Evolution & Natural Selection - Njcu.info

Evolution & Natural Selection

ADAPTABILITY OF LIFE ON EARTH
-

NASA, Galileo, Copyright Calvin J. Hamilton


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Venus

Evolution and Natural Selection

The Underlying Mechanisms of
Species Diversity

Charles Darwin

"There is grandeur in this view of life, with
its several powers, having been originally
breathed by the Creator into a few forms or
into one; and that, whilst this planet has
gone on cycling on according to the fixed
law of gravity, from so simple a beginning
endless forms most beautiful and most
wonderful have been, and are being
evolved.“


--
The Origin of Species




Charles Darwin

In 1831 Darwin joined the
HMS Beagle
as the naturalist for a
circumnavigation of the world; the voyage lasted five years. It was
his observations from that trip that lead to his proposal of natural
selection to explain the diversity of organisms.










It was not until 1859 that Darwin finally published his
Origin of
Species.

Darwin’s Finches

"
The most curious fact is the perfect
gradation in the size of the beaks

in the
different species of Geospiza, from one as
large as that of a hawfinch to that of a
chaffinch, and (if Mr. Gould is right in
including in his sub
-
group, Certhidea, in the
main group), even to that of a warbler. The
largest beak in the genus Geospiza is shown
in

Fig. 1
, and the smallest in

Fig. 3
; but
instead of their being only one intermediate
species, with a beak of the size shown in
Fig.
2
, there are no less than six species with
insensibly graduated beaks. The beak of the
sub
-
group Certhidea, is shown in

Fig. 4
. The
beak of Cactornis is somewhat like that of a
starling; and that of the fourth sub
-
group,
Camarhynchus, is slightly parrot
-
shaped.
Seeing this gradation and diversity of
structure in one small, intimately related
group of birds, one might really fancy that
from an original paucity of birds in this
archipelago, one species had been taken
and modified for different ends

[
stress

added]."

Charles R. Darwin, 1845,
The Voyage of the Beagle

[Edited by Leonard Engel,
1962, NY: Doubleday], pages 380
-
381.

Darwin’s Four Premises

1.
Each species produces more offspring
than will survive to maturity.

2.
Individuals in a population exhibit
variation.

3.
There are limits on population growth
imposed by the environment.

4.
There is differential reproductive success
among individuals within a population.

What is Evolution?

•
Descent with modification.

•
Change in the genetic structure of a
population.



Mechanisms That Change the
Genetic Structure of a Population
And Cause Evolutionary Change?

1.
Genetic mutations

2.
Genetic drift (isolation of populations and
different accumulations of mutations)

3.
Founder effect (small initial reproductive
populations with limited genetic diversity)

4.
Natural selection (differential reproductive
potential)

Speciation

•
Intercontinental
migrations of
members of the
camel family

•
Camels originate in
North America
during the Eocene
(55.8
-
33.9 Ma)

•
Migration through
land bridges

•
Geographic and
ecological barriers

Spreads
northward

and southward

and separates

Arctic Fox

Gray Fox

Different environmental

conditions lead to different

selective pressures and evolution

into two different species.

Adapted to cold

through heavier
fur, short ears,
short legs, and
short nose.
White fur
matches snow
for camouflage.

Adapted to
heat through
lightweight

fur and long
ears, legs, and
nose, which

give off more
heat.

Northern

population

Southern

population

Early fox

population

Present

65 million years ago

135 million years ago

225 million years ago

Geologic Processes affect
natural selection


Continental Shelf Area



Separating and isolating
populations

Fig. 4
-
4, p. 67




18,000

years before

present

Modern day

(August)

Northern Hemisphere

Ice coverage

What Is Natural Selection?

•
Differential survival and reproduction
among individuals of a population.


•
Response to selection pressures.

Relationship of Evolution and
Selection Pressures to
Environmental Science

1.

Biodiversity arises through evolution.

2.
Human disturbance changes selective
pressures.

3.
Conservation of individual species.

Process of Evolution through Natural
Selection

1.

Overproduction

2.
Resources limit population growth

3.
Heritable variation in traits

4.
Differential survival and/or reproduction

Potential Selective Pressures

Abiotic



Temperature



Precipitation



pH (acidity)

Biotic



Predation



Disease



Competition

Example of Natural Selection:
Peppered Moth

Peppered Moths

Fossil Evidence

•
Fossils

preserved remains of animals,
plants, and other organisms

•
Paleontology, the study of fossils across
geological time, how they were formed,
and the evolutionary relationships between
taxa

Gradualism

•
Evolution of the Horse

•
Fossils preserved in
consecutive formations
exhibit sequential
morphologic changes

•
Paleocene: small browsing
animal the size of a dog,
with 4 toes on the front feet
and 3 on the back, low
crown and weak enamel on
teeth (woodland
-
leaves)

•
In progressively younger
rocks the fossils exhibit
larger size, reduction of side
toes, increase in height and
complexity of teeth
(grasslands
-
grasses w/ silt)

Evolution of the Horse

Hyracotherium

ancestral horse, ancestor of all perissodactyls, small

4, 3 toed animal to
Equus
, large complex enamel molars, one toe

EXTINCTION

•
The rapid disappearance of a group of
organisms

•
As a response to an ecological catastrophe

–
Climatic Change

•
The extinction of one group releases the
resources for another group to thrive

•
Background Rate as a result of random factors:

–
competition, predation, changes in temp., changes in
salinity

•
Mass extinctions >> Catastrophic

–
asteroid collision, rapid oceanic turn
-
over;
accelerated rates of plate tectonic (volcanism)

Interactions = Relationships or
Associations Between Members of Two
or More Different Species

Type of
Interaction

Effect on
Species 1

Effect on
Species 2

Competition

-

-

Predation

+

-

Herbivory

+

-

Parasitism

+

-

Mutualism

+

+

Commensalism

+

0

Endemic Species

are found in

a
particular

region
and nowhere else
in the world. Since
these species are
not widespread
and may be
confined to only
one or two
protected areas,
they are of great
conservation
concern and may
become extinct
like the Golden
Toad.

Niches

•
A niche is
the way an organism interacts
with other living things and with its
physical environment.



•
A fundamental niche = the roles/functions
that the organism could play (i.e., where
could it live).


•
A realized niche = the role/function that the
organism actually fulfills (i.e., where does it
actually live).


Ecological Niches

•
Generalists

–
an organism which consumes a variety of food
sources and is usually able to adapt to more than one
ecological niche.

–
Omnivores are generalists, but herbivores which eat a
variety of plants are also considered generalists.

•
Specialists

–
A specialist animal, by contrast, generally favors a
single food source and terrain type.

–
A well
-
known example of a specialist animal is the
koala bear which subsists almost entirely on
eucalyptus leaves and the Giant Panda which eats
bamboo

china.mrdonn.org/panda.html

Animal.discovery.com

Louisiana heron

wades into water

to seize small fish

Black skimmer

seizes small fish

at water surface

Ruddy
turnstone
searches
under shells
and pebbles

for small
invertebrates

Avocet sweeps bill
through mud and
surface water in
search of small
crustaceans, insects,
and seeds

Brown pelican
dives for fish,
which it locates
from the air

Dowitcher probes

deeply into mud in

search of snails,

marine worms, and

small crustaceans

Herring gull

is a tireless

scavenger

Flamingo feeds on

minute organisms

in mud

Scaup and other diving

ducks feed on mollusks,

crustaceans, and aquatic

vegetation

Piping plover
feeds on insects
and tiny
crustaceans on
sandy beaches

Knot (sandpiper)

picks up worms

and small crustaceans

left by receding tide

Oystercatcher feeds on

clams, mussels, and other

shellfish into which it

pries its narrow beak

Factors That Restrict the Realized
Niche of an Organism

Limiting environmental factors may be:


1.

The physical environment

2.

Biotic factors (e.g., competition)

Limiting Factors

Summary of Community Structure

The numbers and types of organisms that exist in
an ecological niche are dependent upon both the
physiological resources available and the
relationships between different species.


Resources are limited in an ecosystem, and
species survive because of strategies that ensure
adequate access to the resources and minimize
competition for resources with other species.

Summary of Community Structure

As resources change and species interactions
change over time, those members of the species
best adapted to the new conditions are the
individuals that live to reproduce and pass on
their genetic information.


Thus, because of our ever changing world, over
time there are changes in the gene pool of a
population (i.e., evolution). Evolution
is not

a
directed choice, it is the consequence of natural
selection. In many cases natural selection leads to
the loss of an entire species (e.g., the dodo).

Genetic Engineering

•
Genetic engineering
,
genetic modification/
manipulation (GM)

and
gene splicing

are terms that
apply to the direct manipulation of an organism's genes

•
Genetic engineering is different from traditional breeding
(artificial selection), where the organism's genes are
manipulated indirectly.

•
Genetic engineering uses the techniques of molecular
transformation to alter the structure and characteristics
of genes directly.

•
Genetic engineering techniques have found some
successes in numerous applications

–
Food crops

–
Drugs

–
Pest
-
resistant plants

–
Rapidly growing animals