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Conservation Biology identifies 5 threats with Respect to Genetics:

(p. 147 Van Dyke)

1. Inbreeding Depression

2. Loss of Genetic Variation and Heterozygosity

3. Accumulation of Harmful mutations

4. Introgression/Hybridization

5. Outbreeding Depression

Quickly lose rare alleles in bottlenecks

Cheetah Major Histocompatibility

Complex

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Drift

When populations number less than a few hundred individuals random events become more important to

genetic structure of population than natural selection

3,000-10,000 breeding adults

Cyprinodon macularius

Desert Pupfish

Photograph Courtesy of John Rinne

Desert pupfish declined due to the introduction and spread of exotic predatory and competitive fishes, water impoundment and diversion, water pollution, groundwater pumping, stream channelization, and habitat modification.

Healthy population of almost 10,000 fish inhabits this oasis. This last refuge of a unique fish is being actively managed.

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Cyprinodon macularius Quitobaquito pupfish (Endangered since 1986)

This tiny fish was once part of a widespread population, the range of which included the Colorado, Gila, San Pedro, Salt and Santa Cruz rivers and their tributaries in Arizona and California. The ancestors of the Quitobaquito and Sonoytariver pupfish are believed to have been cut off from their relatives in the Colorado River drainage about one million years ago.

The warm, slightly brackish water at Quitobaquitois ideal habitat for pupfish. Pupfish can tolerate salinity levels ranging from normal tap water to water three times saltier than the ocean. Therefore, they are well suited to desert environments where high evaporation rates create water with high salinity levels.

Although the water temperature at the spring is a constant 74°F, the water temperature in the pond fluctuates greatly during the year, from about 40°F or cooler in January to almost 100°F in August, especially in shallow areas... very tolerant of rapid temperature change and low oxygen content due to summer heat.

Desert PupfishFamily Cyprinodontidae

Photograph Courtesy of John Rinne

-1-1/4 inches longmax. age of three years

-females are gray and drabmales are bluish, turning bright blueduring spring breeding season.

-feed on insect larvae and other organic matter from pond bottom.

-prefer shallow pond depths, about12 to 18 inches deep.

Introgression

RED WOLF (Canis rufus)Coyotes, Gray wolves, Dogs

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Techniques

mtDNAnuclear DNA

Galapagos Marine Iguana (Iguanidae)

Amblyrhynchus cristatus

Only lizard to feed at sea-algae, seaweed

Up to 10 or 12 m deepUp to a hour-long dives for large males

(Darwin shipmate)

Highly social8,000 indivs/ km of coast

16 islandsCold upwelling water nourishes algae

Fernandina/Isabelamales to 10+ kgfemales to almost 3 kg

Genovesamales only to 1 kgfemales to < 1kg

Why? Water temperature and current strength

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Martin Wikelski, Princeton

Katrina Mangin

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Amblyrhynchus cristatus

El Nino lack of food (Why?)

Starvation b/c high cost of salt excretion

Animals may lose 15% body length-bone absorption

Only adult vertebrate known to regularly shrink(astronauts)

Largest animals die-sexual selection-natural selection


What is population viability analysis? (PVA)

Thanks to Margaret Evans, 2003

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Population viability analysis isa quantitative analysis of population dynamics

with the goal of assessing extinction risk

DemographicData

MathematicalAnalysis

Prediction ofextinction risk

•survival and fertility throughout an organism’s life cycle•population size over time•birth and death rates

•matrix model•time series analysis•branching process•stochastic birth-death process•reaction-diffusion equation

•population growth rate (λ)•extinction probability•time to extinction•future population size or structure

Simulation vs. Summary Statistics (role of sampling, endangered species)

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Why do we do population “viability” analysis?

U. S. Endangered Species Act (1973)codifies in law a national policy of avoiding the extinction of species

U. S. National Forest Management Act (1976)“[f]ish and wildlife habitat shall be managed to maintain viable populations of existing native and desired nonnative vertebrate species in the planning area…In order to insure that viable populations will be maintained, habitat must be provided to support at least a minimum number of reproductive individuals and the habitat must be well distributed so that those individuals can interact with others in the planning area”

U. S. Marine Mammal Protection Act (1994 amendments)stock assessment process

What do I mean by “population dynamics”?

populations are dynamic, not static

Grizzly bears,

Yellowstone National Park

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Sheep on the island of Tasmania


Lemmings

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Whales in the Antarctic

Population sizes change over time

Why?What causes change in population size?What regulates population size?

If we can answer these questions, we might be able to make changes that increase populationsof declining (endangered) species

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Many things affect population size

population size

competitionwithin a speciesamong species

other interactionspredation, herbivory,

pollination, etc.

population structure

environmental variation

good years, bad yearssuccession or disturbance

habitat attributesquantity, quality, configuration, and connectivity

chance eventsdemographic

genetic

1. Exponential growthdensity-independent, deterministic

In a closed population (no immigration or emigration),population growth is a function of birth and death rates

dNdt

= (b-d)NRing-necked pheasant

on Protection Island

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exponential growth: an unrealistic model?

Humans on planet Earth

dNdt

= rN K-NK( ) intraspecific competition

stabilizes population sizebirth rates go down and/or death rates go up with increasing population size

2. Logistic growth density-dependent, deterministic

carryingcapacity (K)

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Allee effect

Alternatively,The population growth rate may increase with population size (positive density-dependence)

minimum viable population size

Allee effectHow?

group defense againstpredators

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Allee effectHow?In animals:-group defense against

predators-group attack of prey-mates difficult to find-critical number to stimulate

breeding behaviorIn plants:-pollinator limitation-self-incompatibility-inbreeding depression

The two categories of models we have considered thus far assume that

1. all individuals in a population have thesame birth and death rates

(no genetic, developmental, or physiological differences among individuals)

under some circumstances, this might cause us to inaccurately predict population size

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This is the type of model most often used in population viability analysis

What is meant by “structure”?A population is unstructured if all individuals have the same rates of survival and fertility.A population is structured if differences among individuals in age, developmental stage, or size cause them to have different survival or fertility rates.

3. Structured population modelsdensity-independent, deterministic

Life Tables

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3. Density-independent, deterministic, structured population growth

What else can structured population models tell us?

SensitivityThe sensitivity of λ to each matrix element describes how much λ will be affected by a change in that transition probability

Would it be better to focus conservation efforts on improving the survival of hatchlings or large juveniles or adults???

3. Density-independent, deterministic, structured population growth

What else can structured population models tell us?

ElasticityElasticities quantify the proportional change (e.g., 1%) in the asymptotic growth rate that can be expected given a particular change (1%) in each life history transition.

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-Gilpin Intro to PVA (see course website)-stochasticity!!

Van Dyke p. 178

“Four Horsemen of the Extinction Apocalypse:”

1. Genetic Stochasticity

2. Environmental Stochasticity

3. Demographic Stochasticity

4. Natural Catastrophes

-Panther Article on PVAs over time

-VORTEX-data-population size?-source and sink?-inbreeding problems?-captive breeding?-introgression?-time scale?-HABITAT LOSS

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-time scale?

-data

PVA requires lots of data, which takes time, work, and money, whereas managers want answers (predictions about extinction) now. Few species will get thorough PVA. When should PVA be used and what type of PVA (how complex)?

Predictions from PVA can only be as good as the data that go into the analysis. We can only have degrees of confidence in the predictions from PVA. Populations should not be managed to their “minimum viable population” size.

One of the greatest strengths of PVA is the ability to play “what if” games with the model. That is, what if management were to increase patch sizes or connectivity? What if adult survival were improved?

Last thoughts on PVA

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xx

El Endo

lecture 17, 19 october 2004 - ua site...

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