Transcript Population Viability Analysis and conservation priorities

Conservation Biology (Ecology)
Lecture 8
December 2009
Salit Kark
The Biodiversity Research Group
Department of Evolution, Systematics and Ecology
The Silberman Institute of Life Sciences
The Hebrew University of Jerusalem
Dr. Salit Kark. The Hebrew University of Jerusalem
A dispersal buffer:
an isoline of
dispersal probability
Metapopulation Types
A subpopulation
A. Patchy
B. Classical
Separate
metapopulations
C. Nonequilibrium
D. Mainland-Island
Dr. Salit Kark. The Hebrew University of Jerusalem
Patch isolation
Highly
connected
Patchy
MainlandIsland
Classical
Highly
isolated
Nonequilibrium
MainlandMainland
Disjunct
All small
All large
Patch Size
Dr. Salit Kark. The Hebrew University of Jerusalem
The case study of the Florida Scrub Jay
Aphelocoma coerulescens
Dr. Salit Kark. The Hebrew University of Jerusalem
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
A metapopulation
12 km
3.5 km
A subpopulation
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
Dr. Salit Kark. The Hebrew University of Jerusalem
A subpopulation buffer is the distance where
occupancy rates remain high
Accumulative
Frequency
97%
85%
3.5 km
6.7 km
Dispersal Distance (km)
From natal to breeding territories
1970-1993
Dr. Salit
Kark. The Hebrew University of Jerusalem
Examples of Nonequilibrium metapopulations
3.5 km
12 km
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
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-midlandisland 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
A metapopulation
12 km
3.5 km
A subpopulation
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
Dr. Salit Kark. The Hebrew University of Jerusalem
Total 191
subpopulations
Only Six
subpopulations >
100 birds
Subpopulation Size (# of birds)
Numbers above the bars indicate the number
of subpopulations
Dr. Salit Kark. The Hebrew University of Jerusalem
Frequency
Nonequilibrium
metapopulations
Total 42
metapopulations
Metapopulation Size
Dr. Salit Kark. The Hebrew University of Jerusalem
PVA Model
Biology of Environmental
Individuals
Factors
Population
Dynamics
(demography)
Population Survival or Extinction
Environmental
disturbance
PVA Model
Biology of Environmental
Individuals
Factors
Population
Dynamics
(demography)
--Growth
--Population (n)
--Distribution
Genetic effective P size
Demographic uncertainty
Extinction
Extinction
(Deterministic)
Deterministic extinction:
Extinction resulting from some
inexorable change or force from
which there is no escape.
Such as the effect of:
 Glaciations
 Deforestation, divergence of river
Major loss of habitat
PVA Model
Biology of Environmental
Individuals
Factors
Population
Dynamics
(demography)
Fragmentation
-- Population size
-- Distribution
Extinction
Demographic randomness
Extinction
(Deterministic)
Population Viability Analysis (PVA)
PVA is the study of how the main demographic
factors interact to determine extinction
probability of a population and to estimate MVP.
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 PVA
Uses census data
Assumes all individuals identical
Demographic PVA
Incorporates information about vital rates
vital rates: probabilities of survival and reproduction
Can include population structure
Spatially explicit PVA
Incorporates migration and colonization
Approaches to PVA
Count
Demographic
Spatial
Biological realism
Data requirements
Bias
Precision
Bias—a systematic error that contributes to the difference between the
mean of a large number of test results and an accepted reference value;
Precision—the closeness of agreement among test results obtained
under prescribed conditions.
Why run population “viability”analysis?
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”
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
Sampling Variance
Population Size
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
Population size
120
N=101+
100
% OF
POPULATIONS
PERSISTING
80
60
40
20
51-100
16-30
1-15
31-50
0
10
20
30
40
TIME (YEARS)
50
Extinction rates of birds on Channel Islands as a
function of population size over an 80-year period
60
% Extinction
10 breeding pairs – 39% went extinct
10-100 pairs – 10% went extinct
1000>pairs – none went extinct
*
*
30
*
0
1
10
* *
100
*
1000
*
10,000
Population Size (no. pairs)
* - extinction
rate of all species
in a given
population size
class
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.
Some thoughts on PVA
 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.
How do we decide what to conserve?
Setting conservation priorities
Setting conservation priorities
‫קביעת סדרי עדיפויות לשימור‬
‫לפי מינים‬
‫לפי אזורים‬
Species based
Area based
‫קביעת סדרי עדיפויות לשימור‬
‫לפי מינים‬
‫מעמד‬
‫פוטנציאל‬
‫אבולוציוני‬
‫שירותים‬
‫סיכון‬
‫אנדמיות‬
‫תפקיד במערכת‬
‫אסטרטגיות‪ :‬דגל‪,‬‬
‫מטריה‪ ,‬אינדיקאטור‪,‬‬
‫מפתח‬
‫נדירות‬
‫פגיעות בית הגידול‬
‫אטרקטיביות‬
‫(ניצול ע"י האדם)‬
‫קצב הכחדה‬
Setting conservation priorities
Species based
Status
services
evolutionary
potential
risk
rarity
Decline rate
Habitat
vulnerability
Attractiveness
(human
exploitation)
endemism
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 status
IUCN = 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 status
IUCN Species Survival Commission (SSU)
– Provide conservation status in IUCN red list of
threatened species
– Updated yearly
http://www.redlist.org/info/categories_criteria2001.html
The IUCN Red List Categories &
Criteria have several specific aims:
 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 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