Overharversting - T Flashcards
Climate change hypothesis for extinctions in late pleistocene
cold-adapted animals couldn’t handle the warmer climate
Overkill hypothesis evidence for extinctions in early North America (4)
extinctions occurred rapidly
large animals decimated (hunters’ selection)
extinctions followed the spread of humans
large mammals survived in Africa, where humans and big animals had co-evolved
evidence against overkill hypothesis
some herbivorous mammals were not the focus of hunting but also went extinct
some species were hunted still survived
some extinctions before for the Bering Land Bridge formed
Austrian extinctions started before humans
effects of loss of keystone species
may cause secondary extinctions because of secondary effects
ex: elephants keep grasslands open
when elephants are decimated, shrubs/trees grow in place of grass
causing other grassland mammals to decline
total fish caught consequences
has increased 5-fold in 50 years
worldwide decline in stocks of large predatory fish
fishing down
early fisheries focused on large carnivorous species
at high trophic levels
as those fish became depleted, focused on small fish at lower tropic levels
mean body length of commercial fish has decreased over last 50 years
role of predators in ecosystems (3)
- regulate productivity through top-down effects
- maintain community diversity by controlling dominant species (sea otters, kelp and urchins or starfish and mussels)
- control pest outbreaks by keeping prey well below carrying capacity
top down control vs bottom-up control
system is regulated by consumer
system is regulated by primary production (upward flow of energy)
without predation…
herbivore (prey) density will increase, increases extinction risk for each plant
what happens as trophic levels increae
with 2: plants are controlled
with 3 (a predator enters): plants are released
with 4 (bigger predators enters): plants are controlled
