Identifying refugia from the synergistic threats of climate change and invasive species

Abstract. Climate change may reduce available habitat for native species, while simultaneously increasing suitable habitat for invasive species, which then compete with or predate on native species. Thus, climate change and invasive species can interact synergistically to negatively affect native species. It is important to identify climate refugia that are likely to be both suitable for native species and unsuitable for invasive species, under both present and future climate conditions. We propose a refugia habitat metric (RHM) based on ecological niche modelling. We demonstrate the utility of the metric via a case study of an endemic freshwater crayfish, or kōura (Paranephrops planifrons), which is threatened by both climate change and predation from the invasive brown bullhead catfish (Ameiurus nebulosus) in Aotearoa / New Zealand. We used maximum entropy (MaxEnt) ecological niche models to predict current and future habitat suitability for the two species across Aotearoa / New Zealand. By the period 2080–2100, suitable habitat will increase across the northern and western North Island for catfish, while suitable habitat for kōura will decrease overall and shift southwards and towards more mountainous regions. Using the refugia habitat metric, we identified areas of habitat within the current range of kōura, with significant potential refugia habitat outside the species current range. Using the refugia prioritization metric will allow conservation managers to identify habitat for protection and potentially translocation target sites for vulnerable native species.