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Chapter 18

BIOC50H3 Chapter Notes - Chapter 18: Niche Differentiation

Biological Sciences
Course Code
Marc Cadotte

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Chapter 18
Case study not mentioned in lecture
Community membership
Species richness differs among communities due to variation in regional species pools,
abiotic conditions, and species interactions
1.Distribution and abundance of organisms within communities depend on three factors
1.Regional species pool and dispersal ability (species supply)
2.Abiotic conditions
3.Species interactions
1.Species supply is the first cut to community membership
oControlling effect of dispersal on community membership evident in the invasion
of communities by non-native species
oWe now learn that humans serve as vectors of dispersal of species
Eg. Ballast water carried by ships (ship picture in slides)
Sea water is pumped into and out of ballast tanks. This serves to balance
and stabilize cargo
Mostly, water contains pelagic organisms. Along with water these
organisms are taken up and released close to ports
Organisms have the opportunity to colonize near shore communites (5000
One example: zebra mussel arrived in north America, great
lakes, spread to rivers, has community changing effects, high
2.Abiotic conditions play a strong role in limiting community membership
oSpecies may become physiologically unable to tolerate abiotic conditions of the
3.Who you interact with makes all the difference in community membership

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oFinal cut requires coexistence with other species
oSpecies may depend on other species for growth, reproduction, survival, or
eliminated by competition, predation, parasitism, or disease
oBiotic resistance: failure of some non-native species to be incorporated into
communities has been attributed to interactions with native species that exclude
or slow the growth of the non-native species (not accepting new species)
oStudying invasions and coexistence: three schools of thought about what controls
diversity (textbook only has two, slides have three)-
Equilibrium theory: ecological and evolutionary compromises that result
in partitioning of resources for stable coexistence
Nonequilibrium theory: fluctuating conditions keep dominant species
from monopolizing resources
Neutral theory: species do not differ and diversity patterns are a product
of dispersal, speciation and demographic stochasticity.
Resource partitioning
Resource partitioning among the species in a community reduces competition and increases
species richness
Resource partitioning: competing species are more likely to coexist when they use
resources in different ways
Resource partitioning allows more species to coexist along a resource spectrum
oIn resource spectrum:
More overlap=more competition, less species richness
Extreme overlap= can lead to species exclusion
Less overlap=more specialization, resource partitioning, less competition,
more richness
Broad spectrum=more resources, more species richness
Sometimes when there is high overlap, but species are generalists: high
richness/diversity but less population of each species
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