Feeding ecology of free-living nematodes.

This chapter provides overview of the feeding habits and food sources of aquatic nematodes. The environmental constraints on feeding, food recognition, and feeding selectivity are also addressed, together with the complex, indirect trophic interactions between nematodes and their microbial prey. To raise awareness of the inherent methodological and/or interpretational problems in studies of nematode feeding ecology, the chapter ends with a brief look at the methods that have been adapted to quantify feeding rates in nematodes.

Role of nematodes in the food web: nematodes as predator and prey.

This chapter provides information on the role of nematodes in the food web, including their participation in matter and energy fluxes within ecosystems. It highlights that nematodes are both predators and prey for organisms ranging from protozoans to vertebrates, based on gut analyses and direct observations. Functional response experiments, microcosm studies, and enclosures/exclosures in the field can be used to investigate the intensity of these trophic interactions and their impact on individual species as well as entire communities.

Freshwater nematodes as bioindicators in field studies - the NemaSPEAR[%]-index.

This chapter, after a general introduction to quality assessments of freshwater habitats, reviews the use of freshwater nematodes as in situ bioindicators, including in monitoring the ecological quality of freshwater habitats. By drawing on studies of nematode communities in unpolluted and polluted habitats as examples, it highlights both the different methods used to assess the quality of freshwater ecosystems and their applications. A focus of the chapter is the development of a new index that uses freshwater nematodes to assess chemically induced changes in the ecological status of freshwater habitats, the NemaSPEAR[%]-index (Nematode SPEcies At Risk).

Single- and multi-species toxicity testing with nematodes.

This chapter discusses the utility of nematodes in experimental ecotoxicology, and specifically in the study of freshwaters. Drawing on reports in which nematodes were used as test organisms in single-species tests as well as studies investigating nematode communities in model ecosystems (i.e. microcosms), the suitability of nematode-based experimental approaches in prospective and retrospective risk assessments of chemicals in freshwater sediments is examined. Several examples are presented of the use of Caenorhabditis elegans as a test organism in single-species bioassays, in order to demonstrate the versatility of this nematode for ecotoxicological investigations.

Freshwater nematodes in metacommunity studies.

This chapter discusses the application of the metacommunity concept to data on freshwater nematodes. First, the theoretical concepts, terminology, and methods used in metacommunity analyses are introduced. Second, metacommunity studies of freshwater nematodes are summarized and the results are compared with those obtained from studies of other organismal groups. Finally, research gaps in metacommunity ecology in general and freshwater nematodes in particular are highlighted.

Introduction to freshwater nematodes in ecology: current knowledge and research.

This chapter provides information on nematode morphology and reproduction; role of nematodes in freshwater ecosystems; and distribution and dispersal of free-living nematodes and their role in food webs.

Case studies with nematodes from the individual to ecosystem level.

Organisms smaller than 2 mm in size are ideal candidates for laboratory and field experiments with a theoretical focus. This chapter illustrates this point by drawing on recently published works in which studies of nematodes have informed theories within population and community ecology. Case studies examining the following are presented: (1) Life cycle experiments (individual level), (2) The interactions of two nematode species - competition experiments (population level), (3) Nematode community-based assessments of sediment quality (community level), (4) Nematodes in a detritus-based food web model (food web level).

Species composition and distribution of free-living nematodes in lakes and streams.

This chapter provides an overview of the distributional patterns of nematodes in lakes, rivers, and streams worldwide and of the factors that affect the structuring of nematode communities in the field. Drivers of variability in species composition such as habitat texture, flow rate, temperature, water chemistry, oxygen, vertical distribution of nematodes in the sediment, water depth in lakes, microphytobenthos, macrophytes, heterotrophic microbes, interspecific competition, and predation, are discussed.

Dispersal of free-living nematodes.

This chapter considers the possible reasons underlying the ubiquity of nematodes and their high abundances in nearly all of their habitats. It discusses three phases of dispersal. The first section considers the drivers and mechanisms of the emigration of nematodes from their original habitat. The second section outlines active and passive modes of transfer and provides estimates of transfer distances. In the last section, immigration is addressed, including an overview of the density and species composition in developing nematode communities during colonization.

Sampling and processing of freshwater nematodes with emphasis on molecular methods.

This chapter provides an introduction to current methods of nematode sampling and processing, with the latter including molecular methods as well. It highlights that nematode sampling and processing for different habitats will require different sampling methods; nematode identification can be achieved with morphological or molecular approaches; the analysis of specific gene fragments can be used to delimitate nematode species; and molecular species identification can give further information about phylogenetic background and cryptic species.