Notes: Chapter 43
Population Growth and Regulation

Ecology - study of the interaction between organisms and their environment, environment composed of abiotic (nonliving) and biotic (living) factors

"Ecology" is derived from the greek work oikos, meaning "a place to live"

Abiotic component - soil, altitude, climate (temerpature, humidity, wind, etc.), latitude, other

Biotic component - predators, prey, parasites, competitors

Ecosystem: A complex, interrelated network of living organisms and their nonliving surroundings (a prairie, lake, forest)
Population: all the members of a particular species (hawks)
Community: all the interracting populations in an area (hawks + trees + rabbits)

How Populations Grow

Factors the determine how much a population will change

1. births
2. deaths
3. migration

Stable populations occur when as many individuals join (birth or immigration) as leave (death or emigration)
Population change = (birth - deaths) + (immigrants - emigrants)

Biotic Potential: maximum rate at which a population could grow given optimal conditions (food, water, space)

Factors that influence biotic potential:

1. age of reproduction
2. frequence of reproduction
3. number of offspring produced
4. reproductive life span
5. average death rate under ideal conditions

Environmental Resistance: Decreases the birth rate, or increases death rate, related to environmental conditions, such as food & space.

Density Independent Factors: weather and other natural disasters
Density Dependent Factors: food, space, water, parasitism, competition

Growth rate (r) = birth rate (b) - death rate (d)

Population growth = rN

(r = growth rate, N = original population size)

 

J-shaped curve showing exponential growth of a population

This population has not yet reached its carrying capacity.

S-shaped curve shows how a population becomes limitied by environmental factors

Carrying Capacity: the maximum size of a population that an area can support

Boom and Bust Cycles

Rapid population growth followed by a massive die-off
Populations that are influenced by seasonal weather patterns, such as cold and drought

Predator-Prey Cycles

Most populations fluctuate in cycles. The prey population rises, causing the predator population to also rise. Predators then overfeed on prey, causing the prey population to drop, Once the prey population drops, the predator population drops due to lack of food. The cycle repeats indefinitely.

Competition

Resources limit the size of populations as individuals compete

Interspecific competition: occurs between members of different species
Intraspecific competition: occurs beweeen members of the same species

Scramble competition: free-for-all, plants disperse seeds and as they grow they choke out other seedlings

Contest competition: social interaction in animals that leads to the gaining of resources

Contest competition: social behaviors, territoriality
Dominance heirarchies: pecking orders within members of a species, dominant individuals get more resources or mating priveleges

Simulation of Predator Prey Interactions

Population Patterns in Space and Time

Distributions

Clumped
Random
Uniform

Survivorship curve

Early loss
Constant loss
Late Loss