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Biology 1210
Lecture 4
Chapter 2
Introduction to
Evolution and Ecology
More on these ideas later in course
Two Key Concepts
Evolution: Changes that occur in
organisms’ traits over time
Ecology: How organisms live in their
environment
important
The great diversity of
life on earth
is the result of evolution
And evolution is
the consequence
of ecology over time
2.1 Darwin’s Voyage
• In 1831, twenty Charles Darwin set out for a five year
voyage around the world.
• He read, thought, collected specimens, observed, and
asked questions.
Great
Britain
Europe
North
America
Pacific
Ocean
Atlantic
Ocean
Africa
Galápagos
Islands
Equator
South
America
Andes
Australia
Cape of
Good Hope
Cape Horn
Tierra del Fuego
Tasmania
New
Zealand
• He asked himself why fossils of South America were more similar to
modern South American species than to fossils from other continents.
• He observed the diversity of life on the Galápagos Islands, such as
blue-footed boobies and giant tortoises.
• In all Darwin observed 13 (14) different finch species in Galapagos
• They differed mainly in beaks and feeding habitats and resembled finches
on the mainland
• He believed it was “descent with modification” from a common ancestor
(evolution).
Fig. 2.5
2.3 The Theory of Natural Selection
• Darwin observed that
– organisms produce more offspring than the environment can support
– organisms vary in many characteristics
– these variations can be inherited
• Darwin concluded that
– individuals best suited for a particular environment are more likely to
survive and reproduce than those less well adapted
– As a result, the proportion of individuals with favorable characteristics
increases
– Populations gradually change in response to the environment
• Darwin called “the preservation of favorable variations” natural selection
• Darwin drafted a preliminary transcript in 1842
– However, he shelved it for 16 years because of its controversial nature
• Alfred Russel Wallace (1823-1913) independently developed a similar
theory
– Correspondence between the two spurred Darwin to publish his theory
– In 1859, Darwin published On the Origin of Species in which he proposed
that evolution occurs through natural selection
• Fossils and the fossil record strongly
support the theory of evolution
• The fossil record shows that organisms
have appeared in a historical sequence
• Many fossils link early extinct species with
species living today
– These fossilized hind
leg bones link living
whales with their
land-dwelling ancestors
Hominid skull
•
In addition to Paleontology (the fossil record), there is an overwhelming convergence of
evidence consistent with the theory of evolution from such diverse fields as
–
–
–
–
–
–
–
–
Biogeography
Comparative anatomy
Comparative embryology
Comparative physiology
Genetics
Geology
Molecular biology
etc
Human
Cat
Whale
Bat
for a compilation of evolutionary
data see origintalk.org
or Richard Dawkins 2004
The Ancestor’s Tale
– Data from different field converge
Human
Rhesus monkey
Last common
ancestor lived
26 million years
ago (MYA),
based on
fossil evidence
Mouse
Chicken
Frog
Lamprey
80 MYA
275 MYA
330 MYA
450 MYA
Figure 13.3B
Chimps exact match with humans 104 aa
Rhesus 1 aa difference
The genes of diverse organisms have accumulated
mutations that alter the DNA sequence.
The longer it has been since any two species
shared a common ancestor,
the more differences there are.
Comparative anatomy and fossil record are consistent
with molecular data
• When humans choose
organisms with specific
characteristics as breeding
stock, they are performing
the role of the environment
– This is called artificial
selection
– Example of artificial
selection in plants: five
vegetables derived from
wild mustard
– Example of artificial selection: dog breeding
German shepherd
Yorkshire terrier
English springer
spaniel
Mini-dachshund
Golden retriever
Hundreds to
thousands of years
of breeding
(artificial selection)
Ancestral dog
mtDNA data is consistent with the origin of domestic dogs 15,000 years ago
from a single gene pools of Old World Grey wolves in East Asia
Scientists can observe natural selection in action
• Evolutionary adaptations have been
observed in populations of birds, insects,
and many other organisms
– Example: camouflage adaptations of mantids
that live in different environments
***The evolution of insecticide resistance is an
example of natural selection in action
***IMPORTANT
Insecticide
application
Chromosome with gene
conferring resistance
to insecticide
Additional
applications of the
same insecticide will
be less effective, and
the frequency of
resistant insects in
the population
will grow
Survivor
The evolution of antibiotic resistance in bacteria
is a serious public health concern
• The excessive use of antibiotics is leading to
the evolution of antibiotic-resistant bacteria
– Example:
Mycobacterium
tuberculosis
Two Key Concepts
Evolution: Changes that occur in
organisms’ traits over time
Ecology: How organisms live in their
environment
important
The great diversity of
life on earth
is the result of evolution
And evolution is
the consequence
of ecology over time
2.4 The Beaks of Darwin’s Finches
• Darwin collected finch species from the Galapagos Islands in 1835
• Darwin observed a correlation between the beaks and the food source of
the birds and concluded that the beaks had been shaped by evolution
Fig. 2.10 A diversity of finches on a single island
2.4 The Beaks of Darwin’s Finches
• In 1938, David Lack set out to test Darwin’s
hypothesis
• Lack’s five-month observation seemed to
contradict Darwin’s proposal
– Lack found many different species of finch
feeding together on the same seeds
• So was Darwin wrong or is there something
else going on?
2.4 The Beaks of Darwin’s Finches
• In 1973, Peter and Rosemary Grant embarked
on a study of the medium ground finch
– Geospiza fortis feeds preferentially on small
tender seeds abundantly available in wet years
– It resorts to larger, harder seeds in dry years
• The Grants found out that the beak depth
changed predictably year after year
2.4 The Beaks of Darwin’s Finches
Fig. 2.11
Large-beaked finches
increase in number
Small-beaked finches
are more common
• The Grants’ research supported Darwin’s hypothesis
2.7 A Closer Look at Ecosystems
• Ecosystems: the fundamental units of ecology
• All organisms in an ecosystem require energy
– Almost all energy comes from the sun
• Energy is lost at each step of the food chain
– This limits the number of steps
Sun
Plants
Herbivores
Carnivores
Food chain
•
Raw materials are not used up when organisms die
– They are recycled for use by other organisms
2.8 Species Evolve to Occupy
Different Niches Within an Ecosystem
•Character displacements
–The changes that evolve in two species to reduce competition
–This is clearly seen among Darwin’s finches
bills of similar sizes
when living apart
bills of different
sizes when
living together
Fig. 2.8
2.9 Patterns of Population Growth
• Innate capacity for increase
– The rate at which a population grows in the
absence of limits
– Also termed the biotic potential
• Realized rate of population increase (r)
– # of individuals added minus the # lost
– Thus:
r = (birth + immigration) – (death + emigration)
Life History Strategies
• The particular set of adaptations that adjusts an
organism’s growth rate to its environment
r-selected life history
K-selected life history
Rapid growth
Slow growth
Short lifespan
Long lifespan
Transient environments
Stable environments
Large no. of offspring
Small no. of offspring
No parental care
Parental care
Life History Strategies
Fig. 2.20 K-selected life history
Fig. 2.19 r-selected life history
2.10 Human Populations
• Throughout most of our history, human
populations have been regulated by
– Food availability
– Disease
– Predators
• Two thousand years ago, the human
population was ~ 130 million
– It took one thousand years for it to double
– And another 650 years for it to double again
2.10 Human Populations
• Starting in the 1700s,
technological changes gave
humans more control over their
environment
– These changes allowed
humans to expand the
carrying capacity of their
habitats
• Currently, the human
population is growing at a rate
of ~ 1.3% annually
– Doubling time at this rate is
only 54 years!
Fig. 2.21
Population Pyramids
• Human population growth is not uniform
• Human lives are also shaped by resource
partitioning!
Consumption in the Developed World
• The vast majority of the world’s population is in developing countries
– However, the vast majority of resource consumption is in the
developed world
• This disparity can be quantified by calculating the ecological footprint
– The amount of productive land required to support a person throughout
his or her life
Fig. 2.24 Ecological footprint of individuals in different countries
Resource use by humans
is now 1/3 greater than the
amount that nature can
sustainably replace