Introduction: concepts of habitat

To an insect, the world consists of a hierarchy of habitats, which many ecologists divide somewhat arbitrarily into ‘macrohabitats’ and ‘microhabitats’. Hanski (2005) used the felicitous term ‘habitat matrioschkas’ to reflect this hierarchy of scales, whereby habitats are nested in the same manner as the famous Russian dolls. He exemplified the concept by referring to the European saprophilous pythid beetle Pytho kolwensis, for which the relevant matrioschka has the sequence: boreal forest; sprucedominated forest; spruce-mire forest with high temporal continuity of fallen logs; a fallen spruce log with the base above the ground; a particular stage in the decay succession of phloem under the detaching bark. The first three of these were regarded as macrohabitat, and the last two as microhabitat. Reflecting their small size and ecological specialisations, many insects depend on resource-based ‘microhabitats’ for their wellbeing and sustainability, but these in turn depend on the continued presence of the embracing macrohabitats. Thus, attributes of ‘place’ (categorised broadly by major ecosystem: here, boreal forest, and commonly referred to as ‘biotopes’) intergrade with more specific needs that may be viewed as progressively more tangible resources at finer scales. The major practical lesson, as emphasised by Hanski (2005), is that much of insect species conservation planning must heed and focus on microhabitats, commonly to a far greater extent than for many vertebrate conservation plans. Whereas many a bird or endemic marsupial in Australia may have its habitat classified satisfactorily merely as ‘eucalypt woodland’ or some similar broad descriptive term, most insects found in that vegetation association will have far more precise needs and defining their habitat will need correspondingly finer descriptors, as with Pytho in southwestern Finland.