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Biology 20
Unit 20B: Ecosystems and Population Change
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Biology 20
Unit 20B: Ecosystems and Population Change
Chapter 4: Characteristics of Ecosystems
4.1 Interactions within Ecosystems

ecology: study of interactions between organisms and their living and non-living environment
 at the level of a single organism
 abiotic factors: a non-living factor that influences an organism
- sunlight and temperature
 biotic factors: a living factor that influences an organism
- amount of food or mates
Ecotones and Biodiversity
sharp boundaries
 organisms can move back and forth
from one ecosystem to another
 grey area between ecosystems
where organisms from both
ecosystems interact with each
other
- contain species from both
bordering ecosystems
- contain greater biodiversity
(more species) than either
ecosystem
 greater biodiversity
ecosystems are less fragile
 more prey for predators
since it is a fusion of two
ecosystems

Roles in Ecosystems
niche: organism’s role in an
ecosystem
 it’s place in the food web
 it’s habitat
 it’s breeding area
 time of the day at which it is most active
 ecological
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
higher the number of different niches in an ecosystem, the more organisms will be found
 more biodiversity in a natural forest than a planted forest
Competition for Niches
new species that enters an ecosystem causes a disturbance
- exotic species: not a native species to an ecosystem
 animals can move into an out of ecosystems
 plant seeds are carried by the wind or animals transport them to new areas
- a new route in an area can open up, allowing organisms that were separated to mix
 can create a new evolutionary species
 new species comes into the niche to compete with one or more of the species already in the
ecosystem

Introduction of Exotic Species

new species caused by human introduction is one of the main causes of species depletion and
extinction (loss of habitat is second)
 ecosystem lacks the natural population controls of the introduced species
- no predators or disease giving the species an advantage over the native species
- native species cannot compete successfully for space, food or reproductive sites
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Unit 20B: Ecosystems and Population Change
Example:
in 1935 the Cane Toad was introduced into Australia, in an
attempt to rid sugarcane fields of cane beetles. Native to South
and Central America and thrives in Australia since it is poisonous
and has no predators or disease to kill them.
4.2 Terrestrial and Aquatic Ecosystems
biome: large geographical region with a specific range of temperatures and precipitation
 plants and animals are adapted to those conditions of
temperature and precipitation
 biomes have a particular dominant species
- taiga biomes has coniferous trees
- grassland biome has prairie grasses
 each biome contains many different ecosystems
- each defined by different biotic and abiotic factors
 Canada has four major terrestrial biomes
 Tundra, taiga, grassland and temperate deciduous forest
 as well as two major aquatic biomes
- freshwater: lakes, rivers and pond ecosystems
- saltwater: marine and ocean ecosystems
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Unit 20B: Ecosystems and Population Change
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Biology 20
Unit 20B: Ecosystems and Population Change
Terrestrial Ecosystems

Alberta’s terrestrial ecosystem are found within two
major biomes: taiga and grassland
Ecosystems of the Taiga Biome
also called the boreal forest
 can be found from Northern Alberta and along the
Rocky Mountains
- can be found in every province in Canada
- 80% of all our forested region are taiga
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dominated by conifers
 well adapted to the warm, moist summers and cold, dry winters
 thin needle-like leaves provide less surface area for water loss
 thick cuticle of wax coats the needles
 prevents water loss and protection against
frost damage
 pyramid shape of the tree and the flexible
branches shed the crushing weight of a heavy
snowfall
 tiny needles trap little snow
- amount of sunlight varies depending on the
height above the ground
 canopy: upper layer of vegetation in a forest
 usually mature trees (pine and spruce)
 suitable food source for only 50 species of
birds
 including seed-eaters that have a strong,
thick beaks capable of cracking cones

forest floor is in almost continuous shade since little sunlight filers through the canopy
- forest floor has shade-loving plants
(shrubs, mosses and ferns)
 animals have to have effective
camouflage
- primary consumers: moose, voles and
white-tailed deer
 available shelter is also determined
by these shade loving plants
- predators: black and grizzly bears,
weasels, owls and wolverines
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Muskeg Ecosystems
 climate is the average conditions of temperature and
precipitation
- warmer ground temperatures increases decomposition of
organic matter
 results in good soil
 decomposition of needles produces acidic soil
 certain plants will only grow in acidic soils
 black spruce trees
- colder climate in the north has a permafrost layer beneath
the soil
 soil never melts
 permafrost: permanently frozen soil
- rain and melted snow cannot drain away and is absorbed by the decomposing plants and peat
moss
 muskeg: soil above the permafrost that is swampy or boggy in summer
 supports different organisms than are found in a conifer forest ecosystem
 decomposition of plant and animal matter is slow
- low temperatures limit the growth and reproduction of soil bacteria and fungi
- limits the amount of organic matter in the soil
 plants best for this ecosystem grow close to the ground
 have fibrous root systems that anchor the stunted conifers
 plants include: lichens, mosses, tall grasses, small shrubs and stunted conifers
 numerous pools provide abundant water for plants and animals
- ideal breeding conditions for black flies and mosquitoes
- supports come larger animals like caribou
Ecosystems of the Grassland Biomes
black earth is the most fertile in the world
- short lived grasses have deep roots that
provide a large biomass for decomposition
- warm temperature for rapid decay and a rich
layer of humus
- grass length controlled by precipitation
- have only one layer to support the biotic
community
 limits the diversity and number of
organisms
 Alberta’s grasslands include rough fescue,
wheat grass and spear grass
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- primary consumers: deer, squirrels and rabbits
Deciduous Forest Ecosystems
 edges are dominated by trees
- before it turns into the taiga
 aspen, balsam poplar and birch are the most common trees
- require low amounts of water than coniferous trees
- found in areas where rain is sporadic between the true grasslands and the taiga
- deciduous trees can be found around rivers, lakes and ponds
 warmer temperatures and more precipitation
- large amount of humus from the leaves provide a rich soil in deciduous forests
 early spring, most of the sunlight reaches the forest floor and the understory
- understory: below the canopy layer consisting of shrubs and smaller trees
 summer the canopy is full leaf and only 6% of sunlight reaches the understory
- undergrowth is well established
- broad leaves of the deciduous trees maximize light capture for photosynthesis, promoting rapid
growth

deciduous forests support great diversity of animals
- thick layer of leaf litter provides an ideal environment for many types of insects
- insect-eating birds and mammals live in deciduous forest ecosystems
 fly-catchers and shrews
- rich vegetation of the understory shrubs and lower branches
 supports primary consumers like deer and moose
 home to many species of birds and some climbing mammals
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Name
Taiga Ecosystems
Abiotic Factors
 northern and central Alberta forests
 changeable weather
 soil contains some water and is
acidic
 precipitation: 50-250 cm/a
Muskeg Ecosystems

Grassland Ecosystems

Deciduous Forest
Ecosystems

cold temperature
 short growing season
 permafrost layer beneath soil
 low precipitation: 50-150 cm/a
central and southern Alberta
 increased sunlight and warmer
temperatures than muskeg or boreal
forest ecosystems
 rich fertile soil
 precipitation: 25-100 cm/a
central Alberta
 increased sunlight and warmer
temperatures than muskeg or taiga
forest ecosystems
 rich fertile soil
 precipitation: 75-250 cm/a
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Biotic Community
 black and grizzly bears
 wolverines
 weasels
 moose
 deer
 grouse
 owls
 spruce and pine
 shrubs, ferns, mosses and lichens
 black bear
 caribous
 ptarmigans
 rapidly flowering plants
 mosses and lichens
 bison
 deer
 rabbits
 hawks
 yellow-bellied sapsuckers
 fescue grasses
 grasshoppers
 black bears
 weasels
 moose
 deer
 woodpeckers
 deciduous trees
 shrubs
Aquatic Ecosystems
water covers 2/3 and 97% is salt water
 supply freshwater through evaporation
 water based communities as either freshwater or marine water
 marine waters include oceans, coastlines and some land surfaces
 freshwater is on land surfaces
- ponds, bogs, sloughs and other types of wetlands
 estuary: place where rivers enter the ocean where the water is brackish
 brackish: mixture of fresh and salt water
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Unit 20B: Ecosystems and Population Change
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Lake Ecosystems
 amount
of light available, water temperature and oxygen levels can vary
 watershed: land that drains toward a lake or other body of water
Littoral zone
 edge around a lake or pond where the water is shallow
- determined by the depth of the lake and the slope of the lakebed
- ends when there are no more rooted plants
 bulrushes and water lilies grow where the water is shallow
- permits the growth of aquatic emergent vegetation
 most productive part of the lake
- algae and plants take advantage of the sunlight to carry out photosynthesis
Limnetic Zone
 open water area of a lake where photosynthesis can occur
- extends downward to a depth at which there is insufficient light for photosynthesis
 plankton organisms are present
- includes autotrophic and heterotrophic microorganisms
 heterotrophic plankton (invertebrate animals) feed on autotrophic plankton (tiny plants and
algae)
- both kinds of plankton are food consumers in the higher trophic levels
 fish, tadpoles and birds
Profundal Zone
 region of a lake where there is not enough light for photosynthesis
- no photosynthetic plants
- usually not found in ponds
 only source of nutrients is decaying matter falling from the limnetic zone
- benthic detritus feeders: detritus is slowly broken down by bacteria or consumed by otherbottom dwelling invertebrates and fish
- benthos: bottom of any body of water in the benthic zone
 extremely low levels of oxygen since bacteria uses oxygen to decompose the detritus
- absence of sunlight and plants to replenish the oxygen causes an extreme depletion of oxygen
- only larger organism that can survive in low oxygen levels survive
 includes invertebrates and very few fish species such as carp
Biology 20
Unit 20B: Ecosystems and Population Change
4.3 Factors Affecting Ecosystems
Factors Affecting Terrestrial Ecosystems
 quality
and amount of soil are critical for the size and
health of the plant community
 directly affects biodiversity of the ecosystem
 series of layers, each with a distinct colour and texture
 move deeper down the less organic matter that is
present
 litter: composed of partially decomposed leaves or
grasses
- acts like a blanket
 limits the temperature variations in the soil
 reduces water loss by evapouration
 topsoil: composed of small particles of rock mixed with
subsoil
Soil
bedrock

regions all function as a system
each ecosystem has independent biotic and abiotic
factors
- can limit the size of the populations
- can determine the number of species that can survive
in each ecosystem
topsoil
 terrestrial
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humus
- humus: black decaying plant and animal matter
- contains a rich supply of minerals and other nutrients plants require to grow
- air and water spaces are between the soil particles
 decomposing bacteria requires oxygen
 less oxygen the slower decomposition
 subsoil: usually containing more rock particles and less organic matter than the topsoil
- lighter in colour since there is a lack of humus
- contains large amounts of minerals
 aluminum, iron and phosphorous
 bedrock: composed of rock and marks the end of the soil
 can be acidic, basic (alkaline) or neutral
 pH of the soil is determined by the nature of the rock and the plants that grow in it
- decomposing matter can cause an accumulation of acid in the soil
- acidity of the rain, snow and groundwater
- humans burning fossil fuels can increase the soil acidity
 releases SO2 and NOx into the air
 creates acid rain/snow when combine with water drops
Available Water
 overall
climate of the area
 determined by the amount and type of precipitation
 amount of available water is determined by
 how long it stays in the upper layer of the soil
 how much it collects beneath the soil
 collects in lakes, rivers, ponds and seepage into porous rocks below the soil
 groundwater: water in the soil or rock below the Earth’s surface
 water table is the area between the saturated soil and unsaturated soil
 leaching: water seeping down, collecting organic matter and minerals from the soil, deeper into the
soil
 serious problem since it remove nutrient that plants need to grow
 branching roots extend deep into the soil and help pump minerals and other chemicals back to the
surface
Temperature
 overall
climate of the region
 can vary significantly affecting both biotic and abiotic factors
- hot temperatures can evaporate water faster
 plants need longer roots
- colder temperature hold water in the soil longer
Biology 20
Unit 20B: Ecosystems and Population Change

plants need shorter roots
Sunlight
 ecosystems
close to the equator receive constant amounts of light throughout the year
 northern and southern hemispheres have varying amounts of light throughout the year
 plants in the ecosystem can also cause the sunlight to be blocked from other plants or organisms
Factors Affecting Aquatic Ecosystems
Chemical Environment
 includes
the type of water
 freshwater ecosystems seldom survive in saltwater ecosystem and vice versa
 amount of oxygen dissolved in the water
 organisms can only get their oxygen from the water
 amount of oxygen depends on the temperature of the water, pressure and salt
 naturally occurring minerals are also found in the water
 phosphorous and nitrogen
 also chemical pollutants can be in the water
Temperature and Sunlight
 ecosystems
near the surface of an ocean obtains more light and
has warmer temperatures than one deeper
 life can exist without light
Water Pressure
 800
times more dense than air making it harder to move
through
 restricted by the amount they can move up and down
 at 10 m pressure is double what it is at surface
- pressure increases by 100 kPa for every 10m of depth
Seasonal Variation in Canadian Lakes
 causes
significant changes in abiotic factors in freshwater ecosystems
 water cools it become more dense
 water below 4C starts becoming less dense
- ice floats forming a layer of cold on top of warm
- bottom of the lake is at the lowest temperature of 4C
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Winter Stagnation
 ice prevents the dissolving of atmospheric oxygen
 bottom 4C to the top water 0C
 wind-blown ice allows light to penetrate for photosynthesis
- fish die-off: no light decreases oxygen to a level that cannot
support the biological life
Spring Overturn
 winds, rain and storms mix oxygen into the water
- increases the rate of dissolving atmospheric
- increases the surface area by oxygen stirring-up the water
surface water increases to 4C and sinks to carry oxygen to the
less dense water
 bloom: rapid growth of blue-green algae from the release of
nutrients in decaying matter
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Summer Stagnation
 develops temperature different (thermal) layers
- epilimnion: upper lake water layer that heats up in the summer
 warmer the water the less oxygen it will hold
- thermocline: separating zone from the epilimnion and
hypolimnion
 water temperature drops from warm to cold
- hypolimnion: lower lake water layer that maintains a constant
cold temperature
 lack of mixing blocks the movement of oxygen into the
hypolimnion
 lower temperature holds oxygen more efficiently in the
water
Fall Overturn
 renewed oxygen levels by breaking down the thermal layers
 reversal of spring overturn
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4.4 Limits on Populations and Communities in Ecosystems
Biotic Potential
 biotic
potential: maximum number of offspring that a species could produce with unlimited resources
Limiting Factors
 factors
in the environment can prevent populations from attaining their biotic potential
 food, water, territory and pollution and other toxic chemicals
 fluctuations caused by more than one factor occur naturally in an ecosystem
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Unit 20B: Ecosystems and Population Change
Carrying Capacity
 maximum
number of individuals of a species that can be supported by
an ecosystem
 is determined by the availability of resources
- food and water
- can exceed the carrying capacity of the ecosystem for a short time
 population fluctuate because of an interaction of the many biotic and
abiotic limiting factors
 communities are often stable
Limits of Tolerance
 law
of minimum: the nutrient is the least supply is the one that limits growth
 Shelford’s law of tolerance: organism can survive within (tolerate) a particular range of an abiotic
factor
 Above and below the range cannot survive
 He greater the range of tolerance, the greater the organisms ability to survive
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Density-Independent and Density-Dependant Factors
 density-independent:
a factor that affects members of a population regardless of population density
 fire and flood are naturally occurring events
 affect population regardless of size
 density-dependant: a factor that affects members of a population because of the population density
 food supply, water quality, sunlight, disease and territory

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Density-Independent Factors
flood
fire
spraying with pesticides
change in climate or temperature
destruction of habitat
drought
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Density-Dependant Factors
food shortage
competition for mates, breeding areas (habitat)
disease caused by a microorganism or parasite
introduction of an exotic species
increased predation
competition for water and other resources
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Chapter 5: Evolution
Importance of Adaptation

two levels of biological diversity
 species diversity: number of different species
 genetic diversity: amount of variation of inherited traits between individuals of the same species
 no two organisms are exactly alike is the most important feature for all life – diversity
 all living things show similarities
- all plants and animals share certain characteristics
 regardless of size, shape or level of complexity
 all share requirements for energy, basic cell structure and function plus adaptation to a
particular habitat
 adaptation: inherited trait or set of traits that improve the chances fro survival and
reproduction of organism
 all living organisms are adapted in appearance, behaviour, structure and mode of life
 make them well suited to survive in a particular environment
- adaptations are specific for that organism in that environment
 theory of evolution explains why organism similar in biochemistry and molecular biology are so
different in form and function
 evolution: cumulative changes in characteristics of populations of organisms in successive
generations
- living things change over a series of generations
- does not refer to individual change or development
Types of Adaptation
Structural Adaptations
 most organisms show
clear structural adaptations
to their environment
 can be modifications to
pentadactyl limb or leaves
- forelimb and five
digits adaptations in
humans, seal an bats
 humans to grasp
and hold things
 longer in bats to lengthen and
support the wing for flying
 shorter in seals to support the
flipper for swimming
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- plant leaves and structure to capture insects
 Venus fly traps leaves to capture prey
 pitcher plant leaves are shaped like a jar to capture insects
 these adaptations usually arise from plants not receiving enough nutrients or light for
photosynthesis
 live in bogs and wetlands where soil nitrogen is poor
Physiological (Biochemical) Adaptations
 enables the plant to produce chemicals for the digestion of its prey is less obvious
 production of chemicals for sexual attraction and alarm signals
- pheromones: chemicals secreted by organisms to influence the behaviour of other organisms
 a lot of physiological adaptations involve specialized enzymes that control body functions
- temperature, respiration, digestion, circulation and blood clotting, muscle and nerve
coordination
- enzymes: special protein structures that regulate chemical reactions
Behavioural Adaptations
 key factor in keep organisms alive and enabling them to
reproduce
- southward migration of the Canada goose
- hibernation of certain animals
- storage of nuts by squirrels
 most organisms respond to stimuli and may show
adaptations in the way they behave
- protozoan’s such as amoebas and hydras respond
quickly to touch by moving away
 react to temperature changes and chemical
substance in water
- some organism may move away from or towards the
stimulus
 depends on the stressfulness of the situation
- earthworms will react to touch, light and chemicals in the soil
 react to light by burrowing in the soil and only come out at night
 plants are controlled by chemical hormones
- tropism: orientation of plants according to some stimulus
 phototropism is plants “bending” toward the light
5.1 Classification of Organisms
Taxonomic Systems

taxonomy: science of classification according to the inferred (presumed) relationships among
organisms
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classification systems have two main purposes
1. identify organisms
2. provide a basis for recognizing natural groups of living things
 classification systems are artificial
- developed by scientist to help deal with diversity of life and relationships among organisms
 Carl Linnaeus (1707 – 1778): Swedish botanist who developed the taxonomy system that is still
used today
 based on the physical and structural features
- more features that organisms have in common the closer the relationship
 binomial nomenclature: naming organisms by using two names
- Genus: includes several species
 first letter is always capitalized
- species: group of organisms that look alike and can interbreed under natural conditions to
produce fertile offspring
 two name system has an advantage by indicting similarities in anatomy, embryology and
evolutionary ancestry
- North American black bear: Ursus americanum
- grizzly bear: Ursus horribilis
- giant Alaskan brown bear: Ursus arctos
- polar bear: Ursus maritimus


phylogeny: history of evolution of a species or group of organisms
 represented by a phylogenetic tree (evolutionary tree)
- tree starts from the most ancestral form and includes branching that lead o all of its
descendants
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
dichotomous key: two-part key used to identify living things
 constructed so a series of choices must be made
 each new choice leads to a new branch of the key
 choices are correct – leads to the name of the organism being identified
5.2 Evidence of a Changing Earth
Evidence from Fossils
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palaeontology: is the study of fossils
 ~ 250 000 fossilized species have been found
 fractional representation of the overall population that existed
fossils offer direct evidence of the pathways taken by living organisms in their evolutionary history
(phylogeny)
 fossils: represent species that have become extinct
 living fossils: fossils from species that have changed very little over a long period of time
fossils alone do not provide absolute proof of evolution
 can construct convincing arguments for the process of evolution
How are Fossils Formed?
 fossils can be created by a number of different ways
 hard parts of organisms resist the action of weathering for long periods, particularly in dry
environments
- teeth, bones and shells
 some soft tissues of extinct organisms have been preserved
- mammoths entirely intact preserved by the deep freeze process over 10 000 years ago
 impressions or imprints of plants and animals
- tracks made in soft mud and the fecal material of animals
 organism become entrapped and embedded in amber
- insects in amber
 amber is a hardened gum given off by trees
- animals, birds, mammoths, horses and camels in the old tar pits
 cell cavities and intracellular spaces of the skeletal material of plants or animals are replaced by
mineral matter
 silica, calcite or iron compounds
 makes a petrified structure
 most fossils are found in sedimentary rocks
 formed when sand and rock particles are laid down usually at the bottom of oceans and lakes
- new layers are formed over older ones and the layers compress and harden
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Dating the Past
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
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1000 years to form 30 cm of sedimentary rock
 thickness of the rock layer can determine the approximate age
- must use its location above and below other rock layers
radioactive dating has been used more recently to determine the age of fossils and rocks
 measurements of decay of radioactive isotopes (geological clock)
- absolute age of the Earth with great precision
- changes a particular atom (parent isotope) into daughter isotopes
 radioactive potassium-40 decays into agron-40 or calcium-40
 radioactive uranium-238 decays into lead-206
- half-life: amount of time for half the sample to become stable
 not affected by temperature, moisture or other environmental conditions
radiometric dating: technique used to determine the age of a rock or fossil
 determine both age of the earth and the time that the first life forms appeared
- earth was formed 4.5 billion years ago and life first appeared about 3.8 billion years ago
- fossils of more recent origin represents more complex organisms
 oldest parts of the fossils record contains simple organisms
 time difference between the two groups is great, the difference between the groups is
great
 gaps occur in the record when the layer does not contain fossils of certain kinds
- found in layers both before and after the gap
- gaps are called “missing links
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5.3 Evidence for Evolution From Biology
Evidence from Anatomy

observed through living organisms
 links between existing forms and their ancestors
- physical anatomy and genetic make-up
- supports theory of modern species evolved from ancestral species
Homologous and Analogous Structures
 anatomical evidence reveals structural similarities
among organisms
 organism with similar structures evolved from a
common ancestor becomes increasing obvious
 homologous structures: similar structures and
origin but different functions
- same origin as forearm or leg buds
 bat wing, whale flipper, cat leg and
human arm all share similar bone
arrangements
 all have different functions
 all have the same pattern of early
growth
 analogous structures: similar in function and appearances but not in origin
- similar functions but are quite different anatomically suggests that they do not have the
same evolutionary origin
 wing of a bird and of a butterfly or insect
Butterfly wing
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Embryology
 study of organisms in the early stages of
development
 valuable insight into the process of evolution
 similarity of the embryos is due to their evolution
from a common ancestor
 young forms of these organisms resemble the
young of the related species
 farther the species the early the break in
embryological development
- salamander and chicken are connected but
break away from the pig and human
 longer the embryos look similar the
closer the species are
Physiological Evidence
 physiological studies show the similarities among organisms
 study of the function of any part of an organism
- wastes excreted from the kidney s of birds and reptiles have the same chemical make-up
- certain hormones from sheep and pigs can be injected into humans
 insulin for diabetes is obtained from cow or pig pancrease
Vestigial Feature and Anatomical Oddities

vestigial features: rudimentary structures that sere
no useful function
 present in all species and provide the most
compelling evidence for evolution
 once served as a function in ancient ancestor
- some modern whale and snake species have
vestigial hip and leg bones
 evidence of evolution from fourlegged ancestors
- humans appendix evolved from a
second stomach in ancient humans
- mammals with vestigial toe bones
elevated above ground
- some beetle have winds trapped
beneath fused covers
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- blind cave salamanders have empty eye sockets
 evolved from salamanders with fully functional eyes
Evidence from Biochemistry


many structures are made up of proteins such as muscle and skin cells
 proteins are made up of long chains of amino acids
- each type of protein has a unique number and sequence of amino acids
- many species posses similar proteins
 overtime proteins in similar species become increasing different
 hemoglobin, oxygen carrying molecule, in all invertebrates varies between species that
are less similar
 suggests that hemoglobin molecules evolved to have different characteristics
a variety of chemical analysis techniques
have been used to show that all organism
share similar DNA molecules
 DNA (deoxyribose nucleic acid):
heredity material that determine
characteristics or traits are passed onto
the next generation
- composed from 4 nucleotide bases
that are varied in number and order
 adenine (A) – thymine (T)
 cytosine (C) – guanine (G)
- genes: segment of DNA that
performs a specific functions or
particular traits
 biologists have discovered homologous and vestigial anatomical features, geneticists have
found homologous and vestigial genes in DNA
- found in all species
- humans have defective genes that would allow us to make our own vitamin C
 lost the ability and need to make our own
 we still poses the instructions to do so
 species from different orders are compared the difference in their DNA structure is greater than
when species within the same genus are compared
Biology 20
Unit 20B: Ecosystems and Population Change
Evidence from Artificial Selection
artificial selection: breeding used to alter appearance, behaviour and chemical make-up of plants
and animals
 select individuals with the desired traits and breed them so the offspring will have the same
inherited trait
- breeds today have been selected for over hundreds of generations
 cabbage, broccoli, cauliflower and ornamental kale are all the same species
- farmers selected traits for a single species of sea cabbage
 produce dramatic changes over a short period of time
 supports more dramatic changes in nature over millions of years and countless generations

5.4 The Making of a Theory – Accounting for the Evidence
Early Beliefs


before the 18th century species were thought of as “fixed” from the first time they appeared on
Earth
the second half of the 18th century a number of scholars began to speculate and speak out on the
issue of evolution
 Pierre Louis de Maupertius
- French mathematician
- multiplication of species was a result of accidental recombination of elementary particles
 leads to offspring that are different from their ancestral form
 genes in modern biological terms
 Georges-Louis Leclerc de Buffon
- leading naturalist
- two hypothesis to explain the world distribution of plants and animals
 “creation of species” did not occur in one single place but in a number of “centers of
creation” (form hybrids)
 species were not created in a perfect state but underwent modifications over time
 Carl Linnaeus (1760)
- Swedish botanist and the founder of biological nomenclature
 Erasmus Darwin (1794)
- Charles Darwin’s grandfather
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- physician and naturalist
- all life had developed from a single source
Lamarck’s Theory
Jean-Baptiste de Lamarck (early 1800’s)
first theory of evolution that included a mechanism
 spontaneous generation: belief that living things arose from non-living matter
- new, very simple species were continually being created and gradually became more
complex
 organisms have an imaginary “force” or “desire” to change themselves for the better
- must be able to produce new parts to satisfy the needs in
order to become better adapted to the environment
 use and disuse of certain structures could be passed off to the
offspring
- more the structure is used the stronger the parts
 one generation of the giraffe might have obtained
food from higher trees
 continual stretching of the neck would lead to a
slight elongation over time
 trait was passed onto offspring and generations later
the neck progressively became longer
 inheritance of acquires characteristics: “Lamarckism” is the false
concept of inheritance of features acquired during the life of an individual

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30
Darwin’s Theory
Charles Darwin (1809-1882)
1831 set sail on HMS Beagle to travel around the world and returned in 1836
 came back with questions and observations
1. unusual fossils that resembled a variation of sloths and armadillos living in the same region
- inference: living forms might have descended from the fossilized species
2. species in African tropic did not resemble the species in the South American tropics
- resembled the species living in cooler parts of South America
- inference: each landmass acted like an isolation nursery
 allows each species to evolve independently
3. harsh landscape of the Galapagos Islands were home to 13 very similar species of finches
- found nowhere else on Earth but resembled a species living 1000 km off the coast of South
America
- inference: all had evolved from a single species that had arrived from Galapagos from
South America
4. fossil deposits of corals at the elevation of 3000 m in the Andes Mountains
- inference: geological forces over a vast period of time could account for the fossils in the
mountains
 through artificial selection discovered that all species possessed inherited variations
 that could be selected to change the traits of the species in desirable ways

Biology 20
Unit 20B: Ecosystems and Population Change

published On the Origin of Species by Means of Natural Selection in 1859
 based on a simple set of observations and logical reasoning
- observed: all species exhibited inherited variations
- reasoned: variations allowed some individuals to be better adapted to survive and
reproduce that other
- inherited traits provided the survival advantage and would become more common in the
population
Natural Selection
differential reproductive success of individuals
caused by variations in their inherited
characteristics
 can be divided into six distinct ideas:

1. variation:
differences amount traits occur among
members of the same species
 no two individuals are exactly alike
- variations including acquired variations
are passed on from one generation to the
next

2. overproduction:

number of offspring produced by a new
species is greater than the number that can
survive, reproduce and live to maturity
3. populations of species are stable in size
4. struggle for existence (competition):

organisms of the same species and those of
different species must compete for limited resources
- food, water and place to live
5. survival of the fittest (natural selection):

individuals of a species with traits that give them an advantage are better able to compete,
survive and reproduce
- all others die without leaving offspring
- nature picks who survives, the well adapted one to their environment
- not random
6. origin of new species by inheritance of successful variations (speciation/evolution):

new species arise by accumulation of inherited variations
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32
- type is produced that is significantly different from the original, a new species has
arisen
5.5 Sources of Inherited Variation
Mutations
DNA is founding the chromosome of cells
 composed of 4 nucleotide bases in a sequence that forms a code
- translated by the cell gives the organisms the specific inherited traits
- genes are segments of DNA that code for specific traits
 each gene ahs a specific DNA sequence
 DNA is like a blueprint for a particular individual organism
 DNA will remain the same throughout its life unless mutated
 mutations: random changes in DNA and provide continuous supply of new genetic information
- caused by environmental factors (chemical or radiation) or arise from errors when the cells
use or make copies of the DNA molecule
- loss or duplication of an entire section of DNA or simple
changes to the DNA sequence
- relatively rare in individuals ranging from one new
mutation per sex cell
 large populations reproduced over many generations
gives rise to a substantial number of mutations
 effects of mutations depend on the what DNA sequence is
altered and how it is affected
 neutral mutation: has no effect on the organism
- fitness: organism’s reproductive success
 harmful mutation: reduces the organisms fitness
- selected against the species and do not accumulate over
the generations
 beneficial mutation: enhances an organisms fitness
- selected for and may accumulate over the generations
- not many mutations in nature are beneficial, majority
are harmful or neutral

Biology 20
Unit 20B: Ecosystems and Population Change
5.6 Speciation and Evolution
Speciation
speciation: formation of new species
 species: a group of similar organisms that can interbreed and
produce fertile offspring in their natural environment
- population of individuals who are reproductively isolated
 not capable of breeding with individuals of other
species under natural conditions
 there are more species present today than in the past
 two ways in which a new species can arise:
 populations or parts become isolated and must adapt to
conditions
 selective pressures also vary where species are not created
instantly but evolves over a long period of time

Geographic Isolation
 separation caused by physical obstacles such as
mountains, canyons or water
- barriers created by humans such as damns or
canals
- into two or more groups that are isolated from
each other
 mutations that occur are not shared with the
other population
 natural selection works on the separated groups
resulting in inherited differences between the two
populations
 genetic flow between isolated and the main group
ceases
- individuals over time become so different they
cannot interbreed
 different adaptations in separate
environments
 different gene frequencies and different mutations over a long time
Reproductive Isolation
 geographic isolation can lead to reproductive or genetic isolation
- both populations split and live in the same geographic region over a short time
 still gives rise to speciation
- reproductive isolation occurs when organisms in a population can no longer mate and
produce offspring
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
- still occurs even after the
barrier has been removed
contributors are mating habits
and courtship patterns
- seasonal differences in
mating
- inability of sperms to
fertilize eggs
- even if fertilized genes and
chromosomes cannot
interact
The Rate of Evolution
theory of gradualism: idea that speciation
takes place slowly
 some fossils support this with small
changes in species
 theory of punctuated equilibrium: idea that
species evolve rapidly followed by a
period of no or little change
 supported by the fossil record
 three main ideas
1. many species evolve very rapidly in
evolutionary time
2. speciation occurs in small isolated
populations
- intermediate fossils are very rare
3. after initial burst of evolution, species
are well adapted to their environment
- do not change significantly over long
periods of time

Macroevolution: Diversification and
Extinction

trend of increase diversity has been interrupted
by “extinction events”
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divergent evolution: evolution into many different species that are vaguely similar
 marsupial distribution in Africa, Australia and South America can be explained by continental
drift that followed the Pangaea break-up
- similar marsupials developed in different contraries but with similar environments
 convergent evolution: development of similar forms from unrelated species due to adaptation to
similar environments
 mammals which did not appear until after the break-up of Pangaea are limited in their distribution
 each type of mammal tends to be unique to a specific continent
