Flashcards in lecture 8 Deck (21)
Individuals do not live in isolation...
• Individuals of the same species have similar requirements for survival, growth, reproduction
• demand for resource may exceed supply
• individuals may compete for resources...
= an interaction between individuals of the same species (intra) brought about by a
shared requirement for a resource in limited supply
– Results in:
• Reduced survival, growth, and/or reproduction of some individuals
– possible reduction in fitness Competition acts as a selective pressure in nature
How does competition arise?
- Resources are not evenly distributed (distributed in patches)
- Aggregative Response
- competitive interactions
predators concentrate where prey density is high
o due to high consumption rates
- can lower consumption rates
- patch with highest prey density is not always the best!
Types of Competition
1. Exploitation (Scramble) Competition
2. Interference (Contest) Competition
• Exploitation (Scramble) Competition
– an individual responds to a decreased level of a limited resource remaining after it has been
exploited by other individuals
– individuals donotinteractdirectly
• Interference (Contest) Competition
– an individual actually prevents another from exploiting a limited resource within a portion
of the habitat
– individuals interactdirectly
Intraspecific Competition What is the result of Competition?
net energy gain - energy loss ↑ +/or energy gain ↓ due to competitive interactions
-Consumption rates decrease with increasing numbers of competitors
Reduced Growth, Reproduction
Reduced Growth, Reproduction & survival
How do individuals balance the attraction to patches of high prey abundance and the repulsion by the presence of competitors?
Use Behavioural Ecology to study how an individual’s behaviour is adapted to it’s environment
Ideal Free Distribution Model Assumptions:
1. There are a number of prey patches that vary in quality
2. Competitors are ‘free’ to exploit all patches (can move ‘freely’ among
3. Individual prey consumption rates decline with increasing numbers of
competitors in the patch increases
4. Individuals have equal competitive abilities
5. Animals distribute themselves ‘ideally’ among patches to obtain highest
consumption rates (maximize net energy gain to ensure high fitness)
As competition ^ in high quality patch
the patch quality v (leading to lower consumption rates)
Individuals in an area reach an equilibrium distribution, where:
• all patches occupied
• more individuals in higher quality patches...
At the equilibrium distribution...
the consumption rates of individuals are equal for all competitors in all patches
Can be a dynamic equilibrium
– individuals are constantly moving among the available patches
... but individuals in the lowest quality patch will not gain access to more prey if they move to a higher quality patch
Generalized Experimental Design:
• Prey arrives in the patch at a particular rate
• Prey is consumed immediately
• Scramble/Exploitation Competition -competitors do not interact directly