1. Factors that affect populations

2. 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.

3. open population closed population immigration emigration density-dependent density-independent VulnerableThreatened ExtirpatedEndangered Extinct Keywords

4. 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)

5. 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.

6. 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)

7. 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.

8. 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.

9. 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.

10. 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.