Population Viability Analysis

Critically Endangered Threatened Endangered Criterion Reduction in population size 10 yrs 3 generations >80% >50% >30% <100 km 2 <5000 km 2 <20,000 km 2 <50 <250<1000 >50% >20% >10% 10 yrs20 yrs100 yrs Or 3 genor 5 gen Small range Very Small population Quantitative analysis Probability of extinction IUCN RED LIST

Population Viability Analysis (L14 and L15) What is it? How do the models work Uses Issues Accuracy More uses - case studies Additional reading (FYI) Papers for next week Principles of Conservation Biology pp Intro to Conservation Genetics Ch 20

Small population Exotic species Poaching Pollution Management options Human impact Disease Life history 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

BASIC APPROACH Collect population data size and number populations birth and death rates habitat capacities (K) frequency and effect of threats Put into PVA model package VORTEX, GAPPS, RAMAS, ALEX Predict extinction probabilities

BASIC MODEL- count-based PVA One Pop’n N Census Breed Immigrate Supplement Death Emigrate Harvest Truncate at K Run for Generations

BASIC MODEL - count based PVA PVA models are NOT deterministic Models need following data Variance in fecundity Variance in survival Variance in K Form of density dependence Frequency/magnitude of catastrophes Covariance in demographic rates Q. What does deterministic/variance/covariance mean?

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

Cyclone-Jan or April One Pop’n N Census Breed Death Truncate at K Run for 100 years Set K

MODEL OUTPUT N Year Chance of extinction in 100 yrs = 15%

ADDING COMPLEXITY 1. Individuals are different Eg 1 Elephants only breed after 10+ years productivity increases and then declines have age specific mortality rates Eg 2 Red cockaded woodpeckers breed in groups may float prior to joining a group one male breeds, others help Q. How would you alter the PVA model?

MORE COMPLEX MODEL N at each AGE or STAGE Census Each St(age) Breed Immigrate Supplement Death Emigrate Harvest Truncate at K Individuals age or change categories

Stage-structured PVAs Additional Data Requirements St(age)-specific productivity St(age)-specific survival Transition probabilities between stages

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

Multi-site PVAs Additional Data Requirements IFM - ??? Spatially explicit individual based- ??? Data needed – check metapopulation and corridor lectures

WHAT ARE PVA models HOW DO THEY WORK USES OF PVA 1. Assessing extinction risk ISSUES WITH PVAs ACCURACY of PVAs ALTERNATIVE USES

1. Assessing the extinction risk of population Grizzlies in Yellowstone National Park Shaffer (1978,1983) and others since Figure 55.11

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 yrsCraighead, YNP Environmental stochasticity -->productivity Demographic stochasticity --->sex of cubs K= 230; M + F + cubsCraighead, YNP

1. Assessing the extinction risk of population Grizzlies in Yellowstone National Park Shaffer (1978,1983) and others since Age-structured model Sex Data - 12 yrs Environmental stochasticity RESULTSSize Probability of persisting 100yrs

AREA REQUIRED Update bears in Yellowstone and rising proposal to delist grizzlies from ESA population 500+ grizzlies delisted - no protection outside park

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

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 depression BUT 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

HOW ACCURATE ARE PVAs? Brooks et al Used 21 long term (> 10 year) datsets Used first half of data to set up models Tested predictions from 5 PVA packages = probability of population decline with what actually happened afterwards = did population decline

HOW ACCURATE ARE PVAs? Brooks et al. 2000

HOW ACCURATE ARE PVAs? Coulson et al Response The 21 studies selected were biased the data available was of very high quality most 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 “PVA is a valid and sufficiently accurate tool for categorizing and managing endangered species”

What sort of PVA model is appropriate? Puerto Rican parrot Black footed ferret DISCUSS What is gained from using PVAs?

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 size 5.Determining numbers to release 6.Setting harvest guidelines 7.Deciding how many (which) populations are needed