Measuring stoat (

Comparisons were made of density indices of free-living populations of ship rats (Rattus rattus) in mixed forest in New Zealand by using footprint tracking tunnels and two kill-trapping methods. Tracking tunnels and snap-trap removal indices of rat densities showed similar trends when run on a 9 ha trapping grid, although immigration onto the grid occurred, thus violating one of the assumptions of the analysis. Tracking rates and snaptrap capture rates were not significantly correlated when run along a trapping line for a 12 month period, although tracking rates and the total number of rats caught in a trapping session were significantly correlated. Time series analysis showed that rat density indices from tracking tunnels and Fenn traps were significantly correlated when run for 27 consecutive months in a rat population with moderate density, but were not correlated in a low density rat population. The findings highlight the importance of habitat, sample size and target species behaviour in influencing relative density indices obtained from tracking tunnels, snap-traps and Fenn traps. Given the widespread use of rodent tracking tunnels in New Zealand, we suggest that tracking tunnels should only be used to compare relative abundance within similar habitat types, and should always be complemented with a second density index. The relationship between the commonly used density indices and true rodent population density requires urgent attention.     

Calibration of tunnel tracking rates to estimate relative abundance of ship rats (

Ship rat (Rattus rattus) and mouse (Mus musculus) density and habitat use were estimated by snap trapping and tracking tunnels at Kaharoa in central North Island, New Zealand. Eighty-one ship rats were caught in an effective trapping area of 12.4 ha. Extinction trapping gave an estimated density of 6.7 rats ha(-1) (6.5-7.8 rats ha(-1), 95% confidence intervals). A linear relationship existed between ship rat trapping and tracking rates. Estimating the density of mice was impossible because trapping rates increased rather than decreased during the experiment. Comparisons of density from tracking and trapping rates of mice may be confounded by interference by rats, but this requires further investigation.     

Effects of habitat complexity on forest beetle diversity: do functional groups respond consistently?

We examined the responses of a beetle assemblage to habitat complexity differences within a single habitat type, Sydney sandstone ridgetop woodland, using pitfall and flight‐intercept trapping. Six habitat characters (tree canopy cover, shrub canopy cover, ground herb cover, soil moisture, amount of leaf litter, and amount of logs, rocks and debris) were scored between 0 and 3 using ordinal scales to reflect habitat complexity at survey sites. Pitfall trapped beetles were more species rich and of different composition in high complexity sites, compared with low complexity sites. Species from the Staphylinidae (Aleocharinae sp. 1 and sp. 2), Carabidae (Pamborus alternans Latreille), Corticariidae (Cartodere Thomson sp. 1) and Anobiidae (Mysticephala Ford sp. 1) were most clearly responsible for the compositional differences, preferring high complexity habitat. Affinities between general functional groupings of pitfall‐trapped beetles and habitat variables were not clear at a low taxonomic resolution (family level). The composition and species richness of flight‐intercept‐trapped beetles were similar in high and low complexity sites. Our study demonstrates that discrete responses of the various functional groups of beetles are strongly associated with their feeding habits, indicated by differing habitat components from within overall composite habitat complexity measures. Although habitat preferences by beetle species may often reflect their foraging habits, clarification of the causal mechanisms underpinning the relationships between habitat complexity and beetles are critical for the development of general principles linking habitat, functional roles and diversity.     

Traits reveal how habitat‐quality gradients structure small mammal communities in a fragmented tropical landscape

Understanding the relationships among community structure, vegetation structure and availability of food resources are a key to unravelling the ecological processes that structure biological communities. In this study, we tested (i) whether the composition of small mammal communities changed across gradients in habitat quality in tropical forest fragments, and (ii) whether any observed change could be explained by the functional traits of species. We sampled 24 trapping grids in fragments of semi‐deciduous forest, in each of two 6‐month periods. We considered each trapping grid as a sampling unit, for which we collected three datasets: an environmental matrix (vegetation structure and food resource availability), the abundance of small mammal species (community structure) and a matrix of functional traits (ecological and morphological traits which express tolerance to habitat disturbance and trophic guild). We used an RLQ approach to evaluate the association between traits and environmental gradients. Forest‐specialist and scansorial–arboreal species were associated with more complex habitat that had greater litter and canopy cover and more fallen logs. In relation to trophic guilds, granivore (fruit seeds), insectivorous and omnivorous species were also associated with higher complexity habitat, while frugivores were associated with shrub cover and availability of fruits. We conclude that functional traits (habitat use, use of vertical strata and diet) provide valuable insights into the distribution of small mammals along gradients of habitat quality in tropical forest fragments. We highlight that communities studies in fragmented landscapes should investigate the different components of biodiversity not only in landscape‐scale but also in habitat scale. Abstract in Portuguese is available with online material.     

Small rodents, their habitats, and the effects of flooding at Wicken Fen, Cambridgeshire

The habitat preferences of small rodents were studied by live trapping methods at Wicken Fen, Cambridgeshire, a relict area of East Anglian fenland. The study sites were chosen to cover areas of managed fields, dominated by sedge ( Cladium mwiscus ) or by litter (grasses with sedges); the adjacent fen carr "bush growth"; and an area of unmanaged sedge. Clethrionomys glareolus is the commonest rodent species, occurring at relatively high densities, and closely associated with sedge growth. It is ubiquitous in unmanaged sedge but in managed sedge and litter field areas there is a marked preference for the field/fen carr transition where sedge growth is not cut. Thick sedge seems to afford the optimum habitat for this species probably because of the three-dimensional vegetation structure which provides dense ground cover with a natural thatch of dead leaves; this decays only slowly, even in succeeding fen carr. Sedge fields provide a less stable habitat and recolonization of a harvested field by Clethrionomys only began after eight months of sedge regrowth. Micromys minutus are caught only in sedge and litter. Apodemus sylvaticus seem to show no marked habitat preference but there are some data which suggest that high Clethrionomys densities can affect Apodemus distributions locally. Microtus agrestis prefers grassy patches within sedge fields; trap success points tending to be associated with the presence of Calamagrostis canescens. Microtus avoids fen carr and unmanaged sedge and is generally caught more often in litter fields than in sedge fields; however, this preference seems to disappear at the end of the Clethrionomys breeding season. During flooding, Clethrionomys found refuge in the dense sedge and sedge/carr transition habitats; prolonged flooding caused a decline in numbers of Clethrionomys and the elimination of Microtus , while the distribution of Apodemus was apparently unaffected.     

Leaf litter and irrigation can increase seed germination and early seedling survival of the recalcitrant‐seeded tree Beilschmiedia miersii

Although regeneration of recalcitrant‐seeded tree species can be affected by prolonged drought, especially in Mediterranean regions, little is known about the response of such species to varying site conditions. A field experiment was performed to determine the effect of irrigation and leaf litter cover on seed germination and early seedling survival of the vulnerable recalcitrant‐seeded tree Beilschmiedia miersii (Lauraceae). Two levels of irrigation (non‐irrigated and irrigated units) and three levels of leaf litter depth (0, 5 and 12 cm) were applied to 72 groups of 30 seeds along a wet ravine of the Coastal Range of Central Chile, equally distributed across sites with different levels of canopy cover. Seed germination was significantly increased by irrigation only under closed‐canopy cover, and by leaf litter cover (>5 cm) under all canopy conditions. The effect of leaf litter on germination increased with canopy openness, while the effect of irrigation did not show any tendency. Meanwhile, early seedling survival was significantly increased by irrigation under intermediate canopy cover, and by leaf litter (>5 cm) under closed‐canopy cover. As a result of its overall positive effect on germination, leaf litter should be maintained within B. miersii communities, particularly under intermediate to closed‐canopy conditions, where it can also increase early seedling survival, and both seed germination and early seedling survival might be increased through additional water inputs. The presence of leaf litter might help retaining such inputs, prolonging their effect on regeneration of B. miersii communities. We see this as a baseline assessment of regeneration and persistence that needs further testing on species with similar traits, given the expected increase in the frequency and length of dry periods into the future.     

Do trappers understand marten habitat?

Previous studies of the effects of fur trapping on marten populations have not considered habitat variation and how trappers use available habitat. We investigated the behavior of fur trappers with respect to roads, waterways, and the forest habitats on trap lines, using registered trap lines in northern Ontario as a study system. The objectives of this study were to 1) develop models for predicting trap location based on access and habitat features, 2) determine whether trappers target the same habitat preferred by American marten, and 3) investigate effects of spatial resolution on predictive models, using a geographic information system (GIS) for coarse resolution variables and direct forest mensuration for fine resolution variables. Distance to roads and water were by far the most influential factors in logistic models for predicting trap presence, accounting for 51.2–61.7% of the observed deviance. At a coarse spatial resolution, trappers selected sites that were close to vehicular access, and in older mixed wood forest stands. Similarly, at a coarse resolution, marten selected old stands, but dominated by coniferous trees. At a finer spatial resolution, trappers selected sites with high basal area of trees, pronounced proportion of black spruce, high canopy cover, and high density of coarse woody debris, consistent with previous studies on marten habitat selection at a fine resolution. Although coarse resolution models are easily applicable because of the wide availability of GIS land cover data, fine resolution models had greater predictive power when considering habitat variables. By quantifying trapper behaviors, these results suggest that the effectiveness of marten sanctuaries used in forest management depend not only on the age and species composition of forest stands left unlogged, but also on the degree to which they are accessible to trappers. © 2012 The Wildlife Society.     

Bioinsecticide and leaf litter combination increases oviposition and reduces adult recruitment to create an effective ovitrap for Culex mosquitoes

Mosquito egg traps, aquatic habitats baited with oviposition attractant and insecticide, are important tools for surveillance and control efforts in integrated vector management programs. The bioinsecticide Bacillus thuringiensis subsp. israelensis (Bti) is increasingly used as an environmentally friendly alternative to chemical insecticides and the combination of Bti with a simple oviposition attractant like leaf litter to create an effective egg trap seems appealing. However, previous research suggests that Bti may itself alter oviposition, and that leaf litter may dramatically reduce Bti toxicity. Here we present results from field experiment designed to link the effects of litter and Bti on mosquito oviposition habitat selection and post‐colonization survival to production of adult mosquitoes. Tripling litter increased Culex spp. oviposition nearly nine‐fold, while Bti had no effect on oviposition. Neither factor altered egg survival, thus larval abundance reflected the effects of litter on oviposition. Both Bti and litter reduced larval survival by ～60%. We found no evidence that increased litter reduced Bti toxicity. Adult production was dependent upon both litter and Bti. In the absence of Bti, effects of litter on oviposition translated into three‐fold more adults. However, in the presence of Bti, initial increases in oviposition were erased by the combined negative effects of Bti and litter on post‐colonization survival. Thus, our study provides field evidence that combined litter and Bti application creates an effective ovitrap. This combined treatment had the highest oviposition and the lowest survival, and thus removed the greatest number of mosquitoes from the landscape.     

Optimal habitat conditions for the globally threatened Aquatic Warbler Acrocephalus paludicola in eastern Poland and their implications for fen management

To identify optimal habitat for the Aquatic Warbler Acrocephalus paludicola, a flagship species of fen mires, we related numbers of singing males to habitat variables in all core breeding sites in eastern Poland. The density of male Aquatic Warblers increased with increasing ground cover by water and mosses and litter layer height, and was highest where vegetation was 60–90 cm tall. Male densities also increased with the biomass of arthropods > 10 mm length, estimated by sweep netting, and with the abundance of spiders, estimated by pan trapping. We suggest that habitat management should take into account species‐specific morphological adaptations, nest safety and arthropod productivity. Prevention of vegetation succession is a conservation priority for open fen mires. However, modern management practices to achieve this, especially mowing using tracked vehicles, should be evaluated and optimized to ensure that such practices do not adversely affect the long‐term development of moss cover and litter structure.     

Habitat use of the ocelot (Leopardus pardalis) in Brazilian Amazon

Amazonia forest plays a major role in providing ecosystem services for human and sanctuaries for wildlife. However, ongoing deforestation and habitat fragmentation in the Brazilian Amazon has threatened both. The ocelot is an ecologically important mesopredator and a potential conservation ambassador species, yet there are no previous studies on its habitat preference and spatial patterns in this biome. From 2010 to 2017, twelve sites were surveyed, totaling 899 camera trap stations, the largest known dataset for this species. Using occupancy modeling incorporating spatial autocorrelation, we assessed habitat use for ocelot populations across the Brazilian Amazon. Our results revealed a positive sigmoidal correlation between remote‐sensing derived metrics of forest cover, disjunct core area density, elevation, distance to roads, distance to settlements and habitat use, and that habitat use by ocelots was negatively associated with slope and distance to river/lake. These findings shed light on the regional scale habitat use of ocelots and indicate important species–habitat relationships, thus providing valuable information for conservation management and land‐use planning.     

Evaluation of macrofaunal effects on leaf litter breakdown rates in aquatic and terrestrial habitats

Abstract Decomposition of the organic matter is a key process in the functioning of aquatic and terrestrial ecosystems, although different factors influence processing rates between and within these habitats. Most patterns were described for temperate regions, with fewer studies in tropical, warmer sites. In this study, we carried out a factorial experiment to compare processing rates of mixed species of leaf litter between terrestrial and aquatic habitats at a tropical site, using ?ne and coarse mesh cages to allow or prevent colonization by macroinvertebrates. The experiment was followed for 10 weeks, and loss of leaf litter mass through time was evaluated using exponential models. We found no interaction between habitat and mesh size and leaf litter breakdown rates did not differ between ?ne and coarse mesh cages, suggesting that macroinvertebrates do not influence leaf litter decomposition in either habitat at our studied site. Leaf breakdown rates were faster in aquatic than in terrestrial habitats and the magnitude of these differences were comparable to studies in temperate regions, suggesting that equivalent factors can influence between‐habitat differences detected in our study.     

Do rats mind getting their feet dirty? Observing the behaviour of ship rats (Rattus rattus) towards footprint tracking tunnels

Monitoring rat populations by standard tracking tunnels assumes that rats do not avoid treading on the tracking ink. We observed the behaviour of 20 rats in four groups of five, spending 2 nights each (40 trials) in large observation pens. In only 10 of 40 trials did the rat run through a tunnel without hesitation on first encounter, while in four trials a rat approached the tunnel up to 35 times but refused to run though it all night. Most rats approached and turned away between two and 34 times before running through. Observations through transparent tunnels of rats pausing for a mean of 3.2 s before stepping on the ink suggest that they probably could detect it, but they usually chose to ignore it. Experience of encountering the ink pad inside a black tunnel did not deter rats from running across another one, and would not affect indices of rat abundance reaching levels high enough to trigger conservation concern, but variation in behavioural reactions to tracking tunnels could possibly affect the detection rate of rats at low density.     

Experimental manipulation reveals the importance of refuge habitat temperature selected by lizards

Refuges provide shelter from predators, and protection from exposure to the elements, as well as other fitness benefits to animals that use them. In ectotherms, thermal benefits may be a critical aspect of refuges. We investigated microhabitat characteristics of refuges selected by a heliothermic scincid lizard, Carlia rubrigularis, which uses rainforest edges as habitat. We approached lizards in the field, simulating a predator attack, and quantified the refuge type used, and effect of environmental temperatures (air temperature, substrate temperature and refuge substrate temperature) on the amount of time skinks remained in refuges after hiding (emergence time). In respone to our approach, lizards were most likely to flee into leaf litter, rather than into rocks or woody debris, and emergence time was dependent on refuge substrate temperature, and on refuge substrate temperature relative to substrate temperature outside the refuge. Lizards remained for longer periods in warmer refuges, and in refuges that were similar in temperature to outside. We examined lizard refuge choice in response to temperature and substrate type in large, semi‐natural outdoor enclosures. We experimentally manipulated refuge habitat temperature available to lizards, and offered them equal areas of leaf litter, woody debris and rocks. When refuge habitat temperature was unmanipulated, lizards (85%) preferred leaf litter, as they did in the field. However, when we experimentally manipulated the temperature of the leaf litter by shading, most skinks (75%) changed their preferred refuge habitat from leaf litter to woody debris or rocks. These results suggest that temperature is a critical determinant of refuge habitat choice for these diurnal ectotherms, both when fleeing from predators and when selecting daytime retreats.     

Fine‐scale microhabitat selection for dense vegetation in a heathland rodent,Rattus lutreolus: Insights from intraspecific and temporal patterns

Abstract Vegetation is a dynamic habitat component and successional changes in vegetation structure can lead to concomitant changes in the communities of animals living in a particular area. Heathland rodents are a classic example, with vegetation at different ages post fire being dominated by different species. While broad associations are often demonstrated between the distribution and abundance of species and vegetation structure, the causal relationships are poorly understood. Studies of temporal and sex‐ or age‐specific patterns can provide strong insights into the processes underling patterns of habitat selection. In an attempt to better understand the mechanistic links between rodent successional patterns and vegetation structure in heathlands, we conducted a detailed study of microhabitat use by the swamp rat, Rattus lutreolus, in a native heathland in south‐eastern Australia. Rattus lutreolus typically occurs in late‐succession heath and is frequently associated with high vegetation density. Our assessment of vegetation at trapping stations, and also along trails used by the animals (using the spool‐and‐line tracking technique), revealed strong selection by the rats for dense vegetation by both day and night. The spool‐and‐line tracking approach revealed distinct intraspecific and temporal patterns. During the day, females foraged in vegetation of much higher density than did juveniles, with males behaving intermediately. During the night, however, all animals selected dense vegetation irrespective of sex or age, although the mean density of vegetation selected during the night was lower than it was during the day. These patterns were independent of daily maximum and minimum air temperature and were therefore unlikely to be related to microclimate. We propose instead that high vegetation density acts as a source of protection from predators, allowing R. lutreolus to forage safely both by day and by night.     

Litter‐trapping plants: filter‐feeders of the plant kingdom

Litter‐trapping plants have specialized growth habits and morphologies that enable them to capture falling leaf litter and other debris, which the plants use for nutrition after the litter has decayed. Litter is trapped via rosettes of leaves, specially modified leaves and/or upward‐growing roots (so‐called ‘root baskets’). Litter‐trappers, both epiphytic and terrestrial, are found throughout the tropics, with only a few extra‐tropical species, and they have evolved in many plant families. The trapped litter mass is a source of nutrients for litter‐trapping plants, as well as food and housing for commensal organisms. Despite their unique mode of life, litter‐trapping plants are not well documented, and many questions remain about their distribution, physiology and evolution.–© 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 179 , 554–586.     

Habitat selection of the long‐nosed bandicoot,Perameles nasuta (Mammalia,Peramelidae), in a patchy urban environment

Habitat selection in an omnivorous marsupial, the long‐nosed bandicoot, Perameles nasuta Geoffroy, was investigated in an urban environment with both natural and highly modified habitats at North Head, New South Wales, Australia. Habitat use at both macro‐ and microhabitat scales was determined using live‐trapping, and P. nasuta was shown to be a habitat specialist at this site. At night, animals used open grass macrohabitats disproportionately more for foraging than other macrohabitats. Trap‐revealed macrohabitat use was supported by radiotracking three males. Lack of understorey and absence of leaf litter were the major microhabitat features affecting habitat choice, although soil type probably also had some effect. Open areas may provide a more abundant and/or accessible food supply for P. nasuta, although better manoeuvrability or increased visibility to detect predators may also be important. Diurnal nest sites, located using radiotracking, were primarily in dense scrub vegetation, often comprising introduced species of plants. The dependence of P. nasuta on: (i) dense undergrowth for diurnal nesting and temporary nocturnal sheltering; and (ii) open areas for foraging indicates the importance of conserving a mosaic of open and dense vegetation to ensure the continued persistence of this endangered population at North Head.     

Habitat utilization patterns of sympatric populations of Pseudomys gracilicaudatus and Rattus lutreolus in coastal heathland: A multivariate analysis

Abstract Habitat usage characteristics of two species of native murid rodents, Pseudomys gracilicaudatus and Rattus lutreolus were investigated on an area of coastal heathland at Myall Lakes National Park. A grid of 151 trap stations comprising 17 traplines was positioned across a mosaic of habitats. At each trap station 19 structural vegetation and physical variables known to affect the microdistribution of small mammals were measured. Multivariate statistical procedures identified those microhabitat variables that contribute to individual species' habitat use and habitat partitioning, and reduce potential competition for space. Cluster analysis classified trap stations into one of six habitat types that were mapped on the study area, identifying a heterogeneous assemblage of interlocking habitats. The pattern is a consequence of topographic variation on the site and, to a lesser extent, its fire history. Trapping results show P. gracilicaudatus and R. lutreolus exhibit similar macrohabitat selection, preferring topographically low habitats, with both species predominantly occupying short dense heath with dense sedge cover. The high overlap in macrohabitat use is greatly reduced when considered trap station by trap station, so that discriminant function and multiple regression analyses demonstrate marked microhabitat selection. Elevation was a highly significant variable, accounting for 41% and 27% of the variance in the habitat used by P. gracilicaudatus and R. lutreolus, respectively. This variable represents a soil moisture gradient that determines changes in the floristic and structural components of the biotic environment. Two other structural vegetation variables and vegetation height contributed 30% of the variance in P. gracilicaudatus distribution. Sedge cover was found to be significant and explained 13% of the variance in R. lutreolus distribution. Within-habitat separation was explained best with a linear combination of variables in a discriminant function, rather than by any single variable. Differential microhabitat selection, interference competition and diet separation appear to be the major factors facilitating coexistence of these two species.     

The effectiveness of poison bait stations at reducing ship rat abundance during an irruption in a Nothofagus forest

Abstract

Ship rats exhibit large increases in abundance (irruptions) following heavy beech seedfall in New Zealand's Nothofagus forests. Predation by rats at high density severely damages native fauna populations. In 2006 the Department of Conservation undertook a management experiment in the Eg‐linton Valley to see if they could protect endangered species during a rat irruption. Poison (0.15% 1080, followed by 0.0375% coumatetralyl, or Racumin®) was laid in bait stations, and the consequences for rat abundance and survival were estimated. All 10 radio‐tagged rats died, suggesting that 1080 had a high impact on the rat population. The two rats that made the smallest daily movements survived longer than the others. Live trapping documented a reduced abundance of rats within the poison area (450 ha) after 1 month of poisoning. However, after 4 months of poisoning, the abundance of rats had begun to recover. Further investigation is needed on acceptance of Racumin® to rats, optimum spacing of bait stations for rats, and bait competition between rats and mice when densities of both species are high.     

Habitat use of American eel (Anguilla rostrata) in a tributary of the Hudson River,New York

American eel Anguilla rostrata populations are declining over much of their native range. Since American eels spend extended periods in freshwater, understanding their habitat requirements while freshwater residents is important for the management and conservation of this species. As there is little information on American eel habitat use in streams, the ontogenetic, diel, and seasonal habitat use as well as habitat selectivity of three size groups (i.e. ≤199 mm total length, 200–399 mm, ≥400 mm) of eel were examined in a tributary of the Hudson River. American eels in Hannacroix Creek exhibited ontogenetic, diel, and seasonal variation in habitat use as well as habitat selection. During both summer and autumn all sizes of American eels used larger substrate and more cover during the day. American eels ≤199 mm exhibited the strongest habitat selection, whereas eels 200–399 mm exhibited the least. During the autumn all sizes of American eels occupied slower depositional areas where deciduous leaf litter accumulated and provided cover. This may have important implications for in‐stream and riparian habitat management of lotic systems used by American eel.     

The interaction between propagule pressure,habitat suitability and density‐dependent reproduction in species invasion

Seedling recruitment limitations create a demographic bottleneck that largely determines the viability and structure of plant populations and communities, and pose a core restriction on the colonization of novel habitat. We use a shade‐tolerant, invasive grass, Microstegium vimineum, to examine the interplay between seed and establishment limitations – phenomena that together determine recruitment success but usually are investigated individually. We add increasing amounts of seed to microhabitats containing variable levels of leaf litter thickness – with reduced leaf litter simulating disturbance – to investigate whether reduced seed limitation overcomes the establishment limitation posed by litter cover. We do this across gradients in understory light, moisture and temperature, and quantify germination, survival, and then per capita adult biomass and reproduction in order to understand the implications for invasion across the landscape. We find that the combined effects of seed and establishment limitation influence recruitment; however, propagule pressure overwhelms the inhibitory effects of leaf litter thickness. Leaf litter reduces germination by 22–57% and seedling survival by 13–15% from that observed on bare soil. However, density‐dependent reproduction compensates as 1–3 plants can produce far more seeds (approx. 525) than are required for persistence. As such, just a few plants may establish in understory forest habitat and subsequently overwhelm establishment barriers with copious propagule production. These results, for a widespread, invasive plant, are consistent with the emerging perspective for native plants that seed and establishment limitation jointly influence recruitment. The ability for an exotic plant species to compensate for low population densities with high per capita seed production, that then overrides establishment limitations, makes its invasive potential daunting. Further work is required to test if this is a common mechanism underlying plant invasions.