9. Patterns in biodiversity are predictable

Question 1

What is the best predictor for patterns in species richness (S)?

Answer 1

Latitude

Question 2

What are the reasons behind latitudinal trends?

Answer 2

1. More primary production in the tropics because of photosynthesis.
2. Older habitats haven’t been decimated as much as northern habitats
3. Implications: need more reserves in the tropics, but more people live there.

Question 3

What are the most threatened ecosystems/biomes on Earth? Not just about species

Answer 3

Grasslands honour population density are really low in prairies, so the species are threatened.

Question 4

Describe the area effect

Answer 4

Bigger islands have more species, reptiles and amphibians

Question 5

Why do bigger areas have more species?

Answer 5

• Increased diversity of habitats (larger populations give bigger chunks of habitat)
• Larger populations are less likely to go extinct
• Bigger target for colonizing species (Island biogeography theory)

Question 6

Explain island biogeography theory.

Answer 6

(See graph)

• When you are on the bottom right, that means you have a lot of species on ground, so you can’t have more immigrants. (Immigrants = species, not individuals)
• So the rate of immigration goes down the more species you have (they can be full complements)
• Curve: Falls quickly and then flattens (Best dispersers are already there. Fewer remaining species in the mainland pool)
• Extinction: curve goes up (the more species you have, the more extinction rate there will be. More species to go instinct. Smaller populations due to competition)
• Species on island: equilibrium number of species
• The closer you are to the mainland, the bigger the number of species you will have. (the immigration rate is higher because you are easier to get to. But the extinction rate is the same because they are equal islands *for a given number of species, the extinction rate should be the same. The bigger the island, the more space you have, the smaller the rate of extinction. Will have more species. Higher immigration rate. More species: mainland > island. Area effect is also on ecological islands.