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Lecture 24

BIO SCI 94 Lecture Notes - Lecture 24: Scarlet Kingsnake, Tritia Obsoleta, Cerithideopsis Californica

Biological Sciences
Course Code
Brandon Stuart Gaut

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Lecture 24: Couity Ecology
Community Ecology
Study of biological communities, which consist of all of the species that interact in a certain area
Life is in communities
Community ecologists studying the interaction among species ask:
o Why do some places have more species than others?
o How much competition between species occurs in nature?
Are they competing for resources?
Is one a predator and one a prey?
o What happens to a community after large changes--for example, after a volcano or increased
Ex: CA - wildfires
Species Interactions
4 types:
1. Commensalism: when one species benefits w/ no effect on the other species
Somewhat hard to prove definitively
2. Competition: 2 species competing for the same resource
3. Consumption: one species eats or absorbs nutrients from another species (includes herbivory,
predation and parasitism); it's a direct interaction
4. Mutualism: when 2 species interact in a way that confers fitness benefits to both
Species 1
Species 2
3 reasons species interactions are important
1. They help define the distribution and abundance of particular species
Ex: Tsetse fly & cattle in Africa
Ex: Lynx-hare interaction
2. Agents of natural selection
Differential reproductive success; "success" refers to the competition between individuals of
the same species
3. The outcome of interactions between species can be difficult to predict, b/c they vary over time &
Lowers the fitness of individuals b/c competitors are using some of the resources
Intraspecific: w/in species
o Differential reproductive success (natural selection)
o Exponential growth, logistic growth, density dependence
o When resources become limiting, individuals of the same species start to compete & that slows the
growth of populations
Interspecific: between species
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Niche: the range of resources that the species can use and/or the range of environmental conditions it
can tolerate
o Includes all aspects of its habitat, how it makes a living, & the physical environment in which it is
o Ex: niche defined in terms of seed size
*From textbook
o When the niche of 2 species overlap, they compete
*From textbook
2 outcomes
1. Symmetric competition: lessens fitness of both; they are equally good competitors -->
both species may persist in the 'niche overlap'
Will eventually lead to niche differentiation
2. Asymmetric competition: one species competes better than the other; the loser species
will be removed from the 'niche overlap'; this is called niche displacement
o 2 types of niches:
Fundamental niche: theoretical range of environmental conditions (including resources) in
which a species can live
Realized niche: the portion of the fundamental niche that a species actually occupies, due to
limiting factors such as competition w/ other species
Realized niche can only be the same size or smaller than the fundamental niche
o Niche displacement: one species outcompetes the other, so that one species loses its niche
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