Rates of expansion of invasive cane toads in New South Wales

Geographical variation in abiotic and biotic conditions can significantly affect the rate that an invasive species expands its range. The colonisation of Australia by cane toads (Rhinella marina) has attracted extensive research, but mostly in tropical regions rather than cooler climatic zones. We assembled multiple datasets to characterise the historical spread of toads at their southern (cool-climate) invasion front in north-eastern New South Wales (NSW). Perhaps because toads are relatively easy to find, visual and acoustic surveys appear to be as effective as eDNA-based surveys in detecting the species’ presence. Expansion of the toads’ range in NSW has occurred through the establishment of satellite populations as well as by growth of the range-core. Overall rates of spread have been more than tenfold lower than on the tropical front (means of 50 km per year), and in some decades, the toads’ southern range has declined rather than expanded. Overall rates of spread since 1970 have accelerated to the south (through coastal habitats), but not to the west (into montane areas). The toads’ range has expanded most rapidly in decades with dry, warm weather conditions, but predicted future changes to climate are likely to have only minor effects on rates of toad spread. Understanding historical patterns of toad invasion in NSW can clarify probable future spread, and hence identify priority areas for control programs.

Methods
Data on the distribution of invasive cane toads in New South Wales was collated from all available sources, to quantify rates of expansion and to identify correlates of that rate of spread. We also conducted pilot studies to comapre alternative emthods of detecting invasion-front populations of toads in the field.

Usage Notes
The Excel sheet provides data for 342 points that represent the edges of the toad invasion front across a series of decades for which data are available. The dataset also includes climatic and habitat attributes of each of those sites, as determined from relevant GIS layers, as well as estimates of interdecadal changes in the location of the toads' range-edge.

地理环境的非生物和生物条件的变化对入侵物种扩张范围的速率具有显著影响。甘蔗蟾蜍（Rhinella marina）在澳大利亚的殖民化引起了广泛的研究关注，但主要集中在对热带地区的探讨，而非较凉爽的气候区域。我们汇集了多个数据集，以表征蟾蜍在其南部（凉爽气候）入侵前沿——新南威尔士州（NSW）东北部的历史扩散情况。或许由于蟾蜍相对易于发现，视觉和声学调查似乎与基于环境DNA的调查一样有效，用于检测该物种的存在。蟾蜍在NSW的扩张范围通过卫星群体的建立以及范围核心的增长而实现。总体扩散速率比热带前线的速率低十倍以上（平均每年50公里），在某些几十年中，蟾蜍的南部范围有所缩减而非扩张。自1970年以来，总体扩散速率向南（通过沿海栖息地）加速，但并未向西（进入山地区域）扩展。在干燥、温暖的天气条件下，蟾蜍的分布范围在几十年中扩张速度最快，但预测的未来气候变化可能对蟾蜍扩散速率仅有轻微影响。理解新南威尔士州蟾蜍入侵的历史模式可以阐明可能的未来扩散趋势，从而确定控制计划的优先区域。

方法

新南威尔士州入侵甘蔗蟾蜍的分布数据从所有可用来源进行汇编，以量化扩张速率并确定该速率扩散的相关因素。我们还进行了试点研究，以比较在野外检测蟾蜍入侵前沿群体的人口的不同方法。

使用说明

Excel表格提供了代表一系列可获取数据的几十年中蟾蜍入侵前沿边缘的342个点的数据。该数据集还包括从相关GIS层确定的每个地点的气候和栖息地属性，以及蟾蜍分布边缘跨世纪的变更估计。