Transcript Interactions in Ecosystems

Chapter 14
Interactions
in
Ecosystems
AKS Standards
11a - investigate the relationships among
organisms, populations, communities,
ecosystems, and biomes
Habitat v. Niche
A Habitat Differs From a Niche

An organism’s habitat can be described as all of the
biotic and abiotic factors in the area where an
organism lives.
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These factors include all aspects of the environment,
including grass, trees, watering holes, etc.
An organism’s niche is composed of all of the
physical, chemical, and biological factors that a
species needs to survive, stay healthy, and
reproduce.
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You can think of a habitat as where an organism lives
and a niche as how it lives within its habitat.
A niche includes, but is not limited to: food, abiotic
conditions, behavior.
Resource Availability
Resource Availability Gives
Structure to a Community
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A species needs resources such as food, water, and
shelter to be successful in its habitat.
While many species can share similar habitats, it is
impossible for two species to use the same resource
in the same way at the same time…this phenomenon
is known as competitive exclusion.
This principle states that when two species are
competing for the same resources, one species will
be better suited to the niche, and the other species
will be pushed into another niche.
This means, simply stated, that NO TWO SPECIES CAN
OCCUPY THE SAME NICHE WITHIN A SINGLE
ENVIRONMENT.
Competitive Exclusion
Animated Biology
How Long Can You
Survive in This Habitat?
 http://www.classzone.com/cz/books/bio_07/reso
urces/htmls/animated_biology/unit5/bio_ch14_04
30_ab_survival.html
Critical Thinking Activity
Connecting Concepts

Considering the competitive exclusion
principle, why might it be harmful to transport
a species, such as a rabbit, to another habitat
where it currently does not exist?

If a new species in introduced to an area, it may
occupy a similar niche as a native species and
be better adapted for the niche or have no
natural predators. This could drive the native
species into extinction.
AKS Standards
11a - investigate the relationships among
organisms, populations, communities,
ecosystems, and biomes
Competition & Predation
Competition & Predation are
Important Interactions in Ecosystems

Competition occurs when two organisms fight for the
same limited resources. There are two types of
competition in nature:
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Interspecific Competition: occurs when two different
species compete for a limited resource.
Intraspecific Competition: occurs when two members of
the same species compete for a limited resource.
Predation is the process by which one organism
captures and feeds upon another organisms.
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In nature, many predators have become highly
adapted to hunting and killing their prey, and many
prey have become highly adapted at escaping
predation.
Interspecific Interactions
Types of Symbiosis
Symbiosis is a Close
Relationship Between Species
 Symbiosis
is a close ecological relationship
between two or more organisms of different
species that live in direct contact with one
another.
 There are three major types of symbiosis:
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Mutualism
Commensalism
Parasitism
Interspecific Interactions
Interactive Review
Community Interactions
http://www.classzone.com/cz/books/bio_07/resourc
es/htmls/interactive_review/bio_intrev.html
Complete this interactive
review using your virtual
textbook at home. Concept
maps are an excellent way to
organize your thoughts and
review material!
AKS Standards
11a - investigate the relationships among
organisms, populations, communities,
ecosystems, and biomes
Population Density
Calculating Population Density
 Population
density is a measurement of the
number of individuals living in a defined space.
 Calculating accurate population density can tell
scientists about a species.
 When scientists notice changes in population
densities over time, they work to determine
whether the changes are the result of
environmental factors or are simply due to
normal variation in the life history of a species.
Population Dispersion
Understanding Geographic
Dispersion in Natural Populations
 Population
dispersion is the way in which
individuals of a population are spread in an area
or volume.
Survivorship Curves
Analyzing Survivorship Curves
A
survivorship curve is a generalized diagram
shown the number of surviving members over
time from a measured set of births.
Reproductive Strategies
Life History Strategies are Diverse in Nature
 Some
species exhibit big-bang reproduction,
which means that they reproduce once and
die. These organisms are generally referred to
as k-selected species.
 Other species exhibit repeated reproduction,
whereby they produce a large number of
offspring repeatedly. These organisms are
generally referred to as r-selected species.
 Highly variable or unpredictable environments
likely favor big-bang reproduction, while
dependable environments may favor
repeated reproduction.
Critical Thinking Activity
Inferring

An organism has ten offspring. Two of these
offspring die each year over a five-year
period. Is the organism more likely to be a
bird or an insect? Justify your response.

The organism is likely a bird because the
mortality pattern described is closest to type II.
Insects tend to be type III, with many offspring
and high mortality in early life stages.
AKS Standards
11d - assess and explain human activities
that influence and modify the environment
such as global warming, population
growth, pesticide use, and water/power
consumption
Population Growth Patterns
Events that Change Population Sizes
A
population will increase or decrease in size
depending on how many individuals are added
to it or removed from it.
 Changes in a population’s size are determined
mainly by three factors:
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Immigration: the movement of individuals into a
population from another population (increases
population size)
Births: increases population size
Emigration: the movement of individuals out of a
population and into another population
(decreases population size)
Deaths: decreases population size
Calculating Population Growth
Population Growth Equation
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The equation for population growth is
ΔN/Δt = bN-dN
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N = population size
b is per capita birth rate
d is per capita death rate.
ΔN/Δt is change in population N over a small time period t.
The per capita rate of population increase is symbolized by r.
r = b-d

r indicates whether a population is growing (r >0) or declining
(r<0).
Calculating Population Growth
Population Growth Equation
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Population growth is a function of the environment.
The rate of growth for a population is directly
determined by the amount of resources available.
Ecologists express instantaneous population growth
using calculus.
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Zero population growth occurs when the birth rate
equals the death rate r = 0.
The population growth equation can be expressed
as:
dN
 rN
dt
Exponential Population Growth
 The
exponential growth model describes
population growth in an idealized, unlimited
environment.
 During EPG the rate of reproduction is at its
maximum.
 The equation for exponential population growth is:
Carrying Capacity
Incorporating Carrying Capacity
into the Population Growth Model
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Exponential growth cannot be sustained for long in any
population.
A more realistic population model limits growth by
incorporating carrying capacity.
Carrying Capacity (K) is the maximum population size
the environment can support given its available
resources.
Incorporating carrying capacity produces a logistic
growth model, where the per capita rate of increase
declines as carrying capacity is approached.
We construct the logistic model by starting with the
exponential model and adding an expression that
reduces the per capita rate of increase as N increases.
Logistic Population Growth
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The logistic growth equation includes K,
the carrying capacity (number of
organisms environment can support):
As population size (N) increases, the equation ((K-N)/K) becomes smaller
which slows the population’s growth rate.
Logistic Population Growth
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As resources become less available, the growth of a
population slows or stops. The general S shaped curve of
this growth pattern is called logistic growth.
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Logistic growth occurs when a population’s growth slows
or stops following a period of exponential growth.
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Can slow when the birthrate decreases, the death rate
increases, or when both occur at the same rate
Can slow when the rate of immigration decreases, the rate of
emigration increases, or both
Can slow as the population encounters a limiting factor
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The point at which carrying capacity line intercepts the y
axis tells you the size of the population when the average
growth rate is zero.
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That number represents the largest number of individuals
that a given environment can support (carrying capacity).
Phases of Logistic Growth
3
2
1
Graphs of Population Growth
Limits to Population Growth
Limits to Growth
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Limiting Factors are those factors that causes
population growth to decrease or stop.
These factors may be classified as either densitydependent or density-independent, depending on
whether or not they become limiting only in large
populations – or-- if they limit growth in all populations
regardless of size.
Types of Limiting Factors
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Density Dependent factors – include disease, competition,
parasites and food. These have an increasing effect as the
population increases in size.
Density Independent factors – affect all populations
regardless of their size. Most are abiotic factors such as
temperature, storms, floods, droughts and habitat
destruction.
In density-independent populations, birth rate and death
rate do not change with population density. For example,
in dune fescue grass environmental conditions kill a similar
proportion of individuals regardless of density.
In density-dependent populations, birth rates fall and death
rates rise with population density. Density-dependent
population regulation much more common than densityindependent.
Density Dependent
Limiting Factors
 Competition:
as a population becomes denser, the
resources are used up at a much faster rate,
limiting how large the population can grow.
 Predation: the population of a predator can be
limited by the available prey, and the population
of prey can be limited by being caught for food.
 Parasitism & Disease: these spread more quickly
through dense populations because crowded
areas make it easier for parasites or diseases to
move from one carrier to the next. The parasites
and disease can then cause the population size to
decrease.
The Predator-Prey Relationship
Predation Can Affect Population Sizes
Density Independent
Limiting Factors
 Weather:
weather can affect the size of a
population regardless of its density.
 Natural disasters: volcanoes, tsunamis, tornados
and hurricanes can wipe out populations
regardless of density.
 Human activities: human influence as a limiting
factor has had a profound effect on populations
worldwide, regardless of the density of those
populations. These activities include destruction
of habitats, urbanization, pollution, damming
rivers, clear cutting forests, etc.
Animated Biology
What Limits Population Growth?
 http://www.classzone.com/cz/books/bio_07/reso
urces/htmls/animated_biology/unit5/bio_ch14_04
49_ab_popgrow.html
Critical Thinking Activity
Data Analysis: Reading Combination Graphs
Complete the data analysis
activity on page 442 in your virtual
textbook. These activities are
excellent ways to practice
application of concepts at home!
AKS Standards
11c - relate environmental conditions to
primary and secondary successional
changes in ecosystems
Ecological Successions
 Ecosystems
are constantly changing in
response to natural and human disturbances.
 As an ecosystem changes, older inhabitants
gradually die out and new organisms move in,
causing further changes in the community.
 This series of predictable changes that occurs
in a community over time is called ecological
succession:
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Can result from slow changes in the physical
environment
Can result from sudden natural disturbances
Types of Successions
 Primary
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Succession
Occurs as new ecosystems are developing in
areas where NO SOIL currently exists.
 Secondary
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Succession
Are the result of changing an existing ecosystem
WITHOUT REMOVING EXISTING SOIL.
Primary Successions
Secondary Successions
Critical Thinking Activity
Inferring & Predicting
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Does the process of primary succession take
longer in tropical or arctic areas? Explain.
During succession, what might become the
limiting factor for sun-loving mosses as taller
plants begin to grow?
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Primary succession takes longer in arctic areas
because rock is covered with snow part of the
year, the growing season is shorter, and cold
temperatures slow growth and decomposition.
Soil takes much longer to form.
The amount of sunlight becomes the limiting factor.