Odour information: the key to associational effects of neighbours on focal plant susceptibility to mammalian herbivores

Abstract

(1) Neighbouring plants can alter the susceptibility of high-quality focal plants to herbivores by affecting herbivore patch choice. Many herbivores use plant odour to make patch-scale foraging decisions from afar, but the actual information they rely on within complex plant odours is largely unknown. Defining the information herbivores use provides a mechanistic link underpinning herbivore patch-scale foraging decisions. Revealing the information driving herbivore patch selection is key if we are to understand and predict associational effect outcomes of these decisions. (2) Here, our first aim was to test whether herbivores can use odour cues alone to make patch selection decisions facilitating predictable associational effects on high-quality focal plants. Our second aim was then to test whether artificial odour, designed to mimic the informative odour component of low-quality neighbours, is as effective as real plants in providing associational refuge. (3) We tested patch choice by African elephants, Loxodonta africana using a giant Y-maze and real or artificial plant odours as the only cues for the neighbours of a high-quality focal plant. We quantified the probability of various odour treatments being chosen in comparison with the odour of a focal plant alone. (4) Compared with focal plants alone, we found that elephants were more likely to choose patches with the focal plant and either moderate or high-quality neighbours, but less likely to choose patches with the focal plant and low-quality neighbours. We also demonstrated that an artificial subset of odours, designed to be informative, were as effective as real low-quality neighbours in providing associational refuge to the focal plant. (5) Our results demonstrate a key role of plant odour – and specifically informative components within complex odour profiles – in patch choice decisions facilitating plant associational effects on high-quality focal plants. Understanding what olfactory information herbivores use when deciding which patches to visit or avoid, and how it affects focal plant susceptibility is important ecologically. Herbivores' patch selection not only affects individual fitness, but also shapes plant community structure through impacting plant survival and recruitment, causing trophic cascades. Synthesizing odour information could offer a new tool to influence herbivore foraging decisions, with implications for wildlife management and conservation, including plant protection.