Nematodes in Ecological Webs

Abstract

Nematodes, with a simple, tubular body form are the most abundant multicellular animals on earth. Wherever there is active animal life there are nematodes, often with up to 200 species and several million plant and soil nematodes per square metre. Although not active without free water, typically nematode populations are regulated by predators and microbial parasites, and their diverse biological interactions place them in many food webs. Nematode activity may affect plant community composition and succession. Their abundance, diversity and effects on soil processes make indices of nematode assemblage useful indicators of ecosystem condition. Although some parasites cause disease, most nematodes are beneficial, keeping earth's nutrients cycling or enhancing the diversity of natural ecosystems.

Key Concepts:

  • Nematodes are abundant, widespread and diverse.

  • Nematodes require free water and food resources to be active but narrow soil pores may prevent them using some resources.

  • Nematodes excrete the excess nitrogen from their food in plantā€available form.

  • Plant and soil nematodes use a wide range of food resources; other nematodes may be parasites of invertebrates and vertebrates.

  • Nematode populations may be regulated by predators and microbial parasites.

  • The diverse biological interactions of nematodes place them in many food webs.

  • Nematode feeding affects their microbial and plant food resources and may result in trophic cascades.

  • Nematode activity may affect plant community composition and succession.

  • Because of their abundance, diversity and effects on soil process indices of nematode assemblages are often useful indicators of ecosystem condition.

Keywords: nematode; feeding; food resources; soil; predation; nutrient flux; environmental limitation; atmospheric carbon dioxide; forest; grassland

Figure 1.

Post‐embryonic development of Diploscapter coronata, a bacterial‐feeding member of the Rhabditida, shown in lateral view. (a)–(d) represent juvenile stages 1–4 and (e) the adult female. In this species there is increase in size during development (body length of J1∼180 μm, J2∼200 μm, J3∼280 μm, J4∼340 μm and ♀∼500 μm) but there is little change in the body shape, except that the female has a shorter tail; the de Man ratios (a, b, c), which relate body width, pharyngeal length and tail length to total body length, change little. Note, however, there is marked increase in the length of the genital primordium (J1∼4–5 μm, J2∼6–7 μm, J3∼8–15 μm, J4∼25–98 μm and ♀gonad span ∼240 μm). Scale line=50 μm or 0.050 mm. Redrawn from Hechler . With permission from the Helminthological Society of Washington.

Figure 2.

Specialisation of the head region and stoma armature in 10 plant and soil nematode genera. Anteriors of adult females are shown at uniform magnification. Rhabditis, Acrobeles (Order Rhabditida) and Plectus (Plectida) are solely bacterial‐feeding, with rather simple tubular stomas, sometimes with complex lips; Diplogaster (Diplogasterida) and Mononchus (Mononchida) are either predators or bacterial‐feeders and have relatively wide stomas with various teeth for rupturing prey; Actinolaimus (Dorylaimida) is a predator/omnivore. The following four genera all have a protrusible stylet with a narrow lumen (∼0.1 μm in diameter) through which all the food must pass: Tylenchus (Tylenchida) is regarded as plant‐associated whereas related genera feed on fungal hyphae; Rotylenchus, Criconema (Tylenchida) and Xiphinema (Dorylaimida) all feed solely on higher plants; Seinura (Aphelenchida) (not shown) has a similar stylet but feeds as a predator. Reproduced from Yeates .

Figure 3.

Schematic illustration of multiple controls on root‐feeding nematodes utilising marram grass (Ammophila arenaria) in coastal sand dunes of north‐west Europe as a food resource. The interactions illustrated represent a food web centred on nematodes of this trophic group. See text for involvement of nematodes in additional food webs. Redrawn with modification from Van der Putten . With permission from the Ecological Society of America.

Figure 4.

When the nematode Mesodiplogaster is feeding on the bacterium Pseudomonas in either fine or coarse textured soil the population biomass increase over 33 days is much greater when the amoebae Acanthamoeba is feeding on Pseudomonas in narrower pores and then being predated on by Mesodiplogaster. Compiled from Elliott et al..

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Further Reading

Anderson RC (2000) Nematode Parasites of Vertebrates: Their Development and Transmission, 2nd edn, 672pp. Wallingford: CAB International.

Bardgett RD (2005) The Biology of Soil: a Community and Ecosystem Approach, 242pp. Oxford: Oxford University Press.

Coleman DC, Crossley DA and Hendrix PF (2004) Fundamentals of Soil Ecology, 2nd edn, 386pp. Burlington: Elsevier.

Gaugler R (ed.) (2002) Entomopathogenic Nematology, 400pp. Wallingford: CAB International.

Lee DL (ed.) (2002) The Biology of Nematodes, 635pp. London: Taylor & Francis.

Perry RN and Moens M (ed.) (2006) Plant Nematology, 480pp. Wallingford: CABI.

Wall DH (ed.) (2004) Sustaining Biodiversity and Ecosystem Services in Soils and Sediments, 275pp. Washington: Island Press.

Wardle DA (2002) Communities and Ecosystems: Linking the Aboveground and Belowground Components, 392pp. Princeton: Princeton University Press.

Wilson MJ and Kakouli‐Duarte T (eds) (2009) Nematodes as Environmental Bioindicators, 326pp. Wallingford: CAB International. ISBN 978‐1‐84593‐385‐2.

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Yeates, Gregor W(Jun 2010) Nematodes in Ecological Webs. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0021913]