Cost and feasibility of a barrier to halt the spread of invasive cane toads in arid Australia: incorporating expert knowledge into model‐based decision‐making

Abstract

Summary Active engagement with practitioners is a crucial component of model‐based decision‐making in conservation management; it can assist with data acquisition, improve models and help narrow the ‘knowing–doing’ gap. We worked with practitioners of one of the worst invasive species in Australia, the cane toad Rhinella marina, to revise a model that estimates the effectiveness of landscape barriers to contain spread. The original model predicted that the invasion could be contained by managing artificial watering points on pastoral properties, but was initially met with scepticism by practitioners, in part due to a lack of engagement during model development. We held a workshop with practitioners and experts in cane toad biology. Using structured decision‐making, we elicited concerns about the original model, revised its structure, updated relevant input data, added an economic component and found the most cost‐effective location for a barrier across a range of fixed budgets and management scenarios. We then conducted scenario analyses to test the sensitivity of management decisions to model revisions. We found that toad spread could be contained for all of the scenarios tested. Our modelling suggests a barrier could cost $4·5 M (2015 AUD) over 50 years for the most likely landscape scenario. The incorporation of practitioner knowledge into the model was crucial. As well as improving engagement, when we incorporated practitioner concerns (particularly regarding the effects of irrigation and dwellings on toad spread), we found a different location for the optimal barrier compared to a previously published study (Tingley et al. 2013). Synthesis and applications. Through engagement with practitioners, we turned an academic modelling exercise into a decision‐support tool that integrated local information, and considered more realistic scenarios and constraints. Active engagement with practitioners led to productive revisions of a model that estimates the effectiveness of a landscape barrier to contain spread of the invasive cane toad R. marina. Benefits also include greater confidence in model predictions, improving our assessment of the cost and feasibility of containing the spread of toads.

The on‐ground feasibility of a waterless barrier to stop the spread of invasive cane toads in Western Australia

“…A major concern raised by stakeholders in an earlier workshop was whether cane toads could persist throughout the dry season by sheltering in burrows (Southwell et al, 2017). A major concern raised by stakeholders in an earlier workshop was whether cane toads could persist throughout the dry season by sheltering in burrows (Southwell et al, 2017).…”

“…Simulation modeling has identified multiple areas within the Kimberley-Pilbara corridor where excluding toads from approximately 100 artificial water points could halt expansion of the toad front indefinitely (Southwell et al, 2017;Tingley et al, 2013). During the dry season, water sources will be crucial to toad survival in the corridor.…”

“…During the dry season, water sources will be crucial to toad survival in the corridor. In two possible locations the barrier would need to be approximately 70 km wide and, to implement, would cost approximately $4.5 million over 50 years (Southwell et al, 2017). The barrier need only be wide enough to account for toad movement during the wet season, when toads are not reliant on the artificial water points.…”

“…By managing artificial water points, we could create a "waterless barrier," protecting the biodiverse Pilbara region and up to 268,200 km 2 of mainland Australia from the toad's impact (Tingley et al, 2013). Modeling and sensitivity analyses suggest that such a barrier will hold even under a string of extremely wet years (Southwell et al, 2017;Tingley et al, 2013). In two possible locations the barrier would need to be approximately 70 km wide and, to implement, would cost approximately $4.5 million over 50 years (Southwell et al, 2017).…”

“…Previous work has demonstrated that the removal of water bodies has a critical impact on toad populations in semi-arid areas (Florance et al, 2011;Letnic et al, 2015). Second, is it possible that cooler temperatures and heavy dry-season fogs along the coastline will allow toads to survive the dry season regardless of shelter sites (Southwell et al, 2017)? Goanna burrows, for example, are plentiful in the region, and toads use these burrows as refuges throughout much of their current range (Schwarzkopf & Alford, 1996).…”