Mv. Abrahams, OF PREDATION AND ITS INFLUENCE ON THE RELATIVE COMPETITIVE ABILITIES OF 2 SPECIES OF FRESH-WATER FISHES, Canadian journal of fisheries and aquatic sciences, 51(7), 1994, pp. 1629-1633
Experiments were conducted with fathead minnow (Pimephales promelas) a
nd brook stickleback (Culaea inconstans) to determine whether their re
lative feeding rates were affected by risk of predation. Six groups of
both species were observed foraging for food provided by an automated
feeder while two parameters were manipulated: the presence or absence
of a predator, yellow perch (Perca flavescens), and clear or turbid w
ater. It was hypothesized that the armour and spines of brook stickleb
ack would be of greatest benefit during a direct encounter with a pred
ator. I attempted to simulate this condition with turbid water and pre
dator present. Feeding rates of the two species were significantly dif
ferent, with fathead minnow feeding at a greater rate than brook stick
leback in the absence of a predator. In the presence of a predator the
feeding rate of fathead minnow declined significantly whereas that of
brook stickleback was unaffected. This resulted in similar feeding ra
tes for the two species in the presence of a predator. Results demonst
rate that risk of predation can alter the relative competitive abiliti
es of two species in situations where one species possesses a morpholo
gical adaptation against predation. In the absence of predators, these
traits may be detrimental in interspecific competition for food.