Interactions with earthworm communities : a laboratory-based approach with potential applications for soil restoration
The role of earthworms in improving soil fertility and structure is widely recognised. As a result earthworms (often single species populations) have been deliberately introduced into pasture and arable land by man in attempts to improve plant production and into degraded land in order to bring about soil amelioration. The potentioal of earthworms employed in land restoration programmes may be enhanced by inoculating sites with a combination of species from different ecological groupings which have different roles in soil processes. In order to acheive the type of success envisaged by such projects, detailed information on the ecology and interactions between candidate species is required. This research investigated inter- and intra-specific interactions in terms of growth, maturation, cocoon production and survival, between five earthworm species (Allolobophora chlorotica (Savigny), Aporrectodea caliginosa (Savigny), Aporrectodea longa (Ude), Lumbricus rubellus (Hoffmeister) and Lumbricus Terrestris (Linnaeus)) under laboratory conditions. Cultures were initially maintained under optimal environmental conditions. Selected environmental variables (e.g food poison, food particle size and soil bulk density) were manipulated in order to quantify observed species interactions and subject earthworms to condditions that could be encountered at restored sites. Results demonstrated that all species could be successfully cultured under laboratory conditions. Techniques developed during the work may have applications in commercial large-scale rearing of earthworms in addition to production of species cohorts for toxicological testing and further laboratory experimentation. All experimental species were found to co-exist under the specified laboratory conditions, however both positive and negative inter- and intra-specific interactions were recorded throughout the study. The intensity of negative (competitive) interactions was attributed to the degree of niche overlap between earthworms and was dependant upon the species present, their stage of development and ability to adapt th limiting environmental conditions. Some deep burrowing earthworm species were found to increase the production of smaller conspecifics and other smaller earthworm species. it is suggested that this type of positive (commensal) association arose from smaller individuals feeding on concentrated and easily digestible organic matter present in the castings of larger earthworms. In addition to the potential applications of culture techniques described earlier, this research has contributed to the knowledge of an important ecological group, provided data for competition theory and should also prove valuable because of its implications for soil restoration.