In Chapter 53 we established that regional species pools provide the upper limits on the numbers and types of species that can live within communities (see Figure 53.12). An obvious first step to community membership is the presence of species at the regional level, and their ability to disperse to the community. For example, as communities started to recover from the Mount St. Helens eruption, they began to gain species supplied from the regional species pool of the Pacific Northwest of North America. Because they were able to disperse to the mountain, these species began to colonize the new and unique environments created in the aftermath of the devastation.

Maybe the best examples of how species supply affects community membership are seen in the introduction of novel species to communities. Humans have greatly expanded regional species pools, allowing new and potentially invasive species to enter communities. Chapter 55 described the catastrophic effects of the unintentional release of invasive lionfish in Atlantic Ocean and Caribbean coral-reef communities. The lionfish invasion demonstrates that “getting there” is a critical first step to community membership. All it took was the release of this predator, and its extraordinary ability to prey on reef fish, to dramatically change coral-reef communities.