Population Ecology:

1
Population Ecology

• How Do Organisms Interact to Form Populations?

2
What is Ecology?

• Environmental concern is not ecology.
• However, studying vultures scavenging a lion kill
  is of interest to ecologists.
• They are also interested in rats scavenging a
  dumpster in urban America.

3
Ecology is a Branch of Biology

• Ecology
• is the study of organisms in relation to their
  environment

4
Ecology is a Branch of Biology

• Important key factors to remember about ecology
• It is not a social cause
• It is not a movement
• It is not a natural history
• It is not an interesting story about animals in
  nature
• It is a science
• Ecology includes quantitative measurements and
  addresses energy needs, efficiencies and balances.

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Foundations of Modern Ecology

• Biogeography
• Addresses location and environment of living
  organisms.
• Environmental physiology
• How does living in a particular environment
  affect an animals structure and function?
• Limnology
• Study of freshwater ponds and lakes.
• Behavioral ecology
• How does living in a particular area with a
  particular set of characteristics affect the way
  animals behave?

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Foundations of Modern Ecology
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Three Main Branches of Ecology

• Population Ecology
• Focuses on dynamic changes occurring in one
  population or species.
• Systems Ecology
• Studies the dynamics of complex ecological
  communities and is a holistic approach.
• Applied Ecology
• Newest branch
• Predicts the outcomes of human activities and
  recommends courses of action to mitigate certain
  of those activities.

8
Major Task Study Populations

• Humanity has an innate and almost unlimited
  ability to procreate, but a limited ability to
  produce food.
• Humans populations tend to grow and outstrip
  their ability to feed themselves.
• Leads to problems.

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Factors That Influence Population Size

• Population growth rate
• Determined by
• Natality or birth rate
• Death rate
• Also influenced by immigration and emigration.
• Expressed mathematically
• r (b-d) (i-e)

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Factors to Consider When Studying Population

• Straight forward expression of population size is
  absolute number.
• Count up all the individuals in the population.
• More frequently used is density.
• The number of individuals per unit area.

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Factors to Consider When Studying Population

• Range
• The geographic area in which a population or
  species lives.
• Habitat
• Includes the areas the species finds all its
  specific needs.
• Determining the area of the habitat of a species
  can be difficult.

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How Do Populations Grow?

• Two opposing forces affect population size
• Biotic potential
• a populations ability to reproduce.
• Environmental resistance.
• Consists of factors that limit growth.

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Exponential Population Growth

• Under ideal conditions wherein environmental
  conditions are low, populations grow
  exponentially.
• The more the individuals, the faster the
  population grows.
• (dN/dt) rN

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Logistic Population Growth

• Initially populations will grow exponentially.
• However, population growth will slow due it
  reaching a carrying capacity.
• The number of individuals the environment can
  support.

15
Factors That Limit Population Growth

• Density-dependent
• The effect of the factor depends on the
  population density.
• Examples space, predators, disease and food

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Factors That Limit Population Growth

• Density-independent
• Effect of this factor is unrelated to the density
  of the population.
• Examples drought, freezing temperatures

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Two Patterns of Population Growth

• Studying population size can help scientists
  predict how it might change.
• K-selected
• Species that possess characteristics that allow
  them to typically live under stable conditions
  near their carrying capacities
• R-selected
• Species possess characteristics that have them
  typically living in unstable conditions where
  they maximize their reproductive potential
• Most species live somewhere in between

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Two Patterns of Population Growth
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Two Patterns of Population Growth
20
Age Structure Diagrams

• The numbers of individuals in each age class are
  arranged in rows, starting with the youngest on
  the bottom.
• Numbers separated by gender.
• The length of the row indicates the number of
  individuals.

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Age Structure Diagrams
Based on these diagrams, what conclusions can you
draw about these populations?
22
Populations Differ in Their Longevity Patterns

• Two types of longevity patterns
• Physiological
• The life span of the individual under ideal
  conditions.
• Ecological
• The age to which an individual might be expected
  to live in a given environment.

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How Do Populations Interact?

• Populations share space with other populations
• Leads to interactions among them and makes them
  interdependent.
• Niche
• All aspects of the biological and physiological
  environment that are important to a species.

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When Populations Compete, Both are Harmed

• Competitive exclusion principle
• Two species cannot coexist while exploiting the
  same resources.
• Examples
• Paramecium
• Wasps
• Barnacles

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When Populations Compete, Both are Harmed

• Resource partitioning
• The use of resources that are scarce in a given
  environment by different species at different
  times, different places or in different ways.

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Predator-Prey Interactions

• One population benefits at the expense of the
  other.
• Results in the fates of predator and prey
  populations being intimately intertwined.

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Predator-Prey Interactions

• Population size fluctuates due to this
  relationship
• Prey populations may increase, followed by
  increases in predator populations,
• followed by decrease in prey populations,
  followed by decrease in predator populations

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Predator-Prey Interactions

• Predation may lead to extinction
• Seen with introduced species.
• Two categories of predator-prey relationships.
• Plant-herbivore
• Herbivore-carnivore

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Plant-Herbivore Interactions

• Herbivores have developed adaptations to deal
  with fluctuations in available food supplies
• Put on extensive layers of fat during seasons of
  abundance.
• Some will migrate to where food is available.
• Others hibernate during seasons of hardship.
• Respond to seasons of scarcity by making do with
  foods of relatively low nutritional value.

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Plant-Herbivore Interactions

• Plants respond to herbivores by
• Producing enough tissue for herbivores and still
  survive
• Produce distasteful chemicals that deter further
  feeding
• Produce chemicals that affect herbivores
  physiology

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Herbivore-Carnivore Interactions

• Compared to plant material, animal material is
• Easier to digest
• Energy and nutrients are more concentrated
• Drawback
• Herbivores are mobile
• Dangerous when cornered

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Herbivore-Carnivore Interactions

• Mimicry
• When an animal resembles something that it is not
• Looking like something in the environment that
  predators would avoid .

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Mimicry

• Two types
• Müllerian
• When different species, each of which is
  dangerous, announce their undesireableness to
  predators with similar coloration
  characteristics.
• Batesian
• When one species benefits from resembling the
  coloration of a dangerous species as a strategy
  to confound or discourage predators.

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Symbioses

• When populations form intimate associations
• Three types
• Parasitism
• Commensalism
• Mutualism

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Parasitism

• One species benefits at the expense of the other
• Examples
• Tapeworms
• Mosquitoes
• Generally does not result in extinction of the
  host
• Can reduce population numbers

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Commensalism

• One species benefits while the other is seemingly
  unaffected.
• Examples
• Sea anemones growing on the backs of crabs

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Mutualism

• Intimate relationships in which both species
  benefit.
• Most fascinating and important relationships
  known in biology.
• Example
• Flowers and pollinators