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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