More individuals doesn't mean more diversity
- The idea
- Predict
- See it
- Why
- Check
The idea
“The community with more individuals in it is the more diverse one.”
A crowded pond looks full of life, so more animals seems like more diversity. Yet 500 bluegill are still one species.
The short version
The mistake: The community with more individuals in it is the more diverse one.
What's actually true: Diversity comes from how many species there are and how evenly the individuals are split among them.
- Species richness is the number of species. Evenness is how equally the individuals are split among them. Diversity depends on both.
- Simpson's index uses each species' share of the total, n/N. Double every population and every share stays the same, so the index does too.
- Diverse communities tend to resist and recover from disturbance better. Species differ in how they handle drought or disease, so some keep going when others fail.
On the exam: Ignore the total. Count the species, then check whether one of them holds most of the individuals.