Viable population: population capable of self-maintenance without continuing manipulation or intervention

Minimum viable population (MVP)

• Survival probability of a population of a given size for a designated period of time

Minimum viable population (MVP)

• Survival probability of a population of a given size for a designated period of time

• specific to individual species and location; no universal MVP exists

Minimum viable population (MVP)

Key issues:• effect of chance events on

population persistence• time frame for conservation• probability level desired

Minimum viable population (MVP)

Key issues:• effect of chance events on

population persistence - scientific issue• time frame for conservation value • probability level desired judgments

Minimum viable population (MVP)

Example: red-cockaded woodpecker• live in colonies (breeding pair plus helper offspring) requiring about

215 acres

• management plan across species range: 500 individuals needed in each of 15 populations

Minimum viable population (MVP)

Example: red-cockaded woodpecker• live in colonies (breeding pair plus helper offspring) requiring about

215 acres

• management plan across species range: 500 individuals needed in each of 15 populations

• S. Carolina deme had mean time to extinction of 41.5 yrs, 72% probability of extinction within 200 yrs

• annual addition of 3F + 2M for 10 years doubled projected mean time to extinction; probability of extinction in 200 yrs reduced to 4%

Population viability analysis (PVA)

• A process to determine the probability that a population of a given size will go extinct within a given number of years

• Used to identify strategies for conservation

Population viability analysis - estimating MVP’s

• experimentation+ powerful, species-specific tool

–ethical issues for endangered species

–takes too long: conservation plans needed within a decade or two

Population viability analysis - estimating MVP’s

• simulation models+ allow estimation of extinction probability (run 1,000

simulations, tally number of extinction events)

+ indicates which factors are most important in declines

– requires large amounts of data

– not generalizable - build anew for each species

Population viability analysis - estimating MVP’s

• simulation models+ allow estimation of extinction probability (run 1,000

simulations, tally number of extinction events)

+ indicates which factors are most important in declines

– requires large amounts of data

– not generalizable - build anew for each species

• “off-the-shelf” programs available (VORTEX, GAPPS, RAMAS metapopulation)

Basic procedure

Construct a computer simulation that projects the growth of the population into Construct a computer simulation that projects the growth of the population into the future.the future.1.1.Select population growth rate for each time step at random from a distribution Select population growth rate for each time step at random from a distribution or set of possible growth rates. This will result in ‘good years’ and ‘bad years’.or set of possible growth rates. This will result in ‘good years’ and ‘bad years’.2.2.Repeat the project ion (e.g., 1000 x ) to estimate what the population is likely to Repeat the project ion (e.g., 1000 x ) to estimate what the population is likely to do on average.do on average.

Population viability analysis

• simulation models– Bay checkerspot butterfly

current pop’n. trajectory result of simulations (only 3 shown) at current mean rate of population growth (r = 0.002)

Grizzly bears, the ‘original PVA’ – evaluating a single population

Bighorn sheep – Bighorn sheep – evaluating a single populationevaluating a single population

Percentage of populations of bighorn sheep in North America that Percentage of populations of bighorn sheep in North America that persist over a 70-year period reduces with initial population size.persist over a 70-year period reduces with initial population size.

Koalas in Australia – Koalas in Australia – comparing multiple populationscomparing multiple populations

Koala – Koala – Phascolarctos cinereus Phascolarctos cinereus

•Koalas are globally IUCN ‘least Koalas are globally IUCN ‘least concern’; secure in some areas, concern’; secure in some areas, but threatened in others in but threatened in others in Australia.Australia.

•National management strategy to National management strategy to retain viable populations.retain viable populations.

•Two populations modeled for Two populations modeled for viability by Penn et al. (2000): viability by Penn et al. (2000): Oakey (declining) and Springsure Oakey (declining) and Springsure (secure).(secure).

•Populations modeled from 1970s Populations modeled from 1970s to 1990s to estimate extinction to 1990s to estimate extinction probabilities (1000 iterations).probabilities (1000 iterations).

Values used as inputs for Values used as inputs for simulationssimulations of koala populations at Oakey (declining) and Springsure (secure), of koala populations at Oakey (declining) and Springsure (secure), Australia. Values in parentheses are Australia. Values in parentheses are SDSD due to environmental variation. The model procedure involved the due to environmental variation. The model procedure involved the selection of values at random from the range. selection of values at random from the range. CatastrophesCatastrophes are assumed to occur with a certain probability- are assumed to occur with a certain probability- in years when the model selects a catastrophe, reproduction and survival are reduced by the multipliers in years when the model selects a catastrophe, reproduction and survival are reduced by the multipliers shown.shown.

Variables in PVA

Observed koala population trends (diamonds) compared with Observed koala population trends (diamonds) compared with trajectories (triangles ± 1SD) predicted by 1000 iterations at (a) trajectories (triangles ± 1SD) predicted by 1000 iterations at (a) Oakey and (b) Springsure, Australia.Oakey and (b) Springsure, Australia.

Probability of Probability of extinctionextinction

•Oakey=0.380 (380 Oakey=0.380 (380 out of 1000 out of 1000 iterations).iterations).

•Springsure=0.063Springsure=0.063

Elephants – Elephants – determining reserve sizedetermining reserve size

African elephant – African elephant – Loxodonta africanaLoxodonta africana

•African elephants are IUCN Vulnerable.African elephants are IUCN Vulnerable.

•Armbruster and Lande (1992) modeled Armbruster and Lande (1992) modeled population viability in 12 5-year age population viability in 12 5-year age classes through discrete 5-year time steps.classes through discrete 5-year time steps.

•Survivorship and reproductive rates Survivorship and reproductive rates derived from Tsavo NP Kenya.derived from Tsavo NP Kenya.

•Environmental stochasticity modeled as Environmental stochasticity modeled as drought based on Tsavo data.drought based on Tsavo data.

•Habitat area and probability of extinction Habitat area and probability of extinction examined in 1000-year simulations.examined in 1000-year simulations.

Results suggest that an area of 1300 km2 is Results suggest that an area of 1300 km2 is required to yield a 99% probability of required to yield a 99% probability of

persistence for 1000 years.persistence for 1000 years.

Ocelots – Ocelots – assessing management optionsassessing management options

Puerto Rican Parrot (endangered)

Declined due to poaching (pet trade), predation, cyclones, to N = ~13 birds

Puerto Rican Parrot (endangered)

13-14 animals in wild; captive pop’n startedPVA: with 40 birds, 30% prob. of extinction

in 100 yrs- primary risk: catastrophe (hurricanes)

Puerto Rican Parrot (endangered)

13-14 animals in wild; captive pop’n startedPVA: 30% prob. of extinction in 100 yrs

primary risk: catastrophe (hurricanes)Strategy: stockpile food

establish 5 populations

Puerto Rican Parrot (endangered)

13-14 animals in wild; captive pop’n startedPVA: 30% prob. of extinction in 100 yrs

primary risk: catastrophe (hurricanes)Outcome: hurricane devastated forest habitat; captive population saved due to food stockpile

Puerto Rican Parrot (endangered)

13-14 animals in wild; captive pop’n startedPVA: 30% prob. of extinction in 100 yrs

primary risk: catastrophe (hurricanes)

Issues: population fragmentation, diseases from captive birds

Florida panther:

PVA inputs: population size sex ratio age distribution of each sex age at first reproduction maximum breeding age % of each sex breeding each year sex ratio at birth mating strategy number of offspring per year probability of survival at each age harvest probability of catastrophic events estimated carrying capacity

Florida panther:

declined due to habitat loss, poaching, road killsevidence of inbreeding:

low fertility, sperm abnormalities, cowlicks, kinked tails,cardiac defects, undescended testicles, high disease rate

1989 PVA: at N < 50, predicted decline of 6-10%/year, extinction in 25-40 yrs - possible earlier extinction due to disease

Florida panther:

Outbred with sub-species from Texas - added 8 females in 1995

F1 hybrid kittens do not have cowlinks or kinked tailsTexas genes are now 15-29% of totalRoad kills lower due to addition of culverts

PVA in 1999: extinction probability much lower

Proportion of recovery plans written for species listed under the US Endangered Species Act that Proportion of recovery plans written for species listed under the US Endangered Species Act that present information regarding PVA.present information regarding PVA.

PVAs – a work in progressPVAs – a work in progress. . .. . .

Criteria for successful (accurate) PVAsCriteria for successful (accurate) PVAs

• Available data must be of Available data must be of sufficiently high qualitysufficiently high quality to yield accurate descriptions to yield accurate descriptions of all parameter distributions (e.g., population growth rates or rates of survival of all parameter distributions (e.g., population growth rates or rates of survival and reproduction.and reproduction.

• Distributions of population parameters must Distributions of population parameters must hold fairly constant into the futurehold fairly constant into the future. . PVA assumes that future population dynamics will be similar to those captured PVA assumes that future population dynamics will be similar to those captured in the data in hand, which reflect past trends. in the data in hand, which reflect past trends.

Greater kudu - Greater kudu - Tragelaphus strepsicerosTragelaphus strepsiceros

PVA limitationsPVA limitations•Accuracy depends on quality of data.Accuracy depends on quality of data.

•Lack of data on variables problematic.Lack of data on variables problematic.

Mammalian PVAs

The predicted area required to support a given minimum population size varies with – the mammal’s feeding ecology (herbivore vs. carnivore)– the mammal’s environment

• temperate vs. tropic (area required is larger for tropical species)• high environmental variance requires more area

The predicted area required to support a given minimum population size varies with – the mammal’s feeding ecology (herbivore vs. carnivore)– the mammal’s environment

• temperate vs. tropic (area required is larger for tropical species)• high environmental variance requires more area

In general, – larger mammals require smaller populations, but larger habitat areas– carnivores require more habitat area than herbivores– populations with more variation in growth rate must be larger to persist.

– densities tend to be lower in tropics (may be due to greater spp. diversity, leading to greater number & intensity of biotic interactions)

Mammalian PVAs

Model predictions about species persistence in the parks of the world

(Frankel & Soulé 1981 - Conservation and Evolution)

For largest mammalian carnivores (10-100 kg) 0-22% of parks should permit persistence for 100

yrsno parks expected to permit persistence for 1000

yrs

For largest mammalian herbivores (100-1000 kg) 4-100% of parks should permit persistence for 100

yrs0-22% of parks should permit persistence for 1000

yrs