Do now

1. Describe the ecosystem of Easter Island.

2. What are some factors that limited how many people can live on Easter Island?

Do NowWhat are three factors that might limit the growth of a population of lions on the savannah?

Carrying capacity

• The maximum population size of a particular species that an environment can sustain stably

• (how many individuals of a population can live happily in a place)

Example of carrying capacity

Carrying capacity can be expressed as population density

Population density = population ÷ area

Population growth is limited by:

Biotic factors – living things (plants, animals, bacteria)

Abiotic factors – non-living things (water, soil, sun)

Population growth is limited by:• Availability of matter and energy (food if you’re an

animal, sunlight and nitrogen in the soil if you’re a plant). Also water.

• Size of the environment (do you have enough space)

• Presence of competing organisms (other organisms competing with you for matter and energy and space

• Presence of predators (eating you)

Turn and talk – what factors limited population growth of humans on Easter Island?

Some factors that limit growth depend on population density, some do not

• Density independent factors affect populations no matter how dense they are– Natural disasters– Temperature– Sunlight penetrance in the ocean– Human activities

• Density dependent factors only affect populations when they reach a certain density– Competition for resources– Disease and parasites– Crowding– stress

When resources are abundant, populations grow exponentially

When resources become limited, populations grow logistically

• Population growth stops at the carrying capacity

Exit slip – no notes!

1. What are three factors that limit population growth?