Transcript Chapter 11 - Reserve & resource management

BCB 341: Principles of
Conservation Biology
RESERVE AND RESOURCE
MANAGEMENT
Lecturer: James Reeler
IN SITU CONSERVATION
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Requires integration of a number of different concepts:
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landscape ecology
ecosystem management
population genetics
disturbance ecology
At several different scales:
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community
population
species
local
landscape
SMALL POPULATIONS
Minimum viable population size (MVP).
 Based on two parameters:
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acceptable probability of survival
 time period being considered
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Usually insufficient information to draw such
conclusions
 Smaller populations are more likely to go extinct
over a given time period than larger ones
 For a given set of parameters, the given MVP is
highly species dependent.
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OBSERVED VARIANCE & MVP
100
120
100
80
101+
51-100
60
31-50
40
Persistence (%)
Persistence (%)
90
101+
51-100
80
31-50
16-30
16-30
1-15
70
1-15
20
60
0
10
20
30
40
50
Time (years
60
70
a) Study by Berger (1990)
MVP=100
10
20
30
Time (years)
40
50
b) Study by Wehausen (1999)
MVP=50
Persistence of bighorn sheep (Ovis canadensis) in California.
POPULATION VIABILITY ANALYSIS
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Attempts to build models that predict future population
trends
Depends on relationship between popn size (dependent)
& weather, disease, landscape trends (independent)
Simplest model is stepwise:
where S = probability of individual surviving from t to t+1
 B = average number of offspring per individual
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If these variable are measured in the field, the model
can integrate randomly generated stochastic events
Variation in birth rate can be set by assigning variation
level
MEASURING SPECIES DECLINE
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Monitoring is essential to the successful running of a
reserve
Scale is important for monitoring
Up to 90% of species declines are missed due to
inappropriate scale of monitoring
Level of monitoring for British butterlies was ~100km2
(10km x 10km)
Much larger than individual patch (habitat or population)
size
As long as the species is detected within those cells, the
population is not registered as disappearing, although it
may experience huge reduction s within each area
UNDETECTED SPECIES LOSS
 80-90% declines undetected in British butterflies (Cowley et al., 1999)
 Worst amongst widespread species,
MANAGEMENT OF SMALL POPULATIONS
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Often small populations are disproportionally vulnerable
due to genetic inbreeding
Franklin (1980) suggests a minimum of 50 individuals
to proevent rapid loss of genetic variability
Studies on Drosophila suggest 500 as a minimum to
allow for sufficient mutation to counter loss through
genetic drift
Known as 50/500 rule for managing small populations
Complicated by difference between full population and
the effective population (Ne) which is involved in
exchange of genetic material
3 common sources of deviation from perfect population
EFFECTIVE POPULATION
Variance in reproductive output
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large variance means some genes are poorly represented in the
filial generation
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δ2= variance in family size
Unequal sex ratios
means some individuals cannot
breed
 with increasing inequality, Ne goes
down
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Effective population size
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100
90
80
70
60
50
40
30
20
10
0
0
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10 20 30 40 50 60 70 80 90 100
Number of females in population
Population fluctuations
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effectively causes generational bottlenecks that reduce gene
numbers.
DISTURBANCE ECOLOGY
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Until recently conservation management meant preventing all
disturbance to natural areas.
Disturbance is not exclusively anthropogenic
Many areas require disturbance to maintain their biodiversity
Different reserves experience (and require) different disturbance
regimes
Fynbos is a good example of a fire-disturbed ecosystem the requires
regular disturbance
Savannah maintains the balance of trees and grassland through the
interplay of several disturbance regimes:
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fire
herbivory pressure (including migration)
elephants
drought/flood cycle
nutrient enrichment via animal excreta
DISTURBANCE DEPENDENT SPECIES
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Certain life cycle attributes denote plants (and some
animals) that profit in a disturbance regime
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short life cycle (from seed to flower)
allocation of most resources to reproduction
long-lived soil-stored seed banks
long-distance dispersal mechanisms
polymorphic seeds so that some are dispersed in time and some
in space
disturbance-cued germination
adult plasticity, meaning that a plant can be big or small, slow or
fast growing depending on the available resources in a patch
vegetative propagation (this adaptation is selected under the
pressure of mammalian herbivores, shifting dune systems or
floods.
These species REQUIRE disturbance over a certain period in
order to maintain biodiversity
Biodiversity
Biodiversity
DISTURBANCE FOR BIODIVERSITY MAINTENANCE
Time since disturbance
Increasing disturbance
DISTURBANCE REGIMES
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Good knowledge of the required disturbance regimes of the
conservation area is required (monitoring!)
For fynbos, burning every 13-15 years is recommended
Does not mean burn EVERYWHERE once every 15 years
Natural landscapes are a mosaic
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of different habitats, and different
burn regimes
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3
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Older veld allows for
reintroduction of species that may
have been burned out
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Young veld provides areas for
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succession to occur in natural
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processes
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Record-keeping essential
DISTURBANCE & SUCCESSION
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After plants die, their nutrients are first consumed by detritivores before
being returned to the soil.
During this period of mineral release, ecosystems are highly vulnerable.
Depending on rate of sprouting & repopulation compared with runoff &
leaching, nutrients may be lost to the system or retained in new plants
Clearance of small blocks of vegetation tends to lose less nutrients (since
they are taken up by the roots of surround plants).
Salts such as K, Mg & Na are lost first (highly soluble) although in arid
environments they may form a salt crust that prevents seedling growth
Disturbance reducing a single species may cause cascade losses in other
species (eg: rinderpest)
Hunting of elephants in central Africa
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led to increased bush encroachment, and reduced savannah species.
reduction in poaching in conservation areas swung the balance the other way,
with losses of some large trees and reduction in browsing species
increased poaching has led to reduction in grassland
each change caused large shifts in plant and insect diversity as well as large
mammals
SUSTAINABLE HARVESTING
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Some wild populations are still harvested, and in certain
reserve types (biosphere reserves) areas are set aside
for limited take)
Central to the idea of harvesting is the concept of
sustainable yield
This is any level of harvest that can be taken from the
population indefinitely without detriment to the
population
From a commercial point of view, the best amount to
remove would be the maximum sustainable yield
Calculation of this is based on the carrying capacity of
the land, and the logistic equation for population growth
SUSTAINABLE HARVESTING
Growthexceeds
Harvest exceeds
harvest;
growth;population
population
increases
declinestotoK/2
extinction
Harvest exceeds
growth; population
declines to K/2
dN/dt
rK/4
0
K/2
Population size (N)
b)
a)Fixed
Fixed quota
harvest
method
effort method
K
PROBLEMS
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Fixed harvest effort is a better method, but it still requires a good
assessment of the carrying capacity for the species.
Assumes all individuals have equal reproductive potential, and hence does
not take into account age structure of the population (in age-structured
populations, MSY may be between 50 & 75% of K)
Assumes harvesting mortality is compensated by reduced natural mortality
(no evidence)
Assumes no knock-on effects for interacting species
(predators/competitors/prey) which may change carrying capacity of the
environment
Ignores harvest rate of pre-reproductive individuals, body growth rate, etc.
This has led to development of more detailed models which describe
biomass as a function of different processes (recruitment, natural mortality,
etc)
Despite repeated efforts to achieve sustainable yield of Atlantic cod, stocks
are still plummeting.
LANDSCAPE ECOLOGY
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Island biogeography & metapopulation biology influence reserve
selection and management processes
Depend on relative rates of colonisation & extinction, which in turn
depend on:
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spatial distribution of patches
suitability of patches for reproduction
permeability of the space between patches
mobility of species
Shift away from conservation as self-regulating systems to dynamic
non-equilibrial systems has led to integration of reserves into the
broader landscape
Use a management hierarchy such as the biosphere concept
Utilisation of corridors (natural and manufactured
Integration of agricultural alternatives and communal wildlife
management as a means of broadening the potential gene pool and
land availability (Wine & Biodiversity initiative, Campfire)
ECOSYSTEM FUNCTION
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Ecosystem process is essential for population persistence, and so
large scale conservation should aim to protect these systems.
Meyer (1997) nominated 7 principles for ecosystem conservation:
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ecosystems are open, which should lead to a focus on conserving fluxes
(flow) across ecosystem boundaries
ecosystems are temporally variable & bear the legacies of past
disturbance
spatially heterogeneous on a variety of scales, which is vital for
functionality
most effects in ecosystems are indirect, making knock-on effects
unpredictable
component biological communities must be conserved to maintain
ecosystem function
although several species may perform the same function in the
ecosystem, they have different responses to biotic & abiotic environment
(reduced variation in functionality in a changing environment)
humans are part of all ecosystems, and no ecosystems are unaffected
by human activity.
ECOSYSTEM FUNCTION
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How usefully a management policy integrates this
holistic approach may depend on
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how impacted an ecosystem is by human/economic
activities,
how well we understand the processes
Meyer (1997) cites the example of the Knowles Valley
(USA) which underwent extensive logging & roadbuilding
in 1950-1985
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shifted sediment load from uplands to valley
decreased storage capacity in valley meant much was
washed out of the catchment
degraded habitat for coho salmon, which had greatly
reduced migration to the sea
By replanting trees & reducing sediment loss, a recovery
programme stopped this.
ECOSYSTEM FUNCTION
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Sometimes too much transformation has occurred, and it is
necessary to allow short term, small scale losses to
accommodate longer term restoration
Guiding principles for ecosystem management (Maltby,
1999):
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management objectives are a matter of social choice
ecosystems must be managed in a human context
ecosystems must be managed within natural limits
change is inevitable
management & monitoring must occur at the appropriate scale, &
use the full range of protected areas
needs to address global issues but act locally
must maintain ecosystem structure & functioning
should use appropriate scientific tools
follow the precautionary principle
needs a multidisciplinary approach.