Species interactions (competition, predation, herbivory, etc.) are important determinants of community structure (how many of which species occur at a location). Species interactions can change over space, or time, because of environmental variation, and changes in other ecological processes (e.g., storm frequency, nutrient loading, larval settlement). Understanding how and why species interactions change is difficult because they are so complex, but gives us insight into why we see different communities in different places, and how they might change in the future.