Lecture 6 - hyperdiversity Flashcards
what is the simplest measure of a species diversity/ biodiversity but what is the problem with it?
species numbers e.g. species count - tells us nothing about interactions and roles in ecosystem/community
describe tropical forests diversity
hyperdiverse - lots of species per hectare
what are the problems of hyperdiversity?
1) why do we have such exceptional hyperdiversity?
2) unusual compared with similar systems
describe the pattern of tree diversity in the Amazon?
- the amazon is the biggest ecosystem on the planet in terms of trees
- home to lot of rare tree species
- 227 ‘hyperdominant’ tree species represent 50% of all trees in the Amazon
- 62% of all species are expected to have populations under a million individuals and are equivalent to 0.12% of all trees in the Amazon
what are the two must abundant tree species?
1) Euterpe precatoria
2) Protium altissimum
- both pioneer species - interesting what this tells us about the type of species that drive abundance
describe native tree diversity in the Amazon
30x higher than in GB and Ireland (temperate forests)
4 examples of other hyperdiverse systems
1) coral reefs
2) desert plants
3) phytoplankton
4) sewage
what do modern definitions of species diversity incorporate?
functional diversity and phylogenetic diversity - they offer different perspectives on the diversity measure
- expected to be a relationship between the 2 e.g. more species means more output and more phylogenetic diversity means more different species which means more functions
what is functional diversity?
- represents the sum of the roles that species perform in the community - most important
- refers to those components of biodiversity that influence how an ecosystem functions
what are the 2 key outcomes of functional diversity in tropical forests?
1) productivity - rate (tropical forests are the most productive systems)
2) carbon storage - amount (direct function of productivity)
what underpins productivity and what drives it ?
underpins = species richness and community composition
- functional traits of species within a community are important in driving productivity
what is more important that diversity itself?
evenness - not enough to have lots of species in a community, the distribution of their abundances is also important
what are functional traits?
how species grow - strategies for survival e.g. shade tolerance - richness, evenness and shade tolerance are not independent of each other - as you increase richness, evenness and phylogenetic diversity of the community you increase the trait diversity and hence productivity
relationship between diversity and carbon storage
increasing phylogenetic diversity (genus richness) carbon storage increases - increase above ground biomass
- this phylogenetic diversity is important in addition to functional diversity
what are the 3 problems of diversity
1) competitive exclusion - species similar to each other competing for resources - species too similar cannot coexist
2) limiting similarity - due to competitive exclusion there are limits to the similarity of species within ecological communities - only room for 1 species per niche
3) not enough niches - in hyperdiverse communities there simply cant be enough niches - limited set of required resources
describe a way in which species can divide niches
gap dynamics - species may be adapted to exploit different stages of succession from gap opening to closing
- this generates diversity in species number and ecological strategies
what are the 2 theories of diversity?
1) equilibrium theory - overall species richness is maintained as a constant by a balance in losses and gains - implies processes that balance diversity i.e if species become rare then they should increase
2) non-equilibrium theory - disturbance/stochastic events prevent equilibrium being reached - competitive exclusion delayed
what are problems with theories of diversity
- most theories are ecological i.e explain how species can coexist - fewer are evolutionary i.e. why do we have so many species
- difficult to evaluate - time and spatial scales are huge and data is difficult to obtain
what is the intermediate disturbance hypothesis
- species diversity in communities relies on disturbance - too much or too little aren’t good - middle allows maximum diversity
- disturbance delays competitive exclusion but doesn’t prevent it
describe the significance of disturbance
- disturbance doesn’t explain hyper-diversity but does play a role in it
- any theory about diversity must incorporate disturbance
why is is the Amazon so impressive ?
- evidence that the Amazon rainforest dates back to atleast the late Cretaceous
- evidence that rainforests have withstood severe environmental disturbances
what is significant about the age and robustness of rainforests
- should promotes diversity - some evidence that this is the case but not universally supported
- diversification rates are higher in tropical forests
what is evidence that disturbance and diversity are related?
- disturbance only shows deterministic extinction- unless something else is going on (e.g. adaption to different environments)
- trade offs between competition and dispersal
- adaption to gap dynamics fits with evidence that disturbance promotes diversity
