Biology · Biodiversity and Conservation · NEET
Both, but on different scales. When you plot species richness (S) directly against area (A), the curve is a rectangular hyperbola: S goes up fast at first, then flattens near a limit. When you plot the same data on a logarithmic scale (log S against log A), the curve becomes a straight line. NEET can ask either form, so remember: normal axes = rectangular hyperbola, log axes = straight line.
S = species richness (number of species). A = area explored. Z = slope of the line, also called the regression coefficient. C = the Y-intercept (a constant). This is the straight-line form of the species-area relationship. For NEET, learn the full equation exactly as NCERT writes it, because match-the-column and fill-in questions test the letters directly.
For small areas within one region (like birds in California or molluscs in New York), the slope Z stays between 0.1 and 0.2, no matter the group or place. But across very large areas like entire continents, more unique species add up, so the line becomes steeper and Z rises to 0.6 to 1.2. NCERT gives one exact example: frugivorous (fruit-eating) birds and mammals in tropical forests of different continents have a slope of 1.15.
Alexander von Humboldt, the German naturalist and geographer, first observed it during his explorations of South American jungles. He noticed species richness increased with explored area, but only up to a limit. NEET asks this as a named-scientist fact, so pair Humboldt with species-area relationship (do not confuse him with Robert May, who estimated 7 million global species, or Tilman).
A steeper slope means the number of species rises more sharply as area increases. So a small increase in area adds many more species. This happens over continent-sized scales because you cross into new regions with their own distinct, endemic species, unlike within a single small region where species overlap.
Alexander Von Humboldt described for the first time
Match List I with List II. A. Robert May B. Alexander von Humboldt C. Paul Ehrlich D. David Tilman | I. Species-Area relationship II. Long term ecosystem experiment using outdoor plots III. Global species diversity at about 7 million IV. Rivet popper hypothesis
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Within a region, species richness increases with the area explored, but only up to a limit, giving a rectangular hyperbola.
log S = log C + Z log A, where S = species richness, A = area, Z = slope (regression coefficient), and C = Y-intercept.
For small areas within a region, Z lies between 0.1 and 0.2, regardless of taxonomic group or region.
For continent-sized areas, the slope is steeper, with Z between 0.6 and 1.2. For frugivorous birds and mammals in tropical forests, it is 1.15.
A rectangular hyperbola on normal axes, and a straight line on a logarithmic scale.
