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How populations grow and Limits to growth
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Three important characteristics of a population are 1. Geographic distribution 2. Density 3. Growth rate Characteristics of Populations
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A term that describes the area inhabited by a population. Vary in size. Geographic distribution (range)
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Number of individuals per unit area. PD = number of individuals / unit area OR PD = number of individuals divided by unit area Population Density
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Three factors affect population size: 1. Number of births 2. Number of deaths 3. Number of individuals that enter or leave the population. Immigration – movement of individuals into an area. Emigration – movement of individuals out of an area. Population Growth Rate
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Animals emigrate. Decline Animals immigrate. Growth More births than deaths. Growth More deaths than births. Decline Same number of deaths to births. Stays the same Population growth or decline?
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Two types of population growth graphs 1. Exponential growth 2. Logistic growth Population growth graphs
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Exponential growth A population with Abundant space Abundant food Protected from predators and disease Under ideal conditions with unlimited resources, a population will grow exponentially.
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Logistic Growth As resources become less available, the growth of a population slows or stops. Occurs when a population’s growth slows or stops following a period of exponential growth.
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Logistic Growth Carrying capacity – the largest number of individuals that a given environment can support Consider your own house’s carrying capacity.
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Review Break! Suppose that the total penguin population was 1200 at the beginning of the year and 1600 at the end of the year. What was the population’s growth? Answer: increase of 400 penguins Suppose 250 penguin chicks died during the year. What was the population’s growth? Answer: Net increase of 150 penguins Suppose that 200 adult penguins also died during the year. What was the population’s growth? Answer: A net decrease of 50 penguins
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Review Break! List three characteristics that are used to describe a population. Answer: Geographic distribution, density, growth rate What is the equation for population density? PD = number of individuals/unit area What is carrying capacity? Answer: largest number of individuals that a given environment can support.
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What is a specific limiting factor we have discussed before? Limiting nutrient Limiting factor – a factor that causes population growth to decrease Examples: Competition, predation, parasitism/disease, drought and other climate extremes, human disturbances Limiting factors
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A limiting factor that depends on population size Examples: Competition, predation, parasitism, and disease. Density-dependent limiting factor
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When populations become crowded, organisms compete with one another for food, water, space, sunlight, and other essentials. Competition occurs between members of the same species and different species. Density-dependent limiting factor Competition
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Regulation of a population by predation takes place within a predator-prey relationship – population control Density-dependent limiting factor Predation
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First, why is this density-dependent? Parasites are like predators – take nourishment at expense of hosts, often weakening and causing disease or death. Density-dependent limiting factor Parasitism and Disease
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Affect all populations in similar ways, regardless of the population size. Examples: Unusual weather, natural disasters, seasonal cycles, and certain human activities – such as damming rivers and clear-cutting forests Density-independent factors
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Contrasting density-dependent/density- independent 1. Competition 2. Human activities 3. Predation 4. Parasitism 5. Unusual weather 6. Disease 7. Natural disasters Review Break!
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Are density-dependent limiting factors abiotic or biotic factors? Answer: Biotic factors Are density-dependent limiting factors abiotic or biotic factors? Answer: Abiotic factors Review Break!
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