David R. Lindberg
Many ecological studies begin with the premise that modern-day communities represent fully integrated settings that evolved synchronously. This approach circumvents consideration of the temporal and spatial histories of the constituent organisms, their probable historical interactions, and how a system may have changed through time. A study of 20 kelp forests finds age and assembly differences between the northern and southern hemispheres. In the northern hemisphere, predators are oldest in warm temperate waters and herbivores are the youngest lineages originating after the kelp at all latitudes. The sea otter is the youngest component in North Pacific kelp forests. In the southern hemisphere, most herbivores and predators are substantially older than the kelp; the herbivores are the oldest lineages and have low latitude ancestry. Kelp forests in the North Atlantic show patterns similar to the North Pacific; probably due to recent migrations. This study shows that not all kelp forests have the same evolutionary trajectories and that region-specific models will be necessary to accurately estimate and predict impacts associated with climate change.