Chapter 4: Population Biology. Population group of organisms, all of the same species, that live in...
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Transcript of Chapter 4: Population Biology. Population group of organisms, all of the same species, that live in...
![Page 1: Chapter 4: Population Biology. Population group of organisms, all of the same species, that live in a specific area.](https://reader035.fdocuments.us/reader035/viewer/2022081506/56649f1d5503460f94c341f1/html5/thumbnails/1.jpg)
Chapter 4: Population
Biology
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Population
• group of organisms, all of the same species, that live in a specific area
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How fast do populations grow?
• Not linear growth – so it is not a straight line
• Graph- starts to increase slowly, then resembles a J-shaped curve
• Initial increase slow, b/c # of organisms that reproduce is small
• Increases b/c the total # of individuals that can reproduce has increased
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Is Growth Limited?• J-shaped growth curve illustrates exponential
population growth
• Exponential Growth – means that as a population get larger, it also grows at a faster rate
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What Can Limit Growth?
Population growth does have limits
• Limiting Factors – food, disease,
predators, or lack of space will
Cause population growth to SLOW
• Under these conditions the population may stabilize in a S-shape growth curve
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Carrying Capacity
• the number of organisms of one species that an environment can support indefinitely
• Developing population – more births than deaths and the population increases until the carrying capacity is reached or passed
• When a population overshoots the carrying capacity, limiting factors come into affect
• Deaths begin to exceed births and the population falls below the carrying capacity
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Reproduction Patterns • Life-History Pattern- organisms
reproduction pattern
• Slow life-history pattern – slow rate of reproduction and produce relatively few offspring– Ex. Elephant
• Fast life-history pattern – reproduce rapidly and produce many offspring in a short period of time– Ex. Mosquito
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Rapid Life- History Patterns• Common among organisms in changeable
or unpredictable environments • Organisms have:
– Small body size– Mature rapidly– Reproduce early– Short life span
• reproduction rises rapidly then decline when environment becomes unsuitable
• population survives and will reproduce again when the environment is favorable
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Slow Life- History Patterns
large species that live in more stable environments– Elephants, Bears, Whales, Humans, and plants
(trees)• reproduce and mature slowly• long-lived• maintain population sizes at or near carrying
capacity
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Density Factors and Population Growth
3 Patterns of Dispersal:1. Random
2. Clumped
3. Uniform
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Density-Dependent Factors
• disease
• competition
• predators
• parasites
• food
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• increasing affect as the population increases
• Example- corn fields
• Crops grow close together
• Disease can spread rapidly and kill off the whole crop
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Density-Independent Factors
can effect most populations regardless of their density• Most are abiotic factors
• Volcanic eruptions• Temperature• Storms• Floods• Drought• Chemical Pesticides• Major habitat destruction
Usually affect smaller organisms more– Example – Mosquitoes – severe winters kill the adults of most species
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Population Size
• limited by abiotic and biotic factors
• controlled by various interactions among organisms that share a community
• Predation – can effect population size in minor and major ways
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• Locusts eat acres of lettuce on a farm
• Brown snake introduced into Guam, there were no native predators, and it preyed freely on native birds – drastic effect on the population size
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• predator- prey relationships are known to experience cycles or changes in their numbers over periods of time
• prey population increases and there is more food for the predator, so the predator population increases
• predator population increase and predation increase, therefore – the prey population declines.
• With less food, the predator population decrease. • Cycle starts again
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Competition within a Population
• density dependent factor
• few individuals compete for resources, usually no problems
• When population increase and the demand exceeds the supply, the population size decreases
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Crowding and Stress• populations become
crowded, individuals exhibit stress
• stress symptoms– Aggression– decrease in parental care– decreased fertility– decreased resistance to
disease
• all have negative effects on a population
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Human Population• Demography – study of human population size
– density and distribution– movement– Birth and death rates
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Human Population Growth
• Humans change their environment• Developed methods for producing
more food• infant mortality rate decreased• clean water• All enable people to live longer and
produce more offspring• Population Grows
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Calculating Growth Rate
• Birthrate – number of live births per 1000 population in a given year
• Death rate – number of deaths per 1000 population in a given year
• Immigration – movement of individuals into a population
• Emigration – movement of individuals out of a population
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Calculate a population’s growth rate by
• (Birthrate + Immigration Rate) – (Death rate + Emigration Rate) = Population Growth Rate
• PGR = (B + I) – (D + E)
• Immigration and emigration are not always accurate use:
• PGR = Birthrate – Death rate
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• Positive Growth Rate– unless the growth rate becomes negative the
population continues to grow, just slower
• Doubling Time – time needed for a population to double in size
• Age Structure – refers to the portions of the population that
are in the different age levels
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