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#species abundance

2 public questions tagged with this topic.

BIODIVERSITY & IDH

Diversity due to differences in abundance of species is called:

Evenness measures how uniformly individuals are distributed among the species present. Two communities may contain the same number of species yet differ greatly in diversity if one is dominated by a single species while the other has comparable abundances throughout. Richness counts species without considering their relative numbers, whereas dominance emphasizes concentration in one or a few taxa. Turnover instead describes compositional change across places or times. Thus abundance differences are captured specifically by evenness, an essential component of indices such as Shannon diversity. Mechanistic reasoning is essential here: classifications should follow measurable consequences for survival, reproduction, resource acquisition, or detection. Context can modify interaction strength, but it does not erase the defining contrast among the alternatives presented. At population level, this mechanism can influence abundance, coexistence, and evolutionary selection. Separating immediate individual effects from longer-term community outcomes gives the selected concept a clearer ecological meaning and avoids relying only on memorized terminology.

Ref: NCERT Biology Class 12, Ch. 15 Biodiversity and Conservation

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BIODIVERSITY

A community with 10 species, each with 10 individuals has:

Ten species represented by ten individuals each have identical relative abundance, pᵢ = 10/100 = 0.1. This is perfect evenness because no species is numerically dominant. For a fixed richness, equal abundance maximizes both Shannon diversity and the Gini–Simpson index. Shannon diversity would be H′ = −10(0.1 ln 0.1) = ln 10, and Pielou’s evenness H′/ln S would equal 1. Simpson dominance would be 10(0.1²) = 0.1, relatively low, while 1 − D would be 0.9. The community also has a richness of ten species; whether that richness is “high” depends on the taxon, area, and comparison community, but it is not low merely because each species has ten individuals. High dominance is excluded by the equal counts, and low diversity is inconsistent with the simultaneous richness and maximum evenness. This illustrates why abundance data improve on a species count alone. Two communities may each contain ten species, but one with 91 individuals of one species and one individual of each remaining species would have markedly lower evenness and composite diversity.

Ref: NCERT Biology Class 12, Ch. 15 Biodiversity and Conservation

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