NOTES 31 – Population Ecology

What is population ecology? The study of a species population living in an area to see how the population behaves, adapts to its environment, and grows Population Density – the number of individuals in a population in an area (EX. the number of humans on planet Earth) If a population has all the resources needed for survival, density should increase forever

Growth Rate – the amount by which a population’s size changes in a given time Growth rate is affected by 4 main factors in a given time: Birth rate – how many individuals are born Death rate – how many individuals die Immigration rate – how many individuals move into the population Emigration rate – how many individuals move out of the population

If the population is increasing, then the growth rate is positive If the population is decreasing, then the growth rate is negative

Snowshoe Hare and the Lynx

What limits population growth? A population’s ability to grow is limited by certain factors in the environment Carrying Capacity – the largest population density that the environment can support for a species population

What limits population growth? At carrying capacity, the birth rate equals the death rate and the population stays the same

What limits population growth? A population below the carrying capacity will have a positive growth rate

What limits population growth? A fast growing population may increase past its carrying capacity, but will eventually decrease in size

As populations grow, the amount of resources in an area usually stays the same, so competition increases Density-dependent Factors – resources in an environment that affect population density because they become harder to get as the population increases The availability of these resources depends on the number of individuals in the population

Density-Dependent Factors EX. food, water, habitat (places to live), disease As a population nears its carrying capacity, density-dependent factors slow growth

Density-independent Factors – things that affect population density that have nothing to do with the size of the population These factors do the same thing to individuals if the population is small or large EX. fires, freezes, droughts, floods, earthquakes, volcanic eruptions, other natural disasters Both density-dependent and density-independent factors affect population size

The Human Population of Earth – What goes up must come down?