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Lecture 13, 07 Oct. 2008Small Population Probs

Conservation BiologyECOL 406R/506R

University of ArizonaFall 2008

Bonine & Epps

Lab Friday-Sunday 17-19 October (leave 1230 Friday [west side BSE], return 1830h on Sunday)Hat, water bottle, food [plate, cup, utensils?], snacks, $?, sunscreen, close-toed shoes, layers, pants, binos, (cooler?, jug), ID/VISA- Readings on Course Website

506 meet at 1505h today

Upcoming ReadingsThurs 09 October (Con Gen): Edwards et al. 2004; HOGL, Conservation Projects website; read for big picture: DeSalle & Amato 2004Tues 14 October (~PVA): Primack CH6; Marmontel et al. 1997; optional: Gilpin 1996

-506 Thurs

Primack Ch5&6, Panther PVA (skim)

NO LAB 31 OCTOBER

THANK YOUs

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406/506 Exam 1 fall2008mean = 74.9%max = 98.7%min = 42.7%

00.5

11.5

22.5

33.5

30 36 42 48 54 60 66 72 78 84 90 96More

N = 30

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Quiz (07 Oct 2008)

1. Draw and label a graph that represents the concept of the equilibrium theory of island biogeography (MacArthur & Wilson, 1967) (3 pts)

2. Please explain this figure from your Thomas and Reid article from Thursday last week (& Kathy Gerst’s lecture). (2 pts)

3. What does MVP stand for in the context of this course? (1 pt)

5. What are you preparing for the creativity exhibition on 02 December? (1 pt)

4. Explain the distinction between endogenous and exogenous disturbances. Use examples. (2 pts)

0. Name. Date. (1 pt)

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1. Island BiogeographyQuammen Excerpt from Song of the Dodo (p.52-55)

LyellWallaceDarwin

MacArthurWilson

Frogs vs. Birds

Oceanic vs. Continental

Size, Age, Distance

dispersal

succession

~equilibrium

Revisit

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Intermediate Disturbance Hypothesis

“supercompetitors”“succession reset”

Revisit

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Populations &

Extinction

(see Primack Ch 5 & 6 etc.)

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Species’ Vulnerability to Extinction, LIST A

1. Small geographic range

2. One or only a few populations

3. Small population size(s)

4. Declining population size(s)

5. Actively harvested by humans

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Small population size(s)

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Species’ Vulnerability to Extinction, LIST B

1. Individuals have large home ranges2. Individuals have large bodies3. Poor dispersers4. Seasonal migrants5. Low genetic variability6. Specialized habitat7. Only in stable, pristine environments8. Individuals aggregate9. Evolved isolated from humans10. Species with threatened/extinct relatives

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Populations, Genetics&

PVA (population viability analysis)

(thanks to Margaret Evans)

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11Groom, Meffe, & Carroll 2006

Population Dynamics

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populations are dynamic, not static

Lemmings

Cause of cyclic change in population not completely understood. Cycle length average 3.8 years. Mass migration in response to high density with decreasing food supply, sometimes swimming involved.

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populations are dynamic, not static

Whales in the Antarctic

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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

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1. Exponential growthdensity-independent, deterministic

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

dtRing-necked pheasant

on Protection Island

= (b-d)N

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exponential growth: an unrealistic model?

Humans on planet Earth

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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

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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 behavior

In plants:-pollinator limitation-self-incompatibility-inbreeding depression

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Allee effectHow?group defense against

predators

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

- 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 predictpopulation size

What would Darwin & Wallace say?

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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

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Life Table

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25Life Table

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3. Density-independent, deterministic, structured population growth

What else can structured population models tell us?Sensitivity

The 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???

(Lambda = population growth rate)

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When lambda is greater than 1 the population increases in size

When lambda is less than 1 the population decreases in size

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Van Dyke p. 178

“Four Horsemen of the Extinction Apocalypse:”

1. Genetic Stochasticity

2. Environmental Stochasticity

3. Demographic Stochasticity

4. Natural Catastrophes

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Small Populations-reduced gene flow-inbreeding depression-drift-stochasticity-effective population size (Ne)

(Vs. Declining Populations)

Genetic Diversityand

Population Size

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Effective Population Size

• Ne = 4NmNf / (Nm+Nf)

• Eg: a population of seals with 6 males and 150 females?

• Ne = (4*6*150)/(6+150) = ~23

(Number or Breeders)

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Van Dyke 2003

Inbreeding Coefficient, F(2 alleles identical by descent)

1% Rule (Frankel and Soule)

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Quickly lose rare alleles in bottlenecks

Cheetah Major Histocompatibility

Complex

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Genetic 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?

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Cyprinodon maculariusDesert 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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Population Extinction Vortex(problems with small populations)

F Vortex: inbreeding depression, lethal equivalents(homozygous recessives)

A Vortex: genetic drift and loss of variation(can’t adapt)

R Vortex: r = spontaneous rate of increase(coupled with environmental stochasticity)

D Vortex: discontinuity (isolation)

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37VanDyke 2003

F

A

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R

D

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Hardy Weinbergand Heterozygosity

two alleles: p, q

(p + q)2 = p2 +2pq + q2

Under Hardy Weinberg EquilibriumHe = 2pq

Ho can be calculated

If p=0.6, q=0.4, then 2pq = 0.48 = He

Inbreeding, if Ho < He

Outbreeding, if Ho> He

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Equilibrium Heterozygosity (∆H = 0)

H* = 2Nm

H = heterozygosityN = population sizem = mutation rate

Therefore, smaller populations have lower equilibrium heterozygosity

Assumption: reduced genetic variation in a population correlated

with reduced ability to adapt to changing environmental conditions.

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Minimum Viable Population (MVP)(Frankel, Soule, Franklin, Shaffer)

50/500/+ Rule

Short term

Mid term

Long Term

PVA…

42Groom, Meffe, & Carroll 2006

Population Viability Analysis

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IN: Population Viability Analysis. Steven R. Beissinger and Dale R. McCullough, eds. Univ. of Chicago Press, Chicago. xvi + 577 pps.

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-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

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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?

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