Step by Step
Lvls
Three levels of biodiversity
Genetic diversity: variation within a species (allelic diversity). Essential for adaptation and disease resistance. Low genetic diversity → vulnerability (cheetahs, Florida panthers). Species diversity: number and relative abundance of species in an area. Measured by species richness (number of species) and evenness (relative abundance). Ecosystem diversity: variety of habitats, communities, and ecological processes in a region.
Memory trick: Genetic (within species), Species (between species), Ecosystem (between communities). GS&E.
Alp
Alpha, Beta, Gamma diversity
Alpha diversity: species diversity within a single site/habitat. Beta diversity: turnover of species between different sites — how different are the communities? High beta diversity = different species at each site. Gamma diversity: total species diversity in a region = all species across all sites. Alpha × Beta ≈ Gamma.
Memory trick: Alpha = at one spot. Beta = between spots. Gamma = grand total of the region.
Pat
Global patterns of biodiversity
Species richness increases toward the tropics (latitudinal diversity gradient) — tropical regions have the highest biodiversity. Reasons: longer evolutionary history, more stable climate, higher productivity, greater habitat complexity. Biodiversity hotspots: regions with exceptional biodiversity AND significant habitat loss (e.g., Madagascar, California Floristic Province, Atlantic Forest of Brazil, Western Ghats of India). 25 hotspots cover ~1.4% of Earth's land but contain ~44% of all plant species and 35% of vertebrates.
Memory trick: Tropics = most biodiversity. Hotspots = high diversity + high threat.
HIPPO
HIPPO — the five threats to biodiversity
H: Habitat destruction/fragmentation (biggest threat). I: Invasive species. P: Pollution. P: Population growth (human). O: Overharvesting/overexploitation. Habitat destruction is by far the most significant driver of current biodiversity loss. The current extinction rate is estimated at 100-1,000× the background extinction rate — many scientists call this the Sixth Mass Extinction.
Memory trick: HIPPO eats biodiversity. Habitat loss is the hungry hippo.
Applied Walkthrough
1
Madagascar: isolated for 88 million years → 90% of species are endemic (found nowhere else). Deforestation has reduced forest cover from 90% to ~10% → enormous biodiversity loss. Classic hotspot.
2
The American chestnut: once dominated eastern US forests (4 billion trees). Chestnut blight (introduced fungus, invasive species) killed virtually all adults by 1950. Genetic diversity of the species collapsed. Ongoing bioengineering attempts to restore blight-resistant trees.
3
The passenger pigeon: once the most abundant bird in North America (billions). Overhunted for cheap food → extinct by 1914 (Martha, the last individual, died in the Cincinnati Zoo). Speed of collapse shocked scientists — abundance is not protection.
4
Island biogeography theory (MacArthur & Wilson): species richness on islands = balance between immigration and extinction. Larger islands and islands closer to mainland have more species. Applies to habitat fragments — small isolated forest patches = 'islands' → lower diversity and higher extinction rates.
Exam Application
Exams test the three levels of biodiversity (genetic, species, ecosystem), alpha/beta/gamma diversity, the latitudinal diversity gradient (more species at tropics), the HIPPO threats with habitat loss as primary, biodiversity hotspot definition, and island biogeography theory. The concept that current extinction rates far exceed background rates is important context.
⚠ Common Trap
Students confuse species richness and species diversity — richness = just the NUMBER of species. Diversity also includes EVENNESS — a community with 10 species all equally abundant is more diverse than one where 1 species dominates 90% of individuals. Also: biodiversity hotspots are defined by TWO criteria — exceptional endemism AND significant habitat loss/threat. High diversity alone doesn't make a hotspot.
✓ Quick Self-Check
1. What are the three levels of biodiversity?
Genetic diversity (within species), species diversity (number and abundance of species), and ecosystem diversity (variety of habitats and communities).
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2. What is the difference between alpha and beta diversity?
Alpha diversity = species diversity within a single site. Beta diversity = turnover of species between different sites (how different are the communities).
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3. What is the latitudinal diversity gradient?
Species richness generally increases toward the tropics — tropical regions have the highest biodiversity on Earth.
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4. What does HIPPO stand for in ecology?
Habitat destruction, Invasive species, Pollution, Population growth (human), Overharvesting — the five major threats to biodiversity. Habitat destruction is the most significant.
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5. What defines a biodiversity hotspot?
A region with exceptional biodiversity (especially endemism — species found nowhere else) AND significant habitat loss/threat (typically >70% of original habitat destroyed).
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