Climate and Life on Earth IV: Macroecology

Question 1

Define large scale patterns in diversity

Answer 1

• trends in the distribution of species across the earths surface
• macroecology

Question 2

Define species-area curves

Answer 2

how the number of species recorded increases as the area studied increases

Question 3

Describe latitudinal gradients

Answer 3

the trend towards increasing diversity as you move from the poles to the tropics

Question 4

Describe The Power Function

Answer 4

• as you survey increasing areas, the number of species recorded increases
• increase is not linear
• typically, a 10-fold increase in area leads to a doubling in the number of species

Question 5

How is the Power Function linearised?

Answer 5

• taking logs
• S = cAz becomes Log S = Log c + z Log A
• z is the slope and log c is the intercept

Question 6

Species area curves can be seen

Answer 6

• for islands of different areas within an archipelago
• for pieces of single biotas, e.g. states within USA
• for interprovincial areas, e.g. continents

Question 7

Describe the three main mechanisms used to explain the Power Function

Answer 7

1. The habitat diversity hypothesis
2. The passive sampling hypothesis
3. The equilibrium model of island biogeography

Question 8

Describe the Habitat Diversity Hypothesis

Answer 8

• if there is a wider range of habitat types, a wider range of species can live in an area
• larger areas have more habitats, and species diversity increases with habitat diversity

Question 9

Describe testing of the habitat diversity hypothesis

Answer 9

• area/habitat diversity can be separated
• keep habitat constant and vary area within sampling sites
  or
• keep area constant and vary habitats within sampling sites

Question 10

Describe the passive sampling hypothesis

Answer 10

• often used as a ‘null model’
• assumes the probability that an individual or a species occurs on an island is proportional to island area
• assumes that islands sample individuals randomly and independently

Question 11

Describe the failings of the passive sampling hypothesis

Answer 11

• fails to explain the diversity on small islands
• given enough time, all species should be present on small islands– nothing limits diversity
• does not predict turnover of species

Question 12

Describe the Equilibrium hypothesis

Answer 12

• closer islands will have more species than isolated islands
• large islands will have more species than small islands

Question 13

When there are more species…

Answer 13

fewer species are potential colonists

Question 14

When there are more species, competition leads to

Answer 14

increased extinction

Question 15

Equilibrium no of species depends on

Answer 15

area and isolation

Question 16

Distant islands are

Answer 16

more difficult to reach, so they have lower immigration rates

Question 17

Small populations on small islands are

Answer 17

more prone to extinction

Question 18

More realistic models have

Answer 18

curved immigration and emigration functions

Question 19

Described curved immigration rates

Answer 19

Strong dispersers colonise easily, then rates of colonisation slow

Question 20

Describe curved extinction rates

Answer 20

• slow initially (many empty niches)
• increases as island becomes saturated with competing species

Question 21

Describe the assumptions of the equilibrium hypothesis

Answer 21

• evolution does not influence species richness
• isolated islands are less likely to be colonised
• big islands have big populations
• big populations are less likely to go extinct
• colonisation and extinction is independent of species composition on the island

Question 22

Describe the predictions of the Equilibrium hypothesis

Answer 22

• substantial turnover in species composition, but species number should be relatively constant through time
• number of species present on an island should decrease with increasing isolation

Question 23

Give examples of the Equilibrium hypothesis in action

Answer 23

• Birds on the Channel Islands (California)
• mangrove islands
• Bahama Islands Birds

Question 24

How are species-area relationships used in conservation

Answer 24

• predict how many extinctions will occur following area reduction
• suggest best ways of slowing the loss (reserve design)

Question 25

Describe the assumptions of conservation wit regards to species-area relationships

Answer 25

- species richness is the primary object of conservation interest - area is the main cause of variations in species richness

Question 26

Predicting how many species will go extinct if area is reduced

Answer 26

depends on z

Question 27

Describe designing nature reserves

Answer 27

- larger areas have more species - SLOSS controversy

Question 28

SLOSS controversy

Answer 28

- should you have a Single Large reserve Or Several Small ones of a similar area? - depends on ‘beta diversity’

Question 29

beta diversity

Answer 29

the degree to which species overlap between areas

Question 30

Describe the basics of latitudinal gradients

Answer 30

- species are not spread evenly over the earth’s surface - habitats with greatest biodiversity on the land and in the sea are both tropical

Question 31

Describe tropical rainforests

Answer 31

- cover 7% of the earths surface - account for >50% of the earth’s biodiversity

Question 32

Describe coral reefs

Answer 32

- cover 1% of the earth’s surface - account for 25% of all marine fish species

Question 33

Describe the biotic explanations for latitudinal gradients

Answer 33

- productivity - competition - predation

Question 34

Describe the abiotic explanations for latitudinal gradients

Answer 34

Time & Stability

Question 35

Describe the Productivity or Species Energy Hypothesis

Answer 35

hottest, most humid places have the greatest net primary productivity

Question 36

Describe the failing of the Productivity Hypothesis

Answer 36

- tropical seas have low productivity but high richness - eutrophic lakes have high productivity but low richness - high productivity does not necessarily lead to high biomass/abundance

Question 37

Describe competition in latitudinal gradients

Answer 37

- constant climate in tropics - most species grow toward their carrying capacity - intense competition - narrowing of niche breadth - closer species-packing - more species can coexist

Question 38

Describe the failings of competition in latitudinal gradients

Answer 38

comparative analysis of strength of competition and niche breadth difficult

Question 39

Describe predation, parasitism and herbivory in latitudinal gradients

Answer 39

- predator-mediated coexistence - more intense mortality from ‘natural enemies’ in the tropics (stable climate) - population sizes of prey kept low - reduces competition: allows overlap in resource use and prevents any one species becoming locally dominant - many species can coexist

Question 40

Describe time and stability in latitudinal gradients

Answer 40

- communities diversify with time - temperate regions have younger communities (glaciation) - tropics relatively unchanged for at least 150 x 10^6 years - stable in the sense of low seasonality - empty niches outside tropics - no ecological or evolutionary time for species to re-invade or evolve to fill them

Question 41

Describe the failings of time and stability in latitudinal gradients

Answer 41

- many exceptions where stable habitats have low diversity (e.g. tropical mountain tops) - many tropical environments have seasonally fluctuating environments

Question 42

Why is explaining the lateral gradient so difficult?

Answer 42

- many of the explanations are circular - most of the explanations make (similar) qualitative, not quantitative predictions - data are often messy (many sources) - sample size is small (n = 1) - doing experiments is difficult

Question 43

Tropics may have...

Answer 43

- lower extinction rates - increased speciation rates

Question 44

Describe the potential lower extinction rates of the tropics

Answer 44

larger populations and refuges from environmental change