Download Biology 30 Chapter 20 - Vegreville Composite High

Chapter 20
Population Growth and
Interactions
Chapter Outcomes
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Describe and apply models that represent
population density and distribution of
individuals within populations
Describe the four main processes that
result in population change and explain
how these processes are related
Analyze population data to determine
growth rate and per capita growth rate
Chapter Outcomes
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Describe how a population’s biotic
potential and the carrying capacity of its
habitat determine its pattern of growth
Compare r-selected and K-selected
reproductive strategies in terms of life
cycles and patterns of population growth
Chapter Outcomes
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Describe the interactions among
population members and among members
of different populations within a
community
Explain how producer-consumer
interactions affect population growth
Describe defense mechanisms that have
evolved within populations
Chapter Outcomes
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Understand that symbiosis includes
mutual, commensal, and parasitic
relationships
Distinguish between primary and
secondary succession
20.1 – Population Growth
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Quantitative measurements of populations
are like snapshots of moments in time
Ecologists often rely on a number of
measurements over a long period of time
to make inferences about population
growth
Both the distribution and growth of a
population can be significant when
studying populations and communities
Population Distributions
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habitat can play a role in how populations
are distributed
population distributions can follow one of
three general patterns:
Patterns of Distribution
1.
Clumped
Patterns of Distribution
2.
Random
Patterns of Distribution
3.
Uniform
Population Size and Density
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population size simply describes the
number of organisms in an area
it is often more useful to compare
populations by describing population
density (the number of individuals in a
given area or volume – for aquatic
species)
Population Density Formula
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D = N / A where:
D = density of organisms (organisms/unit)
N = # of organisms
A = size of area in units
Example:
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Ex: There are 200 lemmings in a 25 ha
area. Determine the population density of
the lemmings:
Population Change
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1.
2.
3.
4.
4 factors determine population size:
Natality –
Mortality –
Immigration –
Emigration –
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if all the factors remain the same except
for an increase in the birth rate,
population increases
population change can be calculated in the
formula:
∆N = (births + immigration) – (deaths + emigration)
We can also calculate a per capita
population growth rate
cgr = (births + immigration) – (deaths + emigration)
Initial number of organisms
Population Growth Example
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Ex: In a Banks Island Breeding site, 40
cranes were born, and there were 55
deaths. There was no immigration or
emigration of cranes. The original
population was 200. Calculate the
population growth.
Biotic Potential
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1.
2.
3.
4.
biotic potential depends on a number of
factors:
Offspring – the maximum number of offspring
per birth
Capacity for Survival – the chances of offspring
reaching reproductive age
Procreation – the number of times per year an
organism reproduces
Maturity – the age at which reproduction
begins
Carrying Capacity
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Generally, growth in small populations
begins slowly and then the rate of growth
increases
However, the growth must eventually slow
because there is a maximum number of
organisms that an ecosystem can support
Growth Phases
1.
2.
Lag
Log (or Exponential
Growth)
3.
Stationary
4.
Death
S-Curves
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Many populations exhibit an S-shaped
(sigmoidal) growth curve
This is also known as a logistic growth
pattern
The population number increases until it
reaches the carrying capacity of the
ecosystem
At this point, the population fluctuates
near the carrying capacity
J-Curves
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J – shaped curves are representative of quick
growth and then a sharp decline in the
population
this occurs when a population quickly outgrows
the carrying capacity of an ecosystem
as a result, there is a crash in the population,
which is followed by a relatively stable stationary
phase
these J-curves are most often associated with
organisms that can reproduce very quickly
(insects, bacteria, etc.)
Comparison of J & S-Curves
http://www.emc.maricopa.edu
Limiting Factors in Populations
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if there are a number of substances required for
growth, then the one with the least
concentration will be a limiting factor for growth
(law of the minimum)
as well, in some cases, too much of a substance
can harm an organism
therefore, the greater an organisms’ range of
tolerance for high and low concentrations of
nutrients, the greater its survival ability
(Shelford’s law of tolerance)
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the overall optimum ranges for abiotic factors for
each species is different because each species
reacts to each factor differently
any abiotic factors that are not affected by
population density are density independent
such factors include temperature & climate
factors that are dependent on the population
density are density dependent
these are factors such as limits to food supply,
disease, and predation
often problems involving density-dependent
factors are alleviated when a population density
returns to lower levels
r and K Selected Populations
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K-selected populations are:
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r-selected populations are:
20.2 – Interactions in Ecological
Communities
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An ecological community is a collection of
interacting populations within an area
In any community, individuals must
compete for limited resources
The competition between populations is
the driving force behind population
dynamics
Intraspecies and Interspecies
Competition
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Gause’s Principle states that if two
populations occupy the same niche, one of them
will be eliminated
this principle would represent a worst-case
scenario in interspecies competition (the
competition between two different species)
there also exists intraspecies competition,
where members of the same species compete
for resources such as food, space and mates
Predation
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predator and prey populations are often
closely tied to one another (for instance, if
a prey population declines, it is likely that
the predator species will as well)
however, predators are important in
ecosystems as they reduce the number of
primary consumers that are feeding on
producers
Populations of Lynx & Hares
Predator-Prey Cycles
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Predator-prey cycles often depend on a
number of factors:
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in some cases, animals develop
camouflage to escape detection (either
by predators or prey)
other organisms produce physiological
adaptations (such as plant toxins)
some animals will engage in mimicry,
where they will develop markings similar
to those on a poisonous or dangerous
animal
often predators and prey coevolve in an
attempt to gain an upper hand
Symbiosis
1.
There are 3 types of symbiosis:
Commensalism
2.
Parasitism
3.
Mutualism
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Succession
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succession is the slow, orderly replacement of one
community by another through the development of
vegetation
climax communities are eventually formed through
this process
a climax community is a stable, mature community
primary succession occurs where there previously was
no community (on places such as barren volcanic
islands)
secondary succession occurs after the partial or
complete destruction of a community
Steps in Primary Succession
1.
2.
3.
4.
5.
Bare land is formed.
Pioneer species, such as mosses and grasses that are
relatively hardy move in and decrease soil temperature
and evaporation, while increasing soil fertility.
Small shrubs that tolerate full sunlight move in,
stabilizing and enriching the soil.
Small, fast-growing trees replace the shrubs and
deplete the soil of nutrients and sunlight.
A climax community forms, produced from shadetolerant trees which have a high sapling survival rate.
Generalizations Regarding
Succession
1.
2.
3.
4.
Species composition changes more rapidly during the
earlier stages of succession.
The total number of species increases dramatically
during the early stages of succession, levels off during
the intermediary phases, and declines as the climax
community is established.
Food webs become more complex and the
relationships more clearly defined as succession
proceeds.
Both total biomass and nonliving organic matter
increase during succession and begin to level off
during the establishment of the climax community.