Community Ecology

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Community Ecology
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Two Views of Communities

• Gleason - individualistic concept. Communities
  are chance assemblages of species in the same
  area because they happen to have similar abiotic
  requirements.
• Clements - interactive concept. Communities are
  closely linked assemblages with mandatory biotic
  interactions that cause the community to function
  as an integrated unit (superorganism)

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Henry Gleason (1882-1975)Ecologist and strong
advocate for the concept of "individualistic
ecology
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Frederick Clements(1874-1945)Successional
ecologist. Strong advocate of the "dynamic"
school of ecology
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Various communities differ in both species
richness and relative abundance.

• Species richness is the number of species making
  up a community
• Relative abundance relates to how many
  individuals of each species are present in the
  community

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• Interspecific interactions are between species
  within a community

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Coevolution.

• The mutual influence on the evolution of two
  different species interacting with each other and
  reciprocally influencing each others adaptation.
  E.g., flowers and pollinators

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Predator-prey interactions

• Predators and their prey are obviously
  interacting. In some cases predators may play a
  role in the regulation of prey populations.
  Predation is good for the predator but bad
  for the prey. Thus prey have evolved defenses
  such as crypsis, fleeing, mechanical barriers,
  chemical deterrents mimicry (Batesian harmless
  mimic and Mullerian harmful mimic).

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Crypsis
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Aposematic coloration
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Batesian mimic
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Mullerian mimic
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Posturing (the very toxic rough skinned newt of
the PNW)
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Interspecific Competition

• 1. Interference involves actual fighting
• 2. Exploitative involves the use of the resource
• 3. Competitive Exclusion Principle (by Lotka and
  Volterra, and then tested by Gause in the
  laboratory).

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Gauses data
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Other studies

• Remember the salamanders
• Barnacles
• Warblers

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Niche

• As a hypervolume according to G. Evelyn Hutchison

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Possible interspecific interactions

• Mutualism
• Predation or parasitism -
• Commensalism 0
• Spiteful --

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Mutualism

• Sea anemone clown fish giant moray eel
  Labroides

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Predation and Parasitism

• Ringneck snake eating
• salamander

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Commensalism

• Shrimp hitchhiking on fire urchin

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Spiteful

• Try to think of examples of spiteful interactions
  between members of two different species

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Community Structure

• Factors that influence the structure (species
  composition) of communities include abiotic,
  resource availability, adaptability of the
  species, interspecific interactions and overall
  patterns and history.
• B. Interspecific competition versus predation
• 1. Some ecologists view interspecific
  competition as one of the most important forces.
• 2. However, predators may affect the community
  structure (e.g., keystone predators).
• 3. Communities may be random assemblages

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Succession

• Over time a community will change (as it ages).
  Succession is the pattern of colonization of an
  area where successional stages are sequentially
  replaced by new stages, basically changing from
  simple to more complex.

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Primary (1o) Succession

• Starts with area devoid of life (e.g., after a
  glacier retreats)

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Secondary (2o) Succession

• Occurs when area is exposed to some perturbation
  that takes it back to an earlier successional
  stage (e.g., hurricane)

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Ecosystems

• Ecosystems consist of the biota and the abiotic
  factors that affect them in a given area. Common
  characteristics of Different Ecosystems include
  primary producers, consumers, detritovores and
  decomposers, food chains or more realistically
  food webs, and biogeochemical cycles through
  which nutrients move

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Food web and Food chain
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Energy transfer

• Sunlight energy is transferred to cpe in ATP and
  then glucose (photosynthesis)- energy is not
  created nor destroyed just converted and some is
  lost as heat
• CPE in glucose of grass is transferred into cpe
  in ATP by bunny and also by grass (aerobic
  respiration) no creation, heat loss
• CPE in bunny tissue transferred into cpe in ATP
  by owl (also aerobic respiration)
• This continues throughout the trophic (feeding)
  levels of the food web

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Limits to number of trophic levels, Pyramid of
energy

• This occurs because of the second law of
  thermodynamics

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Applies to humans as well

• Human
• Plants
• Vs.
• Human
• Other animal
• Plants

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Pyramid of numbers
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Pyramid of biomass
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The Impact of Humans on Ecosystems

• A. Nutrient Enrichment
• B. Acid Precipitation both wet and dry
• C. Toxins. Biological Magnification involves
  the increased concentration of toxins in
  successive trophic levels (see figure 54.23) and
  Bioaccumulation involves the buildup of toxins in
  an individual organism.
• D. Increasing CO2 levels and Global Climate
  Change (see figure 54.24)
• E. Ozone Depletion (see figure 54.27 and 54.28).

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Nutrient enrichment (eutrophication)
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Acid precipitation
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Toxins Bioaccumulation

• Bioaccumulation is a general term for the
  accumulation of substances, such as pesticides
  (DDT is an example), methylmercury, or other
  organic chemicals in an organism or part of an
  organism. The accumulation process involves the
  biological sequestering of substances that enter
  the organism through respiration, food intake,
  epidermal (skin) contact with the substance,
  and/or other means. The sequestering results in
  the organism having a higher concentration of the
  substance than the concentration in the
  organisms surrounding environment.

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Toxins Biomagnification

• Biomagnification is the bioaccumulation of a
  substance up the food chain by transfer of
  residues of the substance in smaller organisms
  that are food for larger organisms in the chain.
  It generally refers to the sequence of processes
  that results in higher concentrations in
  organisms at higher levels in the food chain (at
  higher trophic levels). These processes result in
  an organism having higher concentrations of a
  substance than is present in the organisms food.
  Biomagnification can result in higher
  concentrations of the substance than would be
  expected if water were the only exposure
  mechanism.

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Global Climate Change
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Ozone Depletion