Population Ecology An army of frogs

Characteristics of Populations Geographic Distribution (where populations live) Density (number of individuals per unit area) Growth Rate (how fast the population grows)

3 Factors Affect Population Size Number of births Number of deaths Number of individuals who enter or leave the population (emigration & immigration)

Exponential Growth This kind of growth happens when individuals reproduce at a constant rate. Under ideal conditions (unlimited resources), a population will grow exponentially. Larger population, faster growth! Exponential growth curves are sometimes called J-curves. Do you see why?

But can exponential growth go on forever??? Carrying capacity – the number of organisms of one species that an environment can support. Blue= Ideal Population Growth Purple= Growth that actually happened How many individuals can be supported by this environment?

Logistic growth curves are sometimes called S-curves. Why? When a population reaches carrying capacity, it no longer shows exponential growth, but logistic growth. It’s logical that exponential growth can’t last forever and the population growth slows or stops. Logistic growth curves are sometimes called S-curves. Why?

Do you think humans have reached our carrying capacity Do you think humans have reached our carrying capacity?? What do you think might happen in the future?

Limiting Factors Density dependent factors Factors that happen because of a dense population. (disease, predators, competition, parasites, food availability) Density independent factors Factors that have nothing to do with how dense the population is. (mostly abiotic factors like temperature, storms, floods, etc.)

Human Population Growth The scientific study of human populations is called demography. Some countries have very high growth rates while others have very low growth rates. Where do you think the highest growth is happening? Why?

Demographic Transition The demographic transition is a dramatic change in birth and death rates. 1st: Birth rates are high, death rates are high; slow population growth (Most of human history) 2nd: More births than deaths; very fast population growth (South America, Africa, Asia) 3rd: Birth rate matches death rate; population growth slows down. Demographic transition complete. (United States, Japan, Europe)

Age Structure Diagrams

What is happening in these populations? Which is growing? Shrinking? Stable?