population ecology ch 53 study of the growth, abundance and distribution of populations
DESCRIPTION
Calculating population size: Mark recapture method Capture and tag a population then release it Recapture a population a count number tagged N-= population size m = #captured and tagged n = #second capture x = #tagged in 2nd capture x/n = m/NTRANSCRIPT
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POPULATION ECOLOGYCH 53
Study of the growth, abundance and distribution of populations
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I. POPULATION ABUNDANCE AND DISTRIBUTION
A. Population size and density• Population size = N = Total number of
individuals in the population
• Population Density = Number of individuals per unit area
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Calculating population size: Mark recapture method• Capture and tag a population then release it• Recapture a population a count number
tagged
N-= population size m = #captured and tagged
n = #second capture x = #tagged in 2nd capture
x/n = m/N
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B. Population dispersion: how is the population dispersed in an area
Clumped is often due to availability of resources or social behavior
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Uniform is often due to territoriality
Random dispersion is due to no real interaction between members
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Age structure • The abundance of individuals of each
age • Pyramid shaped curves indicate a
rapidly growing population • Rectangular shaped curves indicate a
stable population
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Survivorship curves • Describes the mortality of individuals
during their lifetime
Type I species: most survive to middle age or older tend to be large mammals that produce few offspring but provide a lot of care
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Type II species: length of survival is random. Equal likelihood of death at any age example rodents
Type III species: most of the individuals die young Tend to be organisms that produce a lot of offspring with very little careexample oysters
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II. POPULATION GROWTH
Population growth rate N B Dt
1. exponential growth: Maximum growth rate of a species under IDEAL conditionsdN/dt = rmaxNResults in J shaped curveRmax = biotic potential
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Factors that affect the rmax of a species • Age at which they reproduce • Average # offspring produced in each
breed • How frequently they reproduce • How long they can reproduce • How many offspring survive to
reproduce
• Greater rmax fly or elephant?
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2. Logistic Growth• Exponential growth is often seen in
very small, newly established populations but can’t be sustained for long
• As the population reaches the carrying capacity of the environment, growth decreases and approaches zero
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• Represented by the following formula:
dN/dT = rmaxN(K-N/K)
• K = carrying capacity (maximum # individuals environment can support)
• N= #individuals• K-N = #of new individuals the
environment can support• K-N/K = fraction of K that is still
available for population growth
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• The smaller N is the closer K-N/K is to 1 and the growth rate approaches the maximum rate (exponential)
• The larger N is the closer K-N/K is to zero and the closer the growth rate approaches zero
• What happens if N>K?
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Carrying capacity: • the maximum number of
individuals of a population that the environment can support
• Some populations overshoot carrying capacity before stabilizing at a certain density
• Some populations fluctuate greatly
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Factors that limit the carrying capacity and biotic potential of a population • Parasites and disease • Resources • Toxic effects of waste • Stress of too many individuals inhibits
reproduction • predators • These are density dependent. What does
that mean?
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III. REPRODUCTIVE PATTERNS ARE THE RESULT OF NATURAL SELECTION
• Any trait that would enhance an organism’s chances to survive and reproduce is favorable
• However, there are tradeoffs between survival and reproduction
• Reproduction requires an investment of energy
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• The greater the chance of survival, the more energy can be invested in reproduction
o Species whose young have a high rate of survival like primates tend to produce few larger young and invest energy in their care
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The lower the chance of survival the less energy will be invested in reproduction
o Species whose young have a lower chance of survival, like insects, produce a lot of smaller young and don’t invest energy in their care
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reproductive strategies can be k-selected or r-selected
K-selected strategies• Tend to operate in a stable environment and is
under the influence of density dependent factors• Selects for traits that are sensitive to population
density
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• Organisms that are extreme k-strategists tend to have the following reproductive characteristics:
o Fewer larger offspringo Lots of parental care o Slower maturityoOften reproduce more than onceoMost offspring survive to
reproduce
• Because most offspring survive they can invest a lot of energy in their young
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R-selected strategies
• Tend to operate in an unstable environment and subject to density independent factors
• Select for traits that maximize reproduction
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• Characteristics of r-strategists:
o many small offspring o little or no parental care o early reproductive age o often reproduce only onceo most offspring die before
they reproduce
• because survival of offspring is low they tend to invest little energy in their young