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Lec04 - Population Ecology.docx

Biological Sciences
Course Code
Mary Olaveson

of 9
Population Ecology
1 population ecology
What is ecology?
What are populations?
How do biologists study populations?
How do ecological conditions affect life histories?
What factors influence population densities?
How are populations regulated?
How are populations managed?
2 what is ecology?
The study of:
o The distribution and abundance of organisms
o The interactions among organisms
Biotic interactions
o The interactions between organisms and their non-living environments
Abiotic interactions
3 ecology is studied at several levels
Emergent properties become evident as we move from one level to the next higher level
o Organism:
Survival and reproduction
Unit of natural selection
o Population:
Population dynamics
Unit of evolution
o Community:
Interactions among populations
o Ecosystem:
Energy flux and cycling of nutrients
o Biosphere:
Global processes
4 what are populations?
To understand human population growth
o Must consider general principles of population ecology
Population ecology
Study of populations in relation to the environment
o A population consists of all the individuals of one kind (a single
species) within a given area
5 how do ecologists study populations?
Examine dynamics of groups of conspecifics
o Emphasize intraspecific relationships
i.e. within species
6 how do ecologists study populations?
The central objective of population ecology is to determine population characteristics and to
follow ecological processes within populations
7 how do ecologists study populations?
o Individual
Age / size / sex / behavior
o Population
Abundance (density) / spatial distribution (dispersion) / age distribution / sex
ratio / size
o Individual
Development / growth / reproduction / death
o Population
Population growth / age distribution changes / mortality / demographics /
8 how do ecologists study populations?
Ecologists study patterns in space and time
o Population structure:
Patterns in space / time
Density / biomass
o Population dynamics:
Changes over time
Age distribution
Sex ratios
Survivorship curves
9 size
The number of individual organisms present at a given time
Does not indicate space occupied or involved
Numbers can increase / decrease / cycle / remain the same
10 density
The number of individuals per unit area or volume
o Determining density of natural populations is possible but difficult to accomplism
o Often impractical or impossible to count all individuals in a population
o Result of a dynamic interplay between processes that add individuals to a population
and those that remove individuals from it
11 distribution or dispersion
The special arrangement of individuals within a space
o Three main distribution patterns
Individuals grouped more closely to each other than if randomly
Organisms distributed independently of each other
Widely spread out in equal spacing from one organism to another
12 demography
Study of vital statistics and how they change over time
Death rates and birth rates are followed by demographers
Use life table
o An age-specific summary of survival patterns
o Best constructed following fate of a cohort
13 demography
Survivorship curves
o Gives average timing of deaths in individual in a population
o Classified into three general types
Type I
Type II
Type III