Effects of Conspecifics and Vegetation On Nest Site Selection in Gasterosteus Aculeatus L

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Abstract
Vegetation and conspecific rivals both exert significant influences on the locations of territories as determined by the nest sites selected by naive male three-spined sticklebacks. The effect of a row of vegetation along one end of a tank depends on the size of the tank. In small tanks (up to I20 cm), a row of vegetation at one end repels males. In the 300 cm tank, a row of vegetation at one end did not appear to influence the overall distribution of nests, but those nesting in the end with the vegetation tended to nest in the vegetation. A row of vegetation at one end of the 600 cm ditch attracted some males who nested in the row. The remaining nests were located in the middle portion of the ditch,, and the end effect in the unplanted ditch disappeared. Thus the effect of a row of vegetation depends on the amount of open space available in front of it. In the 600 cm ditch, a row of vegetation standing away from the end attracted 65 per cent of the males who selected nest sites within and adjacent to the rows compared to 40 per cent when the row was at the end. The difference is not quite significant. With a rival behind a glass plate 30 cm from one end of the otherwise bare 600 cm tank, rival males selected nest sites at the opposite end of the tank. The repelling effect of a rival was effective over a relatively large distance in this bare environment. The repelling effect of the rival was exaggerated in some experiments in which a second glass plate was placed 30 cm from the opposite end. Separate experiments proved that a glass plate attracted males who tended to nest near it. The repelling effects of a rival was greatly reduced when a row of vegetation was placed at some distance from his territory boundary (glass plate).

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