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Biological Communities and Species Interactions

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Formica rufibarbus

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Atelopus, Dendrobates: more charismatic species

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What questions are asked about “species”?

• How do we protect species we want? Multiple species make up “biodiversity” Endangered species receive special

attention “Charismatic species” focus attention

• How do we get rid of species we don’t want? Agricultural pests Invasive species that reduce biodiversity Species that create health problems

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What influences the diversity of a community of species?

• What do we mean by “species”?• What promotes addition to a community?

Local speciation Dispersal to new localities

• What facilitates survival in the space?• What allows reproductive success?

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What is a “species”?

• Consider the group of fish known as “darters”

• Darters share many characteristics Live in relatively fast-

flowing streams Share a common

general shape Most reproduce in

gravel beds Eat insects and other

fish

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Widespread vs. endemic

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Disjunct Distributions (metapopulations)

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Isolation by Distance

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What influences the diversity of a community of species?

• What do we mean by “species”?• What promotes addition to a community?

Local speciation Dispersal to new localities

• What facilitates survival in the space?• What allows reproductive success?

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Adding “species” – Evolutionary divergence in isolation

• Natural Selection - Members of a population best suited for a particular set of environmental conditions survive and reproduce more successfully than competitors. Acts on pre-existing genetic diversity. Limited resources place selective pressures

on a population.• Genetic Drift – Isolated populations

accumulate genetic differences

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Speciation

• Given enough geographical isolation or selective pressure, members of a population become so different from their ancestors that they may be considered an entirely new species. Isolation of population subsets, preventing

genetic exchange, can result in branching off of new species that coexist with the parental line after barriers are removed.

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Galapagos Finches

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Faster addition of species: Dispersal

• All species have dispersal phases in their life history

• Distances vary, depending on the mode of transportation

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What influences the diversity of a community of species?

• What do we mean by “species”?• What promotes addition to a community?

Local speciation Dispersal to new localities

• What facilitates survival in the space?• What allows reproductive success?

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What promotes survival and reproduction?

• Critical Factors and Tolerance Limits Reflect past evolution (Adaptation, Natural

Selection, Speciation) Establishes appropriate habitat (Place or

set of environmental conditions where a particular organism lives)

• Ecological Niche Resource requirements

• Species Interactions

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What promotes survival? Critical Factors and Tolerance Limits

• Von Liebig proposed the single factor in shortest supply relative to demand is the critical determinant in species distribution. Shelford later expanded by stating each

environmental factor has both minimum and maximum levels, tolerance limits, beyond which a particular species cannot survive.

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Tolerance Limits

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Competition

• Interspecific - Competition between members of different species.

• Intraspecific - Competition among members of the same species. Often intense due to same space and

nutritional requirements.- Territoriality - Organisms defend specific

area containing resources, primarily against members of own species.

Resource Allocation and Spacing

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Symbiosis

• Symbiosis - Intimate living together of members of two or more species. Commensalism - One member benefits

while other is neither benefited nor harmed.- Cattle and Cattle Egrets

Mutualism - Both members benefit.- Lichens (Fungus and Cyanobacterium)

Parasitism - One member benefits at the expense of other.

Humans and Tapeworms