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I. Nature of population biology

I. Nature of population biology. A. Major areas of population biology (2)   1. Population genetics   2. Population ecology - this course. 1. Population Genetics    . origin and maintenance of genetic variation and diversity Relative amount of polymorphic vs. monomorphic

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I. Nature of population biology

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  1. I. Nature of population biology A. Major areas of population biology (2)   1. Population genetics   2. Population ecology - this course

  2. 1. Population Genetics    • origin and maintenance of genetic variation and diversity • Relative amount of polymorphic vs. monomorphic • Relative amount of heterozygosity vs. homozygosity b. evolutionary consequences of genetic change 1. Theory based in Mendelian laws and processes of Natural Selection     2. Management - sophisticated hybridization programs used in agriculture, medicine, insect management 3. Rare species – Population Viability Analysis (PVA)

  3. 2. Population Ecology - this course: a. relationships of population to their environment and each other    b. number of individuals, not gene frequency 1. Theory - less basis than population Genetics a. mathematics of growth      b. limits on growth     2. Management - based somewhat on theory but more on empirical data where theory is weak

  4. B. History of Population Ecology • Thomas Malthus - human populations and geometric (exponential) growth cannot continue (1798)   • P. F. Verhulst - logistic growth (1838)    • J. Von Liebig - “law of the minimum” (1840)    • F. F. Blackman - “law of limiting factors” (1905)

  5. History, continued e. A. J. Lotka – predator-prey systems (1925)    f. V. Volterra – predator-prey and competition (1926) g. Raymond Pearl - formalized logistic (1927)    h. G. F. Gause - “The Struggle for Existence” Competition, theory and empirical data; classic experiments (1934) • Nicholson A. J., and J. P. Bailey - population prediction and equilibrium (1935)   

  6. History, continued j. P. H. Leslie - projection matrices for population prediction and determination of equilibrium levels (1945) k. W. F. Lidicker - dispersal theory & regulation of #’s below carrying capacity (1962)    l. George Innis - mathematician turned ecologist - computer modeling and stochastic models - filling the country with modelers (1970's).

  7.  C. Population study - an overview 1. Definition of “population” group of organisms of a single species which occupies a particular space at a particular time. 2. Population has some characteristics of individual • Structure and life history - like individual • Grow, differentiate and respond to environment b. Characters unique to groups • Density, birth and death rates, sex and age structure, spatial distribution • These characters (properties) are the main subject matter of population ecology.

  8. 3. The study of factors affecting spatial and temporal patterns in the number of individuals    • Reproductive rates and mortality    • Dispersal and migration    • population structure    • regulatory mechanisms and    • interspecies relationships 4. Major questions a.What factors are involved in regulation of population size?    • What relationships exists between stability and complexity?    • What are the limiting factors?

  9. 5. Limiting vs. Regulating factors • Limiting: what causes carrying capacity to be at a certain level; K=c    • Regulating factors: what causes change in population level to be zero; Δn = 0    • Controversy     1. David Lack’s food hypothesis vs. Christian’s hormonal (adreno-pituitary) system: n regulated below food level     2. Fluctuating K - use avg. (K)

  10. 6. Density dependent vs. independent • Dependent - a factor which affects a varying percentage of the population depending on its density 1. Parasites, disease, predation and competition (the biotic factors) are often density-dependent b. Independent - factors which affect a constant percentage • Weather (the physical factors)    c. Controversy - entomologists from Australia • A. J. Nicholson: Population equilibrium, especially competition, was brought about by density-dependent effects 2. Andrewartha and Birch - a book in 1954 1) “equilibrium is a fiction” and 2) no environmental factors can operate in a density-independent way.

  11. 7. Solution of ecological problems  a. Objectives and hypotheses    b. Tests of hypotheses     • Sampling and data analysis (empirical)     • Model formulation and analysis c. Predictions and general theory

  12. 8. Laboratory and field studies • Lab: carefully controlled experiments allow for direct hypothesis testing • Insect, plants, and micro-cosm experiments     • Small mammals     • A few larger small-mammal predator-prey studies • Field: important to understand natural populations • Plants and animals     • Short-term vs. long-term a lack long-term data for making needed generalizations

  13. 9. Looking for generalizations: SCIENCE • Not get too caught up in the peculiarities of an individual population, but look for the generalizations that can be made     1. Plant ecologists: afraid of the community idea now (Gleason vs. Clements)     2. Population genetics: not worried about patterns that don’t fit simple allele system - modified    b. Do not over-simplify or be incomplete 1. problems are complex and individual

  14. 10. Mathematical or Quantitative ecology • Not statistics     1. Statistics is a branch of mathematics dealing with number distributions and probability    • Dealing with quantities in ecology     • N • Rates affecting N     • Factors quantitative effect on rates    • Use calculus and statistics     • Calculus: rates of change, solutions to equations, stability, projections, instantaneous rates • Statistics: correlation of factors with population, mean, variance, confidence, significance, etc.

  15. Summary   • Course will cover population ecology • Not very old science with few laws • Variety of population characteristics are studied by using a variety of methods • Highly quantitative by nature

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