Alarm substances elicit limited population-level responses in fathead minnow

Alarm substances, chemical cues released by injured prey, are associated with increased predation risk. In the laboratory, fathead minnows limit conspicuous behaviours, such as foraging and nest guarding, when exposed to these cues. Although such responses could lead to reductions in growth and reproduction, with subsequent demographic consequences (e.g., recruitment), effects of alarm substances at the population level are largely unknown. In three field experiments, ponds and cattle troughs stocked with fathead minnow populations were treated with alarm substances or a water control over the summer breeding and growing season. Alarm substances had no effect on male parental behaviour. In one experiment, spawning occurred earlier with exposure to alarm substances; however, there was no subsequent effect on recruitment of young in this or in the other two experiments. Despite individual-level effects in short-term experiments, repeated exposure to alarm substances over a season had no measureable impact at the population scale.