Lecture 20 (second half). Life History & Population Dynamics

Waste accumulation (density-dependent factor)

Metabolic wastes accumulate at high population densities

Waste accumulation example

Brewer’s yeast produces ethanol as a byproduct consuming carbohydrates

Parasitism (density-dependent factors)

Organism that feeds on cell contents, tissues, or body fluids of another species (host) while in, or on, the host organism

Parasitism example

Bedbug epidemic in United States concentrated in high density populations

Disease (density-dependent factors)

Transmission rate of contagious diseases is higher in dense populations - often spread by parasites

Disease example

Bubonic plague

Predation (density-dependent factors)

Species interaction in which one species (predator) kills and consumes another species (prey)

Herbivory

Species interaction in which an organism eats part of a plant

Summary of density-dependent factors that affect population growth

Physiological factors, competition, waste accumulation, parasitism & disease, predation & herbivory

Allee effect

Individuals have more difficulty surviving or reproducing if population size is too small (positive density dependence)

Benefits of group living:

Increased foraging efficiency, increased awareness of predators, defense against predators

Costs of group living:

Exposure to parasites & pathogens, greater accumulation of wastes, groups more easily detected by predators, greater competition for resources

Age structure of populations

Distribution of age (& sex) in a population

Survivorship curve

Graph of number of individuals surviving at each age interval

Survivorship curves show…

Age structure of population changes over time

Type 1 curve

Low mortality in early & middle years - high mortality in older individuals

Type 2 curve

Mortality relatively constant throughout entire life span

Type 3 curve

Mortality highest in early ages - much lower mortality for individuals that survive past early yearsT

Type 1 survivorship curve…

More likely to die when very old

Type 2 survivorship curve…

Mortality equally likely at any life stage

Type 3 survivorship curve less likely to…

Die when old

Type 3 survivorship curve examples

Oysters, nile perch, trees