Week 4: Management of species in the wild: chpt 7

Course’s learning outcomes

What you should be able to do overall: measure genetic variation

Lecture-specific learning outcomes

You must understand corridors

Genetic management (core idea)

Using genetic principles and tools to improve population survival and fitness in wild and captive populations

Diagnosing genetic problems

First step in management: identify issues like small Ne

Effective population size (Ne)

The number of individuals contributing genes to the next generation; small Ne leads to drift and inbreeding

Bottleneck

A strong reduction in population size causing loss of genetic diversity

Genetic diversity

The amount of variation in alleles; important for adaptability and survival

Inbreeding depression

Reduced fitness due to mating between related individuals leading to expression of harmful alleles

Genetic fragmentation

When populations are isolated and cannot exchange genes

Management options overview

Increase population size

Increase population size

Reduces genetic drift and inbreeding by having more individuals contributing genes

Gene flow

Movement of genes between populations through migration; reduces genetic differences

FST

Measure of genetic differentiation between populations; high FST means little gene flow

Decrease FST

Happens when gene flow increases and populations become genetically more similar

Conservation management actions

Remove threats (habitat loss

SLOSS (Single Large Or Several Small reserves)

Debate about reserve design; best is multiple reserves connected by gene flow

Corridors

Physical connections between habitats that allow movement of individuals and increase gene flow

Effect of corridors

Increase movement and gene flow

Potential negative effects of corridors

Can spread diseases

Landscape genetics

Study of how landscape features influence gene flow and genetic structure

Core question landscape genetics

Which landscape features promote or limit gene flow and by how much

Isolation-by-distance

Genetic similarity decreases with geographic distance (straight-line distance)

Isolation-by-resistance

Genetic similarity depends on landscape features and movement costs

Resistance (landscape genetics)

The difficulty for an organism to move through a landscape (e.g. roads = high resistance)

Resistance map

A map where each area has a movement cost for organisms

Vertex (node)

A point in the landscape grid

Edge

Connection between nodes representing movement paths

Edge weight

The cost of moving between nodes

Connectivity models

Methods to calculate how populations are connected across landscapes

Least-cost path

The single path with the lowest movement cost between populations

Circuit theory

Considers many possible movement paths; more realistic for natural movement

Resistance distance

Measure of how difficult it is to move between populations across a landscape

Conductance

Probability of movement through a landscape (opposite of resistance)

Model validation (landscape genetics)

Compare genetic distances with resistance distances to find the best model

Correlation with genetic distance

The model that best explains observed genetic patterns is most realistic

Barrier (landscape genetics)

Landscape feature that reduces gene flow (e.g. glaciers

Facilitator (landscape genetics)

Feature that increases gene flow (e.g. suitable habitat corridors)

Application of landscape genetics

Identify barriers

Translocations

Movement of individuals between populations to increase gene flow artificially

Key questions translocations

Which individuals

Artificial gene flow

Gene flow created by humans through translocations

One-migrant-per-generation rule

At least one migrant per generation is enough to prevent strong genetic differentiation (FST ≤ ~0.2)

Nem

Number of migrants per generation (Ne × m)

Effect of gene flow on FST

Even a few migrants strongly decrease FST

Trade-off gene flow

Balance between maintaining diversity within populations and preventing populations from becoming too similar

Genetic guidelines translocations

Choose individuals to maximize diversity and match population conditions

Practical challenges translocations

Expensive

Genetic rescue

Increase in fitness due to introduction of new genetic variation into an inbred population

Goal of genetic rescue

Increase heterozygosity and reduce inbreeding depression

Effect genetic rescue

Higher survival

Heterozygosity

Having different alleles; increases fitness and reduces expression of harmful mutations

Outbreeding depression

Reduced fitness when crossing genetically different populations

Causes outbreeding depression

Disruption of local adaptation or coadapted gene complexes

Risk of outbreeding depression

Generally low if populations were recently connected and environments are similar

Benefit of genetic rescue

Improves fitness in most cases (≈93%) and effects last multiple generations

When to use genetic rescue

Small

Which populations to conserve (core question)

Decide which populations are most valuable for conservation

High FST interpretation

High differentiation can mean either local adaptation OR loss of genetic diversity

Allelic richness

Number of alleles in a population; low richness indicates loss of diversity

Genetic uniqueness

A population appears unique genetically

Key insight FST and uniqueness

High FST often results from drift and allele loss

Decision rule conservation

Protect populations if uniqueness is due to adaptation or ancestry

Prioritizing populations

Focus on populations contributing most to overall gene pool and adaptive potential

Corridors vs translocations

Corridors enable natural gene flow; translocations create artificial gene flow

Translocations vs genetic rescue

Translocations increase gene flow; genetic rescue specifically aims to increase fitness

Landscape genetics vs corridors

Landscape genetics identifies where corridors should be placed

Full management strategy

Diagnose problem → choose tool → justify genetically → consider risks and logistics

Learning goal 6 (application)

Use genetic tools (corridors

Why can corridors sometimes decrease population survival

They can spread disease parasites or invasive species and synchronize population crashes

Why can corridors reduce local adaptation

Increased gene flow introduces maladaptive alleles and reduces selection differences between populations

When is a corridor more likely to be harmful than beneficial

When populations are adapted to very different environments or when disease risk is high

Why is 1 migrant per generation often enough to reduce genetic differentiation

Because even small gene flow counteracts genetic drift strongly over time

When is 1 migrant per generation NOT enough

When populations are extremely small strongly selected or highly isolated

Why does small population size increase extinction risk beyond just genetics

Because of demographic stochasticity environmental variation and Allee effects

Why can genetic rescue sometimes fail

If introduced individuals are maladapted or if outbreeding depression occurs

What is outbreeding depression in practice

Reduced fitness due to mixing genetically incompatible or locally adapted populations

When should genetic rescue be used

When a population shows signs of inbreeding depression and low genetic diversity

When should genetic rescue be avoided

When populations are highly adapted to local environments or genetically very different

Why might high genetic diversity not always be beneficial

It can include maladaptive alleles that reduce fitness in a specific environment

Why is FST alone not enough to guide conservation decisions

Because it does not distinguish between adaptive and neutral differences

A population has high FST and low diversity what does this suggest

Strong genetic drift and isolation rather than adaptive divergence

A population has high FST but high diversity what does this suggest

Possible local adaptation or long-term stable separation

Why is allelic richness important for long-term survival

It provides raw material for future adaptation to environmental change

Why does gene flow reduce extinction risk

It increases genetic diversity and reduces inbreeding depression

Why can too much gene flow increase extinction risk

It can swamp local adaptation and reduce fitness

Corridor vs translocation vs genetic rescue in decision making

Corridors allow natural movement translocations are artificial movement genetic rescue specifically targets fitness improvement

When would you choose translocation over corridors

When habitat is fragmented and individuals cannot move naturally between patches

When is doing nothing sometimes the best conservation strategy

When intervention risks disrupting local adaptation or causing outbreeding depression

Why are metapopulations more stable than single populations

Because local extinctions can be offset by recolonization from other patches

Why can synchrony between populations be dangerous

If all populations decline at the same time the entire metapopulation can collapse

How can corridors increase extinction risk at the metapopulation level

By synchronizing population dynamics across patches

Why are large connected populations generally more resilient

Because they maintain genetic diversity and buffer against stochastic events