Antagonistic effects of biological invasion and temperature change on body size of island ectotherms

Abstract

AbstractAimDespite their potentially profound consequences, little is known about the impacts of interactions among environmental change drivers on indigenous species. For biological invasions, much theoretical prominence has been given to additive or synergistic interactions with temperature change. However, empirical investigations are sparse. Here, we investigate the outcomes of interactions between temperature change and biological invasions on ectotherm body size in a temperate system.LocationThe sub‐Antarctic Prince Edward Island group (46°54′ S, 37°45′ E).MethodsWe use long‐term (24 years) body size data on weevil species from Marion and Prince Edward Islands. Invasive house mice, which prey on four of the five weevil species, are present on Marion Island, while the neighbouring Prince Edward Island is mouse free. Theory predicts that with higher temperatures, body size should decline across all species, and previous work suggests that size‐selective predation by mice should enhance this effect on the invaded island. Generalized linear models were used to determine the relative effects of sex, island, altitude and mean annual temperature on body size for each of the species.ResultsTemperature change and biological invasions interact to affect body size in an antagonistic fashion. In weevil species not preyed on by invasive house mice, body size and declining size with increasing temperature are consistent across adjacent invaded and non‐invaded islands. By contrast, species preyed on by mice are smaller on the invaded island and show opposite size‐temperature relationships on the invaded and mouse‐free islands.Main conclusionsSize declines on the non‐invaded island are in keeping with theoretical expectations of declining size with increasing temperatures. By contrast, this expectation is not met on the island invaded by mice, largely owing to what appears to be increased energetic demand of predators in colder years. These results emphasize that interactions among change drivers will take a range of forms, and that humans may have substantial influences on fundamental ecological patterns.