Download Define Variation

Unit B: Ecosystems and Population Change
Themes: Energy, Matter and Systems
Overview: In this unit, students become familiar with a range of ecosystems by studying
their distinctive biotic and abiotic characteristics. Students are introduced to the concept
of populations as a basic component of ecosystem structure and complete the unit by
examining population change through the process of natural selection.
The content in Unit B prepares students for the study of populations and community
dynamics in Biology 30.
Focusing Questions:
What are the major biotic and abiotic characteristics that distinguish aquatic and
terrestrial ecosystems?
What data would one need to collect in a field study to illustrate the major abiotic
characteristics and diversity of organisms?
What mechanisms are involved in the change of populations over time?
In what ways do humans apply their knowledge of ecosystems to assess and limit the
impact of human activities?
General Outcomes: There are two major outcomes in this unit.
Students will:
1. explain that the biosphere is composed of ecosystems, each with distinctive biotic
and abiotic characteristics
2. explain the mechanisms involved in the change of populations over time.
Key Concepts:
The following concepts are developed in this unit and may also be addressed in other
units or in other courses. The intended level and scope of treatment is defined by the
outcomes.
 ecosystem
 natural selection
 adaptation and variation
 limiting factors
 niche
 species
 population
 binomial nomenclature
 biotic/abiotic characteristics
 evidence for evolution
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General Outcome 1
Students will explain that the biosphere is composed of ecosystems, each with distinctive
biotic and abiotic characteristics.
Specific Outcomes for Knowledge
Students will:
 define species, population, community and ecosystem and explain the interrelationships
among them
 Explain the interrelationship of energy, matter and ecosystem productivity (biomass
production); e.g.,
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explain how terrestrial and aquatic ecosystems support a diversity of organisms through a
variety of habitats and niches; e.g.,
o terrestrial: canopy, sub-canopy, forest floor, soil
o aquatic: littoral, limnetic, profundal and benthic zones
identify biotic and abiotic characteristics and explain their influence in an aquatic and a
terrestrial ecosystem in the local region; e.g., stream, lake, prairie, boreal forest, vacant lot,
sports field
explain how limiting factors influence organism distribution and range; e.g.,
o abiotic factors: soil, relative humidity, moisture, ambient temperature, sunlight,
nutrients, oxygen
o biotic factors: competitors, predators and parasites
Interactions within Ecosystems:
Define ecosystem:
Type of Ecosystem
Examples
Prairie, grassland, forest
Pond, lake, stream
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•
Ecosystems rarely have sharp boundaries,
– Organisms can move back and forth from one ecosystem to another.
This area between ecosystems is where organisms from both ecosystems interact with
each other.
Define Ecotone:
Ecotones contain species from both bordering ecosystems
o so they often contain greater _______________________than either ecosystem.
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Describe why ecotones tend to be less fragile. How do ecotones guard against extinction?
Roles in Ecosystems
Define ecological niche:
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In ecosystems, having a different niche is important to _______________ _____________
between species.
Owls and hawks feed on many of the same organisms, but occupy distinctly different
niches.
Example One: The table below summarizes adaptations
that allow Owls and Hawks to occupy different niches
Owl
Hawk
Hunting
Activity
Nesting
Example Two: Figure Two on the left shows different
niches of warbler in one tree.
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Competition for Niches
When a new species enter an ecosystem, it causes a disturbance because it comes into
competition for a niche with one or more of the species already in the ecosystem.
Define Exotic species –
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The introduction of new species happens naturally. Animals are mobile and can move
from one ecosystem to another.
The introduction of new species by humans to an ecosystem is one of the main causes
of species depletion and extinction, second only to habitat loss.
Problems with introducing Exotic Species:
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Define a biome:
Canada has four major Biomes:
1. Tundra
2. Taiga
3. Temperate deciduous forest
4. Grassland
Using page 97 of your textbook, identify the Abiotic and Biotic factors that contribute to the
creation of Albertan Ecosystems.
Name
Abiotic Factors
Biotic community
Taiga
Muskeg
Grassland
Deciduous Forest
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Factors Affecting Terrestrial Ecosystems
Each ecosystem is defined not only by the organisms that live in it but also by the abiotic
factors that affect them.
1. Soil
Soil can be viewed as a series of layers
i. _____________________ - partially decomposed leaves/grasses
ii. _____________________ - small particles of rock mixed with decaying plant &
animal matter called humus
iii. _____________________ - more rock particles with only small amounts of organic
matter.
iv. _____________________ - composed of rocks
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Quantity of each layer will affect ecosystem productivity
Quality of soil can also affect productivity
o E.g. pH, human impact
2. Available Water
All organisms depend on water to live. Availability is determined by:
o
o
o
3. Temperature
Organisms are able to adapt to temperature fluctuations
Why do trees in Alberta can keep their leaves during winter?
What are two other ways organisms escape undesired temperatures
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–
4. Sunlight

Sunlight vary between different ________________
– Less sunlight during winter in Canada vs in Jamaica
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Sunlight can also vary within the ________________
– Less sunlight during winter in Canada vs during summer in Canada
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Factors Affecting Aquatic Ecosystems
1. Chemical Environment
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2. Temperature and Sunlight
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3. Water Pressure
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4. Seasonal Variation
Ice/snow covers lakes and acts as insulators
Therefore, environment underneath the ice is very stable, even if it
gets colder above the ice.
Oxygen can now pass from air into water
Upper level of lake (epilimnion) warms up
Lower level of lake (hypolimnion) remains at low temperature
Middle level of lake (thermocline) drops in temperature from warm
to cold
Water goes from warm to cool and sinks to bottom. This rotates
oxygen levels to the bottom of the lake
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Limits on Populations and Communities in Ecosystems
Define Biotic Potential:
Biotic potential is regulated by four important factors:
Factor
Description and Example
Limiting Factors
Factors in the environment can prevent pollutions from attaining their biotic potential.
Any resource that is in short supply is a limiting factor on a population.
Factors that limit populations are seen in Table 1 on page 108 of your text.
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Carrying Capacity
Populations commonly fluctuate because of an interaction of the many biotic and abiotic
limiting factors. Ecosystem is stable when none of the populations exceeds the carrying
capacity.
Explain what is meant by the carrying capacity of an ecosystem-
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Limits of Tolerance
Carrying capacity for any species is determined by the availability of resources (food, water).
Populations can exceed the carrying capacity of the ecosystem, but not for long.
Organism’s can survive within a certain range of an abiotic factor, above and below the range
it cannot survive.
Law of Tolerance:
Law of the minimum:
The number of organisms in an ecosystem is important when considering the effects of some
abiotic and biotic factors. Population is said to be dense when there is a large number of
organisms in a small area.
Factors that cause Change in Populations:
Factor
Definition
Density-independent factors
Density-dependent factors
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General Outcome 2
Students will explain the mechanisms involved in the change of populations over time.
Specific Outcomes for Knowledge
Students will:
1. Explain the fundamental principles of taxonomy and binomial nomenclature, using modes
of nutrition at the kingdom level and morphological characteristics at the genus species
level.
2. Summarize and describe lines of evidence to support the evolution of modern species from
ancestral forms; i.e., the fossil record, Earth’s history, biogeography, homologous and
analogous structures, embryology, biochemistry
3. Compare Lamarckian and Darwinian explanations of evolutionary change
4. Explain that variability in a species results from heritable mutations and that some
mutations may have a selective advantage
5. Discuss the significance of sexual reproduction to individual variation in populations and to
the process of evolution
6. Explain speciation and the conditions required for this process
Evolution
Evolution means a slow, gradual development or change. If the fossils of the wooly mammoth
of the ice age are compared with the elephants of today, the basic changes that have occurred
can be seen. According to the theory of evolution, the hereditary traits, or characteristics, of a
population of organism gradually change over a period of time. The process of evolution
occurs in a population of organisms as generations pass through time. During evolution, the
gene pool of an entire population of organisms changes. The gene pool contains all the genes
of a population. When the genes change, the traits expressed by those genes also change.
Classification of Organisms
Students will:
Explain the fundamental principles of taxonomy and binomial nomenclature, using modes of
nutrition at the kingdom level and morphological characteristics at the genus species level.
The value of classifying organisms includes:
1. To understand the complex variety of living things
2. The use of data about common structural features assist in identifying organisms
3. Enables prediction of characteristics shared by members of a group
4. Shows evolutionary links; the evolutionary history of a species or a group of related
species (phylogeny)
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Define taxonomy:
The binomial system of nomenclature is a system of naming organisms developed by
Carolus Linnaeus.
– “Binomial” – Two part Latin scientific name.
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Each genus can include many species of related organisms
• Felis sylvestris is the domestic cat
• Felis lynx is the lynx
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Rules or nomenclature:
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The two-name system provides an added advantage by indicating similarities in anatomy,
embryology and evolutionary ancestry.
Level s of Classification
Classification recognizes seven levels in the hierarchy of taxa:
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The filing system groups species into a hierarchy of increasingly ____________________.
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Similar species are grouped in the same genus
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Similar genera are grouped in to the same family
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Families are grouped into orders
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Orders are grouped into phyla
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Phyla are grouped into kingdoms
Each taxonomic level is more inclusive than the one below.
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The more closely related two species are, the more levels they share.
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Today most scientists believe that organisms have changed over time.
Define phylogeny:
Relationships are shown in a diagram called a __________________.
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Starts from oldest (most ancestral) form and branches off to descendants.
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Students will explain the mechanisms involved in the change of population over time.
Define Evolution:
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Evolution does not refer to individual change or development
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Evolution occurs within a population of organisms
Evidence of a Changing Earth
Summarize and describe lines of evidence to support evolution of modern species from
ancestral forms eg fossil record, earth’s history, biogeography
Direct Evidence for Evolution –
There is much evidence to suggest the organisms have changed or evolved over time. Some of
this is direct evidence such as the fossilized remains of plants and animals
Fossils are:
Fossils are formed in three ways:
1.
2.
3.
Radioactivity was discovered in 1903. Radioactive decay provides a form of geological clock
helping scientists determine the absolute age of the Earth and items on it with great precision.
Using decay rates in units called half lives physicists can determine the age of a specimen
Define Radiometric dating:
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Define Biogeography
Earth’s landmasses have undergone great change over time. Fossils of the same species have
been found in different continents suggesting the continents were once joined. Fossils younger
than 150 million years old are not found on different continents suggesting they evolved after
the breakup.
What does evidence from Biogeography suggest?
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Evidence of Evolution from Biology
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Summarize and describe lines of evidence to support evolution of modern species
from ancestral forms e.g. homologous and analogous structures, embryology and
biochemistry
Direct evidence provided through fossils is not the only evidence that supports the theory of
evolution. Some of the evidence for evolution is indirect, gained only by comparing the structure,
function and embryology of present day organisms. Like fossils, observations from living
organisms, show the links between existing forms and their ancestors.
Evidence from Anatomy
Define Embryology:
•
offers valuable insight into the process of evolution.
Homologous structures
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Formed from DIVERGENT EVOLUTION
Define Vestigial Features and give an
example:
What does the presence of a vestigial feature
suggest?
HOMOLOGOUS STRUCTURES: Forelimbs of each of these
creatures are adapted to carryout very different functions yet
have very similar bone structure
Analogous structures:
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Examples: wing of an insect and a bird
Good indicators that these organisms did not evolve from a common ancestor
Analogous Structures illustrates CONVERGANT EVOLUTION
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Biochemical Evidence:
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Similar proteins in species diversify as evolution takes place
DNA and cytochrome enzyme C (respiration) are similar in all organisms
DNA analysis-used determine how closely related organisms are
o suggest a common ancestor
The Making of a Theory – Accounting for Evidence
Students will compare Lamarckian and Darwinian explanations of evolutionary change
Lamarck – 1801 Key Factor-Environment
Description
Theory
Organisms change because they need to change.
e.g. snake needed to crawl through small space so legs were
scrapped off
Use-remains strong. Disuse-weakens and disappears.
Eg. Snake’s legs.
Traits acquired in life time could be passed on to offspring.
E.g. masters of the piano pass on skills to offspring
Nice try Lamarck but acquired traits can't be inherited. Too bad!
Darwin's Theory of Natural Selection
Scholars of the ancient world generally believed that living species had been created
according to some special design for the universe and did not change through time. However
in the last two hundred years time, scholars began to question the concept of unchanging
species. They began to believe that organisms have changed over time through the process of
evolution. Direct evidence (fossils) and indirect evidence (e.g. from living organisms) was
used to support the theory of evolution. Many scientists proposed theories as to how evolution
occurs but the theory of natural selection is generally thought to be the modern view of how
evolution occurs.
The theory of natural selection was proposed by Charles Darwin in 1838. It was based on
the observations he made during a five year voyage to South America and the South Sea
Islands, in particular the Galapagos Islands. Darwin proposed that competition for food, space,
and mates “selects” only the most fit individuals within a species to survive and reproduce. He
argued that if the characteristic was favored by natural selection, it could be passed on to the
young of the selected individuals. As the traits were passed on, the evolution of the species
would result.
1859-Book called The Origin of Species explained a theory of how species developed. Darwin
explained that evolution occurs in five steps:
– Overproduction
– Variation
– Origin of new
–
Struggle for
existence
–
Survival of the
species
fittest
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Darwin’s Theory on Evolution:
Darwin’s Ideas
Description of Idea
Overproduction
Struggle for
Existence
(competition)
Variation
Survival of the fittest
(natural selection)
Origin of New
Species (speciation)
Evolution causes speciation
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Occurs by the accumulation of inherited variations, over numerous generations and is complete
when reproductive isolation occurs.
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“Reproductive isolation” has occurred when two organisms can no longer reproduce
fertile offspring.
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Comparison of Lamarck and Darwin
Darwin
Lamarck
Sources of Inherited Variation
Students will discuss the significance of sexual reproduction to individual variation in populations
and to the process of evolution
Without understanding genetics, Darwin was unable to explain 2 important factors
 What is the source of variation?
 How inheritable traits are passed from one generation to the next?
Define Variation:
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Variation can be beneficial, neutral or harmful depending on the type.
Variation contributes to evolution because of a concept called selective advantage
Define Selective Advantage:
The two main sources of genetic variation are mutations and the genetic shuffling that results
from sexual reproduction
Mutations:
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Gene Shuffling:
Students will explain that variability in species results from heritable mutations and that some
mutations may have a selective advantage.
Natural selection on certain traits can lead to changes in trait frequencies and thus to evolution.
Beneficial mutations may increase the fitness and reproductive success of an individual and
therefore will become more common in a population. These traits are selected for.
In your OWN WORDS fill out the chart below using Table
Darwinian Evolution
Genetic Mechanism
Inherited Characteristics
Population Variability
Source of new variation
Natural selection
Evolutionary change
Speciation and Evolution
Students will explain speciation and the conditions required for this process
Define Speciation:
Behavioral isolation:
Geographic isolation:
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When natural selection works on the separated groups independently the populations evolve
independently.
The Rate of Evolution:
Using your textbook on page 158, describe the modern evolutionary theories:
Punctuated Equilibrium
Gradualism
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