3.1 Biodiversity and evolution

Biodiversity has three linked levels: variety of habitats, variety and abundance of species, and heritable variation within species.

Ask what is varying before choosing the level. A landscape comparison is habitat diversity; species counts and evenness are species diversity; differences among populations or individuals are genetic diversity.

Four forest types in one region show habitat diversity; different beetle species show species diversity; drought-tolerant alleles show genetic diversity.

Genetic diversity, because the variation is within the species.

Species richness alone is not the whole of biodiversity; level and abundance matter.

Diversity can increase recovery options: habitats provide refuges, species provide overlapping functions and genes provide tolerant variants.

The benefit is conditional on which functions and variants exist, how severe the disturbance is and whether organisms can reach suitable habitat.

After drought, a population with drought-tolerant variants may recover better than a genetically uniform population.

Show a surviving refuge, substitute function or tolerant variant—not diversity as a label alone.

High diversity is not a guarantee; the relevant level and disturbance must match.

Evolution is inherited change in a population across generations, not an adjustment made by one individual during its lifetime.

Acclimatization can change an individual without changing inherited frequencies. Evolution is detected when descendants inherit a different trait or allele distribution.

A person tans in sunlight without evolving; a population becoming more UV-tolerant over generations may reflect evolution.

A heritable frequency shift between generations, not a short-term physiological response.

Individuals do not evolve to meet a need; populations change through inherited variation and selection.

Natural selection changes trait or allele frequencies when heritable variants differ in survival or reproduction under current conditions.

Selection acts each generation; adaptation is the longer-term result. It has no planned goal and a trait is advantageous only relative to the environment.

If darker moths leave more offspring on soot-darkened trees, their frequency can rise over generations.

Heritable variants must have different reproductive success; mere presence of variation is insufficient.

Selection is not organisms choosing useful traits; the environment filters existing inherited differences.

Heritable variation plus overproduction, competition and differential reproduction can change a population over generations.

Resources limit survival. Individuals with traits better suited to current conditions tend, on average, to leave more offspring, so their alleles become more common.

If drought kills more shallow-rooted plants, deep-rooted heritable variants may contribute more seeds next season.

Selection changes reproductive contribution; population frequency shifts accumulate across generations.

‘Survival of the fittest’ means reproductive success in context, not physical strength alone.

Speciation becomes possible when isolation reduces gene flow and divergence eventually prevents production of fertile offspring.

Geographic, ecological or behavioural separation lets mutation, selection and chance accumulate differences. Under the biological species model, reproductive isolation is the decisive test.

A river separates populations; if they later meet but cannot produce fertile offspring, the sequence supports completed speciation.

No. It reduces gene flow, but reproductive isolation must be demonstrated or inferred carefully.

Divergence and speciation are not identical; ask whether gene flow and fertile reproduction remain.

Richness counts species; evenness asks how evenly individuals are distributed among them.

Species diversity uses both. Equal richness can hide dominance, so inspect abundance distribution before ranking communities.

Site A has 25 individuals of each of four species; Site B has 97 of one and one of each other. A is more even and usually more diverse.

Counts or relative abundance; richness alone cannot reveal dominance.

More species does not automatically mean a more even or functionally diverse community.

Simpson’s reciprocal index D = N(N−1) ÷ Σn(n−1); higher D generally indicates greater richness and/or evenness.

N is total individuals and n is each species count. Compute every n(n−1), sum, then divide; compare samples with similar effort and habitat.

For counts 5 and 5, N=10 and D=90/40=2.25; equal abundances raise evenness.

This reciprocal form increases as dominance falls and diversity rises.

Do not compare indices from unequal sampling effort or silently switch to a different Simpson convention.

Useful biodiversity monitoring combines broad local observations with agreed protocols, validation and feedback to the people who contribute them.

Citizens expand coverage; agencies coordinate standards; Indigenous knowledge holders add place-based history; trained parabiologists connect surveys to communities. Record metadata and identification confidence.

Repeated community bird counts with photo verification reveal a seasonal decline that can trigger habitat protection.

Known location/time, method, identification quality and a decision it can inform.

More observations are not automatically better evidence if methods and identifications are inconsistent.