about “what organisms do” could be interpreted as the phenotype of the organism,
like phenotypic trait, and then some authors equate the functional diversity to
phenotypic diversity. In this context, Tilman (2001) proposed a more specific
definition: “functional diversity is the value and range of those species and organismal traits that influence that ecosystem functioning.” Thus, a consequence of this
definition is the extent of functional differences among the species in a community.
Petchey and Gaston (2002a) considered functional traits as components of an
organism’s phenotype that influence ecosystem-level processes and established that
the measure of functional diversity requires, ideally, the following steps: first,
appropriate functional information (traits) about organisms to be selected and
included in the measure, and as consequence the irrelevant information needs to
be excluded. The simple answer to which traits to use in functional classifications is
all traits that are important for the function of interest and no traits that are
functionally uninformative. Second, the traits must be weighted according to their
relative functional importance; a common measure of functional diversity is the
number of functional groups represented by the species in a community (Naeem and
Li 1997; Hooper 1998; Hector et al. 1999; Rastetter et al. 1999; Walker et al. 1999;
Fonseca and Ganade 2001; Tilman 2001; Tilman et al. 2001; Petchey and Gaston
2002b; Roscher et al. 2004). Third, trait diversity must statistically measure and have
desirable mathematical characteristics (Mason et al. 2003; Botta-Dukát 2005;
Ricotta 2005). Finally, the measurement of the functional diversity would be able
to explain and predict the variation inside an ecosystem-level process.
Regarding the statistical methods applied to determine the functional diversity,
Petchey and Gaston (2002a) mention that multivariate methods can be associated
with functional grouping and functional dendrograms (FD) could be used because
they are similar to phenetics, grouping organisms based on observed physical
similarities employing primarily multivariate methods proposed by Sokal and
Sneath (1973). These authors also noted that it is very important that even this
analysis is similar to phenetic analysis, it possesses important differences; phenetics
focuses on morphological traits, whereas functional traits are used for functional
groupings; thus, different weightings of functional traits will produce different
functional dendrograms, none of which are, a priori, correct or incorrect. And the
emphasis on FD must be remarked regarding the use of the total branch length of a
functional dendrogram to measure functional diversity. Leishman and Westoby
(1992), Chapin et al. (1996), Díaz and Cabido (1997), and Fonseca and Ganade
(2001) mention that traits must be linked to the function(s) of interest, and Euclidean
distance and the unweighted pair group method with arithmetic mean (UPGMA)
which produced the distance matrix and functional dendrogram, respectively, are
commonly employed. Pace (1997) noted that the greatest research challenge is to
integrate these ecological analyses to microbial ecology and environmental microbiology, because the genetic and metabolic diversity of microorganisms is vast.
Kirk et al. (2004) mentioned that Trevors (1998) and Ovreas (2000) reported that
the methods of studying soil microbial diversity, particularly regarding species
diversity, involve the species richness, the total number of species present, species
evenness, and the distribution of species. Hughes et al. (2001) categorized these
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A. L. Guerrero-Zúñiga et al.
like phenotypic trait, and then some authors equate the functional diversity to
phenotypic diversity. In this context, Tilman (2001) proposed a more specific
definition: “functional diversity is the value and range of those species and organismal traits that influence that ecosystem functioning.” Thus, a consequence of this
definition is the extent of functional differences among the species in a community.
Petchey and Gaston (2002a) considered functional traits as components of an
organism’s phenotype that influence ecosystem-level processes and established that
the measure of functional diversity requires, ideally, the following steps: first,
appropriate functional information (traits) about organisms to be selected and
included in the measure, and as consequence the irrelevant information needs to
be excluded. The simple answer to which traits to use in functional classifications is
all traits that are important for the function of interest and no traits that are
functionally uninformative. Second, the traits must be weighted according to their
relative functional importance; a common measure of functional diversity is the
number of functional groups represented by the species in a community (Naeem and
Li 1997; Hooper 1998; Hector et al. 1999; Rastetter et al. 1999; Walker et al. 1999;
Fonseca and Ganade 2001; Tilman 2001; Tilman et al. 2001; Petchey and Gaston
2002b; Roscher et al. 2004). Third, trait diversity must statistically measure and have
desirable mathematical characteristics (Mason et al. 2003; Botta-Dukát 2005;
Ricotta 2005). Finally, the measurement of the functional diversity would be able
to explain and predict the variation inside an ecosystem-level process.
Regarding the statistical methods applied to determine the functional diversity,
Petchey and Gaston (2002a) mention that multivariate methods can be associated
with functional grouping and functional dendrograms (FD) could be used because
they are similar to phenetics, grouping organisms based on observed physical
similarities employing primarily multivariate methods proposed by Sokal and
Sneath (1973). These authors also noted that it is very important that even this
analysis is similar to phenetic analysis, it possesses important differences; phenetics
focuses on morphological traits, whereas functional traits are used for functional
groupings; thus, different weightings of functional traits will produce different
functional dendrograms, none of which are, a priori, correct or incorrect. And the
emphasis on FD must be remarked regarding the use of the total branch length of a
functional dendrogram to measure functional diversity. Leishman and Westoby
(1992), Chapin et al. (1996), Díaz and Cabido (1997), and Fonseca and Ganade
(2001) mention that traits must be linked to the function(s) of interest, and Euclidean
distance and the unweighted pair group method with arithmetic mean (UPGMA)
which produced the distance matrix and functional dendrogram, respectively, are
commonly employed. Pace (1997) noted that the greatest research challenge is to
integrate these ecological analyses to microbial ecology and environmental microbiology, because the genetic and metabolic diversity of microorganisms is vast.
Kirk et al. (2004) mentioned that Trevors (1998) and Ovreas (2000) reported that
the methods of studying soil microbial diversity, particularly regarding species
diversity, involve the species richness, the total number of species present, species
evenness, and the distribution of species. Hughes et al. (2001) categorized these
240
A. L. Guerrero-Zúñiga et al.