Temperature influences species interactions between a native and a globally invasive freshwater snail

We experimentally assessed the interaction between a globally invasive snail (Potamopyrgus antipodarum) and an Australian native snail (Austropyrgus angasi) under temperatures based on current (1990-2000, mean = 17.94-19.02°C) and future (2100, mean = 19.42-21.65°C) predicted conditions. Temperature treatments were scenarios identified from down-scaled global circulation models. Growth rates (mm/d) for juveniles and adults were measured at low (1000 individuals [ind]/m2) and high (20,000 ind/m2) densities in intraspecific and interspecific interaction trials under the 2 temperature regimes. Juveniles of both species grew at similar rates regardless of temperature and density. On the other hand, adults had dissimilar growth rates among treatments. Under current temperatures, P. antipodarum adults grew significantly faster than A. angasi adults when both species were kept at high densities in the interspecific treatment (interspecific-high) and faster than when they were kept at high densities but with conspecifics in the intraspecific treatment (intraspecific-high). However, we did not detect intra- or interspecific competition effects on either species. Thus, our results suggest that under current conditions, P. antipodarum gained from foraging with A. angasi (unidirectional facilitation effect). Under 2100 temperatures, the facilitative effect of A. angasi on P. antipodarum growth was not apparent, a result suggesting that the facilitation was directly related to the temperature conditions. Our research shows the importance of considering future temperature conditions as a factor that could alter species interactions and potentially influence the ecological effects of invasive species.