Population Ecology

How do Ecologist study populations? Geographic range Density and distribution Random Uniform clumped Growth rate Age structure

Population growth Birth rate versus Death rate Immigration versus emigration

Exponential growth Larger the population grows, the faster it grows Organisms that reproduce rapidly Organisms that reproduce slowly Organisms in new environments “j” shaped curve

Population Questions Your rich uncle has just died and has left you 1 billion dollars. If you accept the money you must count it for eight hours a day at the rate of one dollar per second. When you are finished counting, the billion dollars will be yours and only then may you begin to spend it. Do you accept your uncle’s offer? Why or why not? How long would it take to count a billion dollars at this rate? How long would it take to count a million dollars at the same rate?

Doubling time Bacteria multiply by division. One bacterium becomes two, two become 4, 4 become 8… For some bacteria, the time for this division process is 1 minute. If you put one of these bacterium in a bottle at 11:00pm, the entire bottle will be full at 12am. When would the bottle be half full?

Logistic growth “s” shaped curve As resources become limited, population growth slows or stops, leveling off at the carrying capacity. Follows exponential growth Carrying capacity – max. number of individuals of a particular species that a particular environment can support

Limiting factors to population Separately or together, limiting factors determine the carrying capacity of an environment for a species. Competition Predation Parasitism and disease Unusual weather Natural disaster

Density dependent vs. Density independent Density dependent limiting factors affect density (# of organisms per unit area) when density reaches a certain level. Competition, predator/prey, parasitism Density independent factors – occur regardless of population size Weather, natural disasters

Human Population Tends to increase Exponential growth Less predators/disease Improved nutrition, sanitation, medicine and health care Exponential growth Thomas Malthus predictions, population can only be limited by war, famine and disease

Patterns of human growth Demography – scientific study of human populations. use birthrates, death rates and age structure to predict growth or decline Demographic transition Change from high birthrates and death rates to low birthrates and death rates. Japan, US and Europe have completed the transition South America, Africa and Asia are in stage 2