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Computers Linking

Soil

soil

Biology biodiversity and The taxonomic

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is fundamentalto agricul- organized and retrieved (Danks

ture and forestry, water purification, and biogeochemical cycling, and it is the basis for civilization. Nevertheless, soils are one of the least understood habitats on Earth, while also being among the most biologically diverse. In one handful of rich organic soil there can be millions of organisms representing hundreds of different species, including bacteria, fungi, protozoa, algae, nematodes, annelids, and approximately 20 different lineages of Arthropoda, the most diverse phylum of living organisms (May 1988). This vast but mostly unknown biodiversity is one of the reasons why soil has been called "the poor man's tropical rain forest." The relationship of any particular species to soil ecosystem functions, such as decomposition and nutrient cycling, is also often unclear (Brussaard et al. 1997, Freckman et al. 1997, Groffman and Bohlen 1999). Undoubtedly, part of the scientific community's ignorance of the identity and roles of soil biota stems from the complex and opaque nature of this habitat; as Coleman (1985) has observed, scientists examine its biological components "through a ped darkly." Yet in principle, soil should be no more difficult to study than other spatially complex habitats, such as tropical forests or coral reefs; indeed, a range of direct and indirect sampling and observation techniques are available to help explore this habitat (Carpenter et al. 1985, Crossley et al. 1991, Moore et al. 1996). Species are the functioning entities in soil and sediment, as in all ecosystems. Each species has a unique evolutionary history and set of adaptations, and species are the means by which all biological information is

by Val Behan-Pelletier and Glen Newton February 1999

function-

1988). However, a major challenge for those attempting to link biodiversity to ecosystem processes in soil and sediment is that the taxonomy and classification of the majority of species, along with their biology and function, are unknown. This situation is especially true for the hyper-diverse taxa: bacteria, fungi, nematodes, and arthropods. For example, half of the estimated 50,000 arthropod species represented in North American soils are undescribed (Behan-Pelletier and Bissett 1992). Unfortunately, the "taxasphere"-the global community of systematists-has been declining in numbers in the last few decades, and a listing of taxonomists has only recently become available (TRED 1998). As a result, studies on biodiversity need to rely on collaboration of systematists from many countries. For example, studies of the biodiversity of selected arthropod groups in lowland tropical rain forest in Costa Rica depends on a collaboration of systematists from at least 10 countries (Longino and Colwell 1998). Closer networking between systematists and ecologists is a fundamental prerequisite to addressing the challenge of linking biodiversity and ecosystem function in soil and sediment. In this article, we propose that systematists and ecologists can be networked to one another, to databases on biodiversity in diverse ecosystems, and to interactive computerbased keys, using the Internet as the linking medium. Internet-based systems can, in turn, accelerate the identification of soil biota and understanding of their importance in ecosystems through the linking of distributed knowledge bases (researchers and databases), organizations, industry, decision-makers, and the public.

Mites as models of the taxonomic dilemma Mites (Acari) are representatives of the taxonomic dilemma facing researchers who study soil ecosystem processes. Acari is the major arthropod lineage found in soil. Mites are also common in freshwater sediments and are found in marine systems, including deep-sea vents (Evans 1992). There are approximately 45,000 described mite species worldwide, two-thirds of which are found in soil (Walter et al. 1996). But described species of mites are estimated to represent only 5% of total mite diversity (Walter and Proctor in press). In addition, few compilations of ecological data are available for the described species living in soil and sediment, aside from the catalogue of oribatid mites of the continental United States and Canada (Marshall et al. 1987) and the atlas on aquatic invertebratesof Northern Holland (Steenbergen 1993), which include comprehensive coverage of the literature on the taxonomy and ecology of these groups. There can be up to 250 different mite species and 800,000 individuals in a square meter of the organic layer of forest soil (Figure 1). In addition to sheer numbers, mites exhibit a number of characteristics common to hyperdiverse taxa found in soils and sediments, such as nematodes and fungi; these characteristics have implications for their roles in ecosystem processes. * Mites are phylogenetically diverse. This diversity reflects their ancient lineage, with a fossil record from the mid-Devonian (approximately 450 million years ago), when terrestrial ecosystems first evolved (Norton et al. 1988). There are three main lineages of mites in soil (Mesostigmata, Prostigmata, and Oribatida [the last of which includes Astigmata]), each

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ecologists scale up to functional groups based on knowledgeof only a few species.Functionalredundancyis postulated,often without evidence.If biologists are to tease apart some of the richest sources of biodiversityon earth-soil and sediment-and make connectionsbetweenbiodiversityand ecosystem function, we must be able to identifyindividualspecies and understandtheir biology and ecology.

Linkingbiodiversityand ecosystemprocesses

Figure1. Mites (Acari)extractedfrom a squaremeterof mixed deciduousand 200 speciesarepresent. coniferousforestsoil andlitter;approximately of which is species rich in this habitat. However, descriptionsof species are generally based on adults; immatures,which are often morphologically unlike adults, have been describedfor only 5-10% of species in each group. Furthermore, immatures are often longer lived than adults and more resistant to minimum levels of soil moisture, and they often feed differently from adults; consequently, they can have great impact on ecosystem dynamics. * Mites are ubiquitous in soil and fresh water and also occur in marine habitats (Evans 1992). They are found at every elevation and every latitude, from arctic to antarctic. They inhabit all kinds of soil, from extremely acid to alkaline and from nutrient poor to nutrient rich; they are also found up to 10 m deep in soil and in suspended soils in tree canopies (Walter 1995). * Miteshavea diversityof functionsin the ecosystem,as shown by the range of feedingguildsto whichthey belong (Moore et al. 1988). They include predators, parasites, fungal feeders, root feeders, dead-plant feeders, algal feeders, bacterial feeders, omnivores, and scavengers(Krantz1978). * Mites express a wider range of genetic systemsand life-historytraits (and associated strategies) than any other group of soil arthropods (Norton et al. 1993). For example, 150

manyMesostigmataand Prostigmata have high metabolism, high fecundity, and short life spans; some complete their life cycle in 4-7 days. Such species can respond rapidly to nutrientpulses in their habitat, such as an increase in prey. By contrast, many Oribatida have low metabolism, low fecundity, and long life spans;most take more than a year to complete their life cycle. Thus, nonastigmatid Oribatida do not respond to pulses of nutrients in the environment,andtheirpopulationsin soilarerelativelystable(Norton1994). * Mites are essentialfor efficient decompositionandnutrientcycling(Seastedt 1984). They can catalyze primarydecompositionin soil, activating fungiandbacteria(Mooreet al. 1988). They also contributeto the maintenance and developmentof soil structure because their fecal pellets are a component of soil microstructure. Otherecosystemfunctionsthat mites perform include suppression of soilborne diseases and pests, dispersal and vectoring of helminth parasites, and sequesteringof carbonand other minerals (Brussaardet al. 1997). Even though these general characteristics of mites are known, the role of most mite species in ecosystem functioning is unclear, as is the case with other groups of soil and sediment biota. Thus, of necessity, soil

Biodiversityand ecosystemprocesses are the imperativesof different biological disciplines-systematics and ecology-and the frame of reference of the two disciplines differs, as Moore et al. (1988) recognized. Systematists are most interested in the taxonomy and evolutionary history of a species: the recognition, identification, description, and classification of the species entity (Savage 1995). With notable exceptions (e.g., Walter 1987, Walter and Kaplan 1990), systematistsdevote little time to the ecology of individuals and populations, or to the organization of speciesassemblagesin ecosystems. By contrast, soil and sedimentecologists are most interested in ecosystem processes, such as energy flux, decomposition, and nutrientcycling. They devote little time to community ecology and, except in the case of keystone species, rarely study the ecology of single species living in soil (exceptions include Luxton 1981, Siepel 1990, 1995). In addition, systematists and ecologists are often membersof differentprofessionalsocieties,readdifferentjournals,and are unaware of data development and availabilityin the other discipline. In recentyears, however, computers have altered data management, and the Internetand the World Wide Web have affectedinformationpackaging and dissemination. The Internet has initiated an era of unprecedenteddata sharingthroughthe appearance of international publicdomain databases (Green 1994). Integration of systematic and biodiversity data on the one hand and ecological data on the other, using the Internet and the Web, is now possible. A number of initiatives are leading to this integration. BioScienceVol. 49 No. 2

Taxonomic relational databases. The objective of these relational databases is a directory for all known species that will be updated annually, with contributions from all systematists, as a resource for global studies on biodiversity in natural and managed ecosystems. It seems inconceivable that, although there are telephone directories for all cities and regions in every country in the world, as yet there is no listing for the approximately 1.2 million described species of organisms. Many such databases are being developed, and a continuously updated list is available at the National Biological Information Infrastructure Web site (NBII 1998). An additional source of information on taxa is the phylogenetic information in the Tree of Life (Maddison and Maddison 1996), a Web-based endeavor that has as its goal the inclusion of genetic and evolutionary relationships, photographs, and life histories for every species of living organism. Specimen-based relational databases. Museum collections and culture collections are specimen based-that is, voucher specimens exist that underpin taxonomic data. Many collections have developed their own databases that are searchable on the Web (e.g., CABI 1998). Large biodiversity studies are also specimen based and have a range of data associated with any specimen and with each sampling event. Specimen-based relational databases, such as BIOTA (Colwell 1997), allow a variety of spatiotemporal data to be captured, including date and time of collection, sampling methodology, site, habitat, microhabitat and vegetation fields, and a range of morphological and molecular data, from text to images to molecular fingerprints. Because the exact location of each specimen is known, species distributions can be easily mapped onto other geographical layers, such as soil type or watershed topology. Furthermore, these relational databases can be made available via the Web, and users can perform both geographicand habitat-based searches to explore the distribution of species among microhabitats, vegetation types, and latitudes and to examine the spatial trends of these species February 1999

distributions in relation to environmental gradients. By comparing databases from different regions, ecologists can detect biogeographic trends on continental and global scales. For example, mite species information from the Andrews Forest Long Term Ecological Research project in Oregon (www.fsl.orst.edu/lter/datafr. htm) could be compared with the mite information in the Arthropods of La Selva (ALAS) database (viceroy.eeb. uconn.edu/ALAS/ALAS.html). Computerized keys. The effective use of a group of organisms by ecologists requires user-friendly keys. These may be image-based, interactive computer identification aids, such as COMTESA (Computer Taxonomy and Ecology of Soil Animals), which was developed for the soil mites of the Pacific Northwest (Moldenke et al. 1991), or the CD-ROM that uses DELTA software to identify oribatid mites of Australia (Hunt et al. 1998). In the future, however, more keys will be accessed directly through the Web rather than by distributed software, similar to the key to species of Fusarium (Seifert 1996). Traditionally, identification tools have been based on morphological characters, and within the foreseeable future morphologically based identification will continue with morphologically rich taxa. But molecular techniques for identifying diversity are becoming more widespread. These techniques are initially being used for studying the diversity of bacteria (e.g., Torsvik et al. 1990, Tiedje and Zhou 1996), filamentous fungi and mycorrhizae (Clapp et al. 1996), and nematodes (Blaxter et al. 1998), but as time and cost constraints are overcome, these techniques will be developed for assessments of mite biodiversity. An Internet-based metadatabase of ecological research projects. The importance of the inadequately known soil biota in maintaining the fertility of soils, and the associated need to increase collaboration between taxonomists and ecologists studying soil systems, has been recognized for decades and recently reiterated (Freckman 1994, Wall and Moore 1999). One way to address this need is through the Database of Ecological Research Projects (DERP),

a searchable metadatabase (i.e., a database of databases) of ecology projects linked nationally and internationally with similar metadatabases (Newton et al. 1997). The initial focus of DERP is a metaproject database that records information about soil ecology projects (Newton et al. 1997). DERP allows investigators using the Internet to record a range of information about their project(s). In an attempt to create a rich and useful information base, DERP has an extensive set of fields. These fields include such items as project name, project URL, project time frame, keywords, abstract, contact information, data availability, data URL, size of available data sets, site description(s), site URL, site affiliation, taxa studied, functional group, research topic, methodology, United Nations Food and Agricultural Organization soil type(s), and georeferencing of location. This information can be accessed by investigators, other researchers, and decision-makers searching for information about soil ecology. The soil ecology view of DERP will facilitate collaboration and help address some of the gaps in knowledge of biodiversity and ecosystem functioning in soil that are outlined in Brussaard et al. (1997), Freckman et al. (1997), and Groffman and Bohlen (1999). Electronic "collaboratories" and virtual institutes. Ultimately, the closest linking of biodiversity and ecosystem function will take place at the project level, with taxonomists and ecologists collaborating and addressing the same hypotheses for connecting and interrelating soil and sediment biota with ecosystem processes. This approach, championed by Freckman (1994), is being addressed in linked US and UK projects in which biodiversity and the ecosystem functions of decomposition and carbon flux are being studied in grassland ecosystems. With computers and the Internet, it is becoming possible to: * Transfer specimen images or sequence data between the ecologist and the systematist via video links, allowing online identification; * Have online access to global taxonomic expertiseto solicitexpertopinion; 151

* Develop "digital vouchers" for species, including morphological characters, images, and molecular fingerprints; * Develop site-specific, interactive expert systems for species identification, with links to ecological databases; * Develop an Internet-based, collaborative infrastructure that links researchers and datasets on biodiversity and ecosystem properties and processes and that fosters collaboration between systematists and ecologists on these data sets. This "collaboratory" concept-in essence a "virtual institute"-is already operational in the Worm Community System (CANIS 1998) and is the subject of a growing body of literature in the area of computer-supported cooperative work (Reinhard et al. 1994, et al. 1996). The Fitzpatrick collaboratory concept is a natural information management framework to help address research questions about the interrelationships among ecosystem properties, ecosystem function, and soil biodiversity. These questions are as fundamental as the magnitude of the contribution of individual and key species of hyper-diverse taxa, such as mites, to soil processes; the effects of reducing resource variety (e.g., plant diversity) on the diversity of mites and other soil organisms; and the impact of soil biodiversity on primary productivity (Swift and Anderson 1994). Linking researchers from a range of disciplines (i.e., ecology, systematics, and information management) should allow these questions to be addressed effectively. We believe that adopting and employing techniques and systems for studying biodiversity in soil such as those described in this article will accelerate knowledge of mites and other organisms and their importance in ecosystems. These approaches will help turn the black box of soil biodiversity into a more comprehensible entity and will define more clearly biodiversity's contribution to, and impact on, ecosystem services.

Acknowledgments We thank Diana Wall for the opportunity to contribute to this special series of articles, and Diana, Rebecca Chasan,

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and two reviewers for helpful comments and suggestions on earlier drafts of this manuscript This article is a project of the Committee on Soil and Sediment Biodiversity and Ecosystem a component of Functioning, DIVERSITAS,coordinated by SCOPE.

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cophagous" microarthropods. Ecology 68: 226-229. . 1995. Dancing on the head of a pin: Mites in the rainforest canopy. Records of the Western Australian Museum Supplement 52: 49-53. Walter DE, Kaplan DT. 1990. Feeding observations on two astigmatic mites, Schwiebia rocketti (Acaridae) and Histiostoma bakeri (Histiostomatidae) associated with Citrus feeder roots. Pedobiologia 34: 281-286. Walter DE, Proctor HC. In press. Life at the Microscale: Mites and the Study of Ecology, Evolution and Behaviour. Sydney: New South Wales Press. Walter DE, Krantz G, Lindquist EE. 1996. Tree of Life, Acari.