Population Growth FactorsWhat factors will increase or decrease the size of

a population?

SBI4U RHSA

Describe the population growth

The patterns of population growth are governed by an intersection of many factors. Two common growth patterns for populations are:

1. Exponential Growth

This occurs when there are unlimited resources and no competition so the population skyrockets.

2. Logistic Growth This starts with exponential growth but the

growth slows as population increases, resources become limited and finally the carrying capacity of an ecosystem is reached.

Carrying capacity (K) is the maximum population size that can be sustained in an environment for a long time.

What do all these factors have in commmon?

The two major categories of factors influencing population growth are:

1. Density Independent or Abiotic Factors

These factors cause a population to stop growing or crash long before the carrying capacity is reached. These factors usually produce sudden dramatic declines in a population.

Examples include: Heat waves, fires, floods, droughts, tornados, ice storms, mudslides

2. Density Dependent or Biotic Factors

These factors slow a population’s growth as the population nears its carrying capacity. These BIOTIC factors often lead to sinusoidal growth patterns where the population size fluctuates around K.

Examples include: Immigration and emigration levels, waste accumulation, health/spread of diseases, competition for resources, behaviour like territoriality or predation

This shows sinusoidal population growth as a the population increases over the carrying capacity more individuals die or fail to reproduce thus decreasing the population.

How are these species influencing each other?

Tomato hornworm covered with braconid wasp pupae.

How are these species influencing each other?

Egyptian plovers taking insects off rhino back.

How are these species influencing each other?

Lion defending its’ kill from the hyena

How are these species influencing each other?

Interspecific InteractionsSPECIES A SPECIES B

Positive (+) Neutral (0) Negative(-)Positive (+) MUTUALISM

-cowbirds + cows

Neutral (0) COMMENSALISM-barnacles on whales

NEUTRALISM- probably non-existent

Negative (-) PREDATION or PARASITISM- only the predator or the parasite benefit

AMENSALISM- bread mould produces penicillin that kills bacteria

COMPETITION- both species have decreased fitness

Symbiosis includes mutualism, commensalism, predation and parasitism because in each interaction there is always one species that benefits.

Symbiosis

Two Types of Competition

1. Intraspecific Competition - (within a species) When the population size is large members

of the same species compete with each other for food, breeding sites, shelter, water, sunlight, soil and nutrients.

2.a) Interspecific Competition - (between different species)

When two different species share a similar habitat they can compete for resources. This indicates that the species have similar niches.

This situation leads to the competitive exclusion principle which states that species with the same niche cannot co-exist; one will always exclude the other through evolution. This often leads to a change in the species.

http://www.youtube.com/watch?v=BMsmDy-2jbA&feature=fvsr