Factors that affect populations

• Describe the factors that limit the size of a population.

• Compare density-dependent and density-independent factors

• Understand the terms extinct, endangered, extirpated, threatened, and vulnerable.

open population closed populationimmigration emigration density-dependent density-independent Vulnerable ThreatenedExtirpated EndangeredExtinct

Keywords

Emigration: number moving out of a population

Immigration: number moving into a population

Closed population: (island)Only births or deaths change the population..

Population Growth = (births + Immigration) - (deaths + Emigration)

Open population: (Manitoba) Births/deaths and moving in/out change population.

Population Growth = (births) - (deaths)

Many environmental factors limit population growth.

Density-dependent factors: Affect large and crowded populations.

• Competition – forced to compete for resources.• Stress – overcrowding leads to early deaths.

• Predation – more opportunity for predators.

• Disease – disease spreads faster in dense areas.

Density-independent factors: Affect a population regardless its size / density.

• Natural factors – without human intervention.(bad weather, natural disasters)

• Human activity – because of human intervation.

(pollution, deforestation)

• Populations are restricted by natural ecosystems. • If too dense - density-dependent factors act to limit

the population of that species.

• Density-independent factors limit population regardless of size.

• Populations usually regulated around the carrying capacity.

As the population of a species declines it goes through stages:

Vulnerable:Low or declining numbers. Threatened:At risk, continues to decline. Extirpated:No longer exists in part of its environment. Endangered:Close to disappearing everywhere. Extinct:No longer exists on earth.

Each species in an ecosystem has a niche - a unique habitat and role in a food chain.

When humans bring a new species (non-native) into an ecosystem, it competes with species already in the ecosystem.

Over time the new species will dominate because there is no natural predator to keep it in balance.

*Called an invasive species (exotic species) and they can often have devastating results on the ecosystem.

ZEBRA MUSCLES• Came to North America on boat around 1986. • 1 female can produce up to 40,000 eggs per year.• Caused millions of dollars of damages.• Water colonies have formed layers 1.5 m thick.• 700,000 zebra mussels per square metre in 1989.• Reduce algae species and aquatic food in the food

chain.