 A population is a group of individuals of a single species that occupy the same general area.  Two important characteristics of any population are density and spacing.  Density = number of individuals per unit area or volume  Dispersion – pattern of spacing among individuals

 Mark-recapture method.  Sampling technique used to estimate populations  Take a proportion of catch  N = (# marked in first catch) x (Total # in second catch) / # of recaptures in second catch

 Study of factors that affect the growth and decline of populations  Births - reproduction  Immigration – new individuals from other areas  Mortality - death  Emigration – movement of individuals out of a population

 Number of births.  Number of deaths.  Populations grow when its birthrate is greater than its death rate.  If more individuals die than are born, a population will decrease.

 Number of individuals that enter or leave the population.  Immigration- movement of individuals into an area.  Causes a population to grow.  Emigration- movement of individuals out of an area.  Causes a decrease in population size.

 A variable affected by the number of organisms in a given area  Availability of nesting

 Variables that affect a population regardless of density  Weather  Flood  Fires

 Age specific summary of the survival pattern of a population  Cohort – group of individuals of same age, from birth until death

 Graphic way of representing data in a life table.

 Type 1 curve – relatively flat at start, reflects low death rates during middle life, then drops steeply as death rates increase among older age groups.  Example - humans

 Type 3 curve – very high mortality, but decreased mortality later in life.  Example would be oysters, fish, invertebrates

 Type 2 curve – intermediate between type 1 and type 3.

 Population increase under ideal conditions  J – shaped curve  Assumes unlimited resources

 If a population has lots of space and food, and no predators or disease…that population size will increase.

 Ultimately, there is a limit to the number of individuals that can occupy a habitat  Carrying Capacity – maximum population size that an environment can support at a particular time.  Symbol is K

 Growth pattern in which the individuals in a population reproduce at a constant rate.

 Basically, the carrying capacity is the largest number of individuals that an environment can support.  …there are only so many resources to go around.