Transcript 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
a. origin and maintenance of genetic variation and
diversity
1. Relative amount of polymorphic vs. monomorphic
2. 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)
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
B. History of Population Ecology
a. Thomas Malthus - human populations and
geometric (exponential) growth cannot
continue (1798)
b. P. F. Verhulst - logistic growth (1838)
c. J. Von Liebig - “law of the minimum”
(1840)
d. F. F. Blackman - “law of limiting factors”
(1905)
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)
i. Nicholson A. J., and J. P. Bailey - population
prediction and equilibrium (1935)
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).
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
a. Structure and life history - like individual
1. Grow, differentiate and respond to environment
b. Characters unique to groups
1. Density, birth and death rates, sex and age
structure, spatial distribution
2. These characters (properties) are the main
subject matter of population ecology.
3. The study of factors affecting spatial and temporal
patterns in the number of individuals
a. Reproductive rates and mortality
b. Dispersal and migration
c. population structure
d. regulatory mechanisms and
e. interspecies relationships
4. Major questions
a. What factors are involved in regulation of
population size?
b. What relationships exists between stability and
complexity?
c. What are the limiting factors?
5. Limiting vs. Regulating factors
a. Limiting: what causes carrying capacity to be
at a certain level; K=c
b. Regulating factors: what causes change in
population level to be zero; Δn = 0
c. 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)
6. Density dependent vs. independent
a. 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
1. Weather (the physical factors)
c. Controversy - entomologists from Australia
1. 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.
7. Solution of ecological problems
a. Objectives and hypotheses
b. Tests of hypotheses
1. Sampling and data analysis (empirical)
2. Model formulation and analysis
c. Predictions and general theory
8. Laboratory and field studies
a. Lab: carefully controlled experiments allow for
direct hypothesis testing
1. Insect, plants, and micro-cosm experiments
2. Small mammals
3. A few larger small-mammal predator-prey studies
b. Field: important to understand natural
populations
1. Plants and animals
2. Short-term vs. long-term a lack long-term data for
making needed generalizations
9. Looking for generalizations: SCIENCE
a. 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
10. Mathematical or Quantitative ecology
a. Not statistics
1. Statistics is a branch of mathematics dealing with
number distributions and probability
b. Dealing with quantities in ecology
1. N
2. Rates affecting N
3. Factors quantitative effect on rates
c. Use calculus and statistics
1. Calculus: rates of change, solutions to equations,
stability, projections, instantaneous rates
2. Statistics: correlation of factors with population,
mean, variance, confidence, significance, etc.
Summary
1. Course will cover population ecology
2. Not very old science with few laws
3. Variety of population characteristics
are studied by using a variety of
methods
4. Highly quantitative by nature