how populations grow and limits to growth. three important characteristics of a population are 1....
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SECTION 5-1 AND 5-2 NOTES
How populations grow and Limits to growth
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Three important characteristics of a population are
1. Geographic distribution2. Density3. 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 ORPD = number of individuals divided by unit area
Population Density
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Three factors affect population size:1. Number of births2. Number of deaths3. 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 graphs1. Exponential growth2. Logistic growth
Population growth graphs
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Exponential growthA 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 penguinsSuppose 250 penguin chicks died during the year. What was the population’s growth?
Answer: Net increase of 150 penguinsSuppose 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 areaWhat 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 factorCompetition
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Regulation of a population by predation takes place within a predator-prey relationship – population control
Density-dependent limiting factorPredation
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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 factorParasitism 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-independent1. Competition2. Human activities 3. Predation4. Parasitism5. Unusual weather6. Disease7. 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!