Grasses can tolerate frequent fires while shrubs cannot. Humans have interferred with fire cycles and changed many habitats from grasslands to shrublands. In some cases there are distinct boundaries between communities, especially those broadly classified as biomes. We call the zones of transition between biomes ecotones . In the ecotones we see an edge effect just as we see for populations.
Some species penetrate further into the ecotone than others.
Some species can live in two distinct biomes, and when these biomes are connected by an ecotone then the community structure will be different than if they were not next to each other. This leads to spatial differences in community structure within a biome. For example, a grassland may have share a border with temperate forests and shrublands. Some species from these biomes will be able to invade the grassland to some extent. The community composition will be different depending on where one looks, however, the dominant plant species will be the same.