Download Populations and Communities “Chapter 25”

Populations and
Communities
“Chapter 22”
Curriculum Outcomes
Key Terms
The Importance of Populations
and Communities
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Geese and their annual migration,
breeding ground in the high arctic and
their wintering grounds in the coastal
marshes of Eastern US.
Flats along the shore line turn white as
thousands of these birds spend days
probing for roots of aquatic plants.
Up to 80 000 geese can be seen feeding at
any one time.
Geese
‹ Populations
– a group of individuals
of the same species occupying the
same area at a given time.
‹ Community
– is made up of the
populations of all organisms that
occupy an area.
Habitats, Geographic Range, and
the Ecological Niche
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Geographic range – is a region where a given organism is
sighted. This is a region usually outlined on a map.
Habitat – is the physical area where a species lives. For
example a squirrel would probably be found in a forest
ecosystem, over a grass ecosystem.
Ecological niche – refers to the overall role of a species in
its environment. For example a niche of a flying squirrel
includes it specific feeding habits, its ability to produce
large numbers of offspring, and its capacity to serve as
food for a variety of parasites and predators. The squirrels
body wastes enrich the soil, while its use of seeds for food
help in the distribution of many grasses.
Influences biotic and abiotic factors
Distribution of Populations
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Clumped distribution – occurs in aggregates. The
distribution of organisms is affected by abiotic
factors. (clumped in patches for example in river
valleys)
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Sloughs – are depressions filled with stagnant
water.
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Random distributions – are arbitrary and appear
to be unaffected by biotic factors.
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Uniform distributions – are orderly and appear to
be affected by competition.
Population Dispersion
Questions
‹ Questions
1-5 page 741
Size and Density of Populations
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Ecologists use a number of measurements to
describe populations.
A statement of the size of a population must
include the number of named organisms, the
location of the population and the time when the
numbers were determined.
Example: There were 27 642 northern pike in
Sylvan Lake, Alberta in 1981.
These statements are known as:
Population size – is the number of organisms of
the same species sharing the same habitat at a
certain time
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Population density – is the number of organisms per unit
of space.
A simple formula for calculating density is:
D = density, N the number counted, S the space occupied
by the population.
D=N
S
If 200 lemmings were living in a 25ha area of tundra near
churchill, Manitoba, in1980, their density could be
calculated as follows:
D = 200 lemmings
25 ha
= 8 lemmings/ha
Determining Changes in
Population Density
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Rate of change – refers to the change in a
population over a period of time.
Growth rate = change in number
change in time
Gr = ΔN
Δt
The greek symbol Δ (delta) stands for “change in”
Rate of Change
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Example: 8 lemming per hectare in 1980,
assume that an ecologist determined the
population density in 1990 to be 22 lemmings per
hectare. The rate of change can be calculated by
Gr = D(1990) – D(1980)
1990 – 1980
Gr = 22 – 8
1990 -1980
Gr = 14
10
Gr = 1.4 lemmings/ha/yr
Homework
‹ Review
Questions (old text)
‹ Page 581-582 questions 1 - 9
Population Growth Patterns
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Changes in population size occurs when individuals are
added or removed.
Four factors determine population size:
1) Natality - the number of births per unit of time.
2) Mortality – the number of deaths per unit of time.
3) Immigration – the number of individuals that move
into an existing population per unit of time.
4) Emigration – the number of individuals that move
away from an existing population per unit of time.
Population Growth Formula
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The concept of population growth can be
generalized in the formula below:
PG = (births + immigration) – (deaths +
emigration)
initial number of organisms
PG = (b + i) – (d + e) x 100
n
Sample Exercise
‹ Sample
exercise page 744-745
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Dynamic equilibrium – refers to any condition within the
biosphere that remains stable within fluctuating limits.
(balance)
Open population – is one in which density changes result
from the interaction of natality, mortality and immigration
and emigration.
Closed population – is one in which density changes are
the result of natality and mortality with neither food nor
wastes being allowed to enter or leave the given
environment.
Growth curve – is a graph used to show the changes in a
population over a specific length of time.
Doubling Time
‹ The
time needed for a population
that is growing to exponentially
double.
td = 0.69 (a constant)
cgr (capita growth rate)
Sample exercise page 747
Phases in a Growth Curve
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Lag phase – is the adjustment period prior to
accelerated reproduction by the population.
Growth phase – marks the accelerated
reproduction by the population. Natality exceeds
mortality.
Stationary phase – marks equilibrium between
natality and mortality.
Death phase – marks constant decline in the
population. Mortality exceed natality.
Population Growth Curve
Population Growth Curve
Activity
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Carrying Capacity – refers to the maximum population
that can be sustained by a given supply of resources
(nutrients, energy, and space)
Biotic potential – is the maximum number of offspring
that can be produced by a species under ideal conditions.
Biotic potential is regulated by the following:
1) Offspring – the maximum number of offspring per birth
2) Capacity for survival – the chances and organisms
offspring will reach
reproductive age
3) Procreation – the number of times per year the
organism reproduces
4) Maturity – the age at which reproduction begins.
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Environmental resistance – includes all the factors that tend to reduce
population numbers.
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The dependence of population increase (I) on carrying capacity (K) and
biotic potential can be expressed by the following equation:
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Population increase = biotic potential x # of individuals x relationship
between
carrying
capacity and
resources
available
I = R(max) N(K – N)
K
R(max) = biotic potential
N = number of individual in the pop
K = carrying capacity
I = population change
Questions
‹ Questions
1-6 page 750
Limiting Factors in a Population
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The survival of an organism depends on adequate supplies
of nutrients and the ability to withstand abiotic factors.
Law of the minimum – states that, of the number of
essential substances required for growth, the one with the
minimum concentration is the controlling factor.
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Shelford’s law of tolerance – states that too little or too
much of an essential factor can be harmful to an organism.
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Density independent – factors affect members of a
population regardless of population density (flood, fire)
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Density dependent – factor are factors arising from
population density (food supply) that affect members of a
population.
r and K Population Strategies
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K –selected populations – are found where
environmental conditions are stable. These
populations are characterized by intense
intraspecific competition.
Pops become crowded, and competition between
members become intense.
r- selected populations – undergos many
changes, many of which cannot be predicted.
These populations are characterized by a high
birth rate and short life span.
Individuals are small in size.
Homework
‹ Review
Questions
‹ Page 589 Questions 10-19
Life History Patterns
‹ Some
populations exhibit regular
population fluctuations of growth and
decline known as population cycles.
‹ Rodents
generally have population
cycles that are about 4 years in
length.
Case Study
‹ Page
591
‹ Calculating the size of a small
mammal population.
Population Histograms
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Although populations growth curves show how populations
change over time and allow predictions, they do not tell you
about the age distribution of the members.
The population histogram is useful when studying
populations of animals in which individuals have a life span
of more than a couple of years.
The pyramids allow you to examine the population of an
organism in terms of its age structure and proportions of
males and females at a specific instant in time.
Using this data it is possible to predict whether a population
will grow, stabilize or decline.
Population Histograms
Intraspecies and Interspecies
Competition
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Zero population growth – occurs when the
population of a species shows no increase or
decrease in size over time.
Gause’s principle – states that no two species
can occupy the same ecological niche without one
being reduced in numbers or being eliminated.
Interspecific competition – involves
competition among similar species for a limited
resource (food or space)
Intraspecific competition – involves
competition within an ecological niche between
members of the same species.
Predation
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Predation is most commonly described interaction between
populations.
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Population fluctuations in the hare affect the lynx.
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Camouflage – is an adaptation in form, shape, or
behaviour that better enables an organism to avoid
predators.
Some butterflies are bitter, so bird avoid that certain colour
Mimicry – involves developing a similar colour pattern,
shape or behaviour that has provided another organism
with some survival advantage.
‹ Coevolution
– occurs when two
different species exert selective
pressures on each other.
‹ Example: bats use sound waves to
catch moths, however, moths have
developed thicker powder –like
scales that act as a soundproofing.
Coevolution
Coevolution
Symbiotic Relationships
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Symbiosis – is a relationship in which two different organisms
live in a close association.
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Terms use to describe symbiosis are parasitism and
commensalism.
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Parasitism (tape worm in intestine)
Parasites- live or on another organism, from which they obtain
their food.
Hosts – are living organisms from which a parasite obtains its
food supply.
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Commensalism (shark with remora attached)
Is an association between two organisms in which one benefits
and the other is unaffected.
‹ Mutualism
(honey bee and flowering
plant)
Is a relationship in which two
different organisms living together
both benefit from each other.
Homework
‹ Page
598 Questions 20 -26
Succession in Communities
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Succession – is the slow, orderly progressive replacement of
one community by another during the development of vegetation
in any area.
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Climax community – is the final, relatively stable community
reached during successional states.
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Primary succession – refers to the occupation, by pant life, of
an area not previously covered by vegetation.
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Secondary succession – occurs in an area that was previously
covered by vegetation and still has some soil.
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Pioneer communities – are the first species to appear during
succession.
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Mircoclimates – refers to the climate in a small part of a habitat.
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Seral Stages – are specific stages in succession identified by the
dominant species present.
Homework
‹ Page
603 Questions 27 -31
Case Study
‹ Succession
in Glacier Bay
‹ Page 604 -605 (old text)
‹ Review
Questions 760-761