Mechanisms of population Change

Organisms are constantly being subjected to environmental

conditions that limit their populations. Factors such as
competition for :

Mates

make sure only strong and

Space
well adjusted organisms live
long enough to reproduce.Food

Disease, parasites, and predators also

limit the size of populations.

Owl hunting vole

Sea lamprey attack
lake trout

Individuals of the same species in the

same place
Rainbow trout in the Bow river,

Bison in Wood Buffalo National park

A structure, behaviour, or physiological process

that helps an organism obtain light, water, food
and nutrients.

Adaptations help organisms cope with physical

conditions such as:
- temperature,
- light,
-natural enemies,

Adaptations also allow organisms to reproduce

more successfully and to respond to changes
around them.

1) Structural Adaptations physical

features and special body parts
Eg) Fur or hair structure, Shape of Ears,
Camouflage or Warning Colouration, leaf
shape

Muskoxen: layers
of woolly under
hair and course
guard hairs

Porcupines have
hairs that are
sharp and barbed
for protection

Moose hair is hollow

to help them stay
buoyant swim

Arctic fox has

small ears to
reduce heat loss

Desert Fox has ears

that are large and well
vascularized to give off
heat

Lizards such as
Chameleons
can change their
colours

The stripes are designed Leafy

for twoSea
things:
camouflage and disorientation.
Dragon
Can
you
see
the
Lions are colorblind, so the
wavy
pattern
of
the stripes helps the zebra
blends
in
with
under
creatures?
blend in to the tall, wavy grass.
in large herds, the stripes blend
water When
plant life
together with the other zebra in the herd, making it difficult for lions to
pick out individual animals. This confuses the lions and weakens their
plan of attack.

Poison Tree Frog

Toxic Sea Slug

Bright Colours advertise that these

Owl Butterfly Uses
creatures are toxic and shouldnt be
colouration to frighten
eaten
potential preditors

Spruce tree
Needles are
thin and
covered in
wax to limit
water loss

Cactus Leaves form

Giant Amazon
needles to protect the
Water
Lily:
Leavesplant
andLarge
branches
from
predators
leaves
help thefortowater.
face downward
looking
plant
to
floatamounts
and helpofprevent
allow wings
large
Venus Flytrap
They
also
gather
sunlight
snow to
and
have developed
tofall off
water
loss
from wind
for
photosythesis
prevent
branches
from
close around
insects
and
evapouration
being damaged

Eg) Hibernation, diurnal vs. Nocturnal, Migration, mating rituals

Some birds have
elaborate mating
dances

Dormouse hibernating
during winter when food
is scarce

Bush baby is well suited

to night time food
gathering

Snow geese
migrate

Are systems present in an organism that allow it to perform

certain biochemical reactions Eg)
Wood frog
freezes solid in
winter

Hagfish Produce
Slime as a defence

Spitting Cobra
produces powerful
venom

Angler fish
produces
bioluminescent
molecules in it
barbels to
attract prey

Adaptations have developed in populations

over time: slowly and gradually.
Adaptations develop because of
individual differences in the members of
a population.
Puppies from
the same litter
have
differences in
physical
appearance
as well as
physiological
differences

Eg) A dog and a wolf can reproduce

and the puppies from that litter can
also reproduce. We say that the
offspring are reproductively viable.
This makes dogs and wolves part of
the same species canis lupus.
Eg 2)A horse and a donkey
can mate and have an
offspring (a mule) but the male
offspring cannot reproduce; it
is sterile. Therefore Horses
(Equus caballus) and Donkeys
Equus asinus) are separate
biological species.

Is reproductively
viable

Mules are hybrids,

and are sterile

If a Variation in an individual of a population is

beneficial (helps that individual survive and
reproduce) that variation can be passed on to
the offspring of that individual.

Through generations of this variation helping

individuals survive and reproduce, the variation
will become more common in the population.
Over time the whole population may have this
variation and it becomes an adaptation.

Some variations are not beneficial and

the individual will die before it can be
passed on to future generations. In this
case the variation does not become an
adaptation.
Variation among individuals in a
population
is dueParents
to: pass on units of hereditary to
Sexual reproduction:
their offspring. The number of possible combinations of this
Mutation: Changes in the genetic code. Mutations can
genetic material is astronomical!! Think of all the people on
arise because of mistakes that happen as DNA is
earth and all the differences in the individuals of the same
copied, or mutations can happen when environmental
species (Homo sapiens).
conditions such as radiation or harmful chemicals
cause DNA to be reordered resulting in a different set of
instructions.

-Mutations can be harmful. Harmful mutations may

kill the organism or prevent it from reproducing.

-Mutations can create a trait that helps an organism

survive its environment better. In this case the
organism will reproduce more successfully than an
individual without the trait and subsequently pass
on the beneficial trait. Over time this trait will
become an adaptation in a population.

Example of a beneficial mutation- Fish born without eyes in a

cave have an advantage over fish born without eyes (less
chance for injury/infection and no wasted energy making eyes)
Over many, many generations, the populations of fish in caves
are made up of fish wholly without eyes.

Blind, albino cave fish

next to a closely related
species

Eg1) Extinction of the cold blooded dinosaurs.

Due to severe climate change, mammals
became more successful due to adaptations like
fur, warm blooded etc.
Eg2) The extinction of the Irish Elk due to
climate change. The disappearance of grassland
combined with its huge antlers prevented it
from travelling in forested areas to get food.
Selection advantage turned on the Giant Elk and
it became extinct
Smaller Elk
became more
successful

The environment exerts certain forces on the

organisms within it. These forces can include:

light intensity,
availability and location of food,
water
shelter
the amount and kinds of predators,
parasites and
disease

All of these environmental conditions

exert a pressure on the organisms living
within it, and organisms that are best
suited to living in these conditions thrive
and pass on to their offspring the traits
that made them successful.

Organisms not well suited do not pass

on traits!!

For natural selection to occur we

must have 2 things:
Diversity among the members of the
population (due to reproduction or
mutation), and
Environmental selection pressure.

Examples of Adaptations in Populations:

Eg 1) Prairie plants have adapted to life on the open grasslands
where animals graze on their leaves and dry, windy conditions
and fire are common place (environmental selection pressures).
Over thousands of generations, advantageous traits have
become adaptations in many prairie plants. Examples of these
adaptations include:

-Roots of prairie grasses

extend deep into the ground to
absorb as much moisture as
they can
-Extensive root systems
prevent grazing animals from
pulling roots out of the ground
-Prairie grasses have narrow
leaves which lose less water
than broad leaves
-Grasses grow from near their
base, not from tip, thus are not
permanently damaged from
grazing animals or fire
-Many grasses take advantage
of exposed, windy conditions
and are wind pollinated

Deep root
structure

Albinism is a genetic mutation

which prevents an organism
from producing pigments. If a
prey species (such as a moose)
cannot produce pigment, it can
be easily seen by predators
(environmental selection
pressure).
Because the albino mutation is
not favorable, organisms with
this genetic mutation do not
generally live long enough to
pass on the gene and it doesnt
become more prevalent in the
population.

Similar to natural selection,

but in the case of artificial
selection humans choose
individuals that have the
most desirable
characteristics. By

breeding just individuals

with these characteristics
humans can change the
populations to fit their
needs
Eg) Featherless Chickens,
Modern Cattle, Domestic Dog
Breeds, Dwarf Varieties of
Plants etc.

Science and scientific discoveries develop

as people make observations about the
world around them and strive to seek
answers to their questions about those
observations.

Scientific hypothesis- a statement that

provides one possible answer or
explanation for an observation. In
Science, hypotheses are tested over and
over to see if they can consistently lead
to the same predictions and explanations.

Most people think the word theory simply

means an unproven idea that is not conclusive.
Science is a process that is ever advancing.
Science uses theories, hypotheses and models to
explain the natural world. What we know today
may very well be improved upon tomorrow.

A theory is a system of ideas that can perform

two major functions:

1. It makes sense of the existing information

2. It can be used to make predictions of future
observations

Descriptive How well does this theory describe

experience?
Prescriptive Does it tell you what will happen next?
Evaluative Can we test it to see if it actually works?
Comprehensive- How well does it describe
experience? Does it only describe some aspects of
experience or is it broad?
Parsimony: Being able to say the most with the least.
Precise- The accuracy with which the descriptions
apply.
Empirical Validity: Has to be able to be objectively
tested.

Aristotle (around 350

BC)

- The ladder of life

(Scala Naturae)
- Simplest creatures at
the bottom, man at
the top
- All species had been
created independently
of all others and had
remained unchanged

- Classified living organisms using 2 Latin names (binomial nomenclature) , eg: Canis lupus (dog)
- Believed in scriptural creation of all the species, he just wanted to name them
Deus creavit, Linnaeus disposuit, ' Latin for, "God created, Linnaeus organized".

- Organized organisms into kingdom, phylum, class, order, family, genus, species.

- Organisms that were closely related had similar classifications, those that were very different branched off from each other sooner.

- Wrote a huge book called Histoir

Naturelle
- Said that the original divine creation has
since been modified by nature and this is
why there are slight variations between
related species (Apes and Humans for
example)

-Founder of paleontology (study of fossils)

-Used evidence from the fossil record to show
that different species existed at different times
throughout history. He realized that as he
explored deeper and deeper layers (stratum) of
rock, he found species of creatures that were
very different from the ones on earth today.

Strata are layers

of rock, the
deeper you go
the older the
layer (law of
superposition)

Cuvier Explained the extinction of species as the

result of a series of catastrophes or revolutions.
After each catastrophe, (the most recent of
which was the Flood), the species that remained
alive repopulated the earth. Time and nature
act to destroy species, not create them.

-He Believed strongly in Creationism but

ironically inspired much research into
strengthening the theory of evolution

-Proposed that the earth was molded by slow processes of

wind, water etc. Not catastrophic events. This Theory was

called gradualism and later uniformitarianism.

These theories said that the earth has an on-going

history, and that geological processes operated at the
same rate in the past as they do today.

Instead of large catastrophes occurring, gradualism said

and that slow, ongoing and subtle change was normal and
expected. Thought that maybe these same forces acted
to change life in the same, gradual way.

Because geological change was slow, this was in direct

conflict with scriptural scholars who had counted the
generations back to Adam and determined that the earth
was approximately 6000 years old.

Lamarks theories were very powerful at

the time. In fact, many people to this day,
when discussing evolution are actually
discussing Lamarkism. In Lamarkism the
environment is the key factor in evolution
(true) but rest of his theory is wrong.

1. The Theory of Need: organisms need

or want to change
eg: ancestors of snakes had legs but
changes in the environment made it
necessary for these animals to go
through very narrow spaces. For this
reason they began to stretch their bodies
and crawl.

2. The Theory of use and Disuse: organs

remain active and strong when they are
used, if not used they weaken and
disappear.
eg: snakes used their legs less & less until
finally they shrunk away and
disappeared.

3. The Theory that Acquired Traits can

be passed On to offspring:
Modifications an organism acquires
during its lifetime can be passed to its
offspring
eg: This was shown not to be true in
experiments with mice tails - cut off tails
of 28 generations of mice but each new
generation were still born with tails.

Both published their theories at about the

same time, but Darwin is credited with
having been the first to develop the
concept of natural selection. Published
On the Origin of Species in 1859

Charles Darwin

Alfred Wallace

1. All organisms produce more offspring than

can actually survive in the environment.

eg: An adult female cod might lay 4-6

million eggs in a single spawning

2. Production of more individuals than the

environment can support leads to a struggle for
existence. Competition
3. The characteristics of individuals of a given
species vary
4. The individuals whose characteristics are best
adapted to a given environment survive survival of the fittest
5. Those individuals that survive pass their traits
on to their offspring.

Geology

Fossils simpler organisms in older

strata, more complex ones in newer
strata. There are
also transitional fossils between species.

Transitional
Fossil:
Archaeopteryx
had feathers
like a bird but
teeth and a
bony tale like a
dinosaur

Radiometric
dating the long
age of the earth
(4.5 billion years)
as indicated by the
radiometric decay
of several isotopes.

Eg) Carbon Dating

Plate tectonics
the same fossil
species found on
different continents
indicating that the
continents were
once joined
(Pangaea)

Comparative Anatomy and

Biochemisry

Homologous organs - organs that are

similar in different organisms
eg: bones in Seal flipper, bone in human hand, bones in a bat wing common ancestor?

Analogous organs organs that are

different but perform the same function
eg: wings on a dragonfly and wings on a bird

Vestigial organs - organs which may have

a function in one organism but none in
another
eg: appendix, coccyx (tail bone) in humans

Atavisms the odd appearance of

structures that might have been present
in an ancestor.
Eg: pelvis and hind limbs on whales, anal spurs on snakes

Embryologic studies - eg: appearance of

gill slits and tails in human embryos.
Ontogeny recapitulates phylogeny

DNA studies - all organisms on this planet

use the same DNA structure
- 98% similarity between Ape and human DNA
- lesser similarity as taxonomic distance
increases
Biochemical studies comparison between
the biochemical products found in different
organisms. Closer species have more similar
biochemistryAll cells have cell membranes, All plant cells have cell walls

Species can be formed in one of two pathways and

both are the result of natural selection:
1) Transformation- The evolution of one species
into another as a result of mutation and
adaptation to changing environmental
conditions, replacing the old species.

2) Divergence- the
development of one
or more new species
from a parent
species as a result of
mutation and
adaptation to
changing
environmental
conditions.
This pathway increases
natural diversity

For a new species to form, populations must be

isolated from one another long enough for different
traits to accumulate over many generations.

If populations are isolated from one another long

enough, changes accumulated in the population due
to natural selection will effect reproduction with
other populations and a new biological species will
arise.

Each species that evolves from the common

ancestor population is adapted to its unique
environment, this is called Adaptive radiation

Geographical barriers- a population

can be separated due to physical barriers
such as rivers, mountains, lava flow, the
creation and colonization of newly formed
islands, oxbow lakes, inland seas etc.

Eg) Galapagos island

finches, Australian
Marsupials, grand canyon
squirrels

Biological Barriers- even if species come in

contact with one another, there can be barriers
that keep them from reproducing with one
another.

Anatomical differences- The reproductive structures of

different species dont allow interbreeding; different weasel
species have a baculum that is a specific size and shape witch
prevents them from physically mating with other species. (like a
lock and key).

Behavioural differences- Females of some bird species

respond to courtship dances only done by males of the same
species. Different types of trout spawn at different times of the
year (eg. Rainbow trout in the spring, Brown Trout in the fall)

There are currently 2 theories on how fast

evolution and speciation occur:

Gradualism- Small changes occur over a very long time. These

small changes in populations eventually add up to the larger,
more dramatic changes we see from early fossil forms to modern
species. The fossil record does not support this model.

Punctuated Equilibrium- This model says that there are long

periods where there is very little change in the morphological
characteristics of a species (equilibrium). Punctuated or
dramatic and rapid change occurs when a new species first
diverges from its parent species. (colonizes a new area, recovers
from a catastrophic event etc.)