Abstract
Biological invasions are one of the major causes of biodiversity loss worldwide. In spite of human aided (anthropogenic) dispersal being the key element in the spread of invasive species, no framework published so far accounts for its peculiar characteristics, such as very rapid dispersal and independence from the existing species distribution. We present a new method for modelling biological invasions using historical spatio-temporal records. This method first discriminates between data points of anthropogenic origin and those originating from natural dispersal, then estimates the natural dispersal kernel. We use the expectation-maximisation algorithm for the first step; we then use Ripley’s K-function as a spatial similarity metric to estimate the dispersal kernel. This is done accounting for habitat suitability and providing estimates of the inference precision. Tests on simulated data show good accuracy and precision for this method, even in the presence of challenging, but realistic, limitations of data in the invasion time series, such as gaps in the survey times and low number of records. We also provide a real case application of our method using the case of Litoria frogs in New Zealand. This method is widely applicable across the field of biological invasions, epidemics and climate change induced range shifts and provides a valuable contribution to the management of such issues. Functions to implement this methodology are made available as the R package Biolinv (https://cran.r-project.org/package=Biolinv).
Highlights
Biological invasions are increasingly common phenomena due to the intensification of transportation of both people and goods [1]
There are a number of situations in which this type of model is suboptimal: (1) when the source of propagules is located in the native distribution range, (2) when dispersal is triggered by a request from the receiving end, or (3) when the speed and range of anthropogenic dispersal is much higher than the natural counterpart
Anthropic dispersal of invasive species. We used this method on the real case scenario of the introduction of three species of Litoria frogs from Australia to New Zealand: L. aurea (Green and Golden Bell Frog), L. raniformis (Growling Grass Frog) and L. ewingii (Brown Tree Frog) have been introduced by acclimatisation societies in the 19th century and currently, L. aurea occupies the northern part of the North Island while L. raniformis and L. ewnigii are found across the two main islands
Summary
Biological invasions are increasingly common phenomena due to the intensification of transportation of both people and goods [1]. We tested our method on simulated data to assess whether the performance of all steps of the process are accurate and reliable, as well as resilient to variations in sample size, intensity and pattern of anthropogenic dispersal, and ecological niche width, and survey imperfections– a key feature is that the computations remain tractable even when there are gaps in data collection, and uncertainty about the exact time of the dispersal events We used this method on the real case scenario of the introduction of three species of Litoria frogs from Australia to New Zealand: L. aurea (Green and Golden Bell Frog), L. raniformis (Growling Grass Frog) and L. ewingii (Brown Tree Frog) have been introduced by acclimatisation societies in the 19th century and currently, L. aurea occupies the northern part of the North Island while L. raniformis and L. ewnigii are found across the two main islands. Unwanted Litoria adults are released into freshwater bodies aiding the spread of these species
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