Alpha diversity is the first part of a three-tiered scale for measuring the biodiversity of an area. An area's alpha diversity is a measure of the diversity of species within an ecosystem. Obtaining this measurement usually entails walking the ground and counting or collecting representatives of each species encountered.
Alpha diversity is subtly different from the other two measurements, known as beta and gamma. Alpha diversity deals with species in a single area, while beta diversity is a measure of the difference in diversity between ecosystems in a given area. Gamma diversity is an expression of the overall diversity of an area regardless of the ecosystems where the species are found.