Transcript Conserving Populations (week 11)

Conserving Populations
ESC 556 week 11
Conserving Populations
 Various levels of conservation
 Species  populations
 73% of 2290 plants in NA, < five populations
 Informed action for conservation
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Factors controlling population density
Identification of threats
Predict the effects of management actions
What is a population?
 Fixed geographic area
 Convenience to the investigator
 Scale
 Populations description
 Density
 BIDE
 Structure
Monitoring Demographic Structure
 States of development
 Plants: juveniles, seedlings, reproductive, senescent
 Marsh gentian
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Invasive (bare soils), regressive (high ground cover percentage)
 Individual counts
Census data
 Census data vs. survey data
 Spider orchid
 80% decline in 50 years
 Endangered in Britain
 Chalk & limestone grassland
 Cattle vs. sheep grazing
What is rarity?
 Some species naturally rare
 Changes in population size
 Classifying types of rarity
 Size of geographic range
 Habitat specificity
 Local population size
 Barn owl
 Ospreys
Causes of Rarity
 Anthropogenic effects
 Patterns in the ecology of rare species
 Poor dispersal abilities (sedentary species)
 Plants, invertebrates
 No migration to favorable habitats
 Deterministic vs. stochastic process
 External and Internal Influences
External Influences
 Habitat Change
 Other organisms
 Direct Human Influences
 Environmental Contaminants
 Environmental stochasticity
Habitat Change
 Complete destruction to conversion to less suitable
 36% of all animal extinctions
 100 species/day
 Climate
 Habitat management
Other organisms
 Introduced species
 Coconut moth and its parasitic fly in Fiji
 Thistles and herbivores
 Introduced diseases
Direct human Influences
 Commercial exploitation
 Persecution
 Recreational hunting
 Non-target species
 Disturbance
Environmental Contaminants
 DDT
 Bioaccumulation, biomagnification,
biotransformation
Environmental stochasticity
 Local climate
 Ectothermic species
 Endoterms affected indirectly
 Natural catastrophes
 Effective independently of population size
Intrinsic Factors
 Demographic stochasticity
 Genetic stochasticity
 Loss of heterozygosity
 Inbreeding depression
 Genetic Drift
 Outbreeding depression
 Minimum Viable Population
 Effective Population Size
Demographic Stochasticity
 Excluding external influences  fecundity &
mortality
 Large population  predictions possible
 Small number  chance effects
 Affect social functioning
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Defence, migration, lekking
 Allele effect
Genetic Stochasticity
 Genetic uniformity a disadvantage
 Loss of Heterozygosity
 Allele
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hj = 1 – Σpij2
Recessive lethal alleles
Differences between groups of organisms
Results in inbreeding depression
Genetic Drift
 Chance loss of alleles
 Ht+1 = Ht (1-(1/2N))
 Bottlenecks vs. Founder events
Genetic Drift
Outbreeding Depression
 Outcrossing between divergent populations
 Incompatibilities between local genes
 Mountain ibex - two subspecies
Minimum Viable Populations
 Critical minimum size
 MVA
 Survival probability over time
 Different between species & even populations
 Environmental stochasticity
 50 – inbreeding depression
 500 – genetic drift
 50-100 individuals
Effective Population Size
 50-500
 Based on certain assumptions
 Ne = 0.75N
 Grizzly bears (38 instead of 200)
 0.4 – 0.05
Summary of Influences
 External events
 Catastrophic events
 Demographic stochasticity
 Importance of genetics
 Ex situ conservation
 Extinction vortex
 Heath hen < 50 inds.
 2000 but fire, harsh winter, predation, inbreeding depression
Interaction of factors
 Large Blue
 50% lost by conversion
 < sheep grazing + < rabbits  more vegetation
 Vegetation  ant (Myrmica sabuleti)  butterfly
Prediction Models
 Limitations
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Sufficient data
Replication
 PVA
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Probability of survival for a number of generations
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The model
 Population survival time
 Evaluation of management options
 Monitoring the results
 Northern spotted owl, grizzly bear
 Keystone species
 Small population paradigm vs. declining population
paradigm
Spatial perspective
 Fragmentation
 Size and distance of patches (habitat islands)
Size – species diversity
 Distance – recolonization probability

 Population decline  intrinsic effects
 Some +ve effects
Metapopulations
 Rate of recolonization vs. rate of extinction
 Metapopulation persistence
 Number & size of populations
 Dispersal rate
 Smaller – more isolated populations
 Temporally independent extinctions
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Regionally acting environmental factors
Metapopulations
 Types of meta-populations
Ranges
 Population parameters vary
 Center vs. edge
 Center: optimal conditions
 Birth rate > death rate
 Edge  equal rates
 Outside  only through emigration (Source and sink)
Conservation Implications
 Small populations not always expendable: Source-
sink situation
 Habitat destruction @ the core
 Range size & population density correlation
Corridors
 Connecting the patches – seminatural habitats
 e.g. disused train lines within agricultural landscapes
 Global change corridors
 Pros
 Increase species richness
 Encourage recolonization (Rescue effect)
 Reduce genetic problems (e.g. inbreeding depression)
 Cons
 Spread disasters
 Outbreeding depression
 Large & Expensive
Role of Reserves
 Central
 National Parks or smaller sites
 SLOSS
 Metapopulation considerations
 Design and Dispersal
 The shape – Edge effect
 Not the solution for many species
 Low percentage
Recovery Measures
 Extinction in the wild definite, then what?
 Captive breeding & Reinroductions
 Zoos
 All individuals
 California condor, black-footed ferret
 1000 individuals
 2000 land vertebrate species in the next 200 years
 Small populations
 Control of matings  maximize genetic diversity
 Inoculations from outside
 Differentiation in captivity
Captive Breeding
 Gene Introgression
 Przewalsky’s horse by domestic horse
 European bison by cattle
 Different subspecies
 Behavioural factors
 Cultural transmission
 Predator avoidance
 At introduction
 Removal of the external factors
 Numbers of individuals, how many sites, when
 Probe releases
Translocations
 Transfer from one site to the other
 True introductions, reintroductions, augmentation
 Limited dispersal powers & fragmented habitats
 High population increase rate
 Not good for mammals and birds
 High genetic diversity
 Best at historical core range
 Invertebrates
A Way Forward
 Not all species can be protected
 Charismatic species
 Which groups to concerve?
 Umbrella species
 Keystone species
 Hotspsots
 Global & Local