habitat fragmentation 1. a reduction in total area 2. creation of separate isolated patches from a...
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Habitat FragmentationHabitat Fragmentation
1.1. A reduction in total areaA reduction in total area
2.2. Creation of separate isolated patches Creation of separate isolated patches from a larger continuous distributionfrom a larger continuous distribution
3.3. Leads to overall reduction in Leads to overall reduction in population size and reduced population size and reduced migration among patches.migration among patches.
1.1. A reduction in total areaA reduction in total area
2.2. Creation of separate isolated patches Creation of separate isolated patches from a larger continuous distributionfrom a larger continuous distribution
3.3. Leads to overall reduction in Leads to overall reduction in population size and reduced population size and reduced migration among patches.migration among patches.
Population fragmentationPopulation fragmentation
• Genetic diversityGenetic diversity
• inbreedinginbreeding
• DifferentiationDifferentiation
• ExtinctionExtinction
• These all depend on gene flow among These all depend on gene flow among fragmentsfragments
• Genetic diversityGenetic diversity
• inbreedinginbreeding
• DifferentiationDifferentiation
• ExtinctionExtinction
• These all depend on gene flow among These all depend on gene flow among fragmentsfragments
Population FragmentationPopulation Fragmentation
• Number of fragmentsNumber of fragments
• Distribution of population sizes in the Distribution of population sizes in the fragmentsfragments
• Geographic distribution or spatial Geographic distribution or spatial pattern of populationspattern of populations
• Dispersal ability of the speciesDispersal ability of the species
• Migration rates between fragmentsMigration rates between fragments
• Time since fragmentationTime since fragmentation
• Number of fragmentsNumber of fragments
• Distribution of population sizes in the Distribution of population sizes in the fragmentsfragments
• Geographic distribution or spatial Geographic distribution or spatial pattern of populationspattern of populations
• Dispersal ability of the speciesDispersal ability of the species
• Migration rates between fragmentsMigration rates between fragments
• Time since fragmentationTime since fragmentation
Habitat FragmentationHabitat Fragmentation
Habitat FragmentationHabitat Fragmentation
Population Fragmentation and HPopulation Fragmentation and H
Natural DisastersNatural Disasters
• Hurricane Hugo in 89 wiped out 87% of Hurricane Hugo in 89 wiped out 87% of the active nests in Francis Marion NF the active nests in Francis Marion NF and killed 63% of the population. and killed 63% of the population. Through intensive management it has Through intensive management it has recovered by 33%.recovered by 33%.
• Hurricane Hugo in 89 wiped out 87% of Hurricane Hugo in 89 wiped out 87% of the active nests in Francis Marion NF the active nests in Francis Marion NF and killed 63% of the population. and killed 63% of the population. Through intensive management it has Through intensive management it has recovered by 33%.recovered by 33%.
Population StructurePopulation Structure
• The genetic impacts of population The genetic impacts of population fragmentation can go from insignificant fragmentation can go from insignificant to severe depending on the details of to severe depending on the details of fragmentation.fragmentation.
• The genetic impacts of population The genetic impacts of population fragmentation can go from insignificant fragmentation can go from insignificant to severe depending on the details of to severe depending on the details of fragmentation.fragmentation.
Population structurePopulation structure1.1. Totally isolated population fragments with no Totally isolated population fragments with no
gene flowgene flow2.2. Effectively single large – fragments where gene Effectively single large – fragments where gene
flow is sufficient to result in effectively a single flow is sufficient to result in effectively a single large pop.large pop.
3.3. Island models where migration is equal among Island models where migration is equal among equally sized islandsequally sized islands
4.4. Linear stepping stone models where only Linear stepping stone models where only neighboring populations exchange migrantsneighboring populations exchange migrants
5.5. Two-dimensional stepping-stone models where Two-dimensional stepping-stone models where only surrounding populations exchange migrantsonly surrounding populations exchange migrants
6.6. Mainland-IslandMainland-Island7.7. MetapopulationsMetapopulations
1.1. Totally isolated population fragments with no Totally isolated population fragments with no gene flowgene flow
2.2. Effectively single large – fragments where gene Effectively single large – fragments where gene flow is sufficient to result in effectively a single flow is sufficient to result in effectively a single large pop.large pop.
3.3. Island models where migration is equal among Island models where migration is equal among equally sized islandsequally sized islands
4.4. Linear stepping stone models where only Linear stepping stone models where only neighboring populations exchange migrantsneighboring populations exchange migrants
5.5. Two-dimensional stepping-stone models where Two-dimensional stepping-stone models where only surrounding populations exchange migrantsonly surrounding populations exchange migrants
6.6. Mainland-IslandMainland-Island7.7. MetapopulationsMetapopulations
FragmentationFragmentation
• When a population is subdivided, individual When a population is subdivided, individual alleles and genotypes are distributed alleles and genotypes are distributed among fragments. Fragments will be among fragments. Fragments will be genetically differentiated from the genetically differentiated from the beginning.beginning.
1.1. Fragmentation resulting in an initial genetic Fragmentation resulting in an initial genetic sub-division of a populationsub-division of a population
2.2. Cumulative diversification, through genetic Cumulative diversification, through genetic drift and inbreeding over time in each of the drift and inbreeding over time in each of the population fragmentspopulation fragments
• When a population is subdivided, individual When a population is subdivided, individual alleles and genotypes are distributed alleles and genotypes are distributed among fragments. Fragments will be among fragments. Fragments will be genetically differentiated from the genetically differentiated from the beginning.beginning.
1.1. Fragmentation resulting in an initial genetic Fragmentation resulting in an initial genetic sub-division of a populationsub-division of a population
2.2. Cumulative diversification, through genetic Cumulative diversification, through genetic drift and inbreeding over time in each of the drift and inbreeding over time in each of the population fragmentspopulation fragments
Degree of FragmentationDegree of Fragmentation
• A population of size N separated into f A population of size N separated into f totally isolated equal sized fragments, totally isolated equal sized fragments, the size of each fragment is N/f.the size of each fragment is N/f.
• Each frag will become inbred and lose Each frag will become inbred and lose genetic diversity at a rate dependant on genetic diversity at a rate dependant on N/f.N/f.
• A single pop. Of the same total size will A single pop. Of the same total size will become inbred and lose GD at a slower become inbred and lose GD at a slower rate dependant on its size N.rate dependant on its size N.
• A population of size N separated into f A population of size N separated into f totally isolated equal sized fragments, totally isolated equal sized fragments, the size of each fragment is N/f.the size of each fragment is N/f.
• Each frag will become inbred and lose Each frag will become inbred and lose genetic diversity at a rate dependant on genetic diversity at a rate dependant on N/f.N/f.
• A single pop. Of the same total size will A single pop. Of the same total size will become inbred and lose GD at a slower become inbred and lose GD at a slower rate dependant on its size N.rate dependant on its size N.
Degree of FragmentationDegree of Fragmentation
H declines with the number of fragments compared to a large pop.
FragmentsFragments
• Single pop N=500 ind./Gen.Single pop N=500 ind./Gen.
• Over 50 generations this pop. loses 5%Over 50 generations this pop. loses 5%
• While 2 populations of 250 lose 10% While 2 populations of 250 lose 10% each and 5 populations of 100 lose 22% each and 5 populations of 100 lose 22% each of their initial H. each of their initial H.
• Single pop N=500 ind./Gen.Single pop N=500 ind./Gen.
• Over 50 generations this pop. loses 5%Over 50 generations this pop. loses 5%
• While 2 populations of 250 lose 10% While 2 populations of 250 lose 10% each and 5 populations of 100 lose 22% each and 5 populations of 100 lose 22% each of their initial H. each of their initial H.
Divergence of Allele frequenciesDivergence of Allele frequencies
• Will vary due to random genetic driftWill vary due to random genetic drift
• Each fragment will fix of lose different Each fragment will fix of lose different allelesalleles
• Drift among fragmented populations Drift among fragmented populations reduces overall heterozygosity across reduces overall heterozygosity across all fragments to below the expected HWall fragments to below the expected HW
• Will vary due to random genetic driftWill vary due to random genetic drift
• Each fragment will fix of lose different Each fragment will fix of lose different allelesalleles
• Drift among fragmented populations Drift among fragmented populations reduces overall heterozygosity across reduces overall heterozygosity across all fragments to below the expected HWall fragments to below the expected HW
Impacts of pop structure on repro fitness
Impacts of pop structure on repro fitness
• In island and stepping-stone models In island and stepping-stone models migration and population size are keymigration and population size are key– No migration then Ne of each frag.No migration then Ne of each frag.
• In Source-sink structures then the effective In Source-sink structures then the effective pop. size will depend on Ne of mainland, thus pop. size will depend on Ne of mainland, thus inbreeding and loss of fitness will be much inbreeding and loss of fitness will be much higher in this type than a SL.higher in this type than a SL.
• Metapopulations typically have Ne that are Metapopulations typically have Ne that are smaller than the number of breeding adults smaller than the number of breeding adults due to extinction and recolonization.due to extinction and recolonization.
• In island and stepping-stone models In island and stepping-stone models migration and population size are keymigration and population size are key– No migration then Ne of each frag.No migration then Ne of each frag.
• In Source-sink structures then the effective In Source-sink structures then the effective pop. size will depend on Ne of mainland, thus pop. size will depend on Ne of mainland, thus inbreeding and loss of fitness will be much inbreeding and loss of fitness will be much higher in this type than a SL.higher in this type than a SL.
• Metapopulations typically have Ne that are Metapopulations typically have Ne that are smaller than the number of breeding adults smaller than the number of breeding adults due to extinction and recolonization.due to extinction and recolonization.
MetapopulationsMetapopulations
Genetically Viable populationsGenetically Viable populations
• So how many do we need????So how many do we need????
• What is the minimum Ne to keep What is the minimum Ne to keep genetics healthy?genetics healthy?
• Minimum Viable Population SizeMinimum Viable Population Size
• So how many do we need????So how many do we need????
• What is the minimum Ne to keep What is the minimum Ne to keep genetics healthy?genetics healthy?
• Minimum Viable Population SizeMinimum Viable Population Size
How Big??How Big??
One Horned RhinoOne Horned Rhino
3 goals3 goals
1.1. Retaining reproductive fitness by Retaining reproductive fitness by avoiding inbreeding depressionavoiding inbreeding depression
2.2. Retaining the ability to evolve in Retaining the ability to evolve in response to changes in the response to changes in the environmentenvironment
3.3. Avoiding accumulation of new Avoiding accumulation of new deleterious mutationsdeleterious mutations
1.1. Retaining reproductive fitness by Retaining reproductive fitness by avoiding inbreeding depressionavoiding inbreeding depression
2.2. Retaining the ability to evolve in Retaining the ability to evolve in response to changes in the response to changes in the environmentenvironment
3.3. Avoiding accumulation of new Avoiding accumulation of new deleterious mutationsdeleterious mutations
Estimates of NeEstimates of Ne
How largeHow large
• Generally the goal is 500 = NeGenerally the goal is 500 = Ne
• This means that there must be 5000 This means that there must be 5000 indivs.indivs.
• Maintain long term viabilityMaintain long term viability
• Generally the goal is 500 = NeGenerally the goal is 500 = Ne
• This means that there must be 5000 This means that there must be 5000 indivs.indivs.
• Maintain long term viabilityMaintain long term viability
How large are endangered species pop’s
How large are endangered species pop’s
• Generally population size is smaller Generally population size is smaller then the recommended 500.then the recommended 500.
• Not doomed for immediate extinction Not doomed for immediate extinction but they will suffer depletion of genetic but they will suffer depletion of genetic resourcesresources
• Generally population size is smaller Generally population size is smaller then the recommended 500.then the recommended 500.
• Not doomed for immediate extinction Not doomed for immediate extinction but they will suffer depletion of genetic but they will suffer depletion of genetic resourcesresources
GLTGLT
Genetic goals in managementGenetic goals in management
• The GLT goal is to retain 98% of the The GLT goal is to retain 98% of the genetic diversity for 100 years.genetic diversity for 100 years.
• 630 wild + 360 reintro.630 wild + 360 reintro.
• The Ne/N ratio must be .31 for total or .5 The Ne/N ratio must be .31 for total or .5 for wild animals to meet the goal. for wild animals to meet the goal.
• The GLT goal is to retain 98% of the The GLT goal is to retain 98% of the genetic diversity for 100 years.genetic diversity for 100 years.
• 630 wild + 360 reintro.630 wild + 360 reintro.
• The Ne/N ratio must be .31 for total or .5 The Ne/N ratio must be .31 for total or .5 for wild animals to meet the goal. for wild animals to meet the goal.
The fallacy of small surviving populations
The fallacy of small surviving populations
• A few small populations are surviving A few small populations are surviving but this is not the majority.but this is not the majority.
• A few small populations are surviving A few small populations are surviving but this is not the majority.but this is not the majority.