Populations And how they grow

Populations A population is a group of organisms of a single species that live in a given area A species is a group of organisms that inter- breed and produce fertile offspring Populations change –Stay the same, increase in numbers, decrease in number

Population Growth Rate (1) This is the change in population size Growth rates can be: –Positive –Negative –Zero Growth rate depends on interaction with the other organism in the environment

Population Growth Rate (2) In ideal conditions organisms reproduce faster than their death rate Ideal conditions include: adequate food, protection from predators, shelter –(Remember: food, water, shelter, space) As long as ideal conditions continue the larger a population gets, the faster it grows. This type of growth is called exponential growth –Good example is a bacterial cell growth curve –See graph page 133

Logistic Growth Populations in new environments grow slowly at first Enter an exponential phase Exponential phase does not last long Population growth slows down Population enters the zero population growth phase (the size of the population stays the same) This is a steady state condition (see graph page 134)

Carrying Capacity The average population size in the steady state is the carrying capacity of the environment Environmental factors work to stabilize a population at the carrying capacity –Birth rates rise, death rates decline –Birth rates decline, death rates rise Steady state is not steady but fluctuates up and down year to year

Boom and Bust Cycle Populations grows slowly, then grows exponentially Population goes into rapid decline then grows slowly And repeat

Review Growth Cycles Exponential growth Logistic growth Boom and bust