Introduction to Community Ecology

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Introduction to Community Ecology

• Ecology is the science of communities. A study
  of the relations of a single species to the
  environment conceived without reference to
  communities and, in the end, unrelated to the
  natural phenomena of its habitat and community
  associations, is not properly included in the
  field of ecology. -Victor Shelford (1929)

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Community

• estimated 1.5 million 30 million species that
  live on earth today
• fraction of those species that coexists in space
  and time and interact with one another (and the
  environment)

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Organizational Hierarchy

• sub-organism
• whole organism
• population
• community
• ecosystem
• landscape

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Organizational Hierarchy

• sub-organism
• whole organism
• population individuals of the same species
• community
• ecosystem
• landscape

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Organizational Hierarchy

• sub-organism
• whole organism
• population
• community multiple species interacting (biotic
  elements)
• ecosystem
• landscape

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Organizational Hierarchy

• sub-organism
• whole organism
• population
• community
• ecosystem biotic plus abiotic features
• landscape

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Organizational Hierarchy

• sub-organism
• whole organism
• population
• community
• ecosystem
• landscape
• separations and distinctions between levels are
  artificial (Vitousek 1990)
• should understand processes at least one level
  and one down from your level of interest

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Goal of Community Ecology

• to understand origin, maintenance, and
  consequences of biological diversity

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Major Questions

• How do communities change in space/time?
• What are the organizing features of communities?
• How many species occur and why?
• Which species are dominant and why?
• Which species are common or rare and why?
• What is the relationship between species
  composition and functional diversity?

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Shifts in Community Ecology

• descriptive to experimental
• mathematical modeling
• improvements in statistical techniques

descriptive
models
Modern community ecology
experiments
statistics
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Challenges

• taxonomy
• complexity of interactions
• changing environment
• natural
• anthropogenic
• search for generality
• experimentally intractable

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Long-term Temporal Processes

• evolutionary time

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Short-term Temporal Processes

• affect species occurrences and dynamics
• difficult to simulate/manipulate/plan for

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Temporal trends

• compare sites that differ in time since
  disturbance to study indirectly community change
  (chronosequence)
• assumption sites are ecologically identical,
  except for time since disturbance

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Glacial Retreat Chronosequence
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Spatial Patterns

• species composition may have some degree of
  spatial dependency

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Subsets of Communities

• Guilds similar functions or use similar
  resources
• Taxocene taxonomically related group
• Trophic levels acquire energy in similar ways
• Food chains/webs energy flow between species in
  communities

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Biome

• general type of community
• terrestrial biomes distinguished mostly by their
  plants (see p.9 11, Morin for expanded list)
• determined by climate
• precipitation
• temperature

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Physically Defined Communities

• species found together
• boundaries of habitats
• discrete
• gradual

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Taxonomically Defined Communities

• use major dominant taxa
• Longleaf pine/wiregrass savannas (Pinus
  palustris and Aristida stricta)

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Statistically Defined Communities

• similarity in species composition
• loosely or tightly associated species

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Interactively Defined Communities

• species may be in the same geographic area but
  not interact
• defined by those species that influence each
  others abundances
• of 7 common salamanders in North Carolina
  mountains, only 2 interact (Hairston 1981)

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Community Properties
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Richness

• number of species
• difficult to obtain
• does not include commonness and rarity
• sufficient sampling effort?

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Diversity

• indices of diversity take into account richness
  AND abundance AND evenness
• How evenly distributed are individuals among the
  species present?
• imagine 2 communities with 10 species and 100
  individuals
• One community has 91 individuals of one species
  and 1 individual in the other 9 species.
• A second community has 10 individuals of each
  species present.
• Which is the most diverse?

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Diversity

• takes into account richness AND abundance AND
  evenness
• How evenly distributed are individuals among the
  species present?
• imagine 2 communities with 10 species and 100
  individuals
• One community has 91 individuals of one species
  and 1 individual in the other 9 species.
• A second community has 10 individuals of each
  species present.
• Which is the most diverse?

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Alpha, Beta and Gamma Diversity

• Alpha diversity diversity within a single type
  of habitat
• Beta diversity turnover in species composition
  among different habitats
• Gamma diversity diversity present across the
  broader landscape