lecture 27- overharvesting as global change Flashcards
Does population relate to population size? What does this mean for smaller populations?
No. It relates to genetic diversity.
In a smaller population, there is a greater chance of individuals
being born with a combination of deleterious recessive alleles.
What does a loss in population lead to?
A genetic bottleneck: loss of genetic diversity.
Does a recovered population restore its genetic diversity?
No. Genetic diversity is generated over long periods of time through
survivable rare genetic mutations.
What is the Quaternary Extinction Event (QEE)?
The global trend in selective extinctions in mammals over 44kg.
The lowest overall rate of extinctions occurred in the African continent. The greatest number of species lost happened further away from Africa.
What was occurring globally during the QEE?
1- Ice age with periods of glaciation and inter-glaciation periods.
- but many species which went extinct during the QEE had previously survived similar global climate change.
2- Human migrations
- overkill hypothesis
3- Change in plant diversity
What is the overkill hypothesis?
Human overharvesting is the primary driver in mammal extinctions during the Quaternary Extinction Event
Since climate change overlapped with human migrations, did it cause extinctions?
Perhaps. Either factor alone may not have been enough to cause extinctions.
A combination of both increased the extinction rate.
Explain how the plant diversity changed during the QEE?
Global increase in fire frequency correlating to loss of grass-specialist grazer species.
- Fewer grazers
- More grass, and more fuel for wildfires
Increased fire frequency:
- Global carbon cycle.
What do extinctions in animal species affect?
Biotic systems and abiotic systems
Local and global systems
When are the effects of overharvesting at their worst?
The effects of overharvesting are worse when they occur at the same time as environmental stressors.
Large populations are more resilient to stressors such as climate change.
What are the common patterns in modern overharvesting of
wildlife populations?
- Selective exploitation apex predators
- Removal largest animals from a community
- Targeting of species perceived as “most valuable”
- Eradication of species that are viewed as undesirable
- Wildlife viewed as resources
How are apex predators viewed?
Apex predators are frequently viewed as “pest species”.
They are killed to conserve “desirable” wildlife and domestic species.
However, apex predators exert top-down control on many terrestrial ecosystems.
Explain the phenomenon of the brain worm.
Deer are herbivores: preferred plant species extremely rare in areas with deer overpopulation.
Brainworm: nematode worm which infects brain tissues in cervids.
- Larvae are laid in deer feces
- Snails consume the larvae
- New cervid hosts consume the snails on grass they eat
Deer carry the parasite asymptomatically and can pass the parasite to other species.
- Brainworm is endemic in many populations of white-tailed deer.
Moose are highly susceptible to brainworm
- Causes severe neurological symptoms that lead to death.
The deer move onto the moose’s territory for more food and infect them.
Explain why whales are important for the movement of nutrients.
Whales consume food in the upper layers of the ocean:
- Whale poop and dead bodies bring nutrients to the lowest levels of the ocean.
Whales travel considerable distance: move nutrients to distant locations.
What is the Krill Paradox? What happens instead?
The Krill Paradox: loss of the main krill predator (whales) should have led to increase in krill numbers.
- Classic top-down model
Instead: krill numbers declined with whale populations.
- Bottom-up model: krill are dependent on nutrient input from whale poops.
