Conservation of populations
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Conservation of Populations. Defining Populations Demographics – growth and decline Conservation genetics & populations. I. Defining populations. Spatial disjunction Distribution pattern, groups are separated by location, regardless of other similarities Genetic disjunction

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Conservation of populations
Conservation of Populations

  • Defining Populations

  • Demographics– growth and decline

  • Conservation genetics & populations


I defining populations
I. Defining populations

  • Spatial disjunction

    • Distribution pattern, groups are separated by location, regardless of other similarities

  • Genetic disjunction

    • All individuals in one group share genetic attributes with one another, but not with individuals from other groups

  • Demographic disjunction

    • Individuals from different groups have different demographic properties; birth rate, death rate, sex ratio, age structure


Important characteristics of a population
Important characteristics of a population:

Population Density – number of individuals per unit area or volume

  • Sampling to estimate density

    • Absolute Density

    • Capture-Recapture Method

    • Quadrant techniques


Dispersion pattern of spacing among individuals
Dispersion – pattern of spacing among individuals

  • Limited by abiotic factors

    • Patchy environment will affect dispersion within population

  • Limited by biotic factors, species interactions

Abiotic factors:

Biotic Factors


DISPERSION PATTERNS:

Clumped pattern – individuals aggregated in patches

Uniform pattern – evenly spaced resulting from direct interactions

Random pattern – occurs in the absence of strong attractions or repulsions among individuals


Ii demographics growth and decline
II. Demographics– growth and decline

  • Recruitment, fecundity

  • Immigration

  • Emigration

  • Death

    • survivorship

      Natality (avg. per capita birth rate)

      Mortality (avg. per capita death rate)



B life histories and population size
B. Life histories and population size

  • Traits that affect an organism’s schedule of reproduction and survival

    • Semelparity reproduction

    • iteroparity reproduction

  • Limited resources and trade offs

    • Red deer in Scotland

    • Insect species

    • Perennial plants


Different life histories represent a resolution of

conflicting demands. When an organism engages in one

activity other activities are constrained!

time

energy

nutrients

limited

resources


Population growth models
Population Growth Models

increases if birth rate > death rate

  • Exponential

    • unrestricted growth due to abundance of resources (food/space)…

    • the larger the population, the faster its potential for growth.

    • ΔN = rmaxN

      Δt

  • Logistic

    • ΔN = rmaxN (K – N)

      Δt K


C population growth factors
C. Population growth factors

  • Density Dependent

    • Negative feedback

  • Density Independent

  • Top-down effects

  • Bottom up effects

  • Indirect effects


Iii conservation genetics
III. Conservation Genetics

  • What is Genetic Diversity?

  • Why is Genetic Diversity Important?

  • Genetic threats to populations

  • Case studies


A what is genetic diversity
A. What is Genetic Diversity?

  • Among species

  • Among populations

  • Within populations

  • Within individuals


B importance of genetic diversity
B. Importance of genetic diversity

  • Evolutionary potential

  • Loss of fitness

  • Instrumental value


C genetic threats to populations
C. Genetic threats to populations

  • Small Population Size

    • Effective population size

    • Drift & Bottlenecks

  • Inbreeding depression

    • Loss of genetic variation

    • Accumulation of harmful mutations

  • Introgression and hybridization

    • Outbreeding depression


Small populations are subject to rapid decline due to:

  • Loss of genetic variability and related problems

  • Demographic fluctuations due to random variations in birth & death rates

  • Environmental fluctuations due to variation in predation, competition, disease, natural catastrophes, etc.


Effective Population Size (Ne)-

# of breeding individuals

Vs.

Census Population Size (Nc) – actual number of individuals in a population

  • Unequal Sex Ratio

  • Unequal production of offspring


  • Bottleneck: drastic reduction in population size

    • Founder effect: when a few individuals establish a new population that has less genetic variation than the larger original population


  • Genetic drift: random fluctuations of allele frequencies

  • A loss of certain alleles, especially rare alleles & fixation of others

  • Reduction in the amount of variation in genetically determined characteristics, decline in heterozygosity (H)

the rate at which new (neutral) mutants are fixed is 1/u ; this rate is INDEPENDENT of population size, N.


Due to the fixation of certain alleles, heterozygosity will decline in the case of genetic drift in small populations.

Ht = HO [1 – 1/(2N)]t


2 inbreeding depression
2. Inbreeding Depression

  • Inbreeding = Mating between relatives

  • FI- is the probability that two copies of the same allele are identical by descent (IBD)

  • Example: FIof the offspring of a mating between full sibs is ¼

    • F is the proportion by which heterozygosity is decreased, relative to that in a random mating population with the same allele frequency


Normal lion sperm Abnormal lion sperm from an isolated, inbred population in Tanzania

Inbreeding leads to the expression of recessive deleterious alleles that are suppressed in heterozygotes


3 introgression and hybridization
3. Introgression and hybridization isolated, inbred population in Tanzania

  • When mating occurs between individuals that are too genetically dissimilar

  • Loss of fitness results –

    • “Swamping” of locally adapted genes – adaptive gene complexes in native populations are being displaced by the immigration of genes that are adapted to another environment

    • Breakdown of biochemical or physiological compatibilities between genes in the different populations.


Case studies isolated, inbred population in Tanzania

Due to severe over hunting, by 1892 somewhere between 8 and 20 were left. Since then there has been an almost exponential increase, especially in the northern colonies. In 1957 there were 13,000 elephant seals, in 1976: 48,000. The population is still not at equilibrium (Boveng et al, 1988). In 1991, the total population was estimated at 127,000, with 28,164 pups born that year and there appears to be a 6% annual increase (Stewart et al, 1994)


Marsh rat isolated, inbred population in Tanzania

Silver rice rat

  • 1975, 20 individuals translocated to the island (4 males & 16 females)

  • Total population by 1999 = 650

  • Molecular markers show that these island sheep are much less genetically diverse than those found on the mainland (H = 0.67 as compared to H = 0.42)



- depression symptomsCapra ibex ibex (Austria), C. i. aegagrus (Turkey) & C. i. nubiana(Sinai)


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