Evaluations of the potential distribution of invasive species can increase the efficiency of their management by focusing prevention measures. Generally, ecological models are built using occurrence data from a species' native range to predict the distribution in areas that the species may invade. However, historical and geographical constraints can limit a species' native distribution. Genetic Algorithm for Rule-set Production (GARP), an ecological niche modeling program, was used to predict the potential distribution of the invasive, freshwater New Zealand mudsnail, Potamopyrgus antipodarum, in Australia and North America. We compared the strength of the predictions made by models built with data from the snail's native range in New Zealand to models built with data from the locations invaded by the species. A time-series analysis of the Australian models demonstrated that range-of-invasion data can make better predictions about the potential distribution of invasive species than models built with native range data. Large differences among the model forecasts indicate that uncritical choice of the data set used in training the GARP models can result in misleading predictions. The models predict a large expansion in the range of P. antipodarum in both Australia and North America unless prevention measures are implemented rapidly.

Species assemblages of systems of islands and other fragmented habitats frequently show a "nested-subset" structure in which the biotas of sites with low species richness are non-random subsets of the biotas of richer sites. Much literature suggests that extinction is more likely to produce strongly nested patterns than colonization, although very few experiments have been conducted on the generation of nested-subset patterns. Here, we describe an experiment on nestedness of benthic invertebrates occupying rocks in the littoral zone of a lake in western Victoria, Australia. Data collected from previous work indicated that the invertebrate biotas of rocks were nested. We used initially defaunated, different-sized habitat patches (half house-bricks, full house-bricks, double house-bricks) and followed the time-course of occupation to assess whether nested-subset patterns would emerge, and whether extinction or colonization best accounted for the patterns. We predicted that nestedness would increase through time up to the end of the experiment. This was found to be the case with colonization dominating the establishment of a strongly nested system; extinction appeared to be of relatively little importance over the duration of the experiment. These results suggest that at least in some circumstances, differential colonization may be influential in producing nested-subset patterns but experiments conducted over longer times may be needed to more completely understand the respective roles of extinction and colonization in generating nested-subset patterns in this system.

The complex nature of ecosystems with multiple invaders requires whole-system approaches to ecosystem management. Undesirable, unintended secondary effects may occur if interspecific interactions are ignored. Although degraded riparian zones urgently need effective restoration, broad-scale removal of introduced tree species (e.g., willows [Salix spp.]) and fencing of riparian zones to exclude livestock may facilitate spread of the invasive aquatic grass Glyceria maxima in southeastern Australia. We recorded occurrence of the grass at riparian sites with different amounts of woody vegetation, including willows, and monitored spread for 2 years in locations with and without livestock. Glyceria maxima occurred more frequently at sites with little or no woody riparian vegetation.Larger, older patches fenced from livestock spread fastest. Analyses of costs of controlling G. maxima with herbicide showed that it is more cost-effective to eradicate small patches than large patches if locations are known. However, the cost per m 2 reduction in patch size is cheaper for larger patches. We recommend that small, young patches should be eradicated as soon as detected and show that spread of large source patches can be controlled effectively with continued spraying over several years. If restoration of waterways is to succeed, riparian management strategies must recognize connectivity between riparian and freshwater habitats.

Aquatic invasive species cause deleterious environmental and economic impacts, and are rapidly spreading through ecosystems worldwide. Despite this, very few data sets exist that describe both the presence and the absence of invaders over long time periods. We have used Geographical Information Systems (GIS) to analyse timeseries data describing the spread of the freshwater invasive New Zealand mudsnail, Potamopyrgus antipodarum, in Victoria, Australia, over 110 years. We have mapped the snail's spread, estimated the percentage of stream length invaded through time, calculated the functional form of the spread rate, and investigated the role that the two proposed vectors -fish stocking and angling -have had in this invasion. Since it was first found in 1895, P. antipodarum has expanded its range in Victoria and now occurs throughout much of the southern and central areas of the state. The north of the state is relatively less invaded than the south, with the division corresponding approximately to the presence of the Great Dividing Range. We show that the snail's range has been increasing at an approximately exponential rate and estimate that 20% of total Victorian stream length is currently invaded. We also show that using long-term data can change the outcome of analyses of the relationship between vectors of spread and invasion status of separate catchments. When our time-series data were aggregated through time, the total numbers of fish stocking events and angling activity were both correlated with invasion. However, when the time-series data were used and the number of fish stocking events calculated up until the date of invasion, no relationships with stocking were found. These results underline the role that time-series data, based on both presences and absences, have to play when investigating the spread of invasive species.

With the expected increase in the spread of invasive species, examination of factors controlling distributions at multiple spatial scales and ecological modelling of their potential distributions are important analyses for informed decision-making. The scale-dependence of mechanisms influencing invasion by non-native species has been shown previously, indicating that studies of key factors affecting invasive species distributions at multiple spatial scales are critical for successful management. Freshwater systems are particularly vulnerable to invasive species, yet few studies have examined the environmental factors influencing distributions of invasive species at multiple spatial scales. We examined the effect of environmental variables on the predicted distribution of the invasive aquatic grass Glyceria maxima over continental, regional and local scales in Australia. We undertook an initial critical evaluation of which predictor variables were most appropriate to use at each scale, largely considering prior knowledge. On a continental scale, climatic, topographic and hydrological variables predicted well the potential distribution of G. maxima, identifying temperate regions as most susceptible to invasion. The regional analysis found that dense, woody, riparian vegetation has a strong negative impact on the occurrence of G. maxima, especially at intermediate elevations. The invasive grass was found less often on biotite granite and on fluvial geology. At a local scale, occurrence of G. maxima was related positively to soil phosphorus and nitrogen, and negatively related to soil organic carbon. The identification of key factors affecting invasive species distributions at multiple spatial scales will inform prevention schemes, assist targeted field sampling for the development of monitoring programs, and allow prioritization of control methods.