1. Biodiversity – Chapter 22

2. Biodiversity • Species richness – the total number of species in an area • Simplest measure of biodiversity • Heterogeneity - higher when there are more species and they are equally abundant

3. Determining Species Richness • Species count depends on sample size • Relatively few species are very common • Estimated 5 – 30 million species exist on Earth: Only about 1.4 million are described • ~10% of all life • Taxonomists – people that describe and categorize species

4. Diversity Gradients • Diversity increases towards the equator

5. Factors That Might Cause Diversity Gradients • Eight Factors:

6. History Factor • Evolution = speciation • Tropics  warmer and more humid, so they are more likely evolve and diversify faster • Tropical biotas are mature; temperate and polar are immature • All communities diversify over time

7. Spatial Heterogeneity • The more heterogeneous and complex the physical habitat, the more complex the animal and plant community  the greater the diversity • Topographical relief important for species diversity • More habitats = more species • Highest diversity of US mammals occur in mountainous regions

8. Habitat Diversity Between Habitat (Beta) Diversity Within Habitat (Alpha) Diversity

9. Competition • In tropics: • Animals and plants are more restricted in their habitat requirements  increases between habitat (beta) diversity • Animals may also have a more restricted diet in each habitat, increasing within-habitat (alpha) diversity • Competition is keener in tropics, niches are smaller • Tropical species are more highly evolved and possess finer adaptations than do temperate species

10. Niche Patterns # species determined by niche breadth # species determined by niche overlap

11. Predation • Predators keep prey numbers so low, competition is reduced • Leads to an increase in types of prey, which leads to an increase in types of predators • Removal of a starfish from a tidal shore  decrease in prey diversity

12. Climate and Climatic Variability • More stable the climatic parameters and the more favorable the climate  the more species • Similar to the history theory • Species richness limited by the available energy • Equator to the poles  decrease in diversity • See figure 22.18

13. Productivity • The greater the productivity the greater the diversity: everything else being equal • Data does not support this theory • Can be supported when put in the context of length of growing season (stability hypothesis)

14. Disturbance • If natural communities exist at equilibrium and the world is spatially uniform, then competitive exclusion rules and there will only be a few dominant species. • Moderate disturbance increases species diversity Intermediate Disturbance Hypothesis