• Species composition and biogeographical distribution

Little information is available about the earthworm fauna in the Iberial Peninsula and new species remain to be discovered. A better knowledge of their geographical distribution is necessary in order to get new insights in the role they play in the terrestrial ecosystems.

The present distribution patterns of live organisms are usually explained as the result of two factors. On one hand, the influence of recent local factors, such as climate, altitude, soil type, food availability and predators abundance, which are also in interaction with inherent properties of the organisms (physiological tolerances, habitat preferences, dispersal hability...). On the other hand, large scale processes, fundamentally geological factors, have conformed the distribution and abundance of plants and animals. A more realistic view is obtained when both explanations are included.

Trigo D., Mascato R., Iglesias Briones M.J. & Díaz Cosín D.J. (1990). Lombrices de tierra de Portugal continental. Inventario y citas. Arquivos do Museu Bocage 1: 521-567.

Iglesias Briones M.J., F. Mariño, Trigo D. & Díaz Cosín D.J. (1991). Lombrices de tierra de Asturias, León, Zamora y Salamanca. I. Géneros Allolobophora y Dendrobaena. Boletín de la Real Sociedad Española de Historia Natural 87: 151-173.

Iglesias Briones M.J., F. Mariño, Trigo D. & Díaz Cosín D.J. (1992). Lombrices de tierra de Asturias, León, Zamora y Salamanca. I. Familias Megascolecidae, Acanthodrilidae y Hormogastridae y otros Lumbricidae. Boletín de la Real Sociedad Española de Historia Natural 88: 19-29.

Briones M.J.I., Mascato R. & Mato S. (1994). Biogeographical considerations in Asturias, León, Zamora and Salamanca (Spain) in relation to their earthworm fauna. European Journal of Soil Biology 30: 149-155.

Elvira C., Domínguez J. & Briones M.J.I. (1996). Composición de las comunidades de lombrices de tierra en un vertedero, un estercolero y un depósito de pasta residual. Nova Acta Científica Compostelana 6: 123-129.

Nair G.A., El-Mariami M.A., Briones M.J.I., Filogh A.M.& Youssef A.K. (2005). Earthworm resources of Benghazi, Libya. Journal of Environmental Biology 26: 175-178.

In contrast to other multivariate ordination methods, canonical correspondence analysis allows a one-step, direct relationship between species and environment variables. This analysis identifies those abiotic factors which are responsible for the distribution patterns of the soil community.

In the example presented here DCA analysis was applied to presence data of 13 earthworm taxa from Asturias, León, Zamora and Salamanca (Spain) and to 20 soil factors. From the results it can be inferred that the most prominent factors influencing earthworm distribution in the studied sites are pH, cations such as calcium, magnesium and aluminium and the silt content.

• Biology

Eisenia andrei and E. fetida are commonly employed in estabilising organic materials. Although most earthworm scientists now accept them as different species, they are often mistaken in the literature.

One possible explanation is the lack of external morphological characters to allow a better identification. Finding new characterising criteria, such as differences in their life cycle (growth and reproduction rates, mortality, cocoons and hatchlings size and their viability) could help in their identification.

Elvira C., Domínguez J. & Briones M.J.I. (1996). Growth and reproduction of Eisenia andrei and E. fetida in different organic residues. Pedobiologia 40: 377-384.

Domínguez J., Briones M.J.I. & Mato S. (1997). Effect of the diet on growth and reproduction of Eisenia andrei (Oligochaeta, Lumbricidae). Pedobiologia 41: 566-576.

Elvira C., Sampedro L. & Briones M.J.I. (1998). Caracterización de los capullos y de los recién nacidos de varias especies de lombrices de tierra (Oligochaeta, Lumbricidae). Boletín de la Real Sociedad Española de Historia Natural 94: 33-38.

• Cytogenetic

Sixto M. (1999). Análisis cariológico del complejo "Allolobophora caliginosa” (Oligochaeta, Lumbricidae). Master Thesis, University of Vigo. Supervisors: Dr. J.J. Pasantes and M.J.I. Briones.

• Forest ecology

• Decomposition processes of litter mixtures
  The management of litter mixtures provides important means of manipulating soil organic matter development and nutrient release, yet has received little research attention. However certain mixtures of litters have shown to exhibit positive decomposition interactions, resulting in enhancing nutrient release.
  
• Deforestation effects
  Intensification of agricultural practices is leading to an increased rate of deforestation. This diminuition of tree cover together with the removal of the felling residues has important effects on the soil ecosystems (erosion, soil fertility losses, hydrological changes, etc.) and on the soil fauna populations (namely, higher mortality rates).

Briones M.J.I. & Ineson P. (1996). Decomposition of Eucalyptus leaves in litter mixtures. Soil Biology & Biochemistry 28: 1381-1388.

Uhia E. & Briones M.J.I. (2002). Population dynamics and vertical distribution of enchytraeids and tardigrades in response to deforestation. Acta Oecologica 23: 349-359.