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What is the Species Area Curve?

The species area curve is the linear relationship between the number of species and the geographic area in which the species are found. Studies on species area curves have shown that in general, larger areas tend to contain larger numbers of species (all other influencing factors apart from size of the area being similar).

 

Method for estimating plot sized based on the Species Area Curve-

This method was invented by Swiss ecologist Josias Braun-Blanquet.

  1. A small plot is laid (the size of this initial plot can be arbitrary) and the number of species obtained in it belonging to the group of organisms under study is counted.

  2. Successive plots are laid, each larger than the previous one (the increase in size can also be arbitrary, what matters is that the size of successive plots is larger) and includes the preceding plot within it's boundary. A count of the species is undertaken in each plot (which will include the area belonging to preceding plots as well, as they are in the boundary of succeeding plots).

    determining plot size sp area curve method


  3. The counts of the species of each plot is plotted against the area of the plot. As per the species relationship curve you will get more species for larger plots, but the increase in size of succeeding plots will bring in fewer and fewer increments in species counts.

  4. When successive increments in the species count become negligible or absent, the size of the plot at that point is considered to be the minimal area of the plot necessary to characterize that species community in that particular study area. This should be the size of the plot used as theoretically, larger sizes than this would require more effort without a significant increase in efficiency.

  5. The figure below denotes how the plots would be taken using a hypothetical example. The graph below that shows the graph used to estimate the plot size using hypothetical data presented in the table.

Plot size (sq. m)

Number of species

0.25

2

0.50

4

0.75

5

1

5

 

Graph

 

About the Author of this Article

 References

Gotelli, N. J. 1998. A Primer of Ecology, 2nd edition. Sinauer Associates, Inc., Sunderland, MA.

Species Area Relation - http://math.hws.edu/~mitchell/SpeciesArea/speciesAreaText.html