competition between individuals lecture 4 nick brown pb 1.2
TRANSCRIPT
Competition between individuals
Lecture 4
Nick Brown
PB 1.2
Objective: To describe the effects of
competition on the quality and quantity of individuals.
Competition: a definition“An interaction brought about by a shared requirement for a resource in limited supply.
Competition leads to a reduction in: growth reproduction and/or survivorship
of at least some of the individuals.”
Begon, Harper & Townsend (1996)
1
2
3
The effects of intraspecific competition are density dependent
• Number
• Proximity
• Size
The opportunities for a plant to capture light, water and nutrients depend on:
of neighbours already capturing them.
Density
Density dependent mortality
Plant density
Num
ber
of d
eath
s A
B
Is thisdensity dependent
mortality?
Density dependence in natural plant populations
Most plants do not experience “average” population density
Density dependence in natural animal populations
In island Roe deer (Capreolus capreolus) populations, body size strongly affects the number of fawns produced but density explained <10% of the variation in body size Andersen & Linnell (2001)
The law of constant final yield
Plant population density
Tot
al y
ield
(kg
m-2)
Plants at high densities are unable to grow to a large size. High density is offset by poor individual growth.
The reciprocal yield law
Log10 population density
Log
10 m
ean
plan
t we i
ght
100 days after sowing
50 days after sowing
10 days after sowing
Self-thinning
Log10 number of survivors (ha-1)
Log
10 m
ean
dry
wei
ght p
er p
lant Path followed by a growing
population of plants
Shade?Infertile soil?
Self-thinning rule3
2
Log10 number of survivors (ha-1)
Log
10 m
ean
dry
wei
ght p
er p
lant
W CN
3
2
log log logW C N 3
2
Log
10 v
olum
e (c
m3 )
Log10 number in box
Forestry
• Spacing determines quality and quantity
• High density = high total production
• Low density = high quality
• Thinning: is it worth it?
Negative competition: the Allee effect
Death rate
Birth rate
Density
Per
cap
ita
birt
h/de
ath
rate
Intraspecific competition drives evolutionary diversification
• Competition in a population can drive niche expansion onto new resources for which competition is less severe
Bolnick, D. (2001) Intraspecific competition favours niche width expansion in Drosophila melanogaster. Nature 410 (6827): 463-466