Data from: Disentangling associational effects: both resource density and resource frequency affect search behaviour in complex environments

Neighbouring resources have been found to either decrease or increase the
likelihood that a consumer organism attacks a focal resource. These
phenomena are referred to as associational resistance (AR) and
associational susceptibility (AS), respectively. While associational
effects have been observed in various field studies, little is known on
how resource heterogeneity can cause associational effects. We used a
laboratory approach in which we studied the effects of resource density
and frequency in the search behaviour of Drosophila melanogaster as a
model organism for olfactory-guided behaviour in insects. We first
determined whether D. melanogaster could discriminate between odour
sources that differ quantitatively. Secondly, we determined what the
effect of resource density and frequency was on the search behaviour of D.
melanogaster by combining these resources into various patch arrangements.
Finally, we used the outcome of our experiments to disentangle the role of
resource density and frequency in associational effects. We found that D.
melanogaster has the ability to discriminate between quantitatively
different resources, but that the attraction to resource density is
constrained by an optimum after which attraction decreases. Furthermore,
in heterogeneous environments, flies showed a strong preference towards
the more apparent resource, leading to AS for the more apparent resources
and AR for the less apparent resource. The strength of this interaction
increased with a decreasing frequency of the more apparent resource. These
results imply that D. melanogaster mainly selects patches at the level of
individual resources. Consequently, when a patch contains qualitatively
different resources, the more apparent resource will attract a higher
number of flies than the less apparent resource irrespective of the
frequency of the apparent resource within the patch. Our study shows that
associational effects can be explained by determining the hierarchical
level at which a consumer selects its resources. When a consumer selects
resources at the individual level rather than at the patch level, our
results can be used to explain the population dynamics of host plants and
their associated consumers under field conditions.