8.2 The Multiple Facets of Diversity
8.2.1 Introduction
Life on Earth is diversified at multiple spatial scales, ranging from the molecular
level (genes) to continent-encompassing biomes. Therefore, diversity expresses
itself at all these scales, and no single number or method can account for all this
complexity. Every level of organization has its own rules and structures and its
diversity must be addressed accordingly.
Genetic diversity is a rapidly expanding topic, where huge amounts of data call
for computer-efficient methods of data reduction that fall outside the scope of this
book. Readers are referred to manuals addressing these topics in a way related to this
book, e.g. Paradis (2012), Cadotte and Davies (2016).
Species diversity is at the core of the community-level approach that underlies
this book. For example, the objective of many of the methods presented in Chap. 7 is
to test hypotheses about the processes that generate spatial variation in community
composition, or beta diversity, in ecosystems. In the present chapter, we will explore
some important components of the study of taxonomic (community) diversity.
Switching from species to ecological traits is a mean of generalizing ecological
models, so that they can be applied to ecologically similar habitats irrespective of the
identity of the species found in them. This is the goal of functional ecology, based on
the proposition by Southwood (1977), who stated: “habitat provides the templet on
which evolution forges characteristic life-history strategies”. Functional ecology is
in rapid development. A small subset of its questions are addressed in Sect. 6.11
(fourth-corner problem). However, as of this writing, many different avenues are
being explored, and no unifying framework has been proposed yet. Consequently,
we will refrain from delving into this matter, except in the form of a very short
section (Sect. 8.5).
8.2.2 Species Diversity Measured by a Single Number
8.2.2.1 Species Richness and Rarefaction
The simplest measure of species diversity is q, the number of species or species
richness. Although it looks straightforward, there is a problem with its estimation.
Indeed, what we must rely upon is a sample of the area (or volume in aquatic
environments) of interest. Consequently, the true total number of species in that area
or volume is out of reach in practice. Every sampling unit contains a certain number
of individuals belonging to a certain number of species, and, given the fact that some
species are more rare than others and therefore less likely to be detected, the total
number of species of a sampling unit or a set of sampling units increases with the
sampled area or volume and the number of detected individuals. Consequently, the
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8 Community Diversity
8.2.1 Introduction
Life on Earth is diversified at multiple spatial scales, ranging from the molecular
level (genes) to continent-encompassing biomes. Therefore, diversity expresses
itself at all these scales, and no single number or method can account for all this
complexity. Every level of organization has its own rules and structures and its
diversity must be addressed accordingly.
Genetic diversity is a rapidly expanding topic, where huge amounts of data call
for computer-efficient methods of data reduction that fall outside the scope of this
book. Readers are referred to manuals addressing these topics in a way related to this
book, e.g. Paradis (2012), Cadotte and Davies (2016).
Species diversity is at the core of the community-level approach that underlies
this book. For example, the objective of many of the methods presented in Chap. 7 is
to test hypotheses about the processes that generate spatial variation in community
composition, or beta diversity, in ecosystems. In the present chapter, we will explore
some important components of the study of taxonomic (community) diversity.
Switching from species to ecological traits is a mean of generalizing ecological
models, so that they can be applied to ecologically similar habitats irrespective of the
identity of the species found in them. This is the goal of functional ecology, based on
the proposition by Southwood (1977), who stated: “habitat provides the templet on
which evolution forges characteristic life-history strategies”. Functional ecology is
in rapid development. A small subset of its questions are addressed in Sect. 6.11
(fourth-corner problem). However, as of this writing, many different avenues are
being explored, and no unifying framework has been proposed yet. Consequently,
we will refrain from delving into this matter, except in the form of a very short
section (Sect. 8.5).
8.2.2 Species Diversity Measured by a Single Number
8.2.2.1 Species Richness and Rarefaction
The simplest measure of species diversity is q, the number of species or species
richness. Although it looks straightforward, there is a problem with its estimation.
Indeed, what we must rely upon is a sample of the area (or volume in aquatic
environments) of interest. Consequently, the true total number of species in that area
or volume is out of reach in practice. Every sampling unit contains a certain number
of individuals belonging to a certain number of species, and, given the fact that some
species are more rare than others and therefore less likely to be detected, the total
number of species of a sampling unit or a set of sampling units increases with the
sampled area or volume and the number of detected individuals. Consequently, the
370
8 Community Diversity