Assessing the effects of structural complexity on decision- making in ants

Abstract

The structural complexity of habitats can mediate foraging behaviours. I used artificial habitats to address the questions: 1) How does route complexity affect ant foraging choices, and 2) What are the foraging decisions of ants when faced with resources that vary in route complexity and food quality? I tested the effects of complexity on foraging choice by placing 3D printed discs of four levels of complexity in the field. I identified ants arriving at the discs, noting which species arrived at baits first, and which ones remained after two hours. Twelve species were recorded, however, three species provided sufficient observations for further analyses; Iridomyrmex purpureus, Rhytidoponera metallica and Pheidole sp.. These species were observed more often in simple, complex and intermediate treatments, respectively. Species richness increased with complexity: a drop-off occurred in the most complex treatment. I tested the abilities of R. metallica and I. purpureus to make single-attribute and multi-attribute decisions using a Y-maze experiment. Single-attribute decisions compared species’ preferences between more complex or simple routes, and choosing between high and low-quality food sources. To test multi-attribute decisions, I combined these variables in Y-maze experiments to assess if ants could make effective foraging choices when considering both food quality and complexity. Higher quality food sources were preferred when complexity was held constant. When food quality was held constant, R. metallica preferred low complexity treatments, and I. purpureus preferred complex treatments. I found no evidence of trade-offs between food quality and structural complexity. Unexpectedly, the preferences for complexity contrasted with experiments in question one. Ant decisions to forage in complex or simple areas may be influenced by differences in individual species’ foraging strategies and morphology.