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 plant‐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.