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Concept 10.1: Populations exhibit a wide range of growth patterns, including (4)
exponential growth, logistic growth, fluctuations, and regular cycles.
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Concept 10.2: Delayed density dependence can cause
populations to fluctuate in size.
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Concept 10.3: The risk of extinction increases greatly in -----------
in small populations.
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Concept 10.4: Many species have a metapopulation structure in which
sets of spatially isolated populations are linked by dispersal.
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Logistic growth curves incorporate a
carrying capacity (K)
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Exponential growth only occurs over
short time periods and some conditions
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Few populations exhibit -----------, noise remains
logistic growth
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Many populations exhibit fluctuations in population growth because of
density dependent and independent factors
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Regular cycles most often result from
density dependent factors
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Delayed density dependence results from mismatches between -------------- and ------------------.
prey growth rates and predator growth rates.
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Many factors can drive populations to extinction:
- Predictable (deterministic) factors, as well as fluctuation in population growth rate, population size, and chance events = Genetic Drift
- Demographic Stochasticity
- Environmental Stochasticity
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Why are small populations more prone to extinction?
Random events kill a larger portion of the population
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Genetic drift—
chance events influence which alleles are passed on to the next generation.
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Drift reduces the genetic variation of small populations, but has little effect on
large populations.
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Genetic drift can cause allele frequencies to
change at random from one generation to the next in small populations.
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Small populations are vulnerable to the effects of genetic drift for three reasons:
- 1. Loss of genetic variability reduces the ability of a population to respond to future environmental change.
- 2. Genetic drift can cause harmful alleles to occur at high frequencies.
- 3. Small populations show a high frequency of inbreeding (mating between related individuals
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Inbreeding tends to increase the frequency of ------------- which can lead to reduced reproductive success.
homozygotes, including those that have two copies of a harmful allele,
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Inbreeding: three results
- 1)Increases expression of deleterious alleles
- 2)Decreases reproductive success
- 3)Can lead to lower population growth rates
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Environmental stochasticity—
changes in the average birth or death rates that occur from year to year because of random changes in environmental conditions.
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Demographic stochasticity—
population-level birth and death rates are constant within a given year, but the actual fates of individuals differ.
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Metapopulations—
spatially isolated populations that are linked by the dispersal of individuals or gametes
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Metapopulations are characterized by
epeated extinctions and colonizations.
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species persists because the metapopulation includes populations that are
going extinct and new populations established by colonization.
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Populations of some species are prone to extinction for two reasons:
- 1. The landscapes they live in are patchy (making dispersal between populations difficult).
- 2. Environmental conditions often change in a rapid and unpredictable manner.
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If the -------------- is greater than the ---------------- then the population will go extinct.
- probability of extinction
- probability of colonization
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Habitat fragmentation—
large tracts of habitat are converted to spatially isolated habitat fragments by human activities, resulting in a metapopulation structure.
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Source-sink dynamics:
Some patches are better than others and they produce more propagules that disperse
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Bottom-up control—
increased nutrient inputs caused eutrophication and increased phytoplankton biomass, decreased oxygen, fish die-offs, etc.
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