Biology 10, Las Positas College
Population Ecology
Chapter 39

I-Population Ecology

A-Structure & Growth
B- Human Population Growth

I-Population Ecology
Ecology – study of interactions among organisms & between organisms & the environment.
Population Ecology – focuses on the factors that influence a population’s size, growth rate, density, and features of population structure
Population – group of individuals of the same species living in a given area at a given time.

A-Structure & Growth

1. Population Density
Density = the number of organisms or individuals in a population/unit area. Influences survival.

Population Growth

Exponential Growth Model

J-shaped curve – Number of organisms added = multiply growth rate (birth rate – death rate) X number of organisms in area.
Ideally a population can grow exponentially but it stops as shortages of growth factors eventually limit population = biotic potential.

Wastes accumulate and kill population, run out of resources and population collapses, predators wipe out huge population, etc. Logistic Growth Model

Carrying capacity = the number of individuals within a population that can be supported within a particular environment for an indefinite period.

Population wavers around carrying capacity.
As population grows and its density increases, competition among organisms for resources such as food, shelter, light and mating sites increases and toxic waste products accumulate. Factors that result from the growth of a population regulate its subsequent growth.

Regulation of Population Growth

1. Density-independent limiting factors operate regardless of population size.
2. Density-dependent limiting factors are in effect when a population size increases in a given area.

a. competition for resources
b. waste products accumulate
c. interactions within community may take over
d. sometimes -> population cycles

B- Human Population Growth

Better agriculture, advanced technology, medical care, -> more survivors and decreased mortality -> more people.
Will we reach carrying capacity of the Earth?
Population keeps increasing.
Some resources already declining
People strive for higher standard of living than just having enough food to survive.
If more people or people live better lives, Earth will need to increase capacity or population must decrease.
If want to avoid "bust" of "boom-and-bust" cycle, must voluntarily decrease birth rate.

Age Structure & Population Growth

Expanding-more prereproductively competent potential than numbers than will die
Stable-about same number will give birth as will die, every year
Shrinking-more will die than will give birth

Younger people more productive than older ones. Need younger people to do work and help older people.
If young people reach old age, will need to be helped by more younger people.
How long can this continue? Carrying capacity of world.