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Conservation of Populations

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

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  1. Conservation of Populations • Defining Populations • Demographics– growth and decline • Conservation genetics & populations

  2. 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

  3. 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

  4. 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

  5. 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

  6. II. Demographics– growth and decline • Recruitment, fecundity • Immigration • Emigration • Death • survivorship Natality (avg. per capita birth rate) Mortality (avg. per capita death rate)

  7. Density dependent fecundity in fingernail clams, Musculium securis

  8. 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

  9. 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

  10. 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

  11. C. Population growth factors • Density Dependent • Negative feedback • Density Independent • Top-down effects • Bottom up effects • Indirect effects

  12. III. Conservation Genetics • What is Genetic Diversity? • Why is Genetic Diversity Important? • Genetic threats to populations • Case studies

  13. A. What is Genetic Diversity? • Among species • Among populations • Within populations • Within individuals

  14. B. Importance of genetic diversity • Evolutionary potential • Loss of fitness • Instrumental value

  15. 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

  16. 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.

  17. 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

  18. 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

  19. 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.

  20. 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

  21. 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

  22. 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

  23. 3. Introgression and hybridization • 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.

  24. Case studies 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)

  25. Marsh rat 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)

  26. Insular populations in Sweden exhibited inbreeding depression symptoms • Abnormal scales • Decreased litter size • Increased # inviable progeny

  27. - Capra ibex ibex (Austria), C. i. aegagrus (Turkey) & C. i. nubiana(Sinai)

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