BIOLOGY Volume 1 - A Guide to General Biology - 2004

8. HETEROTROPHIC NUTRITION

8.2. Feeding Mechanisms in Animals

8.2.3. Detritivore Feeding

Detritus consists of fresh or decomposing organic matter typically found on the soil surface. Organisms that feed on detritus are called detritivores or detritophagous animals. Earthworms serve as a classic example of such creatures. Detritivores typically drive the initial stage of dead organic matter Processing and therefore play a vital role in the ecosystem. The earthworm (Fig. 2.58) consumes fragments of detritus, particularly plant remains located on the soil surface or pulled down into its burrow. Food particles are broken down, moistened with an alkaline secretion produced by the Pharynx, and swallowed. Earthworms can also feed on organic matter present in the soil they ingest while burrowing.

The earthworm's digestive tract is a straight tube extending from the Mouth to the anus. Each section is specialized for the Digestion AND ABSORPTION of ingested food. Any undigested material is expelled through the anus in the form of characteristic casting pellets.

Charles Darwin was the first to draw attention to the crucial role earthworms play in maintaining soil Structure and fertility. Fertile soil can contain up to two million earthworms per hectare. As soil passes through the earthworm's gut, it is pulverized and enriched with various elements before being deposited On the surface as castings. This improves soil structure and provides a natural form of tilling (with estimated annual soil turnover reaching around 50 tonnes per hectare). The End products of the worms' Nitrogen METABOLISM, in turn, enrich the soil with nutrients that can subsequently be utilized by plants. Binding excess calcium in the form of its salts reduces soil acidity, thereby promoting overall plant growth. The burrows dug by earthworms ensure excellent soil aeration and drainage, allowing a greater supply of oxygen to reach plant roots. By pulling surface detritus down into their burrows, earthworms accelerate the overall rate of organic matter decomposition and enhance ecosystem productivity.