Extinction Flashcards
Extinction in the Holocene era (10,000 years ago)
Largest ground sloth was the size of an elephant.
Claws could reach 50cm in length.
Ground sloth was nothing like other animals, tiny head, slim shoulders and massive hind quarters.
Herbivores like their modern day tree sloth predecessors.
What is there a long term balance between
Rates of speciation and extinction
How can an equilibrium species richness be predicted
Based on rates of extinction and speciation among existing species
How many species have evolved on earth over the last 3.5 billion years
4 billion
What percentage of the 4 billion species have gone
99%
What does the species we have today represent
A very small proportion of what has been living in the planet
How many mass extinctions has there been
5 so far
What are mass extinctions
Times when the earth loses more than three quarters of its species in a geologically short interval
What are the names of the extinction events
Ordovician Devonian Permian Triassic Cretaceous
How much did the Ordovician event lose
86%
How much did the Devonian event lose
75%
How much did the Permian event lose
96%
How much did the Triassic event lose
80%
How much did the Cretaceous event lose
76%
The main causes of the Ordovician event
Onset of alternating glacial and interglacial episodes
The main causes of the Devonian event
Global cooling followed by warming, tied to diversification of plants
The main causes of the Permian event
Siberian volcanism and global warming
The main causes of the Triassic event
Elevated co2 levels increasing temperature and ocean acidification
The main causes of the Cretaceous event
A meteor causing a global cataclysm and caused cooling . May have also been climate change before
What do mass extinctions account for
4% of total extinctions (background rate is high)
What do mass extinctions do
Disrupt overall development of diversity
What do survivors of mass extinctions tend to be
Generalists and opportunists
How long does it take after a mass extinction to recover biodiversity
10 million years
What is the lifespan of all species
1 million
What does the IUCN red list data say about extinction
27,000 species are threatened.
14% birds
25% mammals
40% amphibians
Why is speciation not a relevant time frame to ya
Because time frame for speciation isolation is longer than extinction
What are traits promoting survival
R-selected traits Large populations. Widespread. High genetic variability. Rapid dispersal. Human commensalism.
Traits promoting extinction
K-selected traits. Small populations. Rare. Low genetic variability. Slow dispersal. Exploited by humans.
What are r species
Opportunistic pioneers. They have been selected for their ability to reproduce rapidly
What are k species
Specialists. Have features that favour populations remaining close to the habitats carrying capacity
Example of an r selected species
Brown rat
6 rats per pregnancy and 6 generations a year
Example of a k selected species
African elephant
1 calf per female every 5 years
What is the potential growth of the female population of rats vs elephants
Over 2 trillion female rats but only 2.4 female elephants
What are the features to look at for r and k species
Habitat Populations Body size Growth Time to mature Reproductive period Offspring Parental care Adult mortality Dispersal ability
What is the habitat like for r species
Unstable, unpredictable
What is the population like for r species
Fluctuate widely
What is the body size like for r species
Small
What is the growth like for r species
Rapid
What is the time to mature like for r species
Short
What is the habitat like for k species
Stable and predictable
What is the populations like for k species
Close to carrying capacity
What is the body size like for k species
Large
What is the growth like for k species
Slow
What is the time to mature like for k species
Long
What is the offspring like for k species
Many, small
What is the parental care like for k species
Little or none
What is the adult mortality like for k species
High
What is the dispersal ability like for k species
High
What is the offspring like for r species
Few, large
What is the reproductive period like for k species
Longer
What is the parental care like for k species
High
What is the adult mortality like for k species
Low
What is the dispersal ability like for k species
Low
How does population size affect extinction
Initial population size defines likelihood of extinction for both animals and birds e.f small is more likely
How does range size affect extinction
Small geographic ranges (species endemic to islands) means more extinction
What are the demographic reasons about why small and isolated population so vulnerable
Unequal sex ratio.
Low change of locating a reproductive partner.
Low fecundity due to age, illness.
Low cooperative interaction in food acquisition, predator detection.
Example of a skewed sex ratio
Selecting hunting of males in elephants seals leads to skewed sex ratio.
Males:females.
10:90 means only 36 are the effective population
How does genetic variation affect extinction
Small populations means low genetic diversity and low genetic diversity limits the ability to respond to new conditions and causes inbreeding depression - leads to higher offspring mortality.
How does dispersal ability affect extinction
High dispersal ability you have lowest rate of extinction to proportion going extinct. Being able to disperse reduces vulnerability to extinction.
How does relationship with humans affect extinction
Some species benefit from humans (commensal species derive food or other benefits from another organism without hurting or helping it) but others have antagonistic relationships with humans.
What is the most likely explanation for global extinction of megafauna in pleistocene
Humans or maybe climate change - depends where and and the species. Synergetic effect. In Africa it’s mainly climate change but in the America it’s mainly humans
What are the parts of the extinction vortex
A mix of directional factors, genetic problems and stochastic factors all affecting each other.
What are directional factors
Habitat loss
Pollution
Over exploitation
Exotic species
What are the stochastic factors
Demographic stochasticity
Environmental variations.
Catastrophes.
What is the extinction vortex
Small fragmented isolated populations -> inbreeding loss of genetic diversity -> reduces adaptability, survival and reproduction -> reduced N -> back to the beginning
What are the predispositions to extinction
Rarity (small range, small populations) Large, slow growing and long lived. Large area requirements. Top of food web/conflict with humans. Specialised needs. Adapted to core habitats. Poor dispersal/insular.
How do forest edge effects on populations
Some species use corridors between rainforest patches e.g generalist ants but others can’t live in the disturbed environment e.g forest specialised ants.
What animals has a large area requirements and conflict with humans
Eurasian wolf
