Evol Ecol Res 1: 333-346 (1999) Full PDF if your library subscribes.
Allochrony: A new way of analysing life histories, as illustrated with mammals
Douglas S. Glazier
and Scott D. Newcomer‡ Department of Biology, Juniata College, 1700 Moore Street, Huntingdon, PA 16652-2119, USA
Author to whom all correspondence should be addressed.
e-mail: glazier@juniata.eduABSTRACT
Many life-history features of animals can be scaled to body size. This allometric approach has provided important insights into the evolution of life histories. Here we propose a new approach which involves scaling life-history features in relation to life span or other life-history time periods. We illustrate this ‘allochronic method’ using life-history data from 190 species and 14 orders of mammals provided by Asdell’s Patterns of Mammalian Reproduction (Hayssen et al., 1993). Among these species, the durations of gestation, lactation and the post-weaning juvenile period were scaled to age at sexual maturity (first conception). Gestation time and lactation time both tended to show negative allochrony (slope < 1.0) with increasing age at first conception, whereas the juvenile period showed positive allochrony (slope > 1.0). These trends appear to be robust, as they are seen within various orders and families, body-size classes, dietary types and foraging modes. These data suggest that species differences in the age at sexual maturity depend more on differences in developmental time during the post-weaning juvenile period than during the pre-weaning period. Ecological comparisons further reveal that faunivorous mammals tend to spend a greater percentage of their maturation time as post-weaning juveniles than omnivores, granivore/frugivores or herbivores. Arboreal mammals also have proportionately longer juvenile periods than scansorial and terrestrial species. These trends appear to be related to the greater time required for the young of faunivorous and arboreal species to develop foraging and locomotor skills sufficient to permit reproduction. We conclude that the ability of the allochronic method to reveal new interesting patterns warrants its further use as a basic tool for analysing life histories.
Keywords: allochrony, body size, diet, foraging mode, gestation time, juvenile period, lactation time, life histories, mammals, maturation time, reproduction, scaling.
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