Ž .Geoderma 93 1999 335–338

On the concept of pedodiversity and itsmeasurement

Julio A. CamargoArea de Ecologıa, Departamento de Geologıa, UniÕersidad de Alcala, E-28871 Alcala de´ ´ ´ ´

Henares, Madrid, Spain

Received 22 February 1999; received in revised form 28 June 1999; accepted 25 August 1999

Ž .Recently, in this journal, Ibanez et al. 1998a have used several algorithms,˜giving special emphasis to indices based on information theory, to analyze thetaxonomic diversity of the world pedosphere on the basis of data compiled bythe FAO at a scale of 1:5,000,000. Drawing a parallel with the concept ofbiodiversity in ecology, the authors conclude that soil patterns of differentclimatic zones are linked in a very well-defined latitudinal gradient. Following

Ž . Ž . Ž . Ž .this, Hudson 1998 , Odeh 1998 , Van Meirvenne 1998 , Vepraskas 1998 ,Ž . Ž .Yaalon 1998 and Wilding and Nordt 1998 have made some constructive

Ž .comments on the work of Ibanez et al. 1998a , and in general on the concept of˜pedodiversity and its measurement. As a consequence of these six independent

Ž .comments, Ibanez et al. 1998b replied to the questions raised by the discus-˜sants. Especially those related to the concept and analysis of taxonomic pedodi-versity.

In my opinion, the concept of pedodiversity in soil science cannot have, andwill never reach, the great significance that the concept of biodiversity has inecology. Owing to the existence of important biotic factors, such as competition,predation and parasitism, that operate throughout a spatial scale continuum inwhich the ecological and evolutionary times overlap and interact, and becausesuch biotic factors may be directly involved in the development, maintenanceand disappearance of biodiversity, it is difficult to find a true parallel betweenthe concepts of pedodiversity and biodiversity. As pointed out by YaalonŽ .1998 , ‘‘there is, however, a basic difference between plant or animal diversityand pedodiversity, which must not be overlooked. Soil bodies or pedons withtheir pedogenic horizons are essentially products of deterministic factors andprocesses and not part of Darwinian evolution,’’ where random genetic instabili-

0016-7061r99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved.Ž .PII: S0016-7061 99 00065-8

( )J.A. CamargorGeoderma 93 1999 335–338336

Ž . Ž .ties e.g., mutation, recombination produce a priori genetic variation withinmetapopulations by increasing heritable differences among individuals and

Ž .antirandom natural selection consumes a posteriori genetic variation withinsubpopulations by increasing the frequency of advantageous genotypes. Further-

Ž .more, if the soil mantle i.e., the pedosphere can be viewed as a continuum inŽwhich the separation of pedotaxa is not always feasible Hudson, 1998; Odeh,

.1998; Van Meirvenne, 1998; Yaalon, 1998 , then such a parallel between theconcepts of biodiversity and pedodiversity is more fiction than fact. It should beobvious that there are no unique soil bodies or pedons as regarded by Dr. Ibanez˜Ž .Ibanez, 1995, 1996; Ibanez et al., 1995, 1998a . There is only a continuously˜ ˜changing mantle in which intergrades between different soil types is rather therule than the exception; the separation of pedotaxa after all is to some extend

Ž .arbitrary and artificial. In this respect I agree with Odeh 1998 , Odeh et al.,Ž . Ž .1992, Van Meirvenne 1998 , McBratney and De Gruijter 1992 that it would

be better to use the fuzzy-sets approach, which takes cognizance of both thelarge variation in soil properties and the soil continuity in space and time. In

Ž .contrast, Dr. Ibanez’s Ibanez et al., 1998b idea that the dilemma of the soil˜ ˜continuum may be referred to Bohr’s Principle of Wave-Particle Complementar-ity seems to me unjustified.

Ž .Additionally, the algorithms used by Ibanez et al. 1998a to measure˜taxonomic pedodiversity are probably not the most appropriate ones. Indeed, theuse of diversity indices based on information theory has been criticised inecology for their dubious ecological interpretation and because of their sensitiv-

Žity to the relative abundances of dominant species see Whittaker, 1972; Peet,1974; Goodman, 1975; Kempton and Wedderburn, 1978; Washington, 1984;

.Magurran, 1988; Camargo, 1992, 1993, 1995 . Other diversity indices, with lessdubious ecological or pedological interpretation and higher sensitivity to the

Ž .number of pedotaxa whenever a proper separation of pedotaxa is possible ,should be used to measure taxonomic pedodiversity. Moreover, because speciesdiversity, as a parameter of community structure in ecology, is intimately

Ž .associated with species dominance that causes an impact on species diversity ,it should be evident that pedon diversity and pedon dominance must be closelyrelated in pedology. Species dominance has been well defined as the appropria-tion of potential niche space of certain subordinate species by other dominant

Ž .species McNaugton and Wolf, 1970 . Dominant species are more abundant andcan lead subordinate species to extinction by competitive displacement; they arebetter able to colonize more localities and, consequently, are able to preempt thecolonization of potential competitors; and they are also prone to experienceadaptive radiations in local environments. Nevertheless, it is hard to understandeither how dominant pedons can make appropriation of the potential niche spaceof subordinate pedons, or how dominant pedons can lead subordinate pedons toextinction by competitive displacement, or how dominant pedons can colonizeother localities and experience adaptive radiations. Soil bodies or pedons, as far

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Ž .as I know, are not self-catalyzed replicating structures as living organisms are .Ž .In this respect I disagree with Dr. Ibanez Ibanez et al., 1998b that the concept˜ ˜

of pedodiversity and the concept of spatial variability of soil properties requiredistinct definitions. My opinion is that both concepts may be analogous.Actually, the concept of pedodiversity has been regarded as the variability of

Ž .soil properties in a specific area or region McBratney, 1995; Odeh, 1998 , thosesoil properties being determined by its constitution, types and attributes.

ŽIn summary, while the concept of biodiversity integrating the concepts of.species diversity and species dominance has great significance and utility in

Ž .ecology, the concept of taxonomic pedodiversity within the scientific disci-pline of pedology remains, for the moment, a mere anecdote. Biodiversity isboth an ecological and evolutionary concept, and we must accordingly recognizethat there is no true parallel between the concept of pedodiversity and theconcept of biodiversity. My overall feeling is that the perspective developed byDr. Ibanez is rather erroneous and will turn out to have little utility in soil˜science.

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