Lecture 3: Geographies of biodiversity 2

Question 1

Productivity confounding factors

Answer 1

There are confounding factors and exceptions relating to energy use however, e.g. much of the solar energy in deserts cannot be used by plants because of low water conditions

• Some ecosystems can be highly productive and yet have high populations and biomass of very few species (e.g. salt marshes, hot springs, eutrophic lakes)

Question 2

Habitat Heterogeneity

Answer 2

Basic rule: the greater the habitat variety, the greater the species diversity

• Early studies highlighted that different bird species foraged differently even within the branches of the same tree (MacArthur, 1958)
• As a simple example, the greater the diversity of tree species, tree heights and foliage distribution, the greater the number of bird species that can use the habitat – this is a worldwide pattern

Question 3

Species/area effects

Answer 3

Strong positive relationship between species richness and area

This has also been suggested as a possible
reason for the latitudinal gradient (the mid-latitude habitats of the Earth are extensive)

Question 4

More on species/area effects

Answer 4

• The logic behind the area effect is also that because the north and south tropics abut, and therefore have a very large combined climatically- similar area
• This translates to larger ranges of species in the tropics
• Larger ranges = higher probabilities of speciation (segregation of metapopulations, so allopatric speciation)
• Larger ranges = lower extinction probabilities (more metapopulations)

Question 5

Glacial disturbance

Answer 5

One possible explanation for the notable difference in diversity of temperate forest trees in Europe (lower) as opposed to North America (higher) is the position of the mountain ranges

Question 6

Altitude

Answer 6

An equally striking pattern exists for elevation in terrestrial habitats
• Higher elevations (e.g. mountains) have cooler climates, and species diversity is less in a similar way to distance from the equator at the global scale
• e.g. tropics of the Amazon basin highly diverse, nearby Andes peaks are similar to the polar ice caps
• Decline in temperature can be confounded by increasing moisture

This pattern is only general, e.g. some herbaceous plant species have their greatest diversity at intermediate elevations on temperate mountains, and some orchids have their greatest diversity on tropical mountainsides

Question 7

Succession

Answer 7

The concept of unidirectional plant succession – each stage has a distinct ecology which creates conditions suitable for the next stage
• The ‘climax community’ is the end point for a particular location and will not change unless disturbed

Question 8

Primary succession

Answer 8

beginning on a bare surface which has not previously been colonised by a plant community

Question 9

Secondary succession

Answer 9

beginning on a surface which was previously vegetated but from which the community has been removed

Secondary succession usually occurs at a faster rate because a seed bank already exists and the soil is more conducive to life than freshly created surfaces

Question 10

Process of succession

Answer 10

The first stage of succession (primary stage) in a secondary succession is therefore relatively short