evolution & maintenance of hyperdiversity (lecture 6)

Question 1

How species diverse are tropical forests?

Answer 1

• species number simplest measure of biodiversity
• rainforests home to 50% all terrestrial species
• 2% earth’s surface
• 2 study plots at Danum Valley
• 511 woody tree species in just 8 hectares
• French Guyana
• 546 tree species in 5ha
• Tanzania
• 512 species in 28ha area
• exceptionally high
• unusual compared to similar systems elsewhere
• why????

Question 2

What are patterns of tree diversity in the Amazon?

Answer 2

• 39 billion trees in Amazon
• ~ 16,000 species
• 227 hyperdominant tree species make up 50% trees
• rarest 11,000 trees = 0.12%

Question 3

How does Amazon tree diversity compare with temperate forests?

Answer 3

great britain and ireland

• 40-50 native tree species
• 316,000km2
• 0.0001 species per km2

amazon

• 16,000 species
• 5,500,000km2
• 0.0029 species per km2
• native tree species diversity by area 29x higher in amazon

Question 4

What are other examples of hyperdiverse systems?

Answer 4

• coral reefs
• desert plants
• phytoplankton
• sewage

Question 5

What is functional diversity?

Answer 5

• components of biodiversity that influence ecosystem functions
• underpinned by species/phylogenetic diversity
• key functional diversity outcomes include productivity and thus carbon storage
• global productivity peaks in 3 main tropical forest regions
• productivity and biodiversity positive concave down relationship

Question 6

How did Zhang et al. (2012) examine the relationship between species diversity and productivity?

Answer 6

• surveyed 54 sites globally
• looked at drivers of productivity
• statistical analysis correlated productivity w range of possible key measures including:
• species richness: count of species at given site
• species evenness: includes estimate of relative abundance

Question 7

What did Zhang et al. (2012) find about the relationship between species richness and productivity?

Answer 7

• both measures of diversity (richness/evenness) drive productivity
• evenness is more important
• distribution of abundances is important
• functional traits also drive productivity
  e. g. shade tolerance means productivity possible even if light levels are low
• richness/evenness/shade tolerance are not independent

Question 8

How did Cauvanaugh et al., (2014) look at the relatioship between carbon storage, environment and diversity?

Answer 8

• fifty-nine 1ha plots across tropics

- carbon storange correlates positively with phylogenetic diversity

Question 9

Why are tropical forests increasing as a carbon sink?

Answer 9

Lewis et al., (1998, 2004)

• long term data from forest inventories
• 30-59 sites across the amazon
• above ground biomass increasing 0.98Mg/ha/yr
• Lewis et al., (2009)
• African tropical forests
• 0.63Mg/ha/yr
• reasons for increase include CO2 enrichment & successional changes
• diversity/functional diversity important and global scale

Question 10

What is competitive exclusion?

Answer 10

• similar species
• consume similar resources
• competition
• more similar species
• compete more strongly
• species too similar can’t coexist
• one competitor expected to outcompete other
• problem for explaining hyperdiversity

Question 11

What is limiting similarity?

Answer 11

• idea that competitive exclusion limits similarity of species wihin ecological communities
• essentially room for one species per niche
• number of species = number of niches

Question 12

Why is limiting similarity a problem for explaining hyperdiversity?

Answer 12

• there is not a niche per speciess in tropical forests

- set of required resources are limited: light, water, N, P, K

Question 13

How can species divide niches?

Answer 13

Gap dynamics:

• exploit different stages of succession
• gap formation to closure
• generates species/ecological strategy diversity

Question 14

What is the equilibrium vs non-equilibrium theory?

Answer 14

Equilibrium theory:

• balance between losses/gains to communities
• overall richness maintained as constant
• processes that balance diversity e.g. if a species becomes rare it should increase
• mathematicaly difficult

Non-equilibrium theory:

• disturbance/stochastic events prevent reaching of equilibrium
• competitive exclusion delayed

Question 15

What is the intermediate disturbance hypothesis?

Answer 15

• disturbance creates diversity
• highest diversity in intermediate disturbance
• recolonisers & climax species
• delays competitive exclusion not prevents

Question 16

How does the age of tropical forests affect hyperdiversity?

Answer 16

• Amazon rainforest in South America dating back to at least the late Cretaceous-Eocene, 47-66 MYA:
• evidence rainforests have withstood severe environmental disturbances (e.g. glaciation)
• the age and robustness should promote diversity
• some evidence that this is the case but not universally supported
• diversification rates higher in tropical forests