Lecture 7 - Models for coexistence and diversity

Question 1

what are the 2 key theories for coexistence and diversity?

Answer 1

1) neutral theory

2) janzen connell hypothesis

Question 2

what is fundamental to both theories?

Answer 2

disturbance and the formation of gaps

Question 3

what is the lotka volterra model?

Answer 3

for competition between two species - used to understand when competitive exclusion occurs

Question 4

how are conditions for equilibrium co-existence restricted?

Answer 4

both mathematically and ecologically - boils down to requiring that species are ecologically different and exploit different niches

Question 5

when do species coexist?

Answer 5

when parameters are very similar it takes longer for exclusion to happen - when they are identical (no superior or inferior) they coexist

Question 6

describe the neutral theory

Answer 6

the more similar two species are the longer it will take for competitive exclusion to happen - a model for diversity in which all species are identical

Question 7

what are the outcomes of the neutral theory

Answer 7

• outcomes are going to be very variable, spatially
• doesnt generate and equilibrium of species
• doesnt maintain diversity but allows species to coexist for a long time
• breaks the competitive exclusion model

Question 8

what is neutral competition the same as

Answer 8

• non- equilibrium model

Question 9

describe hubbels neutral theory

Answer 9

• looks at community dynamics in tropical forests - model for whole ecosystems
• has two scales of organisations
  1) local community - set of species in a given location
  2) meta community - a pool of species from which local communities are formed

Question 10

describe the difference between local and meta communities

Answer 10

dynamics of the meta are much slower than those of the local
think local = island and meta= mainland

Question 11

describe the model for a local community

Answer 11

• community consists of a series of gaps big enough to support a single tree
• community is small and finite - fixed no. of trees can live there - number = constant - community assumed to be saturated with trees
• all individuals are ecologically identical
• competition occurs when individuals die
• lottery for which species occupy the gap (stimulated mathematically)

Question 12

what is fundamental to drive the model for local community

Answer 12

gap formation and competition = gap dynamics

Question 13

describe the neutral model for a local community

Answer 13

allows lots of species to persist for a long time but eventually stochastic extinction will lead to just one species remaining - so needs a source of new diversity i.e metacommunity

Question 14

describe the link from local to metacommunity

Answer 14

• individuals migrate from meta to local
• provides an input of new species
• compensates for the loss of species in the local community through local extinction
• immigration increases diversity despite loss of species at local community level
• model is a theoretical breakthrough - maintains hyperdiversity

Question 15

describe the model for a metacommunity

Answer 15

• wider community from which individuals migrate to smaller communities

Question 16

what is good about the model for a metacommunity?

Answer 16

• good simple model to compare more complex models

- first model to consider what happens to communities on an ecological scale

Question 17

describe the dynamics of the species pool in the model for a metacommunity?

Answer 17

• dynamics of the species pool is governed by speciation-extinction dynamics
• speciation occurs at rate V and is a size of Jm individuals