A delayed response in the area-concentrated search can improve foraging
success.
Abstract
Area-concentrated search (ACS) is a simple movement rule implying that
an animal searches for resources using a ’state-dependent correlated
random walk’. Accordingly, a forager increases its searching intensity
by reducing the directionality of movement (’intensive search mode’ or
ISM) when it detects a resource item, but if it searches unsuccessfully
for a while, it returns to a more straight-line movement to search for
new resource locations elsewhere (’extensive search mode’ or ESM). We
propose a modified ACS, called delayed-response ACS (dACS), which would
be more efficient in resource collection than standard ACS. Instead of
immediately switching from ESM to ISM when encountering a resource, as
is done in standard ACS, an individual foraging in the dACS mode delays
this switch by ’x’ steps so it continues moving in a straight line for a
while before switching to ISM. Our results show that an individual with
a suitable delay parameter ’x’ for the dACS achieves substantially
higher foraging success than an individual with standard ACS (x=0).
Optimal foraging success occurs when ’x’ is approximately similar to the
patch radius ’r’. This is because, with dACS, an individual can
penetrate deeper into a cluster and stay longer within it, ultimately
increasing the number of resources collected. Modifying the
half-saturation constant ’h’ also affects the success of foraging, but
the effects depend on resource density and cluster size. Generally, ’h’
modulates the optimal ’x’ value only slightly. dACS can be interpreted
as a survey movement within a resource cluster before switching from ESM
to ISM. The dACS rule does not rely on complex spatial memory but only
on memorizing whether resources were found or not. It may thus occur in
a wide range of taxa, from organisms without a central nervous system to
animals with complex brain systems.