factors that affect populations. describe the factors that limit the size of a population. compare...
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Factors that affect populations
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• 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.
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open population closed populationimmigration emigration density-dependent density-independent Vulnerable ThreatenedExtirpated EndangeredExtinct
Keywords
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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)
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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.
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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)
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• 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.
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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.
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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.
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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.
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