ESC 556 week 11

Conserving Populations

Conserving Populations

Various levels of conservationSpecies populations

73% of 2290 plants in NA, < five populations Informed action for conservation

1. Factors controlling population density2. Identification of threats3. Predict the effects of management actions

What is a population?

Fixed geographic areaConvenience to the investigatorScalePopulations description

Density BIDE Structure

Monitoring Demographic Structure

States of development Plants: juveniles, seedlings, reproductive, senescent Marsh gentian

Invasive (bare soils), regressive (high ground cover percentage)

Individual counts

Census data

Census data vs. survey dataSpider orchid80% decline in 50 yearsEndangered in BritainChalk & limestone grasslandCattle vs. sheep grazing

What is rarity?

Some species naturally rareChanges in population sizeClassifying types of rarity

Size of geographic range Habitat specificity Local population size

Barn owlOspreys

Causes of Rarity

Anthropogenic effectsPatterns in the ecology of rare speciesPoor dispersal abilities (sedentary species)

Plants, invertebrates No migration to favorable habitats

Deterministic vs. stochastic processExternal and Internal Influences

External Influences

Habitat ChangeOther organismsDirect Human InfluencesEnvironmental ContaminantsEnvironmental stochasticity

Habitat Change

Complete destruction to conversion to less suitable

36% of all animal extinctions100 species/dayClimateHabitat management

Other organisms

Introduced speciesCoconut moth and its parasitic fly in FijiThistles and herbivoresIntroduced diseases

Direct human Influences

Commercial exploitationPersecutionRecreational huntingNon-target speciesDisturbance

Environmental Contaminants

DDTBioaccumulation, biomagnification,

biotransformation

Environmental stochasticity

Local climate Ectothermic species Endoterms affected indirectly

Natural catastrophesEffective independently of population size

Intrinsic Factors

Demographic stochasticityGenetic 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 possibleSmall number chance effectsAffect social functioning

Defence, migration, lekking

Allele effect

Genetic Stochasticity

Genetic uniformity a disadvantageLoss of Heterozygosity

Allele

hj = 1 – Σpij2

Recessive lethal alleles Differences between groups of organisms Results in inbreeding depression

Genetic Drift

Chance loss of allelesHt+1 = Ht (1-(1/2N))Bottlenecks vs. Founder events

Genetic Drift

Outbreeding Depression

Outcrossing between divergent populationsIncompatibilities between local genesMountain ibex - two subspecies

Minimum Viable Populations

Critical minimum sizeMVASurvival probability over timeDifferent between species & even

populationsEnvironmental stochasticity50 – inbreeding depression500 – genetic drift50-100 individuals

Effective Population Size

50-500 Based on certain assumptions

Ne = 0.75NGrizzly bears (38 instead of 200)0.4 – 0.05

Summary of Influences

External eventsCatastrophic eventsDemographic stochasticityImportance of genetics

Ex situ conservation

Extinction vortex Heath hen < 50 inds. 2000 but fire, harsh winter, predation, inbreeding

depression

Interaction of factors

Large Blue50% lost by conversion< sheep grazing + < rabbits more

vegetationVegetation ant (Myrmica sabuleti)

butterfly

Prediction Models

Limitations Sufficient data Replication

PVA Probability of survival for a number of generations

The model Population survival time Evaluation of management options Monitoring the results

Northern spotted owl, grizzly bearKeystone speciesSmall 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 effectsSome +ve effects

Metapopulations

Rate of recolonization vs. rate of extinctionMetapopulation persistence

Number & size of populations Dispersal rate Smaller – more isolated populations Temporally independent extinctions

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 coreRange size & population density correlation

Corridors

Connecting the patches – seminatural habitatse.g. disused train lines within agricultural

landscapesGlobal change corridorsPros

Increase species richness Encourage recolonization (Rescue effect) Reduce genetic problems (e.g. inbreeding depression)

Cons Spread disasters Outbreeding depression Large & Expensive

Role of Reserves

CentralNational Parks or smaller sitesSLOSSMetapopulation considerationsDesign and DispersalThe shape – Edge effectNot the solution for many speciesLow percentage

Recovery Measures

Extinction in the wild definite, then what?Captive breeding & ReinroductionsZoosAll individuals

California condor, black-footed ferret

1000 individuals2000 land vertebrate species in the next 200

yearsSmall 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 otherTrue introductions, reintroductions,

augmentationLimited dispersal powers & fragmented

habitatsHigh population increase rate

Not good for mammals and birds

High genetic diversityBest at historical core rangeInvertebrates

A Way Forward

Not all species can be protectedCharismatic speciesWhich groups to concerve?Umbrella speciesKeystone speciesHotspsots

Global & Local