Lecture 11 CH 26 Extinction and Conservation of Single Species
I am postponing doing the Ecological Footprint Exercise.
Instead, concentrate for Thursday on the part in BOLD below.
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.
9. Genetic stochasticity leads to loss of rare alleles, especially in small populations.
10. Heterozygosity is lost by inbreeding in small populations.
11. Small populations enter into an extinction vortex with positive feedback loops.
12. Rescue of a population is via introduction of new individuals with added genetic
variation.
I. Biodiversity Components 547-8
Ecological: various adaptations to various niches
Genetic: allelic variation within and between populations
Geographic: regions with >>> #, but also endemic species 26.1, 26.3
II. Extinction is natural and forever!
Types: 554
Background (natural) 1 sp/yr
Mass (up to 95% of species)
Anthropogenic (1/sp / day!)
III.Deterministic causes of extinctions: the ‘evil quintet’ 555-562
Habitat destruction or change (67% of all cases) 26.9
Fragmentation and its associated problems
Climate change and barriers to migration 26.10
Overexploitation
Often changes species composition 26.11
Decline reflects human cultural development 26.13
Chains of extinction
Introduction of exotic species
Eliminate native species and alter ecosystem function 26.14
Islands, aquatic systems especially vulnerable
Emerging diseases
IV. Conservation Planning: Approach for Single Species
Focus on rare, endangered species.
A. Components of rarity
1 Geographic range 2 Habitat specificity 3Local abundance
Classic rare = narrow range, endemic in restricted habitat, small pop.
B. Vulnerability to anthropogenic extinction and conservation plans 561-2
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
C.Small populations >risk of extinction via chance (stochastic) events 556-7; 260-262
Demographic stochasticity - wildly fluctuating probabilities of survival and
reproduction
Genetic stochasticity – random loss of alleles from mating patterns in small pop.
Environmental stochasticity and natural catastrophes - wipe out small populations;
particularly when there is only one or few individuals
Allee effect - inability of the social structure to function (e.g., finding mates)
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
(ICA 1)
D. 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? (ICA 2)
Larger populations persist for longer time; but all eventually go extinct
E. 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. (ICA 3)
V. Small populations > risk of extinction via bottlenecks  > genetic stochasticity
A. Reduced genetic variation lost by genetic drift 277-8
Loss of alleles, especially rare ones, is much greater than loss of genetic
variance (or heterozygosity) per se (ICA 4)
1. More alleles are lost in populations with small numbers of individuals.
2. Alleles with a low frequency in the original population tend to be lost
more easily in the small population than alleles with high frequencies.
Short-term: loss of rare alleles not important in benign environment
Long-term: loss of alleles might be crucial if environment changes
Restored by mutation but > mutation in larger population 13.12, 13.13
B. Inbreeding  loss of specific rare alleles or 13.15
 > homozygous recessives  impaired reproduction and increased
mortality
Heterozygosity
1. loss is greater when population founded by few individuals (ICA 5)
2. Small populations of constant size lose heterozygosity through time (ICA 6)
3. Smaller population, the more rapid the loss
4. More generations of small size, the more heterozygosity is lost.
Serious bottleneck every generation; effects cumulative
Perennially low numbers erode genetic variation
Reduced capacity to respond to environmental change
VI. Extinction vortex of small populations due to positive feedback loops (ICA 7)
VII. How Rescue critically endangered species: 566-7
Immigration (natural) or by captive breeding and re-introductions (with
added genetic variation too) (ICA 8)
Summary 5-16.