population viability analysis. critically endangered threatened endangered criterion reduction in...
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Population Viability Analysis
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Critically Endangered ThreatenedEndangeredCriterion
Reduction in population size 10 yrs 3 generations
>80% >50% >30%
<100 km2 <5000 km2 <20,000 km2
<50 <250 <1000
>50% >20% >10%10 yrs 20 yrs 100 yrsOr 3 gen or 5 gen
Small range
Very Small population
Quantitative analysisProbability of extinction
IUCN RED LIST
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Population Viability Analysis (L14 and L15)
What is it?How do the models workUsesIssuesAccuracyMore uses - case studies
Additional reading (FYI)Papers for next weekPrinciples of Conservation Biology pp 433-35Intro to Conservation Genetics Ch 20
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Small population
Exotic species
Poaching
Pollution
Management options
Human impact
DiseaseLifehistory
Inbreeding
Environment
Fluctuating population size
Catastrophes
Habitat loss
PVA models examine the effects of different life histories, environmental and threat factors on the population size and extinction risk of populations
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BASIC APPROACH
Collect population datasize and number populationsbirth and death rates habitat capacities (K)frequency and effect of threats
Put into PVA model package VORTEX, GAPPS, RAMAS, ALEX
Predict extinction probabilities
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BASIC MODEL- count-based PVA
One Pop’n N Census
Breed Immigrate Supplement
Death Emigrate Harvest Truncate at K
Run for 50-100 Generations
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BASIC MODEL - count based PVA
PVA models are NOT deterministic
Models need following dataVariance in fecundity Variance in survivalVariance in KForm of density dependenceFrequency/magnitude of catastrophesCovariance in demographic rates
Q. What does deterministic/variance/covariance mean?
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Model
Initial N=375
Productivity and survival (26 yrs of data)
Catastrophes - cyclones in Jan/April
- chance of event 7.5%
- effect on mortality +22%
K = 450 (± 10%)
BASIC EXAMPLE
Brook and Kikkawa 1998
Silvereyes on Heron Island
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Cyclone-Jan or April
One Pop’n N Census
Breed
Death Truncate at K
Run for 100 years
Set K
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MODEL OUTPUT
N
Year
Chance of extinction in 100 yrs = 15%
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ADDING COMPLEXITY
1. Individuals are different
Eg 1 Elephantsonly breed after 10+ yearsproductivity increases and then declineshave age specific mortality rates
Eg 2 Red cockaded woodpeckersbreed in groups may float prior to joining a group
one male breeds, others help
Q. How would you alter the PVA model?
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MORE COMPLEX MODEL
N at eachAGE orSTAGE
CensusEachSt(age)
Breed Immigrate Supplement
Death Emigrate Harvest Truncate at K
Individuals age or change categories
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Stage-structured PVAsAdditional Data Requirements
St(age)-specific productivity
St(age)-specific survival
Transition probabilities between stages
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2. additional populations---> multi-site PVAs
Simple - presence/absence - use IFM to estimate extinction/
colonisation - model viability of metapopulation
Complex - spatially-explicit individual based models
- track individuals in complex landscape as they are born, move, die
- landscape can be “patches” or “real”
ADDING COMPLEXITY
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Multi-site PVAsAdditional Data Requirements
IFM - ???
Spatially explicit individual based- ???
Data needed – check metapopulation and corridor lectures
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WHAT ARE PVA modelsHOW DO THEY WORK
USES OF PVA1. Assessing extinction risk
ISSUES WITH PVAs
ACCURACY of PVAs
ALTERNATIVE USES
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1. Assessing the extinction risk of population
Grizzlies in Yellowstone National Park Shaffer (1978,1983) and others since
Figure 55.11
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1. Assessing the extinction risk of population
Grizzlies in Yellowstone National Park Shaffer (1978,1983) and others since
Age-structured model (cubs, 1..4, 5…25)Sex (male, female)Data - 12 yrs Craighead, YNP Environmental stochasticity -->productivityDemographic stochasticity --->sex of cubsK= 230; M + F + cubs Craighead, YNP
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1. Assessing the extinction risk of population
Grizzlies in Yellowstone National Park Shaffer (1978,1983) and others since
Age-structured modelSexData - 12 yrs Environmental stochasticity
RESULTS Size Probability of persisting 100yrs10 020 0.3630 0.7440 0.9450 0.98
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AREA REQUIRED
Update1975 - 136 bears in Yellowstone2004 - 580 and rising2005 - proposal to delist grizzlies from ESA2007- population 500+grizzlies delisted - no protection outside park
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Issues with PVA models - 1
Population at risk are typically examined using density-dependent single species model.
Environmental factors are included by varying K
Interactions between populations and environment appear as reduction in realized rate of increase as population size approaches K
Issues with PVA models - 2
Data requirements are far greater than the amount of data available for most species
Rubbish in ----> rubbish out
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Issues with PVA models - 3
PVAs typically do not incorporate all genetic effects on population viability
Q. What genetic processes could influence viability?
PVAs can incorporate inbreeding depressionBUT
how susceptible are populations?what fitness components are affected?how is inbreeding depression related to F?is purging likely?is inbreeding depression greater during catastrophes?etc etc
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HOW ACCURATE ARE PVAs?
Brooks et al. 2000Used 21 long term (> 10 year) datsets
Used first half of data to set up modelsTested predictions from 5 PVA packages
= probability of population declinewith what actually happened afterwards
= did population decline
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HOW ACCURATE ARE PVAs?
Brooks et al. 2000
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HOW ACCURATE ARE PVAs?
Coulson et al. 2001 ResponseThe 21 studies selected were biased
the data available was of very high qualitymost species were not endangered
PVAs will frequently be unreliable because the data to estimate vital rates is limited and vital rates of endangered spp will change
Brooks et al. 2000“PVA is a valid and sufficiently
accurate tool for categorizing and managing endangered species”
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What sort of PVA model is appropriate?
Puerto Rican parrotBlack footed ferret
DISCUSSWhat is gained from using PVAs?
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Next 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 guidelines7. Deciding how many (which)
populations are needed