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Evidence for the dilution effect in the selfish herd from fish predation on a marine insect (1981)

Foster, W. A. ; Treherne, J. E.

[s.l.] : Nature Publishing Group

Nature 293 (1981), S. 466-467

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ISSN: 1476-4687

Source: Nature Archives 1869 - 2009

Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics

Notes: [Auszug] There are two reasons why it has proved difficult to obtain reliable evidence that the grouping of prey animals reduces the risk of predation by a simple dilution effect. First, predation attempts, particularly on vertebrate prey, tend to be relatively rare and it is therefore difficult to quantify ...

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1038/293466a0

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Reproductive behaviour of the ocean skater Halobates robustus (Hemiptera: Gerridae) in the Galapagos Islands (1982)

Foster, W. A. ; Treherne, J. E.

Springer

Oecologia 55 (1982), S. 202-207

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ISSN: 1432-1939

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Summary Field observations on the ocean skater, Halobates robustus Barber showed that the flotillas of adults, unlike those of juveniles, occurred very close to the shore at specific sites from which they were not easily dislodged. The adult flotillas consisted of small all-male groups or aggregations of males and copulating pairs. The proportion of free males in copulating flotillas decreased with increasing group size. There was no correlation between the sizes of the paired males and females. Single adult females, which were not observed in the copulating flotillas, were usually teneral with undeveloped eggs. In contrast, the copulating females contained numerous well-developed eggs. The pairs remained in prolonged genital contact. The behaviour of free males in copulating flotillas was characterized by frequent, non-random encounters with copulating pairs. Experiments with marked individuals established that male take-overs can occur within flotillas. It is concluded that the copulating flotillas are initiated by the males and not only provide protection from predators, as previously shown, but also act as arenas for mate finding and selection. It is presumed that prolonged copulation reduces sperm competition between contending males.