exist with native species, or are the natives eventually excluded? Do exotic species impact soil processes differently in the presence or absence of native species? We conclude that (1) exotic earthworms do invade ecosystems inhabited by indigenous earthworms, even in the absence of obvious disturbance; (2) competitive exclusion of native earthworms by exotic earthworms is not easily demonstrated and, in fact, co-existence of native and exotic species appears to be common, even if transient; and (3) resistance to exotic earthworm invasions, if it occurs, may be more a function of physical and chemical characteristics of a habitat than of biological interactions between native and exotic earthworms.     

Island incidence and mainland population density: mammals from Mediterranean islands

Abstract. The reasons why some species are resistant to extinction or are better invaders of islands than others remain unexplained. In this study, we test the hypothesis that mammals living on the mainland at higher density than predicted by the density/body mass relationship have a much greater chance to colonize a small island successfully, and/or that they are less likely to become extinct when living on small islands. For this, we used data compiled on mammals from a number of Mediterranean islands. We show a nested pattern for mammals on western Mediterranean islands, which suggests that the distribution of mammals on these islands is not the result of a random process. Using two comparative methods, we show that mammal density on the mainland, corrected for body mass, is negatively correlated with island size. Mammals with a high density compared to the density/mass relationship are the best invaders and/or probably have less chance of going extinct on small islands when population size is small.     

The response of native species to removal of invasive exotic grasses in a seasonally dry Hawaiian woodland

Abstract. Non-native perennial grasses form 30% of the live understory biomass in seasonally dry, submontane forests in Hawaii Volcanoes National Park, yet their effects on native species are unknown. We removed these grasses from plots of 20 m × 20 m in 1991 and maintained removal and control areas over the next three years. Two fast growing shrub species, Dodonaea viscosa and Osteomeles anthylidifolia, increased in size significantly more in removal areas than in controls. Individuals of the most abundant shrub species, Styphelia tameiameia showed no net growth response to grass removal. They did, however, change their architecture: many branches along the mid and upper sections of the main trunk died and a proliferation of new leaves and shoots occurred in the lower 40 cm of trunk. Basal diameter increase was very small in Metrosideros polymorpha, the dominant tree species in these sites. All species except Styphelia had significantly increased leaf tissue nitrogen in removal plots by 18 months after removal when compared to shrubs in control areas suggesting that removal plot shrubs had greater access to soil nitrogen. Available soil-N pools, which were generally higher in the removal plots, support this interpretation. Light levels near the soil surface were also higher where grasses were removed than where they were present which may have contributed to increased shrub growth. By contrast, soil moisture was consistently lower where grasses were removed than where they were still present. Shrub tissue carbon isotope values were consistent with the interpretation that shrubs in removal plots had less rather than more water available to them. Hence, the increased growth observed in removal plot shrubs could not be due to release from moisture competition. Lastly, our results showed that seedlings of all woody species except Metrosideros were significantly more abundant in removal plots at both one and three years after removal and initially high sapling mortality was balanced by high recruitment into the sapling class. We believe that over time this will result in increased densities of native shrubs if grasses are kept out. With the presence of grasses, shrub growth in these woodlands is reduced and biomass is shifting towards grasses.     

Conversion of sagebrush shrublands to exotic annual grasslands negatively impacts small mammal communities

Aim The exotic annual cheatgrass (Bromus tectorum) is fast replacing sagebrush (Artemisia tridentata) communities throughout the Great Basin Desert and nearby regions in the Western United States, impacting native plant communities and altering fire regimes, which contributes to the long‐term persistence of this weedy species. The effect of this conversion on native faunal communities remains largely unexamined. We assess the impact of conversion from native perennial to exotic annual plant communities on desert rodent communities. Location Wyoming big sagebrush shrublands and nearby sites previously converted to cheatgrass‐dominated annual grasslands in the Great Basin Desert, Utah, USA. Methods At two sites in Tooele County, Utah, USA, we investigated with Sherman live trapping whether intact sagebrush vegetation and nearby converted Bromus tectorum‐dominated vegetation differed in rodent abundance, diversity and community composition. Results Rodent abundance and species richness were considerably greater in sagebrush plots than in cheatgrass‐dominated plots. Nine species were captured in sagebrush plots; five of these were also trapped in cheatgrass plots, all at lower abundances than in the sagebrush. In contrast, cheatgrass‐dominated plots had no species that were not found in sagebrush. In addition, the site that had been converted to cheatgrass longer had lower abundances of rodents than the site more recently converted to cheatgrass‐dominated plots. Despite large differences in abundances and species richness, Simpson’s D diversity and Shannon‐Wiener diversity and Brillouin evenness indices did not differ between sagebrush and cheatgrass‐dominated plots. Main conclusions This survey of rodent communities in native sagebrush and in converted cheatgrass‐dominated vegetation suggests that the abundances and community composition of rodents may be shifting, potentially at the larger spatial scale of the entire Great Basin, where cheatgrass continues to invade and dominate more landscape at a rapid rate.     

The diversity and origin of exotic ants arriving in New Zealand via human-mediated dispersal

The number of exotic ant species being dispersed to new regions by human transportation and the trade pathways responsible for this are poorly understood. In this study, the taxonomic diversity, trade pathways, and origin of exotic ants intercepted at the New Zealand border were examined for the period 1955–2005. Overall, there were a total 4355 interception records, with 115 species from 52 genera. The 10 most frequently intercepted genera, and the 20 most frequently intercepted species contributed > 90% of all records. Many of the species frequently intercepted are regarded as invasive species, and several are established in New Zealand. The most intercepted species was Pheidole megacephala . Despite a relatively low trade relationship, a high proportion (> 64%) of the exotic ants which were intercepted originated from the Pacific region. However, the majority of species intercepted from the Pacific was exotic to the region (71%), or to a lesser extent, wide-ranging Pacific native species. No endemic species from the Pacific were intercepted. The effectiveness of detecting exotic ant species at the New Zealand border ranged from 48–78% for different trade pathways, indicating a number of species remain undetected. Trade routes associated with specific geographical regions represent a major filter for the arrival of exotic ant species. Despite the importance of the Pacific as a frequent pathway, we suggest that the future establishment of exotic ant species in New Zealand is likely to be mitigated by a renewed focus on trade routes with cool temperate regions, particularly Australia.     

Review of the science and practice of restoration in Argentina: increasing awareness of the discipline

The objective of this work was to obtain an overview of studies on ecological restoration carried out in Argentina to date. By means of the Scopus database, we performed two literature searches, one in Spanish (restau* and Argentina) and the other in English (restor* and Argentina). Between 1996 and 2013, 105 publications were registered, representing 2% of publications in Biology and Ecology. Most of these appeared in international journals (87%), in English (86%), and 28% were coauthored with researchers from other countries, favoring visibility at an international level. We observed an increase in the number of studies per year over time, with a significant increase beginning in 2008. Of the 18 ecological regions in Argentina, we found studies relating to 12 as well as four studies relating to restoration in urban areas. This review of the literature is intended to increase awareness of restoration in Argentina and help identify current gaps relating either to this subject or to specific ecological regions.     

海洋外来物种入侵生态学研究

海洋外来物种入侵已成为最为严重的全球性环境问题之一。海洋生态系统类型多样、环境复杂,其生物入侵的监测、控制与管理难度相对较大。我国对陆地外来生物的入侵已开展了较为深入的研究,但对于海洋外来生物的入侵研究仍处于起步阶段,对其入侵监测、入侵机制、入侵危害的程度以及防治等问题缺乏基础数据。本文在分析国内外海洋外来生物入侵现状的基础上,概述其入侵生态学研究形势及相关成果,包括海洋外来物种的入侵途径、入侵过程、入侵生态效应以及全球变化对入侵的影响等。海洋外来生物的入侵可能对海洋生态系统造成直接或间接的影响,如种间竞争破坏生态环境、与土著种杂交造成遗传污染、病原生物及有毒藻类导致海洋生态灾害加剧等。此外,从政策和法规、入侵风险评估、监测和公共宣传教育、生物信息系统和有效管理机制等方面提出对我国海洋外来物种入侵的防治策略。本研究为我国海洋外来物种的进一步研究提供了参考。     

Species richness of herbivores on exotic host plants increases with time since introduction of the host

Aim Species richness of insect herbivores feeding on exotic plants increases with abundance as well as range size of the host in the area of introduction. The formation of these herbivore assemblages requires a certain amount of time, and the richness of insect faunas should also increase with the length of time an exotic plant has been present in the introduced range. Location Central Europe. Methods We analysed the variation in species richness of leaf‐chewing Lepidoptera larvae and sap‐sucking Auchenorrhyncha (Hemiptera) associated with 103 exotic woody plant species in Germany in relation to time since introduction, range size, growth form (trees versus shrubs), biogeographical origin (distance from Central Europe) and taxonomic isolation of the host plant (presence or absence of a native congener in the introduced area). Results Using simple correlation analyses we found for Lepidoptera and Auchenorrhyncha that species richness increased with time since introduction of the host plant. For the Lepidoptera the increase of species richness with time since introduction remained significant even after removing the effects of all other independent variables. Main conclusions Our results provide some evidence that assemblages of insects on exotic plants do not reach saturation within a time scale of few hundred years. This contrasts with previous findings for crop plants.     

Track analysis of the Nearctic region: Identifying complex areas with mammals

The Nearctic region is located on the North American plate. However, its tectonic history is related to convergence with other plates, which has promoted a complex topography. This complexity should be reflected by the distributional patterns of the biota. We used track analysis with 574 species of mammals to identify generalized tracks and panbiogeographic nodes in the Nearctic region and to propose an updated point of view of complex areas and their boundaries in North America. Seven generalized tracks with nested patterns (California, Columbia Plateau, Mesoamerican, Mexican Plateau, Neotropic, Southern Rocky Mountains, and Western Coast of USA) were identified using a parsimony analysis of endemicity with progressive character elimination. Nine panbiogeographic nodes were identified at the intersections of the generalized tracks, all of which were located in the Sierra of Chiapas and Central America physical features. A total of 192 nodes were identified for the nested patterns, located in only eight physical features. Our analysis revealed evolutionary patterns in generalized tracks, and the panbiogeographic nodes predicted areas with high evolutionary–geologic complexity, shared by other taxonomic groups.     

More is less: agricultural impacts on the N cycle in Argentina

Human impact on nitrogen cycling, in particular the introduction of reactive nitrogen in terrestrial and aquatic ecosystems, can be examined at multiple scales, from the global impact on atmospheric chemistry to the impact of human activities on soil organic matter and fertility at the scale of square meters. Nevertheless, anthropogenic loading of nitrogen cycling in natural and managed ecosystems can be seen most directly at the regional scale, where concentrated human activity results in disruption of the nitrogen balance, with consequences for biogeochemical cycling and their interactions. Differences in land-use and agricultural practices between North and South America, and the importance of economic drivers that determine the fate of new reactive nitrogen demonstrate a contrasting picture of human impact on N cycling when the consequences are considered at the global vs. the regional scale. In particular, in the Pampa region of Argentina, the central agricultural zone of the country, the expansion of soybean cultivation in the last 20 years and the use of synthetic fertilizers have resulted in an influx of reactive nitrogen into these systems, with unexpected consequences for the nitrogen balance. A mass balance of nitrogen for soybean demonstrates that increased nitrogen inputs from biological fixation do not compensate for losses due to seed export, such that most areas under soybean cultivation are currently experiencing a substantive net loss of nitrogen. In addition, other crops that are currently being fertilized still show a net loss of nitrogen also due to the effect of primary exports from these agroecosystems. These simple models demonstrate that socioeconomic factors in large part drive the contrasting effects of anthropogenic impact on nitrogen cycling at global vs. regional scales. The future impact on nitrogen cycling in the Americas requires an integration of both ecological factors and socioeconomic drivers that will ultimately determine human disruption of the nitrogen cycle.     

Determinants for the successful establishment of exotic ants in New Zealand

Biological invasions can dramatically alter ecosystems. An ability to predict the establishment success for exotic species is important for biosecurity and conservation purposes. I examine the exotic New Zealand ant fauna for characteristics that predict or determine an exotic species’ ability to establish. Quarantine records show interceptions of 66 ant species: 17 of which have established, 43 have failed to establish, whereas nests of another six are periodically observed but have failed to establish permanently (called ‘ephemeral’ establishment). Mean temperature at the highest latitude and interception variables were the only factors significantly different between established, failed or ephemeral groups. Aspects of life history, such as competitive behaviour and morphology, were not different between groups. However, in a stepwise discriminant analysis, small size was a key factor influencing establishment success. Interception rate and climate were also secondarily important. The resulting classification table predicted establishment success with 71% accuracy. Because not all exotic species are represented in quarantine records, a further discriminant model is described without interception data. Though with less accuracy (65%) than the full model, it still correctly predicted the success or failure of four species not used in the previous analysis. Techniques for improving the prediction accuracy are discussed. Predicting which species will establish in a new area appears an achievable goal, which will be a valuable tool for conservation biology.     

Vertebrate invaders and their ecological impacts in Chile

The South American country of Chile has been subjected to relatively few invasions in historic times. In comparison to the ca 610 vertebrate species found in continental Chile, only 24 species (3.9%) have invaded the country. Except for two bird and two or three mammal species that expanded their range and crossed the Andean Ranges from Argentina, the remaining 20 species were all introduced, or aided, by humans. Of the 24 invader species that currently occur in Chile, 11 (46%) were first introduced in central Chile, two (8%) in the northern part of the country, nine (38%) in the southern part, and two (8%) in Juan Fernández Archipelago. For ten (42%) of those species there is no information about their effects on the native flora, vegetation, or fauna. For eight species (33%), the information regarding the effects of the invaders is anecdotal. For six species (25%), there is adequate quantitative documentation available on their effects. Of a total of seven convincingly repo rted cases, two involve positive effects (increase in the prey base for native predators) and five have negative effects, of which three are on native vegetation and the remaining two on native fauna.     

Assessing the potential range expansion of the exotic monk parakeet in Spain

In this study we determine favourable areas for the monk parakeet, Myiopsitta monachus , in peninsular Spain to account for its current distribution and predict its future course according to its potential range. We applied a favourability function based on generalized linear models using the presence/absence of breeding colonies of the species and the values of a set of variables on the 5167 UTM 10 × 10 km squares comprising the study area. We calculated the factor of distribution change in presences predicted by the model, and grouped the variables into explanatory factors performing a variation partitioning to assess the explanatory power of each factor. Our model included six predictors to explain the presence and absence of the species. These predictors were grouped into three factors: human activity, climate, and topography. Purely human influences accounted for 63.8% of the variation of the final model, while topographical variables explained 15.2% and climate only 5.7%. We obtained a high distribution change factor in which the presences of the species were predicted to increase between two- and sevenfold. Taking into account highly favourable squares, we conclude that the species is still absent in more than 72% of potential settlement areas, and thus we expect a continuous increase in the distribution of the species. Human activity is the main force moulding the distribution of the species, and lies behind its fast expansion, which is not only active, but is also passive via releases and escapes. We identified the areas of likely future expansion of the exotic monk parakeet in Spain. The pest status of the species in its native range, together to its distribution trend, should be taken into account by wildlife agencies to consider options for management.