Download Species richness and diversity

Species Communities and Niches
Species richness
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The number of species in a community
Increases near equator
Relative abundance
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population of a given species in a specific size ecosystem
Compares the percent of each species
EX. Percent of mallards in pond compared to total bird
population
Species diversity
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Relates the number of species to the
“relative abundance” of each
Species area effect
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Larger areas usually contain more species
than smaller ones
Evident on islands
Individualistic concept
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Community is made of nothing more than
different species that happen to be living
in same area
Holistic concept
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Communities are an integrated unit that
depend on each other for survival.
“super organism”
Trophic cascade
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Interactions among species
(plant – animal) promote species richness.
Elk eat Aspen trees
Wolves eat elk
Ex. wolves influence vegetation
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Wolf predation near aspen trees increases
Elk change browsing habits
Aspen increase
Community stability
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Resistance to change
Biodiversity increases stability
Biodiversity
Ecological Niche concept
Niche
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The role an organism fills in its community
Niche determined by
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Habitat
Place in food chain
Specific food types
When they eat or hunt
Great horned owl and red tailed
hawk have different niches
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Both eat small
rodents
Both live in same
area
BUT owls hunt at
night, hawks
hunt during day
Fundamental niche
• Potential niche – without any competition
Realized niche
• The part they actually use due to
competition. Usually smaller
Competition exclusion
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One Species is eliminated from a
community because of limited resources.
Can not occupy same niche
Example paramecium
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P. Caudatum paramecium declines in
presence of other paramecium
Resource partitioning
When several similar species subdivide a
niche for resources
Ex. 5 different warbler species eating
different areas of a tree
Character displacement
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One Phenotype is selected because of
competition
Ex anoles.
on same island there are populations that
eat different things and occupy different
niches,
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Conceptually we can look at the environment as a limited resource that can be shared by one or
more species Here, an environmental resource, shown in green, must be shared between the
little blue and big red species. It's possible to fill the environments with lots of little blue blocks, a
few red blocks, or a mixture of reds and blues. Note that in this example, four blues equal one
red individual (the blues need 1/4 of the space, food, or other resource as red individuals). From
the environment's point of view, the blues are 0.25 of a red (species A as B; we'll term this as
"a"), Red individuals are worth 4 blues (species B as A; we'll call this term "b"), Although in this
example the two species are symmetric, they don't necessarily have to be.
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Depending on the amount of overlap, competition may be nonexistent, weak or
strong (Figure 3). Fitness varies with the strength of competition. In areas of low
fitness few if any offspring will be passed on to the next generation. Organisms with
medium fitness will pass on some offspring to the next generation but not as many
as those with high fitness
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Figure 4 shows some of the possible outcomes for our two species. Here, the
resource continuum represents the limited resource that is at the center of the
competition. As an example, assume that the resource is seeds and the X axis is seed
size (small, medium, and large). Let's further assume that species 1 and 2 are
finches. Finch 1 takes mostly smaller seeds while . finch 2 take the larger seeds.
Both, however, take medium-sized seeds
Character displacement
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When similar species share same location
they have greater change in traits
(character) ex. Darwin's finches
Different island = similar size
Same island = greater
difference in size