Topic 12 - Properties of Populations

Ecological Consequences

• Distribution
• Demographics (age structure, birth rate, death rate)
• Population size,
• Population growth

Evolutionary Consequences

• Change in genetic / phenotypic frequencies in a population
• Adaptations
• Macroevolution

Ecology

study of organisms and their interactions with their environment

Population Ecology

study of populations and their interaction with the environment

Population

group of individuals of the same species that live in the same place at the same time.

Fundamental Properties of a Population:

1. Density
2. Dispersion
3. Demographics
4. Life History

Density

Absolute Population size (N) = # of individuals in the population

Population Density = # individuals / unit area
- preferred

Dispersion

pattern of spacing of individuals in population

dispersion - clumped

individuals aggregated into patches (most common)

dispersion - uniform

individuals are evenly spaced

dispersion - random

individuals are spaced randomly, unpredictable spacing (least common)

Demography

Study of vital statistics

(- Death rate - Birth rate - Age class structure - Sex Ratio)

Life Table

Summary of survival and reproductive rates for each age cohort in a population

Cohort

A group born at the same time (of the same age)

Survivorship Curve

plots # of individuals (or proportion of individuals alive at each age)

Survivorship curve - type 1

- low mortality of juveniles
- high mortality in oldest individuals

Survivorship curve - type 1 - Causal Factors

- Relatively small number of offspring
- Parental care

Survivorship curve - type 2

uniform death rate across age classes

Survivorship curve - type 2 - Causal Factors

Age-independent predation / parasitism

Survivorship curve - type 3

- mortality high for juveniles
- low mortality for older age classes

Survivorship curve - type 3 - Causal Factors

- Many, relatively small offspring produced
- Little to no parental care

Life History

physiological, behavioral features that affect reproduction, growth, and survival (Age of sexual maturity (rate of development), Size of adult, Parental Care, Longevity)

Principle of Allocation

Energy invested (used) in one life history trait/characteristic can’t be used for another. Results in trade-offs

Life History Strategy

Pattern of growth, development, and timing of events in organism’s life

Semelparity

Produce many offspring once in life

Iteroparity

Produce few offspring many times in life

Density-Dependent Regulation

biotic, a natural process where the impact of resource limits on a population’s births and deaths grows stronger as the group becomes more crowded (competition, predation, diseases)

Density-Independent Regulation

any force or factor in the environment that affects the size or growth rate of a population regardless of how dense or large that population is (natural disaster, weather, human made)