Lecture 3: Geographies of biodiversity

Question 1

Equator latitudinal gradient

Answer 1

A notable pattern exists (and has existed for 100-250 my) so that there is a latitudinal gradient for increased diversity with proximity to the equator (noticed by Wallace, 1878)

Question 2

Latitudinal gradient exceptions

Answer 2

Exceptions include penguins and seals (which have greatest diversity in high latitudes), and coniferous trees, which have their greatest diversity in temperate zones. Many species are confined to the tropics, however.

Question 3

Latitudinal gradient patterns

Answer 3

Patterns are not the same for each species or taxa. For example, there are more birds than mammals in every region, and bird species richness increases roughly x12 in 60o of latitude, while mammals increase only x8. Opposing patterns are also found between flycathers (Tyrranidae) and sandpipers (Scolopacidea).

Question 4

Latitudinal gradient-Non-equilibrial hypothesis

Answer 4

Patterns of diversity observed today are the legacy of the past, e.g. low diversity at high altitudes reflects glacial- interglacial cycles –

species are lost or restricted as they cannot get away from the affected areas and have not yet recolonised.

High latitude forest diversity has increased over the last 10,000 years with retreating glaciers

Question 5

Latitudinal gradient-Equilibrial hypothesis

Answer 5

Pattern reflects the adjustment of biota to current geological, climatic and oceanographic conditions – e.g. latitudinal variation in solar radiation

Question 6

Hotspot land surface

Answer 6

Hotspots land surface 1.32% of global surface but contain ~50% of global land-based species

Question 7

Productivity (energy)- LG

Answer 7

Productivity = fixation of carbon and production of biomass

• Most regions and habitats that contain large numbers of species also have very high productivity and biomass, for example rain forests (and, in the oceans, coral reefs)

Question 8

Productivity (Macarthur)

Answer 8

MacArthur (1972) suggested that more productive environments support more species because species can be more specialized and still maintain populations large enough to avoid extinction

• Assumes that specialists use their resources more efficiently than generalists do = superior competitors

Question 9

Productivity (Brown and Lomolino)

Answer 9

• A more productive environment therefore contains more specialist species

Question 10

Productivity confounding factors

Answer 10

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)