Simulation · Biology · Class 12

Species-area relationship: what Z means

From the lesson Species-area relationship in Biodiversity and Conservation. Change the values and watch what happens.

The idea behind it

NCERT §13.1.2

Exploring South American jungles, Alexander von Humboldt saw that within a region, species richness rose as the explored area grew, but only up to a limit.
For many taxa (angiosperm plants, birds, bats, freshwater fishes) species richness against area is a rectangular hyperbola.
On logarithmic scales the relationship becomes a straight line: log S = log C + Z log A, where S is species richness, A is area, Z is the slope (regression coefficient) and C is the Y-intercept.
Z lies between 0.1 and 0.2 whatever the taxonomic group or region: plants in Britain, birds in California and molluscs in New York state give remarkably similar slopes.
For very large areas such as whole continents the line is much steeper, with Z between 0.6 and 1.2.
For frugivorous (fruit-eating) birds and mammals in tropical forests of different continents, Z is 1.15.
A steeper slope means species richness climbs much faster with area, so losing area costs more species.

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