Lecture 11 CH 26 Extinction and Conservation of Single Species
MAJOR CONCEPTS
1. Biological diversity has many components (ecological, genetic, geographic).
2. Extinction is natural but its present rate is not.
3. Five types of human activities have accelerated the rate of extinction.
4. Rarity has multiple components (Geographic range, habitat specificity, local
abundance).
5. Small and large organisms differ in why they are vulnerable to human extinction and
differ in how to conserve them.
6. Small populations are at great risk of extinction due to chance (stochastic events)
and low genetic variation to confront environmental change.
7. A minimum population size is required that can withstand environmental variation
and lower inbreeding.
8. Population viability analysis can predict the probability of extinction.
Biodiversity
Amount varies among taxa
Components 547-8
Ecological: various adaptations to various niches
Genetic: allelic variation within and between populations
Geographic: regions with >>> #, but also endemic species 26.11
Values of conserving biodiversity 549-553
Extinction is natural and forever!
Types: 554
Background (natural) 1 sp/yr
Mass (up to 95% of species)
Anthropogenic (1/ sp / day!)
Deterministic causes of extinctions: the ‘evil quintet’ 555-562
Habitat destruction and fragmentation (67% of all cases) 26.9, 26.10
Problems associated with fragmentation
Overexploitation
Often changes species composition 26.11
Chains of linked extinctions 26.13
Introduction of exotic species
Eliminate native species and alter ecosystem function 26.14
Islands, aquatic systems especially vulnerable
Emerging diseases
Conservation Planning: Approach for Single Species
Focus on rare, endangered species.
Components of rarity 547-8
Geographic range
Habitat specificity
Local abundance
Classic rare = narrow range, endemic in restricted habitat, small pop.
Vulnerability to anthropogenic extinction and conservation plans 562
Small species due to small range size and human population densities 
must protect threatened habitat
Large species due to instrinsic qualities
long development period, low reproductive rate, low population densities 
must concentrate on increasing survival and reproductive success.
Populations that migrate hard to conserve: multiple habitats involved. 26.16
Small populations > risk of extinction via chance events 556-7; 260-262
Demographic stochasticity
Genetic stochasticity
Environmental stochasticity and natural catastrophes
Stochastic processes produce a probability distribution of population size 12.16
Probability of stochastic extinction increases with time, especially as pop size decreases 12.17
Criteria for long-term survival
Minimum Viable Population (MVP): 562-3
Smallest sustainable pop in face of environmental variation
Wide distribution so local catastrophe doesn’t wipe out
Some population subdivision so disease can’t spread
How small is small?
50 short term – keeps inbreeding low
500 long-term – allows evolution to occur
‘Effective’ population size = 11% of actual size
How big a preserve necessary to have MVP?
Larger populations persist for longer time; but all eventually go extinct
Population Viability Analysis (PVA) 566
Demographic information put into simulation model with:
demographic, genetic, and environmental stochasticity added 
Predict probability of extinction within 100-1000 years
Cumulative prob. of extinction rises more slowly in large than small pops.
Small populations > risk of extinction via bottlenecks  > genetic stochasticity
Reduced genetic variation lost by genetic drift 277-8
Restored by mutation but > mutation in larger population 13.12, 13.13
Inbreeding  loss of specific rare alleles or 13.15
 > homozygous recessives  impaired reproduction and increased mortality
Reduced capacity to respond to environmental change
Extinction vortex of small populations due to positive feedback loops
Rescue critically endangered species: 566-7
Immigration (natural) 275 or by captive breeding and re-introductions (with
added genetic variation too)
Summary 5-16.