What factor could prevent the calculation of an index of diversity?

The calculation of an index of diversity relies on accurate data about the number of individuals within each species in a given habitat. If there is a lack of data on the number of individuals, it becomes impossible to make a meaningful calculation of diversity; this is because the index typically accounts for both species richness (the number of different species present) and the evenness of the species (how evenly individuals are distributed among those species). Without this individual count, the calculation cannot be completed, thus hindering the assessment of biodiversity.

While the other factors can influence biodiversity or its study, they do not directly impede the mathematical calculation of the index itself. For instance, missing information about soil conditions might affect understanding of a habitat but does not directly prevent the diversity index from being calculated if individual counts are available. Similarly, improper sampling techniques might lead to biases in data but wouldn't entirely eliminate the possibility of calculation if the necessary data were still recorded. Environmental changes could mean species are present or absent at different times, but the index can still be calculated based on the existing individual counts during a specific assessment.