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 dens...