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Evolution and Ecology
Chapter 2
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Outline
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Darwin
Theory of Natural Selection
 Finch Beaks
Clusters of Species
 Drosophila - Cichlids - Buttercups
Ecology
Patterns of Population Growth
Life History Strategies
Human Populations
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Darwin and the HMS Beagle
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1831 - 22 year old Charles Darwin was
selected to serve as naturalist on a five-year
mapping expedition around the coast of
South America.
 Observed series of related but distinct
forms of life on Galapagos Islands near
Ecuador.
- Formed an explanation that natural
selection drives evolution.
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Darwin’s Evidence
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At the time, common belief was that the earth
was only a few thousand years old.
Darwin was, at first, fully convinced species
were immutable.
 During the voyage, he became intrigued
that plants and animals on the young
volcanic islands resembled those on
nearby South American coast.
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The Theory of Natural Selection
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Darwin studied Thomas Malthus who pointed
out populations of plants and animals tend to
increase geometrically.
 Unchecked reproduction should spiral out
of control.
Darwin was also aware of variation and
artificial selection in domesticated animals.
 Proposed such selection could occur in
nature (Natural Selection).
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The Theory of Natural Selection
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Darwin drafted a manuscript in 1842, but
shelved it until 1858 when he received a
similar manuscript from Alfred Wallace.
 Origin of Species published in 1859.
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Finch Beaks
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Darwin collected 31 finch specimens from
three islands in 1835.
 Ornithologist John Gould determined they
were a closely related group of distinct
species, all similar except for their bills.
- Correspondence was found between the
beaks and the food source of each
specimen, leading Darwin to conclude
the beaks had been shaped by
evolution.
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Clusters of Species
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Adaptive Radiation - Process producing a
cluster of species, occupying a series of
similar habitats, all evolving from a recent
ancestor.
Galapagos finches comprise four groups:
 Ground finches
 Tree finches
 Warbler finch
 Vegetarian finch
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Hawaiian Drosophila
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At least 1,250 species of Drosophila in the
world; more than a quarter found only in the
Hawaiian islands.
 Native Hawaiian flies are closely
associated with native plants.
- When ancestors first reached the
islands, they probably encountered
many empty niches, thus facilitating
diversification and speciation.
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Lake Victoria Cichlid Fishes
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Lake Victoria was home to a cluster of over
200 cichlid species.
 Researches estimate first cichlid entered
the lake 200,000 years ago from the Nile.
- Many species probably originated as the
lake dried down 14,000 years ago,
isolating populations.
 Diversity reduced due to competition
from exotic species.
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New Zealand Alpine Buttercups
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More species of Alpine Buttercups
(Ranunculus) grow on two islands of New
Zealand than all of North and South America
combined.
 Research found evolutionary mechanisms
behind high diversity is recurrent isolation
associated with recession of glaciers.
- Repeated invasion with glaciation
followed by isolation.
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Ecology
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Earnst Haekel (1866) - Study of how
organisms interact with their environment.
 Populations - Individuals of the same
species living together.
 Communities - Populations of different
species living and interacting.
 Ecosystems - A collection of communities
and associated non-living factors.
 Biomes - Major distinct terrestrial
assemblages that occur over a wide area.
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Biomes
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Ecosystems
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Almost all energy flowing through
ecosystems ultimately comes from the sun.
 Sun - Plants - Herbivores - Carnivores
- Food Chain
 Useful energy is lost at each step,
severely limiting the number of steps
in a food chain.
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Patterns of Population Growth
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Innate Capacity for Increase - Rate a
population grows in the absence of limits.
Realized Rate of Population Increase (r) Number of individuals added to the
population minus the number lost.
r = (birth + immigration) - (death + emigration)
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Exponential Growth
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To determine population growth rate, r must
be adjusted for population size
 Population Growth rate = r N
- r = realized rate of population growth
- N = number of individuals in population
Exponential Growth
 Rapid at first, but slows down as resources
become exhausted.
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Carrying Capacity
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Carrying Capacity (K) - Number of individuals
that can be supported indefinitely in a
particular area.
 Population Growth Rate = r N (K-N/K)
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Life History Strategies
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Adaptation of reproductive rate to the env.
 r - rapid growth, no stabilization
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
K - slow growth, reaches carrying capacity
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Human Populations
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Throughout most of history, human
populations have been regulated by food
availability, disease, and predation.
 Starting in 1700’s, technological changes
enabled humans more control over their
environment and allowed escape from the
confines of logistic growth.
- Expanded carrying capacity
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Population Pyramids
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Demographic trends can be predicted only
when a population’s age structure and sex
ratio is considered.
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Uncertain Future
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Rapidly growing human population may
constitute the greatest future challenge to our
biosphere.
 Key element in continued growth is uneven distribution among countries.
- Rapid population growth in developing
countries will increase the gap between
rich and poor.
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Review
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Darwin
Theory of Natural Selection
 Finch Beaks
Clusters of Species
 Drosophila - Cichlids - Buttercups
Ecology
Patterns of Population Growth
Life History Strategies
Human Populations
Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies
Copyright © McGraw-Hill Companies Permission required for reproduction or display
Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies