Download chapter 20 How do species avoid competition?

Reading - Tuesday & Thursday lectures
chapter 20: Coevolution & Mutualism
(p. 381-383; 389-390)
chapter 21: Community Structure
(p. 399-407)
chapter 22: Community Development
(entire chapter) -lots of photos
easy reading.
chapter 23: Biodiversity
Co-evolution of Competitors
Ricklefs 2001: chapter 20
How do species avoid competition?
Evolve different niches.
This would be favoured by natural selection.
Interacting populations evolve in response
to each other
• European rabbits introduced
into Australia in 1859 became
a major pest
• To decrease populations, introduced
the myxoma virus in 1950…
epidemic of myxomatosis
transmitted by arthropods
Myxoma virus seen with
an electron microscope
Initially 99.8% of rabbits killed, but
mortality declined with additional
treatments…some rabbits had genetic
resistance
Ricklefs 2001
Fig. 20.1
Co-evolution: each species influences the
evolution of all species with which it interacts
• rabbit-virus system left
on its own would have
resulted in an equilibrium,
but…various strains
used as control agents.
Species avoid competition by evolving
different niches
Niches of 2 species
%
5
7
Food Size (mm)
In evolutionary time,
the populations
(species)diverge to
avoid competition.
5
7
Reduction of niche
overlap allows species
to coexist without
severe competition.
3
9
Food Size (mm)
Conditions favouring this...
Species #1
Species #2
Allopatry
Allopatry
Sympatry
Competition can only occur in sympatry
Ricklefs 2001, Fig. 20.12
Character traits of two closely related species
differ more in sympatric regions than in
allopatric regions of their geographic ranges.
A common example of character displacement
is the size & shape of a food gathering a apparatus
Morphological changes