S. Merilaita et V. Jormalainen, Different roles of feeding and protection in diel microhabitat choice of sexes in Idotea baltica, OECOLOGIA, 122(4), 2000, pp. 445-451
In Idotea baltica, a marine isopod that lives and feeds on the brown alga F
ucus vesiculosus, microhabitat choice differs between sexes so that males a
re found more often than females on the light-coloured and exposed apical p
arts of the alga. We investigated how the requirements of avoiding visual p
redators and feeding were related to microhabitat choice in relation to diu
rnal and life-cycle stage in males and females. Faced with a choice between
an apical and a basal piece of the alga, females spent more time than male
s on the basal piece, but this difference was not due to food choice. Faced
with a choice between a dark, concealing and a light, exposing background,
the preference for a dark background was stronger at day than at night, an
d stronger in females than in males. This suggests that a sex difference in
the importance of avoiding visual predators can explain the sex difference
in microhabitat choice. Further, the preference for a dark background and
night feeding both increased with age, suggesting that feeding is increasin
gly subordinated to the need to avoid visual predators. Our experiment foun
d no effect of the presence of the opposite sex on microhabitat choice. Our
results support the hypothesis that the sexes trade off feeding against pr
edation risk differently, presumably because growth is more important to ma
les than to females, which have more to gain by protection and therefore sp
end more time on the lower parts of the alga.