Biodiversity & Ecosystem Services
- Distinguish the three levels of biodiversity — genetic, species, and habitat
- Classify the four categories of ecosystem services with real examples
- Calculate and interpret a Simpson’s Diversity Index for a community
Biodiversity has three levels
Biodiversity is the variety of life, and it is measured at three nested scales. Genetic diversity is the variety of alleles within a single species — the raw material for adaptation. Species diversity combines species richness (how many different species) with evenness (how balanced their abundances are). Habitat (ecosystem) diversity is the variety of ecosystems in a region. High diversity at every level makes an ecosystem more resilient — better able to recover from disturbance — because there is more genetic and functional backup when conditions change.
Why genetic diversity is the safety net
A population with high genetic diversity carries many different alleles, so when a new stress arrives — a disease, a drought, a pesticide — some individuals are likely to carry alleles that let them survive and reproduce. A genetically uniform population (a monoculture crop, an inbred endangered species) can be wiped out by a single new pathogen because no individual has resistance. This is why loss of genetic diversity, even without extinction, threatens a species’ long-term survival.
Ecosystem services: nature’s free work
Healthy ecosystems perform work that humans would otherwise pay for. These ecosystem services fall into four categories. Provisioning services are tangible goods — food, timber, fresh water, medicine. Regulating services control natural processes — pollination, water purification, flood control, climate regulation, and pest control. Cultural services are nonmaterial benefits — recreation, tourism, spiritual and aesthetic value. Supporting services underlie all the others — photosynthesis, nutrient cycling, and soil formation. When biodiversity falls, these services degrade, often at enormous economic cost.
A meadow sample contains 4 species: 3 daisies, 4 clover, 2 buttercups, and 1 thistle. Calculate Simpson’s Diversity Index (D).
- 1.Find N, the total number of individuals: 3 + 4 + 2 + 1 = 10.
- 2.Compute n(n − 1) for each species: daisy 3×2 = 6; clover 4×3 = 12; buttercup 2×1 = 2; thistle 1×0 = 0.
- 3.Sum them: Σ n(n − 1) = 6 + 12 + 2 + 0 = 20.
- 4.Compute N(N − 1) = 10 × 9 = 90.
- 5.Apply the formula: D = 1 − (20 / 90) = 1 − 0.222 = 0.778.
A wetland naturally filters agricultural runoff, removing excess nitrogen before it reaches a river. Which category of ecosystem service is this?
Separate richness from evenness. Two forests can have the same number of species (equal richness), but the one where individuals are spread evenly among species has higher evenness and a higher diversity index. A forest that is 97% one tree species is species-poor in practice even if a few rare species are present.
A wild potato population survives a new fungal blight because a few individuals carry a resistance allele, while a cloned commercial potato field is destroyed. What does this best illustrate?
When a Simpson’s Index problem appears, the formula is provided on the AP equation sheet — your job is to plug in correctly. The classic error is forgetting the "−1": use n(n − 1) and N(N − 1), not n² and N². Always carry your work; the calculation earns points even if the final decimal is slightly off.
Answer the 2 checkpoints as you read.
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