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 population immigration emigration density-dependent density-independent VulnerableThreatened ExtirpatedEndangered Extinct 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 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 Reduce algae species and aquatic food in the food chain.