Population Biology Concepts
• population ecology
• carrying capacity
• reproductive
strategies
• survivorship
Sunday, October 7, 12
Assigned Readings
Sunday, October 7, 12
•
Hardin, Garrett. “The Tragedy of the Commons,” Science, Volume
162, pp.1243-1248.
•
Wright, "Population Growth and Economic Development," pp. 5-6
•
Wright, 2.4 "The Human Presence," pp. 47-50
•
Wright, 3.4 "Implications for Human Societies," pp. 73-77
•
Wright, 4.1 "Dynamics of Natural Populations," pp. 82-85
•
Wright, 4.2 "Mechanisms of Population Equilibrium," pp. 85-94
•
Wright, 4.3 "Evolution as a Force for Change," pp. 95-102
Choose One
Please choose one of the following books to read this semester.
•
Eaarth: Making a Life on a Tough New Planet, by Bill McKibben, 2010
•
Hot, Flat, and Crowded: Why We Need a Green Revolution - And How It Can
Renew America, by Thomas L. Friedman, 2008
•
The World Without Us, by Alan Weisman, 2007
•
The Population Bomb, by Paul and Anne Ehrlich, 1968
Please complete this reading, as well as all highlighting and annotation, by
the date of our mid-term exam in December (TBA.)
Sunday, October 7, 12
Population Ecology
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Levels of Organization
• Biotic communities: grouping or assemblage of
plants, animals, and microbes.
• Species: different kinds of plants, animals, and
microbes in the community.
• Populations: number of individuals that make up
the interbreeding, reproducing group.
• Associations: how a biotic community fits into the
landscape.
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• Populations evolve by becoming genetically different.
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• Populations evolve by becoming genetically different.
• Genetic variations are the first step in biological
evolution.
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• Populations evolve by becoming genetically different.
• Genetic variations are the first step in biological
evolution.
• Genetic variations occur through mutations in
reproductive cells.
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When environmental conditions change, populations
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When environmental conditions change, populations
➡ Adapt
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When environmental conditions change, populations
➡ Adapt
➡ Migrate
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When environmental conditions change, populations
➡ Adapt
➡ Migrate
➡ Become extinct
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Arctic Fox
Northern
population
Early fox
population
Spreads north
and south
and separates
Different environmental
conditions lead to different
selective pressures and evolution
into two different species.
Gray Fox
Southern
population
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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.
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• Niches can be occupied by native and non-native species.
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• Niches can be occupied by native and non-native species.
• Non-native species may include invasive, alien, and exotic
species. They may spread rapidly. Not all are villains.
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• Niches can be occupied by native and non-native species.
• Non-native species may include invasive, alien, and exotic
species. They may spread rapidly. Not all are villains.
• Indicator species can be used to monitor environmental
quality: trout, birds, butterflies, macroinvertebrates, frogs.
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• Niches can be occupied by native and non-native species.
• Non-native species may include invasive, alien, and exotic
species. They may spread rapidly. Not all are villains.
• Indicator species can be used to monitor environmental
quality: trout, birds, butterflies, macroinvertebrates, frogs.
• Keystone species include pollinators and top predators.
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• Niches can be occupied by native and non-native species.
• Non-native species may include invasive, alien, and exotic
species. They may spread rapidly. Not all are villains.
• Indicator species can be used to monitor environmental
quality: trout, birds, butterflies, macroinvertebrates, frogs.
• Keystone species include pollinators and top predators.
• Foundation species create or enhance their habitat, benefiting
other species.
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Autotrophs = Producers = Self feeders
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Consumers = Heterotrophs
• Primary consumers = herbivores
= rabbit: eat plant material
• Secondary consumers =
carnivores = predators = coyotes:
prey are herbivores and other
animals.
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Trophic Categories
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Symbiotic Relationships
• Interspecific Competition
• Predation
• Parasitism
• Mutualism
• Commensalism
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Has the Southern Sea Otter recovered from the
brink of extinction?
• Habitat issues
• Hunted in early 1900s
• Partial recovery
• Why do we care?
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Resource Partitioning
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Population Dynamics
Populations differ in
• Distribution
• Numbers
• Age structure
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Changes in population structure are often due to:
• Temperature
• Presence of disease organisms or harmful chemicals
• Resource availability
• Arrival or disappearance of competing species
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Density Dependence and Critical Numbers
Factors of environmental resistance are either:
• density-independent: effect does not vary with population
density; e.g., adverse weather
• density-dependent: effect varies with population density;
e.g., infectious disease
• Critical number: the lowest population level for survival
and recovery
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Population Distribution
Population distribution
• Clumping
• Uniform dispersion
• Random dispersion
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Population Size
population change = (births + immigration) - (deaths + emigration)
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Mechanisms of Population Equilibrium
• Predator-prey dynamics
• Competition
• Interspecific
• Intraspecific
• Introduced species
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Keystone Species
• Predator-prey dynamics
• Competition
• Interspecific
• Intraspecific
• Introduced species
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Carrying Capacity
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No population can grow indefinitely.
• Biotic potential
• Intrinsic rate of increase (r)
• Individuals in populations with high r
• Reproduce early in life
• Have short generation times
• Can reproduce many times
• Have many offspring each time they reproduce
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Logistic Growth of a Sheep Population in
Tasmania 1800-1925
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Population Cycles for the Snowshoe Hare and
Canada Lynx
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Humans are not exempt from natural
population controls.
• Bubonic Plague, 14th century
• Irish Potato Famine, 1845
• The global AIDS epidemic.
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Reproductive Strategies & Survivorship
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Many offspring with
low parental care
J-shaped growth curve
Few offspring with
high parental care
S-shaped growth curve
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• Population stability is related to
“recruitment,” the percentage within a
generation that make it to reproductive
maturity and are able to reproduce.
• This is a direct function of mortality, and
can be largely influenced by reproductive
strategy.
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Lab & Field
Tragedy in the Making
Estimating Population Size
Population Growth in Lemna minor
Exploring Biodiversity
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