Lecture 20. Life History & Population Dynamics

Acquisition of resources

Each individual organism acquires a finite amount of resources

Resources are allocated to required life processes:

Basic maintenance, growth, repair, resource acquisition, escaping predators, reproduction, etc.

When resources are abundant:

Extra resources allocated to growth, reproduction, etc.

When resources are scarce:

Resources allocated to basic maintenance

R

Resources

P

Proportion of R invested in survival

1 - P

Proportion of R invested in reproduction

Life history

The schedule of organism’s growth, development, reproduction, & survival

Life history traits include…

Age at sexual maturity, frequency of reproduction, number & size of offspring

Semelparity

Organism reproduces once before death

Iteroparity

Organism reproduces multiple times before death

Reproduction always has a cost

Energy put into reproduction cannot be used for growth, repair, etc.

K-selected species

Present in stable & predictable environments (populations near carrying capacity)

Characteristics of K-selected species

Produce fewer offspring, longer gestation periods, greater parental care

R-selected species

In unstable or unpredictable environments where offspring have low chance of survival

Characteristics of r-selected speices

Produce many offspring, small body size, short time to maturity, short generation time, little parental care

Invasive species tend to be…

R-selected

Density-independent factors

Effects of factors do not depend on pop. density

Density-dependent factors

Effects of factors depend on population density

Density-independent examples

Seasonal cycles, natural disasters, human effects

Density-dependent examples

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

Intrinsic physiological factors can…

Regulate population size

Intraspecific competition

Competition within species

Interspecific competition

Competition between species