Gallardo et al. Application of bioclimatic models coupled with network analysis for risk assessment of the killer shrimp, Dikerogammarus villosus, in Great Britain. Biol Invasions (2012) 14:1265–1278 DOI 10.1007/s10530-011-0154-0
Freshwater systems are particularly prone to invasive species. Propagules lead to established populations when the invaded system matches the species’ ecological requirements. The environmental match between native and foreign systems are commonly modeled using SDM, which climate as the main driver. Dispersal of established species are limited by hydrological connectivity; this can be modeled as a network. The authors combine these two approaches to model the potential spread of killer shrimp in Great Britain, which is currently established in 3 confined locations.
First, areas in Great Britain of climatic similarity to the native range were identified. These areas are considered high risk. A total of 248 European occurrences and a set of 6 bioclimatic factors were used to build a 2 class support vector machine. The data set was split 80/20 into training/testing. Pseudo-absences were drawn from a European-wide background, and used to evaluate the model via AUC. The minimum training presence was also reported. The SVM model was projected onto Europe, where probabilities could be derived via Platt’s (ie. fit a logistic regression model to the estimated decision values). Models were converted to binary outcomes based on the threshold that maximized specificity and sensitivity. Hydrological networks were used to model 3 different speeds of dispersal: high (100km/yr) medium (60km/yr) and low (20km/yr). Areas that would be colonnaded within 5 years were considered highest risk.
SVM had a high accuracy score (AUC=0.97), in the minimum training presents was relatively low (11%). Based on the model, habitat suitability was greatest altitude below 500 m, maximum temperature between 20 and 30°C, minimum temperature between -5 and 5°C and annual precipitation lower than 1000 mm. Unfortunately, 44% of Great Britain showed climate suitability higher than 50%. Regardless of speed, the network analysis indicated the north east part of the study site is at high risk of being invaded in the next 5 year. Areas of highest suitability within Great Britain already support a well-established and abundant population of a Ponto-Caspian species (zebra mussel).