Modelling seasonal habitat suitability and connectivity for feral pigs in northern Australia: towards risk-based management of infectious animal diseases with wildlife hosts

Abstract

Infectious animal diseases are a major biosecurity threat in an increasingly connected world.Wildlife hosts are a well-recognized risk factor for disease introduction, establishment and spread.Northern Australia is vulnerable to disease incursions from neighbouring countries, and widespread invasive feral pigs (Sus scrofa) can seriously complicate post-border disease management. The aim of this thesis was to generate new regional-scale spatial knowledge of feral pig populations in northern Australia to inform risk-based management of directly transmitted infectious animal diseases for which feral pigs are a host.Due to environmental variability and empirical knowledge gaps across this vast region, I adopted a resource-based modelling approach, based on expert knowledge but rooted in landscape ecological theory, to answer three research questions at multiple levels of biological organisation.Specifically, I conceptualized feral pigs in northern Australia as a metapopulation and the landscape as displaying a patch-corridor-matrix structure. At the level of individual feral pig breeding herds, I explored the selection of supplementary and complementary resources within home ranges. At the level of local subpopulations, consisting of several herds with adjacent or overlapping home ranges, I used a habitat suitability modelling approach to investigate the distribution of potential patches of breeding habitat emerging from the interactions between resources and home range movements. At the metapopulation level, I examined potential dispersal pathways between many such patches using a habitat connectivity modelling approach. As feral pig movements and distributional patterns vary with conditions, I applied models to two seasonal scenarios (wet and dry) corresponding to northern Australia's annual rainfall cycle.This thesis contributed methodological advances and new ecological insights. I developed a novel combined methodology, spatial pattern suitability analysis, for capturing feral pigs' resourceseeking home range movements based on expert-elicited response-to-pattern curves and spatial moving window analysis. Based on landscape ecological principles, this methodology improves the application of resource-based Bayesian networks models to mobile animals. I found that habitat suitability for persistent feral pig breeding in northern Australia is dependent on spatial interactions between four key habitat requirements: water and food resources as well as protection from heat and from disturbance. Through scenario analysis and empirical validation I showed that habitat suitability at the regional scale is most reliably modelled as a function of distance to supplementary and complementary resource patches. When applied to a wet season and a dry season scenario, mapped model results indicated that the spatial distribution of feral pig habitat patches varied markedly. Importantly, empirically validated findings suggest that dry season conditions restrict overall habitat suitability for feral pig breeding in northern...

Applying a versatile, comprehensive, attribute-based waterhole classification scheme to ecosystem-based management challenges

“…reliability of water presence); (3) dominant vegetation; and (4) available shading. These attributes reflect many of the critical requirements for feral pig habitat in northern Australia, which can be simplified to food, water, shade, and protection from threats (Froese 2017). The attributes selected directly relate to the environmental constraints that exert population and behavioural pressure on feral pigs.…”

“…Feral pigs are omnivorous and opportunists, with 80-95% of their diet consisting of vegetation (reflecting vegetation abundance and availability in the landscape) and opportunistic vertebrate and invertebrate consumption, which is likely to be an important element for breeding success (Choquenot et al 1996;Ross 2009). Froese (2017) indicates that the complementarity and density of habitat with these variables are important for determining feral pig distribution. A new attribute was also identified, oceanic influence on the waterhole.…”

“…Categories for water permanence and timing predictability were reviewed with permanent and nearpermanent categories merged, and intermittent split based on the predictability of water availability. The availability of water in the late dry season can result in greater impacts on the remaining waterholes but also concentrates feral pig populations, which can then be used to plan management responses (Froese 2017). The grass, herb or sedge category in dominant vegetation attribute was further split for the typology to identify preferred feral pig diet (e.g.…”

“…In the context of feral pig management, the presence and type of waterhole and associated resources can be used to predict the abundance and distribution of feral pigs (Froese et al 2017a). The density and location of waterhole types that are high value for feral pigs provide a means of quantifying habitat connectivity and likely movement paths, likelihood of re-invasion following control, connectivity between populations for epidemiological models, and limits to breeding success (Froese 2017).…”

“…Comparison of area of dry season highly suitable habitat mapped using published habitat suitability index(Froese 2017) and waterhole typology method for the Archer River basin.…”