ECOSYSTEMS PART 3

Populations

INTERACTIONS IN ECOSYSTEMS

Biotic Interactions: SymbiosisPredationCompetition

Battle at KrugerWhat interactions are happening here?

COMPETITION

Intraspecific CompetitionMembers of the same species compete for

the same resource in an ecosystem.Ex: food, light, nutrients, space.Ex: two wolves compete for a rabbit.

Interspecific Competition Individuals of different species compete

for the same resource in an ecosystem.Ex: food or living space.Ex: cheetah and lion compete for zebra.

THINK ABOUT IT...

Is there competition among plants?

POPULATION

A group of organisms of one species that lives in the same place, at the same time, and can successfully reproduce.

THINK ABOUT IT...

If all of the rocks are removed from a desert ecosystem, what would happen to the population of rock dwelling lizards, and in turn the animals which eat them?

A ten mile area of trees is removed from the tropical rainforest. How will this affect the amount of water and the amount of oxygen in the area?

THINK ABOUT IT...

When does a population increase?

When does a population decrease?

POPULATION

The size of the populations are continually adjusted by the species interactions with biotic and abiotic factors.

Populations tend to increase exponentially when there are abundant available resources.

POPULATION GROWTH

Exponential growthAccelerating population growth“J”-shaped graphUsually only occurs for a

short time under certain conditions Organism finds new habitat

with lots of resources When other pressures are

removed (i.e. hunting ban)

POPULATION GROWTH

Population growth can’t happen forever. If resources are used up the species is

unable to survive long enough to reproduce.

POPULATION GROWTH

As population rises, resources decline.

If the growth is too rapid, resources are rapidly depleted and a population crash can occur.

POPULATION GROWTH

More often what happens is that the resources slowly decrease, the growth rate slowly increases, and they meet.Carrying CapacityThis is called an s-shaped

or logistic curve

POPULATION DECLINE...

Swallow Population Decreasing in CanadaCBC NewsSeptember 15, 2014

LIMITING FACTORS

Factors that limit the growth, distribution, or amount of a population in an ecosystem.

As a population increases in size, each individual has access to fewer resources, limiting the growth of the population.

TYPES OF LIMITING FACTORS

Density Independent FactorsDo not depend on the number of members

in a population. Usually abiotic factors

Ex: natural phenomena, weather, fires, pollution, etc.

TYPES OF LIMITING FACTORS

Density Dependent FactorsDo depend on the number of members in a

population.Usually biotic factors

Ex: disease, parasites, predation, competition

CARRYING CAPACITY

The largest population of a species that can be supported by an environment.

Controlled by: Abiotic factorsBiotic factorsLimiting factors

GRAPHING CARRYING CAPACITY

Population y axis (vertical) Time (year) x axis (horizontal)

GRAPHING CARRYING CAPACITY

If the line of the graph is: Going up: population is increasingGoing down: population is decreasingHorizontal (flat): population is at its carrying

capacity for that species in that ecosystem.

During which months is the population increasing?

What is the carrying capacity of hares in Sackville?

When is the population at its carrying capacity?

What is happening to the population?