Patterns of biodiversity

Question 1

biodiversity

Answer 1

• the variety of life

- species richness

Question 2

Historical theories of biodiversity

Answer 2

• stability-time hypothesis
• museum hypothesis
• unstable/stable environmentalist

Question 3

Equilibrium theories

Answer 3

• greater habitat diversity = greater resource gradient length & available niche space
• large population sizes with large geographic ranges have reduced risk of extinction
• but boreal forest also covers very large are but has low diversity than Mediterranean

Question 4

Northern Canada vs Amazon Basin

Answer 4

• poor soils, vary flat/uniform topography and uniform habitats
• but massive difference in biodiversity
• little seasonal change in temp, moisture, daylight etc.

Question 5

if environment is stable

Answer 5

• best adapted species can cause competitive exclusion of less adapted species
• results in decrease biodiversity

Question 6

Environmental disturbance

Answer 6

• creates spatial heterogeneity
• environmental conditions not constant for long enough to allow dominant species to drive other to extinction
• too much disturbance leads to extinction of sensitive species or those with small populations
• rainforests can withstand occasional fires but not frequent ones, eventually it would turn into savanna

Question 7

intermediate disturbance hypothesis

Answer 7

• biodiversity will be highest in systems in which the rate of displacement of species by competition is low and the rate of disturbance is also low

Question 8

competition hypothesis

Answer 8

• evolution in mid-high latitudes driven by physical stresses (temp & moisture)
• evolution in the warm, moist tropics driven by interspecific competition, leads to evolution of species with specialised niches
• greater species packing in a given area
• may apply to certain animal groups but unclear how it applies to tree species
• also, unclear why competition should be greater in low latitudes than high latitudes

Question 9

Predation hypothesis

Answer 9

• high number of predator and parasite species generates high biodiversity by keeping prey populations low
• prevents competitive exclusion of one prey species by another
• consistent with pattern of tropical tree species

Question 10

why does this pattern exist

Answer 10

• no one theory is adequate explanation, so maybe a combination of reasons
• temp and moisture probably key

Question 11

productivity or energy hypothesis

Answer 11

Tree species:

• strong correlation between species richness and evapotranspiration
• strong correlation between evapotranspiration and NPP
• more energy available for photosynthesis in the tropics than high latitudes
• more NPP = more biomass = more complex vegetation structure
• more complex vegetation structure = more niches & micro habitats for animals
• diversity of micro-climates