Nematode Ecology
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Introduction
  Nematodes are known to be found in virtually every habitat from sea, fresh water, and land (Brusca, 1990). However, the majority of Nematode species are aquatic. Most Nematodes live in the interstial spaces between soil particles, or other substratum. Their ecology is dominated by such physical properties as viscosity, surface tension, gascous diffusion, water percolation, and humidity (Nicholas, 1984).
Terrestrial Nematodes
  Soil dwelling Nematodes are usually quite close to the surface, roughly between 10 to 20 cm deep. The greatest populations of Nematodes are located in the rich organic soils, where decomposition occurs the fastest.

Nematode populations seem to fluctuate in size over the course of a year. Studies completed in the early 70's by Yeates showed that Nematodes have their peak populations in May and their low in February. The low temperatures of winter probably restricted recruitment, while the heat of the summer increases the numbers (Nicholas, 1984).

The most productive habitats for Nematode populations are the temperate grasslands and deciduous (fully developed) forests. Populations of Nematodes are considerably lower in coniferous (Evergreen and Pine cone type) forests and tropical forests. There are two basic stratagies that nematode populations fall under:
  1. R-Strategist: They have a short generation time and high offspring count, rapidly using up their transient resources. Many of these Nematodes are bacteria-feeding, who probably thrive best in temperate grasslands and deciduous forests.
  2. K-Strategist: They have a long generation time, which is thought to be once a year for most. This type of strategy would best be served in coniferous forests and tropical forests (Nicholas, 1984).
Predation of Nematodes in Soil
There are some fungi species that are specialized to feed on Nematodes. There are two different types of predatory fungi:
  1. Fungi that use an extensive predatory hyphal system, which invades entrapped Nematodes.
  2. Endoparasites, where the fungi's hyphal is confined to the Nematode's body (Nicholas, 1984).
Marine Nematodes
  Nematodes are found in a variety of marine sediments from tidal zones to the deep ocean. They can be found on rocks near shores and marine plants. Most marine sediment Nematodes are found only 5 to 10 cm from the sediment. These measurements vary as the habitats on the beach shift from sandy to rocky (Nicholas, 1984). The different sediment types have a direct correlation with the type of Nematode family associated with each habitat.

Feeding
"Bacteria-feeding Nematodes are also common in many ecosystems that it is important to assess their importance in decomposition of organic matter and the recycling of nutrients and to understand their population dynamics" (Nicholas, 1984). Many of the bacteria-feeding Nematodes are R-Strategists, which have short generation times. Larger Nematodes relay on feeding off of soft-bodied organisms (other worms or small organisms).
1. Brusca, Brusca Invertebrates. Sinaurer and Associates. 1990

2. Warwick, Nicholas L. The Biology of Free-Living Nematodes. Clarenden Press, Oxford; 1984