Linking climate change and biological invasions: Ocean warming facilitates nonindigenous species invasions

Abstract

The spread of exotic species and climate change are among the most serious global environmental threats. Each independently causes considerable ecological damage, yet few data are available to assess whether changing climate might facilitate invasions by favoring introduced over native species. Here, we compare our long-term record of weekly sessile marine invertebrate recruitment with interannual variation in water temperature to assess the likely effect of climate change on the success and spread of introduced species. For the three most abundant introduced species of ascidian (sea squirt), the timing of the initiation of recruitment was strongly negatively correlated with winter water temperature, indicating that invaders arrived earlier in the season in years with warmer winters. Total recruitment of introduced species during the following summer also was positively correlated with winter water temperature. In contrast, the magnitude of native ascidian recruitment was negatively correlated with winter temperature (more recruitment in colder years) and the timing of native recruitment was unaffected. In manipulative laboratory experiments, two introduced compound ascidians grew faster than a native species, but only at temperatures near the maximum observed in summer. These data suggest that the greatest effects of climate change on biotic communities may be due to changing maximum and minimum temperatures rather than annual means. By giving introduced species an earlier start, and increasing the magnitude of their growth and recruitment relative to natives, global warming may facilitate a shift to dominance by nonnative species, accelerating the homogenization of the global biota. P redicted increases in global temperature (1) likely will have dramatic effects on the structure and function of ecosystems worldwide (2-4). One approach to predicting the biological effects of climate change has been to examine the direct physiological consequences to resident species of changes in temperature or CO 2 concentration (5-8). Other studies have focused on the indirect consequences of altered temperature on interactions among resident species and the cascading effects on local community composition (9-12). Climatic warming on the time scale of decades also may alter the composition of the resident biota by facilitating the poleward spread of species characteristic of warmer temperature regimes (9, 13-15). However, it is also possible that climate change could facilitate quantum leaps in the range of species across ocean basins or continents. Humans already inadvertently transport countless species around the globe (16), and, although many of these inoculations presumably fail because of inhospitable climate in the recipient region (17, 18), global warming may relax this constraint. Despite considerable interest in predicting the spread and success of ''invasive'' species because of their significant effect on native communities (19), there are few data to evaluate the effects of climate change on this type of invasion...

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