Populations

Section #1:How Populations Change in

Size

Population:

•all the members of a species living in the same place at the same time

•a reproductive group – breed with each other

•also deals with the number of individuals

Population

described in terms of:•size – how many•density – the # of per unit area

or volume•dispersion – arrangement of

individuals within a given space

How Does a Population Grow?

growth rate = births – deaths

growth rate = change in the size of a population over a given period of time

•can be positive, negative or zero

How Fast Can a Population Grow?

Biotic Potential – the fastest rate at which a population can grow

Reproductive Potential – the maximum # of offspring that each member of a population can produce

Reproductive Potential

increases when individuals:•produce more offspring at a

time•reproduce more often•reproduce earlier in life

(generation time – the time it takes to reach sexual maturity)

Exponential Growth

•a large # of individuals is added to the population in each succeeding time period

•population has plenty of food, space, no competition, little disease

What Limits Growth?

•natural conditions that are neither ideal or constant

•lack of resources•environmental change•disease

Carrying Capacity

•the maximum population that the ecosystem can support indefinitely

•capacity can change over time•populations may increase beyond this #, but cannot stay

Carrying Capacity Example

•Australia originally did not have rabbits until they were introduced in 1859

•no competition, no predators, & plenty of food led to rapid growth

•population eventually crashed because of disease & starvation

Resource Limits

•plant growth is limited by water supplies, sunlight, & mineral nutrients

•a species reaches its carrying capacity when it consumes a particular natural resource at the same rate at which the ecosystem produces the resource

Competition

•members of the same population compete for the same resources as the carrying capacity nears

•can also compete for social dominance, territory, mates, etc.

Density Dependent or Independent

•cause of death is density dependent when populations are crowded (limited resources, predation, disease)

•ex. = disease carrying beetle can spread quickly through dense pine forests

Density Dependent or Independent

•cause of death is density independent when a certain # of individuals die regardless of density

•ex. = severs weather, flooding, storms, etc. that affect all populations in that area equally