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The Evolution-Ecology Connection
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Evolution: ‘unfolding’ –
process by which species are
altered
Species change over
generations
New species appear
Species become extinct
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How are evolution and ecology
related?
•
Ecology involves
understanding of relationships
of organisms with each other
and with their environment
•
Evolution involves changes in
species in response to
interactions with each other
and with their environment…
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Contributions to Modern Evolutionary
Thought
“Malthusian catastrophe”
• Thomas Malthus – economist, social
philosopher – populations of all organisms
eventually out-grow available resources
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• Gregor Mendel (1822-1884): concepts and
patterns of inheritance
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Catastrophism Vs Uniformitarianism.
• Catastrophism- he Earth’s surface has been
scarred by catastrophic natural disasters
• Charles Lyell: theory of uniformity – surface of
earth has gradually changed, earth much older
than previously recognized
"The Present is the Key to the Past"
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Darwin’s Voyage
Fig. 2.3
Charles Darwin:
synthesis of theory of
evolution based on
natural selection
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Out of this study grew several
related theories:
• one, evolution did occur;
• two, evolutionary change was gradual, requiring
thousands to millions of years;
• three, the primary mechanism for evolution was
a process called natural selection; and
• four, the millions of species alive today arose
from a single original life form through a
branching process called "speciation."
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Forces driving evolution:
over-reproduction
genetic variability
selective pressure
environment –(food, temperature, etc.)
disease
predators
survival and reproduction of organisms
best suited to their environment
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• Read Scot Norris’ paper Evolution's "Driving Force" Shifts Based on
Behavior, Study Says
http://news.nationalgeographic.com/news/2006/11/061116-lizardevolution.html
• Read Jonathan Losos' paper "Adaptation and speciation in Greater
Antillean anoles"
http://biosgi.wustl.edu/%7Elososlab/losos.2004.adaptivespeciationb
ook.pdf
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Genetics and Evolution
• Trait: appearance/ability to carry out some
process
 Phenotype: appearance of an organism
due to a specific trait or combination of
traits
• Gene: genetic information (region on a
chromosome) which codes for a specific
trait.
 Allele – variant form of a gene
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Natural selection can
favor, disfavor, or
conserve the genetic
make-up of a
population:
 Stabilizing Selection
 Directional Selection
 Disruptive Selection
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•
Stabilizing Selection- also known as
‘Purifying Selection’
Stabilizing selection acts to impede changes
in a population by acting against extreme
phenotypes and favoring average
phenotypes.- prevents divergence from form
and function but genetic diversity decreases
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•
Directional Selection
Directional selection leads to changes in
phenotypes by favoring an extreme
phenotype over other phenotypes in the
population. Increase frequency independent
of dominance
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•
Disruptive Selection- also called
‘Diversifying selection’
Disruptive selection creates bimodal
distributions by favoring two or more extreme
phenotypes over the average phenotype in a
population.- driving force of sympatric
speciation- (Finch population Darwin)
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Fig. 2.18
‘Ecosystems’ ability to
absorb shocks and
disturbances
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• What is a species?
‘A group of similar appearing organisms
which share the same gene pool’
• Species evolve to fill different niches
• Example: Finch evolution in Galapagos
Islands
• Result: Radial Evolution
– Single ancestral form
– Many generations  unique species for
different niches
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Fig. 2.10
Speciation of Finch on Galapagos Islands- C. Darwin
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How do new species arise?
1. Sympatric speciation
2. Allopatric speciation
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Sympatric speciation:
• occurs as a species fills different niches
within the same habitat or geographic area
– Spread of species into new areas
– Founding population in isolated location
– Geologic changes – gradual process
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Allopatric speciation:
• spatial isolation – occurs due to
geographic isolation
– Genetic changes (as ploidy levels in plants)
– Disruptive selection: divergent genotypes
favored
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Geographic Variation Within Species
• Cline: measurable, gradual change in a
trait over geographic region
• Ecotype: Population adapted to particular
local environment
• Geographic isolate: reproductively isolated
populations
– subspecies
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Gause’s Lawcompetative exclusive principle
Georgii Frantsevitch Gause
• a theory which states that two species
competing for the same resources cannot
stably coexist, if the ecological factors are
constant. Either of the two competitors will
always have an advantage over the other
that leads to either the extinction of the
inferior competitor or its evolutionary shift
towards a different ecological niche.
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Geographic Isolation
of Ensatina
escholtzii
populations in CA
• ‘ring species’ –
geographically
isolated populations
surround
uninhabitable area
• Adjacent
populations can
interbreed
• Reproductively
incompatible at
extremes (black)
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Local
E.escholtzii
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Changes within a species are due to changes
in its gene pool – causes:
• Selective pressures
• Genetic drift and bottleneck effects
– Isolated populations
– Effect greater in small populations
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Variation Within Populations
•
Variation in Plant Populations
 Many plant species differ
dramatically in form from one
elevation to another.
 Clausen et.al. found
evidence of adaptation by
ecotypes to local
environmental conditions
in Potentilla glandulosa.
 Distinctive ecotypesdistinct entity of animal
or plant or organism
closely linked to its
ecological surroundings
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Variation in Plant Populations
•
Molecular and Morphological Information
 Hansen et. al. used randomly amplified
polymorphic DNA (RAPD) along with
morphological data to support separation
of three species of Potentilla.
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•
•
Ecotypes – Potentilla
glandulosa – sticky
cinquefoil
3 ecotypes:
 Alpine
 Midelevation
 lowland
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• How genetically different are ecotypes?
• Work with Potentilla nivea (a species
complex)
• Morphological (appearance) observations
suggest three species
• Molecular analysis via RAPID study supports
morphological species distinction
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Fig. 8.6
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Summary:
• Organisms become ‘tailor made’ for
their role niche within an environment
by processes of evolution
• New species arise from preexisting
species
• New species arise as organisms
become reproductively isolated
• Reproductive isolation may often
result in genetically different
populations
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Questions
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How do we know that a species is a species if we
do not directly observe whether it can interbreed
with other organisms?
If one population is the ancestor to another, how do
we decide if they are more than one species?
Does extinction imply mistakes by an "intelligent
designer"?
How, in terms of Gause's law, does a catastrophic
event influence subsequent evolutionary events.
Which (and why) are more likely to become extinct,
a highly specialized species extremely well
adapted to a particular niche, or a less specialized
generalist?
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