Population Ecology

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Population Ecology
Caribou herd Alaska
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Ernst Haeckel

• Coined the term Ecology from the Greek root
  Oikos meaning house ecology is the study of
  Natures house - 1866

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What is ecology?

• Ecology is the scientific study of the
  distribution and abundance of organisms and the
  interactions with the biotic and abiotic world
  that determine distribution and abundance. -
  Begon, Harper and Townsend

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We study interactions via

• Description
• Modeling verbal, graphic, or mathematical
• Experiments in Nature

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Why are ants so successful?
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E.O. Wilson Ant Expert and Ecologist
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Population Ecology

• A population is a group of individuals of the
  same species that live in a particular area and
  have the potential to interbreed.

Flock of Starlings at Dusk U.K.
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Population Structure
Ecological properties outlined in yellow
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Population Dynamics
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The Fundamental Equation of Ecology Harper 1977

• ? N B D I E
• Change in Number Births Deaths Immigration
  - Emigration

John L. Harper 1925-2009
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Fundamental Equation of Ecology

• ?N B - D I E
• Change in number births deaths immigration
  emigration
• Or - N1 N0 B D I E
• Where N1 population in the future N0
  population now
• We can group immigration and emigration together
  as dispersal, often considered to be equal to
  zero as many come in as leave, e.g. I E
• So then N1 N0 B D

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Organisms normally at high density
Termites
Bluegrass
Deer mice
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Organisms normally at low density
Luna Moth
Grey Wolf
Walnut
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Population Distributions in Space
(b) Uniform. Birds nesting on small islands,
suchas these king penguins on South Georgia
Islandin the South Atlantic Ocean, often exhibit
uniformspacing, maintained by aggressive
interactionsbetween neighbors.
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Life History Characteristics

• Growth for at least part of their life history,
  all organisms grow by assimilating energy and
  nutrients growth rate is critical
• Change of form - many organisms have dramatically
  different forms or stages in their life cycle
• Dispersal - at some time in their lives, most
  organisms go through dispersal
• Timing of reproduction has a strong influence on
  population growth - typically the earlier a
  species starts reproduction, the faster the
  population will grow
• Age distribution - Populations also have a
  characteristic age structure or distribution -
  there will be certain numbers of young
  individuals, mature individuals and old
  individuals
• Size at birth or germination
• Number, size and sex of offspring
• Age at Death

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Life History - Growth

• Growth for at least part of their life history,
  all organisms grow by assimilating energy and
  nutrients growth rate is critical

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Golden Mayfly

• Mayflies are in the order Ephemeroptera the
  adults do not feed and live as little as 24 hours

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Life History Change of Form

• Change of form - many organisms have dramatically
  different forms or stages in their life cycle

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Life History - Dispersal

• Dispersal - at some time in their lives, most
  organisms go through dispersal

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Dispersal Spiders Ballooning
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Dispersal Milkweed Seeds
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Dispersal Champion Arctic Tern
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Dispersal vs. Migration

• Dispersal usually refers to the movement of
  individual organisms
• Migration is the directed, mass movement of large
  numbers of individuals in a population from one
  location to another

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Life History Timing of Reproduction

• Timing of reproduction has a strong influence on
  population growth - typically the earlier a
  species starts reproduction, the faster the
  population will grow
• However, in many species, the parent needs to
  gain sufficient energy or knowledge to be able to
  reproduce successfully, so often reproduction may
  be delayed until the parent reaches a particular
  age or size

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Life History Age Distribution

• Age distribution - Populations also have a
  characteristic age structure or distribution -
  there will be certain numbers of young
  individuals, mature individuals and old
  individuals

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Population Pyramid for France on Jan. 1, 1966
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Population Pyramid for Canada
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Life History Trade-Offs

• As we saw in the discussion of timing of
  reproduction, there are frequently trade-offs in
  life history characteristics

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Black backed gull
Females that lay large clutches have lower
survival than females with smaller clutches
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Semelparous - Species with a single reproductive
event
Pacific Salmon
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Agave Century Plant Reproduces Once
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Samoan Palolo Worm
Palolo epitokes swimming
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Australian Red-Backed Spider
Female Male
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Iteroparous - Few offspring produced at one time,
but many reproductive events in a lifetime
African elephant
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White Oak
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General Relationship between Offspring Size And
Number of Offspring
Many
Number Of Offspring
Few
Small Large
Offspring Size
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Trade off between longevity and number of
offspring
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Phylogenetic constraints

• Evolution of species life history is limited by
  the species evolutionary history

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Phylogenetic constraints on offspring number in
Laysan Albatross
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Phylogenetic constraints on offspring number in
primates
Gorilla nursing infant