Population Viability Analysis Lecture15

What sort of PVA model is appropriate?

Puerto Rican parrotBlack footed ferret

DISCUSSWhat is gained from using PVAs?

USES OF PVA

1. Assessing the extinction risk of population

QuestionsWhat type of model to use?Simple - 1 population, all individuals equal

- 1 population, with st(age) structure

- multisite- patch occupancy models

Complex - multisite, structure+ spatially realistic

IssuesData qualityParameter values may

change

MORE USES OF PVA

1. Assessing the extinction risk of population

2. Comparing the relative risk in 2+ populations

3. Identify key life history stages to protect

4. Determining minimum reserve size5. Determining numbers to release6. Setting harvest guidelines

2. Compare relative risks of populations

Pacific salmon populations Allendorf et al. 1997

Aim: Assess threat, rank priority of acting

2. Compare relative risks of populations

Allendorf et al. 1997

Approach: use PVA to assess threat

Used Stage-structured models

Designated three levels of riskVery high: 50% within 5 yrsHigh: 20% within 20 yrsModerate: 5% within 100 yrs

Q. What additional factors may impinge on ranking management priorities?

2. Compare relative risks of populations

Allendorf et al. 1997

Combined estimated extinction risk with

123

To get overall priority for management

E.G. RED COCKADED WOODPECKER

Endemic to southeastern USNest in cavities in old pinesEndangeredLive in groupsMales - breeder, helper, floaterFemales - breeder, floater

3. Identifying key stages for management

STRUCTURED MODEL

STRUCTURED MODEL

Modelling approachIdentify stages (age/types)Data needed - transition probabilities

- stage specific survival/fecundityTrack numbers of each stageASK - What parameter influences viability

Sensitivity analyses

Sensitivitychange in due to small absolute changein stage specific vital rates

Elasticitychange in due to small % changein stage specific vital rates

Parameter (M=male, F=female, Fldg =Fledgling)

Q What factors had the biggest impact on lambda

STRUCTURED MODEL

RESULTSModel most sensitive to1. Changes in female mortality2. Mortality of female dispersers3. Fledglings/brood

RECOVERY PLAN1. Enhance dispersal to new sites

by making nest cavities2. Remove competing flying

squirrels

4. Estimating the reserve size necessary to protect grizzlies in BC

Aim: establish 1 benchmark population/biogeoclimatic zone

benchmark = unhunted, naturally regulated population

How many bears and how big an area?

Approach- use PVA to get N with low risk of quasi-extinction (ie risk of falling below 100) in 20 years

cubs yearlings Sub-adult F Adult F

Data from 6 different grizzly bear popn’s ----> mean±SDAge-specific survivalAge at first birthFecundity (female cubs/adult female/year)Maximum age

Stochasticity - environmental +demographic

- no catastrophes

Density dependence - none below K

RESULTSInitial N Pextinction Textinction (years)100 1 1150 0.7 2200 0.05 19250 <0.01 >20

Density Area neededFlathead Valley, seBC 6.4/100km2 3900 km2

South central BC 2.3/100km2 10,700 km2

But bears can/do move outside any fixed area--->Recommendation??

Wielgus 2002 Biol Conservation

Final recommendation for 6 reserves MVP = 250 animals = 11-15% BC pop’n

Total area51,000 km2 5% of land area of BC

Uses of PVA5. How many individuals can be released

Bearded vulturesDisappeared from Alps in 19th centuryRestricted to Pyrenees, southern Balkans, Corsica and Crete

Uses of PVA5. How many individuals can be released

1970’s reintroduction attempt - fails---> captive breeding program

1986 2nd reintroduction program1993 100 captive, 53 released into Alps

Demand for captive birds was increasingHow many birds can be released per year?When is the wild population viable?

Bustamente 1996 Cons Biol 10 822-831

ApproachDo PVA on captive population with varying numbers of fledglings used for reintroductions

PLUG DATA INTO VORTEX

Age specific mortality Fecundity - breed 7-31yrs; not density dependentNo Inbreeding depressionCatastrophe 1% chance Initial pop’n 50m 39f > 1 yrK = 200 set by $$$ cost

Kids released extinction rate time (% in 200 yrs)

3m3f 1.6 884m4f 8.6 705m5f 22.8 716m6f 52.6 647m7f 74.4 62

Q. How would you inform captive breeders what would best increase numbers to be released?

actual

How viable is the reintroduced population?

ApproachPLUG MORE DATA INTO VORTEX

Data availableFecundity - Pyreneean populationMortality - from released birdsInbreeding - likelyVariance ???

OUTPUT - IF mortality as low as minimum estimates current population < 5% chance extinction in 200 yrs with no additional releases

Uses of PVA6. Setting harvest limits for American ginseng

Panax quinquefolium(COSEWIC)

1988 “threatened”1989 export discontinued

Harvest continues - but what is sustainable?

Approach used Nantel et al. 1996 Cons Biol 10

Stages in the life of a long lived perennial plant

SeedSeedling1-leaf2-leaf3-leaf4-leaf

Assess mortality transitions and seed production

4 populations southern Ontario /Quebec

Incorporate variance

use between yr/between population variation

SeedsSeedling1 leaf2 leaf3 leaf 4+ leaves

Produce seeds

Death

Harvest

Seedling1 leaf2 leaf3 leaf 4+ leaves4+ leaves

Estimate growth rates of 4 populations under different harvest regimes

Estimate minimum viable population Ie lowest N0 where extinction < 0.05 over 100 yrs

MVP with no harvest estimated as 170 plants

Quebec 3 popn’s >500 most <50Ontario populations average 10-20 plantsCanada 12 known popns > 170

ImplicationsMost pop’ns too small to harvestAnnual harvest >10% will lead to extinctionRotation 5+ yrs would be prudent

The Major Challenges for PVA models

Data requirementsDeveloping robust variance estimatorsIncorporating change to the environment

What makes a good PVA? Understanding of the species ecologyenvironmental disturbances/threatsSpecies response to threatsAssessment of Current state of populationFuture risksEvaluation of habitat as well as populationRelevance to managers

But NOT necessarily amount of dataWhy?

Burgmann and Possingham 2000

PVAs - the bottom line

Stochastic population modelsTool for evaluating risk to populations

Numerous uses-Accuracy - debated -- but allow assessment of the relative value of management options

Major value may be that they organise information, engage stakeholders