Life-history tactics of soil microarthropods

Abstract

A sound basis for defining life-history tactics was obtained by reviewing life-history traits. This involved an explanation of the ecological implications of thelytoky (automictic or apomictic), arrhenotoky, amphitoky, sexual reproduction, semelparity, iteroparity, seasonal iteroparity, and the relationship between semelparity and juvenile development. Several forms of synchronization of life cycles with environmental conditions were classified, ranging from the ability to overcome harsh seasonal conditions to obligate diapause dormancy. Ecologically, this involves adaptations to environmental conditions ranging from irregularly occurring and unpredictable events to regularly occurring and predictable conditions. Dispersal traits were grouped as directional migration (phoresy) and undirectional migration (anemochory). Distinctions were made between facultative and obligate phoresy and between carrier-specific and carrier-unspecific phoresy. A multi-dimensional system of tactics was outlined, based on well-defined underived traits. This system was compared with one- and two-dimensional schemes described by MacArthur and Wilson (1967), Grime (1977), and Southwood (1977) and with the multi-dimensional system described by Stearns (1976). For each tactic, relationships with the main biotopes in which it occurs were defined. Examples of species showing certain tactics were selected from the taxonomic orders of microarthropods. The generality of the traits for various groups of organisms and of the classification of life-history tactics developed was explored.