Simulating the spread of Hieracium lepidulum in heterogeneous landscapes

Abstract

The invasion of non-indigenous species represents a severe threat to the health of native communities world-wide. In order for us to be effective and efficient at mitigating the economic and ecological impacts of these invasions, it is critical that we improve our understanding of how specific traits of the invader interact with characteristics of their new environment. Understanding these dynamics can help to improve the efficacy and economy with which we are able to apply control efforts. At the same time, we can examine if there are predictable patterns of spread which are produced from those interactions, and generalise those patterns to other invasions. In order to address these aspects of invasion, I developed a simulation model utilising a highly detailed and expansive data set which reflects the demography and dispersal of one particular species, Hieracium lepidulum, as it invades a mountainous area on the South Island of New Zealand. The scope and fidelity of this dataset is such that it permits me to develop models of the demography and dispersal of the species reflecting habitat-specific variation within the invaded area. These models are then combined using a customised simulation software to create a spatially and temporally explicit simulation of H. lepidulum spread. These simulations are applied across a range of hypothetical landscapes which are constructed to represent varying degrees of abstraction of the actual landscape; the simulations are applied at different scales, and the landscapes represent mixtures of the component habitats at varying degrees of complexity and spatial configurations. The outcomes of these simulations are then used to address a number of general questions intended to identify if there are some simplifying principles that can be used when evaluating invasive spread, and to examine how these results compare to currently postulated theories regarding the spread of invasions, and how their progression is influenced by context of the landscape.