Lecture 26: Overharvesting

Question 1

What is overharvesting?

Answer 1

over-exploitation of biological resources

Question 2

Why did larger animals go extinct in north amer. during the last pleistocene?

Answer 2

1. climate change hypothesis –> cold adapted mammals couldn’t handle warmer climate
2. Overkill hypothesis –> human hunters wiped them out

Question 3

What is the evidence for the overkill hypothesis?

Answer 3

1. extinction was rapid (< 1000 years)
2. large animals decimated (rather than small ones)
3. extinction patterns followed spread of humans
4. large mammals survived in africa (where there was co-evolution)

Question 4

How does the loss of one species affect others? (elephant example)

Answer 4

Elephants kept grasslands open in africa –> overpoaching elephants meant shrubs and trees grew instead of grass –> grassland mammals decreased

Question 5

What is “Fishing down” food webs?

Answer 5

Fisheries start with larger fish. When those get depleted, smaller fish become more abundant and fisheries focus on those (one trophic level down)

Question 6

What are the roles of predators in ecosystems?

Answer 6

1. regulate activity through top-down control
2. maintain diversity by controlling dominant species
3. control pest outbreaks by keeping prey below carrying capacity

Question 7

what is top down control?

Answer 7

When a system is regulated by consumers (higher trophic levels control population size below them)

Question 8

What is an example of predators controlling dominant species to maintain diversity?

Answer 8

sea otters eat purple sea urchins, which eats kelp. With fewer urchins, there is more kelp for manatees to eat.

Question 9

What is carrying capacity?

Answer 9

the maximum size of a population supported by available resources.