L26: The 6th Extinction Flashcards
What are the main causes of modern extinction?
1) Habitat loss and fragmentation
2) Invasive species
3) Overharvesting/ overhunting
4) Climate change
Percentages threatened with extinction?
Globally, 12% of birds, 20% mammals, and 32% of amphibians are threatened with extinction.
What are anthropogenic biomes?
Anthromes, also known as Anthropogenic Biomes, or Human Biomes, are the globally significant ecological patterns created by sustained interactions between humans and ecosystems.
What are some components of the 6th mass extinction?
1) Evidence of defamation (Dirzo et al., 2014)
2) Evidence of risk and rate of extinction (Ceballos et al., 2015)
3) Minimum viable population (Flather et al., 2011).
What is mass extinction?
Episode of relatively abrupt (few million of years) replacement of virtually all biotas.
What is the 6th mass extinction?
The ongoing anthropogenic decline in biodiversity (Leaky and Lewis, 1995).
6th mass extinction
Defaunation
Much like deforestation, means the loss of animals in all its myriad forms, including extinction, extirpation, or population declines.
Size selective defaunation gradient (larger mammals die out).
(Dirzo, 2014).
What kind of behavioural/ physiological consequences can defaunation have?
Foraging
Movement
Diet
Habitat selection
Defaunation
What kind of ecological consequences can defaunation have?
Short/ mid term:
Standing diversity
Structure
Long term: Ecosystem processes (ecoservices)
What kind of evolutionary consequences can defaunation have?
Phenotypic changes
Genetic structure
What was the Kenya Long Term Exclosure Experiment?
Large wildlife are effectively removed by fences, as evidenced by mean different in dung abundance.
Positive effects for almost all small body consumers.
Negative impact on ticks.
Alteration of mutualism between ants and the dominant tree.
(Dirzo, 2014).
What are the causes behind defaunation?
1) Habitat loss/ fragmentation including deforestation
2) Overexploitation of species for “meat”, medicine, or trophies.
3) Invasive species.
Extinction is not only the loss of a species from the face of the Earth…
There’s a loss of critical ecosystem functioning in which animals play a central role that we need to pay attention to as well.
(Dirzo, 2014).
What kind of habitat changes are being experienced in the global oceans?
Loss of coral cover
Increase in namer of marine wind turbines
Increase in container port traffic
Loss of mangrove area
Increase in seabed mixing contracts
Increase in number of dead zones
Comparison of range contractions for select marine and terrestrial fauna
On many levels, defaunation in the oceans has, to data, been less severe than defaunation on land.
Risk and rate of extinction
Rates of species extinction are difficult to determine on “natural conditions”.
The high rate of species extinction is largely a result of ecosystem degradation by humans.
Establishing species conservation priorities and recovery goals is often enhanced by extinction risk estimates.
Biologist focusing on conservation at the population and species levels follow two main approaches:
The small population approach (minimum viable population): the population size required to provide probability of persistence for a given period of time.
The declining-population approach (also relevant for risk and rate of extinctions).
What do we do the in declining population approach?
1) Confirm that the population is in decline
2) Study the species natural history and environmental factors that cause the decline
3) Apply the results of the diagnosis to manage for recovery
Evolutionary implications of small population size
1) A small population is prone to inbreeding and genetic drift
2) The key factor is loss of the genetic variation necessary to enable evolutionary responses to environmental change.
3) Small populations and low genetic diversity do not always lead to extinction.
(Lomolino et al., 2011)
What are the processes driving an extinction vortex?
Small population leads to…
Inbreeding/ genetic drift and therefore…
Loss of genetic variability and…
Reduction in individual fitness and population adaptibility leading to…
Lower reproduction/ higher mortality and….
A smaller population.
What does a meaningful estimate of MVP require?
Determining the effective population size, which is based on the population’s breeding potential.
What does Flather et al, 2011 conclude long term persistance requires?
Approximately 5000 adult individuals without taking into account taxonomy, life history or environmental conditions
Case study of minimum viable population
(Berger, 1990)
Persistence of 120 bighorn sheep populations followed for up to 70 years in the US southwest.
All the populations with fewer than 50 individuals went extinct within 50 years.
Define mass extinction
(Hallam & Wignall, 2002)
Mass extinction refers to “the extinction of a significant proportion of the world’s biota in a geologically insignificant period of time”.
Raup (1992) suggests that approximately half the earth’s surface must be environmentally affected in order for a mass extinction, on par with previous mass extinctions, to occur.
