Global biodiversity: is it in the mud and the dirt?

The components needed ,o study the role of sigat traits in speciation are clearly aw,ilable in the D, melonogasrtr complex. The combination of withio- an,f betweensptcies studies with an easilr measured isolatblg trait provides a powerful m ~del system. Wetenolnation of the geneoc basis of these traits is already well advancedand ultimatelv it should be oossible to ideotifv and sequ&ce the @ne$involved. The n&t step will be to investigate the selection pressuresoperatingon hydrocxbonditferences, through lurther population cornpart. sons and studyofposslbleareasol contact between the two hydrocarbon forms.

stusrl ii. Ruddey Tom Tragema Roger K. Butlln

Global biodiversity: is it in the mud and the dirt? between soil and sediment birr L’.mks dwwslty and ecosystetemfunctionwere the topic of a symposium organized by Diana Wall freckman, at the American Association for the Advancement of Science (nnas) annual meeUng in Seattle in February 1997. The goalof the symposium was to highlight the vast unexplored biodiversity of the soil and sediment biota and the importance of these biota to ecosystem function at small and large spatial and temporal scales. Areas were high lighted where a lackof informatia on the soil and sediment biata criticaffy limits our ability to understand and mawa@ terrestrial and aquatic ecosystems. Soil has been called ‘the ooor man’s tropicaf forest’. In a square m&r of soil. there we tens of miUio”s of bacteria. tens of meters of length of fungal mycelia. millions of protozoa and xmatodes and up to a nZ!!too arthropods. reported Valerie

khm-Pelletter

~Research trr;lch. U!icul-

tore Canada, O&a). But what doihese creatures do? And perhaps more mysteriously, does each of thesecreatures have a unique ftmctf(lrml role in the soil ecosystem?lfthebtodiwrsity ofthesoitdeclines.

becaosr of hiima ~a for agriculture or forestry, or deposition d acid rain or heavy metals, will the ability of soil to support plant growth, store carbon and cleanse pollutants from water decline? If we cut down the ooor man’s trooical forest. till we lose a’vast reservoir.of biodiversity and critically affect soil functions? The n&e and extent of our ignorance at the soil biota are staclerino. Freckman (Colorado State Untvers~~. Ft &tins, USA) presented concepptoalfw! web diagrams for soil systems, emphasizing that !here were few data on the soecifics of these toad webs. This ignoran’ce is Iriglltening, because we lmow that the soil and sediment biota are responsible for processing c. 80% of the oreantc material that is pro duced by pla&~lobally. converti”~ this productton into CO2 and other atmospheric trace gases (e.g. methane, a.trous oxide) and into soil organic matter, which is critical to maintaining the physical, chemical and biological integrity of the soiixoryrtem. Research is indicating that extreme environments and low diversity systems, such 3s those found in hot and cold deserts. could be used a8 models for

understanding the linkage between ecosystem function and biodiversity of soil communities. There. thelinkases between diversity ad function are not masked by theovenvhelmingdivi~fo~d inother terrestrialecosystems. Freckmaowasable to demonstrate that many of the ignored components of the soil community, such as nematodes. are imoortint to oreanic matter cor~!ralled bi nit properties (e.g. :dinity. nutrient avai!ability). are highly sensitive to disturbmse and are amenable to management. Behan-Pelletier described recent ettorts to directly address links between soil biodiversity and ecosystem function questions. using mites as a model for ‘he roil fauna. Mites are ideal for emlorin~ re latfonships between biodiversi&and & > system function because they are phyla genetically diverse. ubiquitous in nail, and are a practically tractahie gvp to address. Though lobally only about 15% of mitespeciesare taxonomicafiydescrthc~, diversity of mites in any single temperate habitat rarely exceeds about 350 species. most of which are morphologically dis tinct. so that an ecoloeist can recomize morphospecies. And, kost import&tly, there are systematists in North America who work on mites, can develop identification keys to species, ard can interaCt with ecologists. Behan-P&tier suggests that studies of relationships between mite diversityandeeosrstemfunctioncanservt as a model for studies of other soil and

processing, are

NEWS

&

COMMENT

sediment organisms. providing guidance for asking general questions about biodiversity and soil hmction and creating bnportant disclpllnary llnb between sys-

temalists. scclogists mnd soil scientists. She described some of these studies and presented rove detail on World-WideWeb-based twmomic c!irecfories being compiled by several collaborative international research groups. The symposium was not restricted to soils, but included sediments as well. Margaret Palmer (University of Maryland. College Park. USA) suggested that while the bmmrtance 01. and threats to. fresh-

Paul Snelgrove (Memorial University of Newfoundland. Canada) and Cheryl Ann tlutman (Woods Hole Oceanographic Institutlon. hlA. USA). Diversity, community structure and ecosystem function appear to varv wstematicallv with sediment texture (;g.snndstom;ds)just astheydoin solls. This parallel suw?sts that an lmportant area of research will be the study of phystcal stro~to~ea~aco11strainton biotic structure. diversity and function. Perhaps the most mysterious sedimentary habitats are those that Snelgrove described in the deepsea. Although these cold and lightless

habitats appear to be

major concern.For example. the function and ecology of the San Francisco Bay ecosystem has been changed drzmatlcally and probably irreversibly by the introduction of the Chinese clam and other specles. In short. marine wstetns areshowing wlnerabillty to biodiv&sity loss and ec& system Iunction. In my own contrfbutlon I discussed

principles that cut across terrestrial. freshwater and marine habitats and addressed the significance of relationships between soil and sediment biodlversfty and ece system functionat large (regional and global) scales. lsuceested that the etnereence

waler &zoutces are well known. the roleol sediment biota in the maintenance of the quality of these resources has received KU toa little attentton. Slmtlartosoils. the number of undescribed species in freshwater sediments Is huge. Palmer noted that she finds a new sp=zciesof crustacean

Inhospitable to life. they cover some 65% oftheplanet,appeartohave substantially higher diversity than shallow-water habitats, and routinely produce large numbers of previously undescribed species with each sampllngtrip. Most marine sedlmen. tary habitats are poorly described, but

ation 01 ecosystem impairment. Measuring these functions. and determlnlng the importance of specific organisms and of

inabouteverv5Uthsamolesheorocesses. and a new skies of rohfer in &ery sam: pie. She emphasized that it is not at all clear if proper ecosystem functioning de pendsfundamentally on species diversity. While there are examples of cases where single species play an important role in some speclftc lonction. for example a single species of detritivorous shrimp is crfticatly impmtant to organic matter de composition in some tropical rainforest streams in Puerto Rico, general relationshipsbetwe2ndiversi~~dfunction have hernelusive.Palmeremphasizedtheneed functionalcl~silcationaof freshwater sedffent owanisms and for identilcation d sensitive id key species.She suggests that streams, which are more amenable to experimentation than rivers or oceans, may be useful model systems for filling these needs. An interesting parallel between the soils described by Freckman and marine sediments was revealed in the talk by

deep-sea habitats makeapxticularlycom-

thediversity

pelling case for biodiversity studies b+ ro;;;,hey are so species rich and poorly

nance. in a variety of ecosystem types, would foster the emergence of general principles relating biodiversity and ecosystem function in solls and sediments. Moreover. it is clear that understanding these llnks Is critical to large scales. Our ability to assess and manage problems ranging from the global methane budget to removal of polychlorinated biphenyls (PCCSS) from large areas of river and estoary sediments fs fundamentallylbnited by a lack of knowledge about the organisms that live in soils and sediments and what theydo.Amajorefforttoleamabat these organisms and their function is clearly warranted.

for

Should we be concer;ned about loss of biodiversity in marine sediments? Many marine sedimentary specfes are thought to havefafrly broad distributionswith few barriers to dispersal. Deep-seasediments are also far from most human activity, so all of these factors suggest that marine sediments might belesswlnerabletospe ties extinctions than many other habitats. But the life history aspects of deep-sea species make them extremely slow to recover fromlocal impacts such as deep-sea tisherfes. Shallow-water areas are subject to intense fisheries Impacts and chemical and nutrient loading over sufficiently broad areas that genetic and species diversity may be at risk our poor knowledge 01 thesesystemsalsomeans that hiodiversity loss may be occurring without our even knowing it. Exotic species are also a

al $eneral pr&iples will be greatI; fostered by the delineation and adaption uf a universalset ofsoilandsediment functions that can be used as a standard for evalo-

of organisms to their main@

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