Fall 2009 IB Workshop Seriessponsored by IB academic advisors

Preparing for Graduate School

Thursday, Oct. 14:00-5:00pm 135 Burrill

Learn about the ingredients for deciding whether and when to go to grad school. Also covered will be the timeline for the GRE and

application and admission process.

Ecological footprints of some nations already exceed available ecological capacity.

Our ecological ‘footprint’…1) meet with CERC director about energy usage2)

Conservation Biology IB 451

- Every other year in the spring

- Next time it will be taught is spring 2011

Ch 26: Biodiversity, Extinction + Conservation

Objectives• Types of biodiversity• Values of conserving biodiversity• Causes of extinction• chance• deterministic factors• small population size• Conservation of single species• population bottleneck + genetic diversity• small populations + inbreeding depression• documentation of loss of alleles/heterozygosity• method of restoring allelic diversity + increasing population size

Biological diversity is incompletely catalogued: 1.5 of 10-30 million!

Components of Biodiversity• Ecological diversity

• Genetic diversity

• Geographic diversity

Values of biodiversity• Moral• Aesthetic• Economics• Ecotourism• Indicate environ. quality• Maintain ecosystem function

Extinction is forever…• Background = natural rate (1 sp. / year)• Mass extinction (up to 95% of all species) • Anthropogenic (1 sp. / day!)

Deterministic causes of extinctions:the ‘evil quintet’

1 habitat destruction and fragmentation (67% of cases)2 overkill3 chains of extinction4 introduced species5 emerging diseases

Natural fragmentation: extinctions and recolonizations related to distance to mainland

1. Habitat reduction and fragmentationlead to endangered species

Smaller fragments support fewer animals.

Habitat reduction and elimination

• Some habitats are eliminated altogether.• Fragmentation causes other problems:• reduced total area• reduced habitat heterogeneity• reduced connectivity• greater inter-fragment distance• unable to migrate with changing climate• reduced interior/edge ratio

3. Overkill for non-food item.

3. Overexploitation + 4. chains of linked extinctions• often changes species composition of a

community

4. Introduction of exotic species--->• Eliminate native species and alter ecosystem• Especially vulnerable are islands, aquatic systems

5. Emerging Diseases

Conservation planning: Approach 1• Focus on ecological requirements and area

needed by individual, often ‘charismatic’ species.

Focus on rare, endangered species. How is ‘rarity’ defined?

classicrare sp.

Difference in vulnerability andconservation plans:

• Small species:

• small range size

• human population densities-->

• must protect threatened habitat

• Large species:

• intrinsic qualities (long development,

low reproduction, low pop size -->

• concentrate on increasing lx + mx

Small populations at > risk to extinction via chance events, e.g. • Demographic stochasticity

• Genetic stochasticity

• Environmental stochasticity and natural

catastrophes

Stochastic population processes produce a probability distribution of population size.

Probability of stochastic extinction XXXXX over time (t), but decreases as a function of XXXXXXXXX.

Criteria for long-term survival:

• Have Minimum Viable Population (MVP) = smallest population that can sustain itself in face of environmental variation---> avoid stochastic extinction

• have wide distribution so that local catastrophe doesn’t wipe out entire population

• have some population subdivision to prevent spread of disease

How small is small?

• 50/500 estimate

• 50 short-term: keep inbreeding low

• 500 long-term: allows evolution to occur

without genetic drift

• Effective population size = 11% of actual

population size

How big a preserve is necessary to ensure MVP?

***What’s main ‘take-home’ message?

>100

<15

Years 5010

100

0

% pop.

persisting

Population Viability Analysis (PVA):

Put demographic info into model with

stochasticity added -->

Predict probability of extinction within

100-1000 years

Useful only if well-studied species

***What’s main ‘take-home’ message?

Years0 1000

Cumulativeextinctionprobability

.01%

.1%

1%

10%

100%

2500 km2 No = 3000

No = 6050 km2

Population Bottleneck: period of small pop. size.

…subject to genetic stochasticity

Populations undergoing a population bottleneck experience founder events and genetic drift,. Each causes a loss in genetic variation.

Allelebecomesfixed = novariation.

+ genetic drift

The drift-mutation balance preserves more genetic variation in large than small populations.

Smaller populations have less minisatellite variation; it has been lost by genetic drift.

Inbreeding decreases the frequency ofheterozygotes in a population. Allows expression of deleterious recessive alleles.

Loss of genetic variability has both qualitative & quantitative

aspects

Qualitatively, specific alleles will either be lost or retained

Quantitatively, genetic variance (or heterozygosity) will be lost

Extinction vortex of small populations due to positive feedback loops.

Population started by 1 pair--> little population growth. Then new male arrives --> explosion. WHY?

Pedigree shows high level ofinbreeding insmall wolf pop.

Selfing reduces reproductive fitness.

Population bottleneck. Partial rescue by immigration from source population.

Bottlenecks will usually have a greater qualitative than

quantitative impacti.e., the loss of alleles,

especially rare ones, is much greater than the loss of

genetic variance (or heterozygosity) per se

Original number of alleles = 4allele freq. = p1 = .70 p2 = p3 = p4 =.10 N = 2 (two individuals)E = # alleles retained

E = 4 - (1- .10) = .6561 (1- .10) = .6561 (1- .10) = .6561

(1- .70) = .0081 - little influence-- large influence-

2x#ind.

E = 4 - (.0081 + .6561 + .6561 + .6561) = 2.02 alleles left of original 4

Loss of alleles:

Table 1 AVERAGE # OF 4 ALLELES RETAINED# INDIVIDUALSIN SAMPLE (N) P1=.70, P1=.94, P2=P3=P4=.10 P2=P3=P4=.02

1 1.48 1.12 2 2.20 1.23 6 3.15 1.64 10 3.63 2.00 50 3.99 3.60 >>50 4.00 4.00

Two conclusions:

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 much more easily in the small population than alleles with high frequencies.

In the short run, the loss of rare alleles is probably not very

important, especially in benign environments.

In the long run, though, such alleles might be crucial; in an

evolutionary sense.

Table 2 # % original percentagefounders heterozygosity lost retained 1 50% 50 2 75 25 6 91.7 8.3 10 95 5 20 97.5 2.5 50 99.5 0.5 100 100 0

Changes following the reduction in size

When numbers are low, a population is, in effect, going through a serious bottleneck

every generation, and the effects are cumulative.

% Genetic Variance (heterozygosity) Remaining after t generationsPopSize (N) 1 5 10 100

2 75 24 6 <<1 6 91.7 65 42 <<1 10 95 77 60 <1 20 97.5 88 78 8 50 99 95 90 36100 99.5 97.5 95 60

Table 3

Conclusions:

• Small populations of constant size always lose heterozygosity through time.

• The smaller the population is, the more rapidly heterozygosity is lost.

• The higher the number of generations a population of small size is bred, the more heterozygosity is lost.

The crucial issue is whether the population remains small or grows to a relatively large size.

It is perennial low numbers that erode genetic variation.

Additional Problems Faced by Populations of Small Size

• Demographic Stochasticity - wildly fluctuating probabilities of survival and reproduction

• Environmental Stochasticity - 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)