Salit Kark

The Biodiversity Research Group

Department of Evolution, Systematics and Ecology

The Silberman Institute of Life Sciences

The Hebrew University of Jerusalem

Conservation Biology (Ecology)

Lecture 8

December 2009

Dr. Salit Kark. The Hebrew University of Jerusalem

A. Patchy B. Classical

C. Nonequilibrium D. Mainland-Island

A dispersal buffer: an isoline of dispersal probability

A subpopulation

Metapopulation Types

Separate metapopulations

Dr. Salit Kark. The Hebrew University of Jerusalem

Patchy

Classical Mainland-Island

Mainland-Mainland

Nonequilibrium Disjunct

Highlyconnected

Pat

ch is

olat

ion

Highlyisolated

All small All large

Patch SizeDr. Salit Kark. The Hebrew University of Jerusalem

The case study of the Florida Scrub Jay

Dr. Salit Kark. The Hebrew University of Jerusalem

Aphelocoma coerulescens

Biology of the Florida Scrub Jay

Florida’s only endemic bird species

Juveniles disperse after one year

Cooperative breeding

The bird was listed as threatened

species in 1987 by the U.S. Fish and

Wildlife Service (USFWS)

Dr. Salit Kark. The Hebrew University of Jerusalem

Distribution of Florida scrub jay groups in 1993. Note the discontinuous distribution and variability in patterns of aggregation

Dr. Salit Kark. The Hebrew University of Jerusalem

Statewide jay distribution with dispersal buffers. Shaded areas depict subpopulations within easy dispersal distance (3.5 km) of one another (191 separate subpopulations). Thick outer lines delineate demographically independent (42 metapopulations) separated from each other by at least 12 km

3.5 km

12 km

A subpopulation

A metapopulation

Dr. Salit Kark. The Hebrew University of Jerusalem

Dispersal Distance (km)

Fre

quen

cy

From natal to breeding territories 1970-1993

3.5 km

85%

97%

6.7 km

Accumulative

A subpopulation buffer is the distance where occupancy rates remain high

Dr. Salit Kark. The Hebrew University of Jerusalem

North Gulf Coast of Florida: each of the 6 metapopulations contains fewer than 10 pairs of jays, except for the centrally located system that contains a single, midland-sized subpopulation

Examples of Nonequilibrium metapopulations

3.5 km

12 km

Dr. Salit Kark. The Hebrew University of Jerusalem

Examples of a “classical” metapopulation from 3 counties in central Florida. Note the occurrence of jays in small islands of intermediate distance from one another.

Dr. Salit Kark. The Hebrew University of Jerusalem

Portion of the largest mainland-midland-island metpopulation in interior Florida.

The large central subpopulation (enclosed by the thin black line) contains nearly 800 pairs of jays. Small subpopulations to the south and east are within known dispersal distance of the large, central mainland. A small metapopulation to the west (in DeSoto County) contains a single subpopulation of 21 territories.

Dr. Salit Kark. The Hebrew University of Jerusalem

Statewide jay distribution with dispersal buffers. Shaded areas depict subpopulations within easy dispersal distance (3.5 km) of one another (191 separate subpopulations). Thick outer lines delineate demographically independent (42 metapopulations) separated from each other by at least 12 km

3.5 km

12 km

A subpopulation

A metapopulation

Dr. Salit Kark. The Hebrew University of Jerusalem

Subpopulation Size (# of birds)

Fre

quen

cy

Numbers above the bars indicate the number of subpopulations

Only Six subpopulations >

100 birds

Total 191 subpopulations

Dr. Salit Kark. The Hebrew University of Jerusalem

Metapopulation Size

Fre

quen

cy

Nonequilibrium metapopulations

Total 42 metapopulations

Dr. Salit Kark. The Hebrew University of Jerusalem

PVA Model

Biology of Individuals

Environmental Factors

Population Dynamics

(demography)

Population Survival or Extinction

PVA Model

Biology of Individuals

Environmental Factors

Population Dynamics

(demography)

Extinction

Environmental disturbance

--Growth--Population (n)--Distribution

Genetic effective P size

Demographic uncertainty

Extinction

(Deterministic)

Extinction resulting from some inexorable change or force from which there is no escape.

Such as the effect of:

Glaciations

Deforestation, divergence of river

Deterministic extinction:

PVA Model

Biology of Individuals

Environmental Factors

Population Dynamics

(demography)

Extinction

Major loss of habitat

Fragmentation

-- Population size

-- Distribution

Extinction

(Deterministic)

Demographic randomness

PVA is the study of how the main demographic factors interact to determine extinction probability of a population and to estimate MVP.

Population Viability Analysis (PVA)

MVP - Minimum Viable Population imply some thresholds for the number of individuals that will insure (at some acceptable level of risk) that a population will persist in a viable state for a given interval of time

Approaches to PVA

Count-based PVAUses census dataAssumes all individuals identical

Demographic PVAIncorporates information about vital ratesvital rates: probabilities of survival and reproduction Can include population structure

Spatially explicit PVAIncorporates migration and colonization

Approaches to PVACount Demographic Spatial

Biological realism

Data requirements

Bias

Precision

Precision—the closeness of agreement among test results obtained under prescribed conditions.

Bias—a systematic error that contributes to the difference between the mean of a large number of test results and an accepted reference value;

U.S. Endangered Species Act (1973) codifies in law a national policy of avoiding the extinction of species

U.S. National Forest Management Act (1976)

“[f]ish and wildlife habitat shall be managed to maintain viable populations of existing native and desired nonnative vertebrate species in the planning area…In order to insure that viable populations will be maintained, habitat must be provided to support at least a minimum number of reproductive individuals and the habitat must be well distributed so that those individuals can interact with others in the planning area”

Why run population “viability”analysis?

Demographic Stochasticity - Random Demographic Variation

Arises because, at any time, individuals of a given age or developmental stage have probabilities of survival and reproduction, called vital rates.

Assuming that these apply independently to each individual, demographic stochasticity produces sampling variances of the vital rates inversely proportional to population size

In any real population, individuals don’t usually produce

the average number of offspring. They usually have

more than the average, fewer than the average, or have

no offspring

As long as the population size is large the average

provides a rather good description of the population

But, once the population size drops below a certain size

(say 50 individuals), individual variation in birth and

death rates begin to cause the population size to fluctuate

randomly up and down

If population size fluctuates downward, then the resulting smaller population will be even more susceptible to demographic fluctuations in the next generation, possibly resulting in extinction

Population Size

Sampling Variance

In contrast to demographic stochasticity, Environmental Stochasticity is represented by temporal changes in the vital rates that affect all individuals of a given age or stage similarly.

The sampling variances of the vital rates are then nearly independent of population size

vital rates: probabilities of survival and reproduction

Some Real World Examples:

One of the best documented cases where demographic stochasticity likely played a role, comes from a study of the persistence of 120 bighorn sheep populations followed for up to 70 years in the US southwest

Berger, J. 1990. Persistence of different-sized populations: an empirical assessment of rapid extinctions in bighorn sheep. Conservation Biology 4:91-98

All the populations with fewer than 50 individuals went extinct within 50 years

n of 50-100 is a threshold

0

20

40

60

80

100

120

10 20 30 40 50 TIME (YEARS)

% OF POPULATIONS PERSISTING

N=101+

51-100

31-501-15

16-30

Population size

Extinction rates of birds on Channel Islands as a function of population size over an 80-year period

0

30

60

1 10 100 1000 10,000**

***

*

10 breeding pairs – 39% went extinct10-100 pairs – 10% went extinct1000>pairs – none went extinct

*

Population Size (no. pairs)

% Extinction

Jones, L. and J. Diamond. 1976. Short-term base studies of turnover in breeding bird populations on the California Channel Islands. Condor 78:526-549.

* - extinction rate of all species

in a given population size

class

PVA requires lots of data, which takes time, work, and money, whereas managers want answers (predictions on extinction) now.

Few species will get thorough PVA.

When should PVA be used and what type of PVA (how complex)?

Predictions from PVA can only be as good as the data that go into the analysis. We can only have probabilities in the predictions from PVA.

Populations should not be managed to their “minimum viable population”size. One of the greatest strengths of PVA is the ability to play “what if”games with the model.

Some thoughts on PVASome thoughts on PVA

How do we decide what to conserve?

Setting conservation priorities

לפי מינים

Species based

Setting conservation priorities

קביעת סדרי עדיפויות לשימור

לפי אזורים

Area based

לפי מינים

קביעת סדרי עדיפויות לשימור

מעמד

סיכון

נדירותאנדמיות

פוטנציאל אבולוציוני

שירותים

קצב הכחדהפגיעות בית הגידול

אטרקטיביות

(ניצול ע"י האדם)

תפקיד במערכת

אסטרטגיות: דגל, מטריה, אינדיקאטור,

מפתח

Species based

Setting conservation priorities

Status

risk

rarityendemism

evolutionary potential

services

Decline rateHabitat

vulnerabilityAttractiveness

(human exploitation)

Role in ecosystem

Strategies: flagship, umbrella, indicator, keystone

Strategies: focal species

flagship, umbrella, indicator, keystone

Focusing on important species may provide short cuts to more successful conservation

Flagship sp: charismatic, public appeal and awareness

Umbrella sp: species providing “shelter” for many others, large and diverse area required

Indicator sp: environmental change, other groups

Keystone sp: predominating ecological role in community and ecosystem functioning

Conservation statusIUCN = The World Conservation Union is the world’s largest

and probably most important conservation network.

The Union brings together 82 States, 111 government agencies, more than 800 non-governmental organizations (NGOs), and some 10,000 scientists and experts from 181 countries in a unique worldwide partnership.

The Union’s mission is to influence, encourage and assist societies throughout the world to conserve the integrity and diversity of nature and to ensure that any use of natural resources is equitable and ecologically sustainable.

Conservation statusIUCN Species Survival Commission (SSU)

– Provide conservation status in IUCN red list of threatened species

– Updated yearly

http://www.redlist.org/info/categories_criteria2001.html

to provide a system that can be applied consistently by different people;

to improve objectivity by providing users with clear guidance on how to evaluate different factors which affect the risk of extinction;

to provide a system which will facilitate comparisons across widely different taxa;

to give people using threatened species lists a better understanding of how individual species were classified.

The IUCN Red List Categories & Criteria have several specific aims:

The criteria can be applied to any taxonomic unit at or below the species level

Category in IUCN redlist EXTINCT (EX) no reasonable doubt that the last individual has died

when exhaustive surveys have failed to record an individual EXTINCT IN THE WILD (EW) known only to survive in captivity CRITICALLY ENDANGERED (CR) facing an extremely high

risk of extinction in the wild ENDANGERED (EN) VULNERABLE (VU) NEAR THREATENED (NT) does not qualify for CE or E, but is

close to qualifying in the near future LEAST CONCERN (LC) Widespread and abundant taxa are

included in this category