Evolution & Maintenance of hyperdiversity

Question 1

rainforests are estimated to be home to 50% of all terrestrial species, despite covering <2% of surface

Answer 1

Can be 500+ species in just 5 ha of forest

Question 2

Estimated to be 3.9 x 1011 trees in the Amazon

~16 000 tree species

Answer 2

227 ‘hyperdominant’ tree species represent ~50% of all trees

Rarest 11 000 species constitute only 0.12% of trees

Question 3

Euterpe precatoria: 5.21 x 10^9 individuals

Answer 3

Protium altissimum: 5.21 x 10^9 individuals

Question 4

GB + Ireland: ~ 40-50 species of native trees
Area: 316 000km2
Species/Area: 0.0001 km-2

Answer 4

Amazon: ~ 16 000 spp
Area: 5 500 000 km2
Species/Area: 0.0029 km-2

Native tree diversity in the amazon is 30x higher than in the GB & Ireland.

Question 5

Tropical forests are not the only hyperdiverse systems, some other examples:

Answer 5

Coral reefs
Desert plants
Phytoplankton
Sewage

Question 6

In terms of species diversity, tropical forests are exceptional. Functional diversity is underpinned by species & phylogenetic diversity

Answer 6

functional diversity – this represents the sum of the roles that species perform in the community. There is expected to be a relationship between both species diversity and phylogenetic diversity and functional diversity. So more species usually would mean more output. And more phylogenetic diversity means more different species which means more functions.

Question 7

Functional Diversity

Answer 7

Productivity: Tropical forests are the most productive ecosystems

Carbon storage: The carbon storage in tropical forests is a direct function of productivity.

Question 8

tropical regions have rates of productivity 3-7 times higher than in the temperate regions.

Answer 8

So clearly productivity is different between tropical forests an other regions of the globe.

Question 9

However the immediate question is, does diversity matter? Do you need 500 species per hectare to achieve this productivity, or would just one species suffice?

Answer 9

a consistent positive and concave-down biodiversity-productivity relationship across forests worldwide

Question 10

Species richness & community composition underpin productivity

Answer 10

In terms of the relationship between diversity and productivity, the key result is that the two measures of diversity are important in driving productivity: but of the two measures of diversity, evenness is more important than diversity itself. That means that it is not just enough to have lots of species in the community, the distribution of their abundances is also important.

Question 11

It is also worth pointing out that the functional traits of species within a community are important in driving productivity. Here the degree of shade tolerance is also important: shade tolerance means that species are able to grow from beneath shade and not just in open light. Having these present means that productivity is possible even if light levels are low.

Answer 11

Notably richness, evenness and shade tolerance are not independent of each other. Some groups of plants are more shade tolerant than others, so that as you increase richness, increase evenness and increase the phylogenetic diversity of the community, you increase the trait diversity and hence productivity.

Question 12

Phylogenetic Diversity and Carbon storage

Answer 12

Carbon storage increases with increased diversity

Question 13

Not only are forests are a significant carbon sink, but also this has been increasing:

Answer 13

Lewis et al. (1998, 2004) used long-term data from forest inventories: 40-59 sites across the amazon

In the amazon Above Ground Biomass has increased by 0.98±0.38 Mg ha-1yr-1

Lewis et al. (2009) showed a similar result for African tropical forests: increase of 0.63 Mg ha-1yr-1

Reasons for increase include CO2 enrichment and successional changes: diversity and functional diversity important at a global scale

Question 14

Competitive exclusion means that species that are too similar cannot coexist.

Answer 14

BUT in hyperdiverse communities there simply can’t be enough niches.

Question 15

Equilibrium theory: balance between losses and gains to communities, such that overall species richness is maintained as a constant.
Implies processes that balance diversity: e.g. if species become rare then they should increase
Mathematically difficult

Answer 15

Non-equilibrium theory: disturbance / stochastic events prevent equilibrium being reached
Hence competitive exclusion delayed

Question 16

The analysis of the data showed that the disturbance was creating diversity: the x-axis shows the species that are recolonisers, representing the severity of the disturbance.

Answer 16

For those plots in which there was no disturbance or extreme disturbance, diversity is lowest. However, for those plots in which there in intermediate disturbance the diversity is highest. It doesn’t matter which way you slice up the data – the three graphs show three different ways of cutting and analysing the dataset, and you get the same result.

Question 17

• Evidence of Amazon rainforest in South America dating back to at least the late Cretaceous-Eocene (47-66 MYA: Burnham & Johnson 2004 Phil Trans B. 359 1595-1610).

Answer 17

Evidence that rainforests have withstood severe environmental disturbances (e.g. glaciation).

The age of the rainforests and robustness should promote diversity

Some evidence that this is the case (Fine & Ree 2006 Am Nat 168, 796-804).

However not universally supported (Mittelbach et al. 2007 Ecology Letters 10, 315-331).

Diversification rates higher in tropical forests.