Download Understanding Our Environment

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”?
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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?
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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”?
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Consider the group of fish
known as “darters”
Darters share many
characteristics
 Live in relatively fastflowing 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?
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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
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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
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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
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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?
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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?
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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
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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
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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
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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
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