RAS question
The alpha diversity refers to:
Correct answer: (B) Diversity within a single community/habitat.
Alpha diversity refers to the biodiversity or species richness within a single local community, habitat, or ecosystem.
Explanation
Alpha diversity is the within-site measure of biodiversity: it looks at how many species are present in a particular local area, community, habitat, or ecosystem. Britannica explains it as species richness at a local scale, smaller than an entire region or a species' full geographic range. That is why option B is correct: the question is asking about diversity inside one community or habitat, not across habitats or across a whole landscape. The contrast matters because beta diversity tracks how species richness changes from one habitat to another, while gamma diversity gives the richness of a larger geography such as a large ecosystem, biome, or country. So alpha diversity is the local, within-community level of biodiversity measurement.
Why the other options are wrong
- (A) Total diversity of a landscape is gamma diversity, because it refers to species richness at a larger geographic scale rather than within one local community or habitat.
- (C) Diversity between two communities is beta diversity, since beta diversity examines how species richness changes from one habitat to another.
- (D) Genetic diversity within a species measures variation inside a species, whereas alpha diversity is about species richness within a local community, habitat, or ecosystem.
Concept
This tests the biodiversity-scale distinction between alpha, beta and gamma diversity. It recurs in RAS environment questions because conservation and ecology items often turn on whether diversity is being measured within a site, between habitats, or across a larger landscape.