Transcript Document

Population Ecology
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Key elements of an
organism’s
environment
include:
– temperature
– water
– sunlight
– Soil
– Classical limiting
factors
Many organisms
actively employ
mechanisms to
maintain
homeostasis, while
others conform to
their environment.
Environmental Variation
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Populations
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A population consists of individuals of a given
species living together at the same place at the
same time.
Population distributions
– Most species have a limited geographic
range.
– Population ranges change through time.
 environment changes
 organisms circumvent previously
inhospitable habitat
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Population Dispersion
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Randomly spaced
– Individuals are randomly spaced within a
population.
Uniformly spaced
– Uniform spacing within a population often
results from resource competition.
Clumped spacing
– Individuals clump into groups or clusters in
response to uneven distribution of
resources in their immediate environment.
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Population Dispersion
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Population Dispersion
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Cost of Reproduction
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A life history is the complete life cycle of an
organism.
– all involve significant trade-offs
 Due to limited resources, increased
reproduction may decrease survival and
chances of future production.
 cost of reproduction
 Natural selection will favor the life
history that maximizes lifetime
reproductive success.
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Cost of Reproduction
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Investment per offspring
– Key reproductive tradeoff concerns the amount of
resources to invest in producing any single
offspring.
 number of offspring versus size of each offspring
 In many species, offspring size critically
affects chances of survival.
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Cost of Reproduction
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Reproductive events per lifetime
– semelparity - organisms focus all
reproductive efforts on a single, large event
– iteroparity - organisms produce offspring
several times over many seasons
Age at first reproduction
– Longer-lived animals tend to reproduce
later, and provide more parental care than
shorter-lived animals.
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Demography
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Demography - statistical
study of populations
Factors affecting growth rates
– sex ratio
 effect also determined
by mating habits
– generation time
 average interval
between birth of an
individual and the birth
of its offspring
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Demography
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Age structure
– cohort - individuals of the same age
 fecundity - number of offspring
produced in a given period of time
 mortality - number of deaths in a given
period of time
– Age structure determined by the relative
number of individuals in each cohort.
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Cohort and Age Structure of Baby Boomers
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Demography
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Life tables
– constructed by following the fate of a cohort
from birth until death
Survivorship curves
– Survivorship is the percentage of an original
population that survives to a given age.
 Type I - full life span
 Type II - mortality unrelated to age
 Type III - early susceptibility
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Survivorship Curves
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Population Growth
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Darwin recognized that organisms can out
reproduce their environmental resources
Biotic potential - the rate at which a
population of a species will increase when
there are no limits on its rate of growth
Mathematical terms -
dN/dt = riN
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dN/dt = riN
Where:
• N = number of individuals in the population
• dN/dt = the rate of change of population
numbers over time
• r = intrinsic rate of increase for that
population (intrinsic capacity for growth)
r is difficult to calculate and is often
considered as the difference between birth
rate and the death rate
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Biotic Potential
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Exponential growth model
– Rate at which a population
of a given species will
increase when no limits are
placed on the rate of
growth.
 Innate capacity for
growth of any population
is exponential.
 Even when rate
remains constant,
actual increase in
number accelerates
as the population size
grows.
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Biotic Potential
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Carrying capacity
– Carrying capacity (K) is the maximum
number of individuals the resources in a
given area can support.
Logistic growth
– As a population approaches carrying
capacity, its growth rate slows as resources
become depleted.
 sigmoidal growth curve
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The Carrying Capacity
K
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The Carrying Capacity
K
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The End
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