| Climate change has already led to widespread alterations of biological systems, and even greater rates of global warming are predicted in the next century. However, we lack an adequate understanding of the mechanisms underlying climate-change effects. At the biogeographic scale, shifts in species' ranges are a predicted and realized consequence of climate change. A review and meta-analysis of marine range shifts revealed that shifts of native species proceeded more slowly than marine invasions, but faster than shifts in terrestrial systems, and that the community-level effects of range shifters were often as great as those of invasive species (Chapter 1). At the community level, species are likely to respond idiosyncratically to climate change, leading to shifts in species' abundances and community composition. Furthermore, climate change may favor invasive species, causing native species to be simultaneously threatened by both the direct effects of climate change and increased competitive pressure from non-natives. I addressed the effects of ocean warming on the composition of the marine fouling community of Bodega Harbor, California, USA. Because space is a limiting resource in the fouling community, I focused on processes responsible for the acquisition and maintenance of settlement space, including recruitment, survival, and growth. I found that the composition of the Bodega Harbor fouling community has changed, with a number of new invaders achieving dominance, over the past 35 years. Although these invaders' success is likely due, in large part, to increased propagule pressure, recruitment of invasive, but not native, species was enhanced at higher temperatures, suggesting that local increases in sea temperature could help to maintain invasive dominance in the harbor (Chapter 2). Invasive species also had higher lethal temperature limits than native species and were favored at higher temperatures because of their greater survival and increases in growth (Chapter 3). Finally, species differed in their resistance to heat waves, highlighting the potential for abrupt changes in community composition as extreme temperature events become more frequent and severe (Chapter 4). These results for multiple demographic processes indicate the potential for further increases in invasive dominance in response to continued ocean warming. |
