PATTERNS OF SURVIVAL AND EXTINCTION OF NEMATODES IN ISOLATED SOIL

The effects of local extinction on the structure of a nematode community were examined by monitoring soil nematode populations in cores that were isolated from surrounding soil. The cores were intact blocks of deciduous forest soil and litter of three different sizes (75, 250, and 920 cm3), maintained in a controlled-environment room, and sampled at 2-month intervals for 16 months. The number of nematode types per sample declined over time, from an initial average of 16 to less than 5 per 100 individuals. Types that were morphologically specialized for feeding on resources that were abundant in the cores persisted. Extinctions were associated with deficiencies of resources and with low initial population size. Nematode types that survived were generally abundant, of low trophic position and small body size. Abundance distributions at the end of the experiment were more strongly dominated by one or a few types and had higher logarithmic variances despite lower richness. Similar findings have been reported from studies of much larger, above-ground animals. Local or regional extinction appears to be a common phenomenon in ecological systems, and may affect the richness and population structure of many natural communities.