BIOLOGY 1B Lecture Notes - Lecture 5: Intraspecific Competition, Interspecific Competition, Ecological Niche
12 Jun 2018
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Lecture 5
10/04
• Competition: when two or more individuals share a resource and consumption by one reduces its
availability for others, causing reduced growth, survival or fecundity
o Competition between leaves of plants for sunlight
o Rodents and ants both eat seeds
▪ Ants are out during day and rodents are out during night
• Competing because both consuming the same resource
o Competition for mates
▪ Individual success can have to do with access to reproduction
▪ Flowers compete for mates w bees carrying seeds as well
o Competition for space
▪ Need place to live to capture other resources
o Competition for nesting locations
▪ Snaps= dead trees that provide critical habitat for woodpeckers
• Intraspecific competition: competition between individuals of the same species; mechanism
behind density dependent population growth
• Interspecific competition: competition between individuals of different species
• Interference : competition involving direct, physical interaction
o hyenas
• Exploitation competition: competition mediated by consumption of shared resource; species don’t
physically encounter each other
o Mouse and ant food competition
• Ecological niche
o Resource partitioning in communities
▪ Species have different niches and different requirements- go into different
gradients and consume resources to allow for high diversity and multi species
occupying same area
• Gause’s Paramecium experiments: Why has one species been victorious over another in the great
battle of life?
o Keep colonies going for long time then dilution and replacing
o Competitive exclusion: If two species are competing for a limited resource, the species
that uses the resource more efficiently will eventually eliminate the other locally
▪ 3 bacteria growing alone in flask
▪ Grow fairly quickly then reach carrying capacity
▪ Put them together: start at low density, all grow, one declines towards extinction
another grows towards K but a little lowered
▪
o Coexistence: ability to live together
▪ Another pair of paramecium- both still in community
• Corollary: species can coexist if they utilize different resources
o The two bacteria feed in open water vs. bottom of flask
• Connell’s barnacle experiment
o Barnacles stay put
o Can occupy different parts of environment
o 2 types of barnacles: chthamalus and semibalanus
▪ chthamalus higher on rocks
▪ maybe they were competing before; experiment with species removal
• remove the semibalanus- the chtamalus expand down
o Competitive exclusion
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