Final answer:
Gamma diversity counts the total species diversity across all habitats within a geographic area and reflects the overall biodiversity of a region.
Step-by-step explanation:
The description that counts the total species diversity in all the habitats in a geographic area is referred to as gamma diversity. Gamma diversity is a key indicator of the overall biodiversity across a large regional landscape, encompassing multiple ecosystems.
Alpha diversity measures the number of species within a particular area or ecosystem, which represents local species richness. Beta diversity, in contrast, reflects the difference in species richness between ecosystems. It focuses on the species uniqueness between areas, essentially measuring the variation in species composition across different habitats. These three types of diversity help ecologists to understand biodiversity patterns at various spatial scales, from a local to a regional level.
The concept of biodiversity includes not just the species richness at a local scale, reflected by alpha diversity but also how this richness varies from one location to another, indicated by beta diversity, and the cumulative species richness over a larger area, denoted by gamma diversity.