Patterns of biodiversity

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Patterns of Biodiversity: How does it vary on small and large scales around the world and why?


1)Species- Area Relationship

  • As the size of an area increases- the number of species it contains increases
  • S=cA^z
  • S=species; A=area, c&z=constants
  • log S=log c + zlog A- produces a straight line

Example: Native plant species around the world (Lonsdale, 1999)

Example: Birds in the Bismarck Islands (Mayr and Diamond, 2001)

Example: Coral reef fish, US Virgin Isalnds (Chittaro, 2002) but differences between patches and continous reefs. 

  • Slope of graph varies with taxon, latitude, size and span of areas but overall around: 0.25-0.3
  • This means if we lose 90% of the area- we'd loose 50% of the species
  • Places rich in one taxon are usually rich in the other

Example: Coral reefs- strong correlation between coral species and fish species- different corals are different shapes- suitable for different sized fish to feed/hide in. r^2=0.92. 

Limitations/other factors

  • sampling effort e.g. quadrats- may not be 100% representative- often labour intensive to get very strong statistics;
  • habitat diversity- more likely to have a variety of different habitats and niches in a larger area; colonisation/extinciton dynamics differ in dfferent areas- change throughout an area;
  • speciation/extinction dynamics e.g. soon after invasive species invaded- brown tree snakes, guam;
  • how long an area has existed for- new volcanic island?
  • vagrant species- do you count migratory species? 260/540 bird species in UK=visitors

2)Local species richness- is normally similar to regional species richness:

  • Most you  can have= 1:1 - theoretically possible to find all the species in a regional area in a local area.
  • Type 1: Unsaturated- don't have as many species are theoretically possible- slightly different environment- not going to have all the niches found in the overall region. 
  • Type 2:


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