Download UNIT B Notes Bio20-2

Biology 20
Unit 2: Ecosystems and Population Change Tannant/McGraw-Hill
UNIT B: Ecosystems and Population Change
General Outcome 1: Explain that the biosphere is composed of ecosystems, each with
distinctive biotic and abiotic characteristics.
Cell Division: Mitosis


Asexual cell division
Body (somatic) cells divide to form two identical daughter cells.
o The DNA is first replicated (copied or doubled)
o Then the cell divides, with a copy of the DNA in each new cell.
 Remember: DNA is organized in chromosomes.
 Individuals have one set of chromosomes from their mother, and
one set from their father
 Example: humans have 46 chromosomes – 23 from their mother
and 23 from their father  or 23 PAIRS of chromosomes
Cell Reproduction: Meiosis


Sexual cell division
Gamete cells (sex cells – egg or
sperm cells) pass through two
divisions in order to produce sperm
or egg cells with half the DNA
o First division – one of each
pair of chromosomes moves
into each new cell
 Only 23 chromosomes
in each new cell (X)
o Second division – the new
cells (with 23 chromosomes)
divide again. Each
chromosome (X) is pulled in
half  resulting in 4 gametes
 Each gamete has 23
single strands of DNA
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Section 3.1: Individuals, Populations, and Communities in Ecosystems
Western science has divided the physical world into living (biotic) and non-living
(abiotic) components in order to describe and explain organisms and their interactions.
Other cultures have different ways of organizing the physical world.


FNMI (North American Aboriginal peoples) consider all the physical world
to be living.
o Have organized the material world into 4 directions (E, N, W, S)
with specific characteristics.
Ancient Greeks debated over what was living or non-living.
o Also divided the physical world into 4 components: Earth, Air, Fire,
and Water
Environment – everything that affects an organism throughout its life, as well as
everything that the organism affects.
Biotic – (Living) bacteria, micro-organisms, insects, parasites, predators, prey,
and the interactions between living things
Abiotic – (Non-living) sunlight, water, minerals (nutrients), heat, weather
conditions, pH, soil, availability of shelter, wind,
Ecologists – scientists who study the interactions of organisms with one another and
their environment.
Levels of the biotic environment:
1.
2.
3.
4.
5.
Organisms
Populations
Communities
Ecosystems
Biosphere
Note: smaller than organisms are individual cells, larger than biosphere is the
solar system…
Organisms – individual organisms.


Scientists study the individuals abiotic environment to learn how it affects the
individuals behavior or physical features or distribution
May study the physiology (physical features) of the organism – specifically
adaptations that allow it to live/survive in a particular environment.
Abiotic conditions affect the distribution of organisms.
Populations – a group of individuals of the same species living in a specific area at the
same time.
Species – organisms that are able to breed with one another and produce fertile
offspring.
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Unit 2: Ecosystems and Population Change Tannant/McGraw-Hill
Population ecologists study:
o Changes in the size of populations
over time
o The distribution (abundance) of
populations
o Rate of population change in size
o Gender and age distributions in the
population
o Factors (biotic or abiotic) affecting
the population
Communities – all of the individuals in all of the
interacting populations in a given area.

Community ecologists study:
o Interactions between different populations in the community
 Competition
 Intraspecific – competition within a population
o Competition for mates
o Competition for food
o Density dependent
Interspecific – competition between
different populations
Predator/prey
o Parasitism
o Diversity of communities within different environments
o Abiotic factor affecting different communities
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Most communities are dynamic – they change continually over time
o As abiotic conditions change
 Seasonally
 In response to human interaction
 Global weather fluctuations
o As populations fluctuate
 Intraspecific competition
 Interspecific competition
 Predator-prey relationships
 Over hunting or over-fishing

Competition results in stress which can lead to:
 Disease
 Lower body size
 Lower birth rate
 Lower birth weight
 Reduced fertility
 Changes in reproductive readiness times between males
and females
 Higher availability of food can cause increases in populations
 Loss of a predator
 Greater input of nutrients into the ecosystem
o As the environment changes
 forest fires or prairie fires
 land slides
 rock slides
 volcanic activity
 glacier recession
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Unit 2: Ecosystems and Population Change Tannant/McGraw-Hill
Ecosystems – a community of populations, together with the abiotic factors that
surround and affect it.

The size of the ecosystem depends upon what you are studying. (Remember,
ecosystems are human constructs, just a description of what we want to
investigate.)
Biosphere – all the ecosystems in the world; the largest possible ecosystem.

Populations are not randomly scattered throughout the biosphere. Species
distribution is dependent on the availability of biotic and abiotic factors (food,
shelter, sunlight, moisture, etc.)
Section 3.2: Classifying and Naming Organisms
When we investigate natural systems, we need to clearly communicate our
findings to others (scientists, media, lay-persons).
Taxonomy – the practice of classifying living things.

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
Aristotle (Greek philosopher) – attempted to classify all known life (1000
different organisms)
o Two main groups – plants and animals – each group called Kingdoms.
o Categorized animals based on their size and the way they moved on land,
in water, or in air.
o Plants were categorized into three groups based on differences in their
stems.
Other philosophers and naturalists used different criteria for categorizing living
things
o Structures
o Reproductive structures
o External tissues
Ernst Haeckel (1866) – after the discovery of the microscope
o Classified micro-organisms based on feeding
 Photosynthetic or non-photosynthetic
 Some micro-organisms have both processes  grouped into a third
kingdom called Protista
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Classification is still changing – due to the findings of biochemistry we now have
a level of classification above kingdom  domain
Domain
Kingdom
Phylum
Class
Order
Family
Genus
Species
Bacteria
Eubacteria
Prokaryotic
Asexual
Heterotropic
Autotrophic
Flagella
cyanobacteia
Archaea
Archebacteria
Prokaryotic
Asexual
Protista
Eukaryotic
Single or
multiple
celled
Chemosynthesis
or
heterotrophic
Distinctive
chemistry
Sexual repro
Eukarya
Fungi
Plantae
Eukaryotic
consumer
by
absorption
no
photosynthesis
Eukaryotic
Photosynthetic
Cell wall
Animalia
Eukaryotic
Cell
membrane
Mobile
Consumers
Amoeba
algae
The classification system moves from large, general categories into successively
narrow, more specific categories, down to species.
Example: Humans
Domaine – Eukarya
Kindom – Animalia
Phylum – Chordata
Class – Mammalia
Order – Primates
Family – Hominidae
Genus – Homo
Species – Sapiens
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Carolus Linnaeus (1707 – 1778) – Swedish biologist


Subdivided each kingdom into smaller and smaller groups of more and more
similar organisms
o Used physical characteristics
o At each level there are more similarities among members of the group
Used the naming system to devise a simple, scientific name for organisms
o Binomial Nomenclature (2 name naming system)
 Used the genus and species names.
 Genus – capitalized.
 Species – lowercase
 Written in italics or underlined if handwriting.
 Can shorten the genus name to the capital letter.
 Example:
 Homo sapiens or H. sapiens
 Puma concolor = North American cougar
 Felix domesticus = common house cat
o To make the naming system universal, we use Latin, a language spoken
in no country, but which (at the time) all educated people understood, and
which forms the basis for many of the Western languages (English,
German, French, Spanish, Portugese, Italian)
Dichotomous Keys
Identification key using observable characteristics (or paired comparisons) to
identify known organisms (already classified organisms). These are arranged in steps –
each step is an ‘either/or’ question.
Example: red or not red.
1. Select one characteristic, then sort the
items/organisms into two groups based
on whether they have this characteristic.
2. Select a second characteristic for each
subgroup, and sort.
3. Continue to subdivide the groups until
you have sorted each item/organism.
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Section 3.3: Studying Organisms in Ecosystems
Climate – the average weather conditions in a
particular region over a period of time, usually 30
years or more.
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Determined by rainfall, which results from
the unequal heating / cooling or Earth,
local geography (topography, altitude,
latitude), snow/ice cover, and the proximity
of large bodies of water.
The pattern of precipitation influences the
type of soil that forms in different regions.
Producer Distribution
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Plant types/abundance is determined by:
o Moisture levels
o Heat - temperature
o Types of soil
o Topography
o Altitude
o Latitude
o Abundance/intensi
ty of sunlight
The types of plants
determines the variety
and population sizes of
non-photosynthetic
organisms (consumers – fungi, decomposers, animals)
Biomes – very large ecosystems or groups of ecosystems with a particular mix of
plants, animals, and other organisms that are adapted to living under the specific
environmental (abiotic) conditions within that region.
-
May be terrestrial or aquatic biomes
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Terrestrial biomes – the abundance of life increases as the temperature and
precipitation increase
o Temperature changes with latitude and altitude, resulting in biome
patterns
-
Aquatic biomes – the abundance of life increases with sunlight and nutrient
availability
o Ocean surface – sunlight availability
o Continental shelf – sunlight and nutrient availability
There are gradual transitions between biomes boundaries resulting in a
gradual change in the composition of plants and animals
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Habitats – (home) a place or area with a particular set of characteristics, both biotic and
abiotic. Organisms within that habitat are specifically adapted to those characteristics.
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Habitat may spread over a large area, or be found in different locations (ex.
Alpine meadows)
Range – the geographical area where a population (species) is found.
-
Range is determined by habitat requirements. The species will only be
found where the habitat is present.
The organism may not live throughout the entire range, but only in its
particular habitat within the range.
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Niches – (job) the role of a species in a community and the total range of biotic and
abiotic requirements that the species need in order to survive.
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Each species has its own specific niche.
No two species can share the same niche.
o If two species occupy the same niche, they will compete for resources,
and one or both will be eliminated.
Niches may be similar (overlapping) but not identical in order for different
species to coexist.
Aquatic Habitats and Niches
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Aquatic ecosystems have
vertical stratification (layering)
of water caused by different
physical and chemical
conditions.
o Sunlight levels
o Nutrient levels
o Temperature levels
o Oxygen levels
Each species in a lake occupies
a niche that it requires for
survival.
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Biodiversity – the greater the variety of habitats and niches, the greater the variety of
species.
Limiting Factors – abiotic or biotic factors that limit
a populations growth.
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Abiotic limiting factors – soil types, pH,
nutrient requirements, moisture, weather,
temperature
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Biodiversity varies
widely depending on
the specific abiotic and
biotic components of
the ecosystem.
-
Monocultures –
(replanted forests,
agriculture fields,
domestic lawns) show a
reduction in habitat
diversity, resulting in a
reduction of biodiversity
(due to loss of habitat)
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Unit 2: Ecosystems and Population Change Tannant/McGraw-Hill
Biotic limiting factors – competition, limited nutrients, predators, parasites,
introduced (exotic) species
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Unit 2: Ecosystems and Population Change Tannant/McGraw-Hill
Sampling Populations – provides information on types of species, their density, and
changes in populations and communities
-
A census is too time consuming, and often impractical
Taking samples – small portions or subsets of the entire population and then
calculating the average is easier
o Transect – lay a line
across the area you wish
to sample.
 May count only
organisms
touching the line,
or may count any
organisms within
a set distance
from the line.
 Calculate the total
area
 Divide the
number of
organisms by the sample area
o Quadrats – a premeasured area (usually 1 m2)
 Several locations within the study area are chosen (random)
 At each location a quadrat is marked out
 The number of individuals within the quadrat are counted
 The density (number of organisms divided by the area) is
determined by taking the average of the quadrats.
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General Outcome 2: Explain the mechanisms involved in the change of populations
over time.
Section 4.1: Adaptation, Variation, and Natural Selection
No two organisms, even within the same species, are identical. Differences may
be physical (observable) – colour, size, or physiological (metabolic functioning, not
directly observable) – disease resistance, ability to tolerate stress. These differences
are examples of variation within a population, and help (or hinder) organisms to survive
within their specific habitat and environmental conditions.
Variation within a population is the result of sexual reproduction. Each sperm or
egg produced contains a different sampling of the parents DNA, so each joining of a
sperm and egg produces slightly different combinations.
Organisms that survive long enough to reproduce have the opportunity to pass
along to their offspring the genetic information that helped them survive. The more an
individual reproduces the more chances that successful genetic material will be passed
along.
Adaptation – the specific biochemical/physical/behavioral
characteristics of an organism that helps it survive within its
environment.
-
Adaptations are the result of a gradual change in the
characteristic of members in a population over time.
Structural adaptations – examples:
Human – opposable thumb, pelvic structure that
enables bipedalism, binocular vision, development of
the frontal cortex in the brain,
Biochemical adaptations – examples:
Human – inability to synthesize vitamin C (ingestion
only), insulin and energy storage within the body,
female reproductive hormones
Behavioral adaptations – examples:
Human – the need for human contact/relationships
Variation – a visible or invisible difference in the
genetic/physical/behavioral make up of an individual.
-
May either be neutral (have no effect), harmful (reduce an
individual’s chance to pass the trait along to its offspring),
or beneficial (help an individual’s chance to pass along
traits to offspring).
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Not all variations become adaptations
Biological Species – a group of reproductively compatible populations.
-
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Members of these populations can interbreed and produce viable (able to
reproduce) offspring.
Offspring have a combination of genetic material from both parents through
sexual reproduction.
o The number of possible variations in genes that offspring can receive
is the basis behind variation among individuals.
Genetic variation in a population is due to the total genetic variation of all the
individuals within that population.
Mutations – changes in the genetic material (DNA) of an organism.
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Mutations happen continuously
o Spontaneously during copying of DNA in cell division
o Mutagens – environmental agents that can cause mutations in DNA.
 UV radiation, radiation, smoking, pesticides, etc.
When DNA mutates, the cell carrying the DNA may show new characteristics.
o Example: a normal rbc versus sickle cell rbc
o Cells may not work properly
o Cells may die
o Cells may begin to divide rapidly (cancer)
If the mutated DNA occurs in a body cell (somatic cell), the changes will not
be passed along to offspring.
If the mutated DNA occurs in a sex cell (gamete – egg or sperm) the changes
may be passed on to succeeding generations.
Mutations are a significant source of genetic variation in populations.
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Selective Advantage – when a mutation enables an organism to better survive in its
environment – and thus more likely to pass on that trait to offspring.
-
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This is more common when an organism’s environment is changing –
mutations that were silent (no advantage or maybe a slight disadvantage) are
now favorable, allowing the individual organism to survive better.
o Examples: housefly’s that are able to resist the pesticide DDT
 Mutation present before the invention of DDT – caused fly’s to
have a slower growth rate  a disadvantage.
 This mutation provided resistance to DDT, allowing these fly’s to
survive the pesticide and produce offspring.
In populations that reproduce quickly (like bacteria) a rapidly changing
environment can lead to rapid adaptation to the change.
Natural Selection – the process that results when the characteristics of a population
of organisms change because individuals with certain inherited traits survive specific
local environmental conditions and, through reproduction, pass on their traits to their
offspring.
-
Requirements for Natural Selection to Occur:
o There must be (genetic) variation within the population.
o The environment selects for helpful traits – environmental pressure
may select FOR some traits or select AGAINST others  Selective
Pressure
o Individuals do not change during their lifetime – the population
changed over generations through the accumulation of specific genetic
traits/variations
o Situational – adaptations to a changing environment are not
anticipated or predicted by the individuals or populations…rather the
variation is already present, and IF it is helpful WHEN the environment
changes, then the individual may survive better.
 Adaptation to one environment may be harmful in another
environment.
 Example: human energy storage for lean times  leads
to obesity in times of excess food.
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Section 4.2: Developing a Theory to Explain Change
-
Scientific knowledge
develops as people
continue to ask questions
and search for new
answers.
Scientific Hypothesis – a statement that provides one possible explanation for an
observation or question.
-
Hypothesis are tested (peer reviewed journals)
Explanations that remain useful after new information is found AND which
provide predictions that later turn out to be accurate are successful and stay
in use for long periods of time.
Scientific Theory – a successful hypothesis that makes accurate predictions about a
broad range of observations.
Example: the Theory of Evolution by Natural Selection – well supported,
widely accepted (evidence to back it up…NOT PROOF!), and able to make
predictions…therefore science uses this theory until a better theory is developed.
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Plato (427-347 BCE) and his pupil Aristotle (384 – 322 BCE)
-
Believed all life existed in a perfected and unchanging form.
This belief was unchanged until after the Renaissance – the movement
towards nature as the ideal and observation the means to study it.
Buffon (1707 – 1788) – published Histoire Naturelle (44 volumes!)
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Noted the similarities between humans and apes
Speculated they might have a common ancestor
Suggested the Earth was older than commonly thought (older than 6000
years)
Cuvier (1769 – 1832) – developed the field of paleontology (study of ancient life
through the examination of fossils)
-
Each stratum (layer) of rock contains specific groups of fossil species
Deeper stratum contain older fossils
Found that over time (through the layers of rock) some species disappeared
and new species appeared – evidence that species could become extinct
Proposed that Earth had experienced many destructive events
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Lyell (1797 – 1875) – Scottish geologist
-
Rejected the idea of catastrophic events in Earths past.
Proposed that geological processes operated at the same rates in the past
that they do today.
Slow processes over a long period of time could result in substantial change
Inspired Charles Darwin…if the earth could change slowly over time, could
change also occur in populations?
Lamarck (1744 – 1829) – Philosophie Zoologique
-
Outlined his theory of how changes occur in a species over time.
Compared current species with fossil forms
Observed a ‘line of descent’ or progression
o A series of fossils (from older to more recent) led to modern species
Thought species increased in complexity over time - until reaching a level of
perfection.
Believed traits (characteristics/variation) was acquired during an organism’s
lifetime which could be passed on to offspring.
Theory of Inheritance of Acquired Characteristics
o While not accurate, he did provide the first theory for inheritance of traits,
and that traits could be passed on to offspring.
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Darwin (and Wallace )
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1809 – 1882
HMS Beagle – naturalist on a multi-year tour of South America
Explored the natural history / environment of many countries/geographical
locations
Didn’t always understand the significance of what he was seeing, but he
documented everything so was able to review the information later.
Wallace did a similar tour and found similar findings.
Communicated with each other, and presented their findings in 1858.
o Both accepted that populations change over time
o Both not sure HOW populations changed.
Malthus (1766-1834)
-
An economist  wrote “Essay on the Principles of Population”
Proposed that populations produced far more offspring than their environment
could support (food supply)
o Populations were eventually reduced by starvation and/or disease
o This idea provided Darwin/Wallace with the key
Natural Selection
-
-
Individuals have physical, behavioral, biochemical traits which help them
survive in their environment.
o Those with the traits that helped them survive long enough to produce the
most (and healthiest) offspring were more likely to pass on those traits.
Competition for limited resources among the individuals WITHIN the same
species selects for successful traits
Nature provides the pressure for the selection process (resources, food, etc)
Present forms of life have arisen by descent and modification from an
ancestral species
Modification is done by natural selection over long periods of time
o All life had descended from some unknown organisms
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o As descendents spread out over different habitats the new environments
‘selected’ for different traits
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Evidence of Evolution
Fossil Record – sedimentary rock with fossils
o Fossils found in young layers of rock are much more similar to species
alive today than fossils found in deeper/older layers of rock
o Fossils appear in chronological order in the rock layers
o Not all organisms appear in the fossil record at the same time
 Amphibians
 Mammals
 Birds
 Reptiles
 All appear at different ‘times’ or layers
o Transitional fossils – fossils that show intermediary links between
groups of fossil organisms and recent organisms
Biogeography – the study of the past and present geographical distribution of
organisms
o Geographically close environments are more likely to be populated by
related species than are locations that are geographically separate but
environmentally similar
 Cacti are found in north, central, south America, but not in Australia
or Africa
o Animals found on islands often closely resemble animals found on the
closest continent
 Suggests that island animals are evolved/descended from mainland
migrants
o Fossils of the same species can be found on the coastline of neighbouring
continents (Africa and south America)
 Continental drift
 Pangea
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Anatomy – vertebrate skeletal structures (forelimbs, pelvic structure, etc) can be
compared between forms
o Forelimbs – can be used for running, flying, swimming, swinging
 All vertebrate forelimbs contain the same set of bones, organized in
similar ways
 Homologous Structures –
similar structure but
different uses
 Inherited from a
common ancestor
 Analogous Structures –
different structures but
similar functions ex. Bat
wing, bird wing, insect
wing….
Embryology – embryos of different (but related) organisms show similar stages of
embryonic development.
o Vertebrates – all vertebrate embryos have similar patterns of embryogical
development
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Molecular Biology and Genetics– studying the molecular/atomic structures of organic
compounds (DNA, protein, etc)
-
All cells consist of membranes filled with water, DNA, proteins, lipids, and
carbohydrates
Proteins called enzymes control biochemical reactions in all organisms
In all organisms, proteins are assembled from amino acids
All cells that can replicate contain DNA
o Comparing the organization of DNA can indicate how closely related two
species are (more differences means more mutations over time, which
means longer time as a separate species)
o All DNA is made up of the same 4 chemicals
Section 4.3: How Species Form
Species – a population that can interbreed and produce a group of viable offspring,
which can also reproduce in nature.
-
Can be described as being reproductively isolated from other species
 Timing of reproductive cycles
 Arrangement of reproductive organs
 Separation by geographic barriers
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Speciation - the formation of a new species, resulting
from accumulated changes in the population over time.
1. Transformation – when the new species
gradually replaces the old species
2. Divergence - One or more species may arise
from a parent species that continues to exist.
Geographical Barriers –
 Mountains
 Rivers
 Landslides
 Island formation
o These barriers must be present for a long enough time for the populations
to become reproductively incompatible with the original population.
o Some species may live in the same general area but occupy different
niches  so don’t encounter each other
Biological Barriers –
o Behavioral barriers
 courtship songs
 Courtship colouring/plumage/displays
o Chemical barriers
 Pheromones for mate attraction
 Utilization of different resources than the parent population 
occupation of a new niche (enzymes to take advantage of the new
resource?)
Adaptive Radiation – the diversification of a common ancestral species into a variety
of species, all of which are differently adapted.
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The Pace of Evolution
1. Gradualism – gradual changes occur steadily, in a linear fashion
2. Punctuated Equilibrium – rapid change after a period of mass extinction, but
little change otherwise
a. Most physical/morphological change occurs with the first divergence from
the parent species
Requirements for Speciation by Natural Selection
1. Life forms have developed from ancestral species.
2. All living things are related to one another by varying degrees through common
descent.
3. All living things on Earth have a common origin (share a common ancestor).
4. The mechanism by which one species evolves into another species involves
random heritable genetic mutations.
a. Some mutations result in a survival advantage for an individual; if so that
individual is more likely to survive and pass this mutation on to its
offspring. Eventually this successful mutation increases in the population
and causes the populations as a whole to start to change.
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