Predator-induced flow disturbances alert prey, from the onset of an attack
Résumé
Many prey species, from soil arthropods to fish, perceive the approach of predators,
allowing them to escape just in time. Thus, prey capture is as important
to predators as prey finding. We extend an existing framework for understanding
the conjoint trajectories of predator and prey after encounters, by
estimating the ratio of predator attack and prey danger perception distances,
and apply it to wolf spiders attacking wood crickets. Disturbances to air flow
upstream from running spiders, which are sensed by crickets, were assessed
by computational fluid dynamics with the finite-elements method for a
much simplified spider model: body size, speed and ground effect were all
required to obtain a faithful representation of the aerodynamic signature of
the spider, with the legs making only a minor contribution. The relationship
between attack speed and the maximal distance at which the cricket can
perceive the danger is parabolic; it splits the space defined by these two variables
into regions differing in their values for this ratio. For this biological
interaction, the ratio is no greater than one, implying immediate perception
of the danger, from the onset of attack. Particular attention should be paid to
the ecomechanical aspects of interactions with such small ratio, because of
the high degree of bidirectional coupling of the behaviour of the two protagonists.
This conclusion applies to several other predator–prey systems with
sensory ecologies based on flow sensing, in air and water.