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Lecture 7

BIOLOGY 173 Lecture Notes - Lecture 7: Sonoran Desert, Intraspecific Competition, Interspecific Competition


Department
Biology
Course Code
BIOLOGY 173
Professor
Marcus Ammerlaan
Lecture
7

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Bio 173 Quiz 2 Study Guide 00:58
Ecology: Plant Interactions
Two major paradigms: competition can influence species diversity and composition of a
community
Competitive Exclusion Principle
oNo two species can coexist utilizing the exact same resource
oOne species, the superior competitor for the limited resource, will always win
Theory of Limiting Similarity
oSpecies that are too similar cannot coexist
Other paradigms
Competition is over a limiting resource (food, water, light, nesting space, pollinators,
etc.)
oIntraspecific Competition
Between members of a single species
oInterspecific Competition
Between members of different species
oIf inter<intra – allows more species to coexist
Competition reduces the numbers of both species
oCompetition doesn’t have a ‘winner’, only a loser and a bigger loser
E.g. ants and rodents in the Sonoran desert
How do so many different species survive in nature?
Resource partitioning
oInferior competitors for one resource may switch to another (less ideal)
resource, lessening competition
Temporal & Spatial patchiness
oThe best competitor may not always find the resources or the inferior
competitor may be able to use them for a time before found
Effects of predators or weather negatively affect the superior competitor

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oMay keep populations small; therefore, the limiting resources may not be
limiting at all
The outcome of competition depends on environmental conditions which vary
Positive Interactions
Commensalism
oOne species gains from an interaction while another neither gains nor loses
Org 1 benefits
Org 2 no effect
Facultative Mutualism
oBoth species gain but neither is completely dependent upon one another for
survival
Obligate Mutualism
oEach species requires the other to survive
Mutualism
oOrg 1 benefits
oOrg 2 benefits
Neutral Interactions
Neutralism
oOrg 1 no effect
oOrg 2 no effect
Negative Interactions
Predation/Parasitism
oOrg 1 benefits
oOrg 2 harmed
Amensalism
oOrg 1 no effect
oOrg 2 harmed
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Competition
oOrg 1 harmed
oOrg 2 harmed
Measuring effects of species interactions (such as competition)
de Wit Replacement Series
oSeeds of two species are planted at a constant combined density but
proportion of each species are varied (normally 0, 25, 50, 75 and 100% are
used) o
Monocultures
o100% of one species
Yielding
oUnder-yielding
Total yield (total height and weight of all plants in a pot) is lower in a
mixture than in a monoculture of the same density.
oOver-yielding
Total yield (total height and weight of all plants in a pot) is greater in
mixture than in a monoculture.
May lead to increased food production (crops)
oCould reflect…
Positive interaction between species
One species increases growth of second, etc..
Niche Partitioning
Interspecific competition is less severe than intraspecific
competition b/c the two species use different resources
Types of replicates
25 or 50 seeds were planted
oProvides info on variation among plants exposed to identical conditions
Variation due to different genotypes
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