Patterns of space use and defence by the pikeblenny, Chaenopsis alepidota, were studied over a 13-month period in 1977–1978 for a population inhabiting a sand/rubble plain in a small bay along the Baja California coast of the Sea of Cortez, The abundance of C. alepidota
varied widely over the year, as did its apparent mobility and territorial behavior. Analysis of size-frequency distributions suggests that in part the change in abundance reflects recruitment and rapid growth of a species that is largely annual. During periods of low population density, resources
appeared to be abundant and individuals appeared to roam widely and were largely non-aggressive, whereas during a period of high density, resources appeared to be in shorter supply, individuals were more site-attached and the incidence of agonistic interactions increased markedly. The apparent
short generation time of the species suggests population densities vary widely among habitats and years (reflecting recruitment variability), with concomitant shifts in a labile social system. The emphasis in the literature on vigorous territoriality in pikeblennies may reflect a bias due
to their conspicuousness during periods of high population density.
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