Given below are two statements:
Statement I: Humboldt observed that within a region, species richness increased with increasing explored area, but only up to a limit.
Statement II: The slopes of the species-area regression line are very different for different taxonomic groups and regions, such as plants in Britain, birds in California and molluscs in New York state.
In the light of the above statements, choose the most appropriate answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Statement I is true but Statement II is false
The species-area relationship links the number of species in a region with its area. On a log scale it is a straight line, and its slope is the regression coefficient Z.
Statement I: Humboldt observed that within a region, species richness increased with increasing explored area, but only up to a limit. — True. During his explorations of South American jungles, Humboldt found that more area explored gave more species, but the rise did not go on without end.
Statement II: The slopes of the species-area regression line are very different for different taxonomic groups and regions, such as plants in Britain, birds in California and molluscs in New York state. — False. NCERT says the opposite: for these groups and regions the slopes are amazingly similar, with Z between 0.1 and 0.2. Only for very large areas, such as entire continents, does the slope become much steeper.
NCERT Extract:
Patterns of Biodiversity – “… During his pioneering and extensive explorations in the wilderness of South American jungles, the great German naturalist and geographer Alexander von Humboldt observed that within a region species richness increased with increasing explored area, but only up to a limit.”
Patterns of Biodiversity – “… Ecologists have discovered that the value of Z lies in the range of 0.1 to 0.2, regardless of the taxonomic group or the region (whether it is the plants in Britain, birds in California or molluscs in New York state, the slopes of the regression line are amazingly similar). But, if you analyse the species-area relationships among very large areas like the entire continents, you will find that the slope of the line to be much steeper (Z values in the range of 0.6 to 1.2).”