Competition Flashcards
(28 cards)
What is competition?
Negative effects which one organism has upon the other by consuming or controlling access to a resource that is limited in availability
What is intra and interspecific competition?
Intraspecific - competition between memebers of same species
Interspecific - competition between memebers of different species
Give some examples of inter/intraspecific competition
When species of paramecium are grown together the densities of both species are lowered so they are sharing the resources - INTRAspecific
Asterionella does less well when it is grown with Synedra, the population declines over time even when it starts out more abundant
What are the two outcomes of competition?
Coexistence - both species can persist living together
Competitive exclusion - one or more species excludes the other
What is the Lokta-Volterra model used for?
Competition between two species - used to understand when competitve exclusion occurs
What does the compeition coefficient mean?
aij - measure of ecological equivalence
If aij = 2 then each member of j is equivalent to 2 of i
AKA
an individual of j consumes aij times as much resource as an individual of i
d = distance between niche space
w = width of niche
When does competative exclusion happen?
aij < 1 and aji > 1
OR
aij > 1 and aij < 1
One strong competitor and one weak competitor
When does coexistence happen?
Interspecific competition is always weaker than intra:
- aij < 1 and aji < 1
OR
interspecific competition is always stronger than intra:
- aij > 1 and aji > 1
What happens when interspecific competition is weaker than intra?
Get competitive coexistence
The stabilising effect of intraspecific is more important than the neagtive effects of interspecific competition
What happens when interspecific competition is always stronger than intra?
Results in unstable competitive coexistence
Destabilising effect of interspecific is more important the negative effects of intraspecific compeition
What can unstable coexistence lead to?
Priority effects - first species to enter a habitat excludes subsequent ones
What are the problems with diversity?
Compeitive exclusion means that species that are too similar cannot coexist - there are limits to similarity of species within ecological communities
Essentialy only room for one species per niche
BUT hyperdiverse communties exist and there simply cant be enough niches
How diverse is the Amazon?
3.9 x 10^11 trees in Amazon
~16,000 tree species
227 hyperdominant species that represent 50% of community
COMAPRED TO TEMPERATE FORESTS
40-50 species of native trees
Native tree diversity is 30 x higher in Amazon
Give some other examples of hyperdiversity not tropical forests
Coral reefs
Desert plants
Phytoplankton
Sewage
What is the equilibrium and non equilibrium theory?
Equilibrium - balance between losses and gains to communities such that overall species richness is maintained as a constant
Non-equilibrium - disturbance/stochastic events prevent equilibrium being reached so competitive exclusion delayed
What is the intermediate disturbance hypothesis?
To little disturbance - get competitive exclusion
Too much exclusion - species driven to extinction by disturbance
Diversity maximised at intermediate levels of disturbance
How are disturbance and diversity linked?
Disturbance only slows deterministic extinction unless something else is going on e.g. adaptation
Trade-offs between competition and dispersal
Adaptation to gap dynamics fits with evidence that disturbances promote diversity
What is neutral theory?
A model for diversity in which all species are identical
What are neutral dynamics?
If everyone is equal there is nothing to decide which species should be the winner
Species or individual identity is irrelevant
If we add randomness to the model we cannot predict the outcome
What is neutral competition?
Species very similar so do not need niche differences
Non-equilibrium model in which species persist for a very long time
What is Hubbell’s neutral theory?
Two scales of organisation:
- local community = a set of species is a given location
- meta-community = a pool of species from which local communities are formed
Dynamics of meta communities are slower than local
Concept derives from island biogeography
Local community allows for lots of species to persist for a long time but eventually stochastic extinction leads to one species remaining - so need a source of new diversity e.g. meta
What are gap dynamics?
Key driver of individual and species turnover in tropical forests
Death of a tree creates a gap in a canopy, forest turnover happens at which competition is intense
What is the Janzen-Connell hypothesis?
All plants are attacked by natural enemies
Many natural enemies are specialists
Specialists will aggregate on high densities of host
If species becomes common then it will attract high number of enemies and rare species attract fewer enemies
Hence rare species should increase and common species become rarer
What is the death zone?
Area beneath a parent tree into which conspecifics cannot recruit aka a species cannot self replace
Intense density dependence kills all seeds/seedlings of that species immediately adjacent to parent tree in death zone
When a gap is created that gap cannot be re-occupied by same species so this enhances diversityn
