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Extinction Risk (primary risk factors for extinction vulnerability (Narrow…
Extinction Risk
primary risk factors for extinction vulnerability
Narrow geographic range
Only one or a few populations
Small population size
Lives on island habitats
Hunting or harvesting by people
Measuring Extinction
background extinction rates
species last about 1-10 million years before it goes extinct or evolves
island biogeography model
explains species-area relationship
islands with large areas have more species than islands with smaller areas
S=CA^Z
used to predict how many species will go extinct to habitat loss
insular biogeography
explores species diversity in isolated natural communities
conclusions
explains how isolated natural communities on the mainland respond to habitat loss.
Humans are causing the sixth mass extinction.
Mass extinctions have unpredictable effects on the evolution of species.
Problems of Small Populaitons
main reasons for local extinction
loss of genetic diversity and related problems of inbreeding depression and genetic drift
genetic drift
random process of allele frequency change
inbreeding depression
an individual receives two identical copies of a defective allele from its parents
demographic fluctuations due to random variation in birth and death rates
environmental fluctuations due to variation in predation, competition, disease, and food supply as well as natural catastrophes that occur at irregular intervals, such as fires, floods, storms, or droughts
factors that determine effective population size
unequal sex ratio
variation in reproductive output
population fluctuations and bottlenecks
founder effect
when a few individuals leave one population and establish a new population
stochasticity
random variation in the biological or physical environment
extinction vortex
the smaller a populations becomes, the more vulnerable it is to the combined effects of low genetic diversity, demographic variation, and environmental stochasticity
The Meaning of Extinct
types of extinction
extinct in the wild
individuals of the species only remain alive in captivity
locally extinct
the species is no longer found in a specific area it once inhabited
functionally extinct
it persists at such reduced numbers that its effects on the other species in its community are negligible
extinct
no member of the species is found alive anywhere in the world
human-caused mass extinction
elimination of large mammals from Australia and the Americas when humans first colonized these continents
extinction rates in aquatic environments
some of the highest rates of extinction have been recorded for freshwater fishes
Vulnerability to Extinction
features predictive of extinction
narrow geographic range
only one or a few populations
small population size
island habitat
hunting or harvesting by people
additional features that put species at risk
large home range
large body size
slow reproduction
limited dispersal ablility
little genetic variation
specialized niche requirements
low tolerance for disturbance
permanent or temporary aggregations
