Data from: Olfactory and visual plant cues as drivers of selective herbivory

Food quality is an important consideration in the foraging strategy of all animals, including herbivores. Those that can detect and assess the nutritional value of plants from afar, using senses such as smell and sight, can forage more efficiently than those that must assess food quality by taste alone. Selective foraging not only affects herbivore fitness but can influence the structure and composition of plant communities, yet little is known about how olfactory and visual cues help herbivores to find preferred plants. We tested the ability of a free-ranging, generalist mammalian browser, the swamp wallaby Wallabia bicolor, to use olfactory and visual plant cues to find and/or browse differentially on Eucalyptus pilularis seedlings grown under different nutrient conditions. Low-nutrient seedlings differed from high-nutrient seedlings, having lighter coloured leaves, red stems and lower biomass and nitrogen content. In the absence of visual cues, wallabies used odour to differentiate vials containing cut seedlings. They visited and investigated patches with high-nutrient seedling odour most, followed by patches with low-nutrient seedling odour, and patches with no added odour least. However, when visual and olfactory cues of seedlings were present, wallabies reversed their foraging response and were more likely to browse low- than high-nutrient seedlings. This browsing difference, in turn, disappeared when long-range visual cues were reduced by pinning seedlings horizontal to the ground. We suggest that visual cues overrode the effects of olfactory cues on browsing patterns of intact seedlings. Our study shows that herbivores can respond to odours of higher nutrient plants but in ecologically realistic scenarios they use a variety of visual and olfactory cues, with a context-dependent outcome that is not always selection of high nutrient food. Our results demonstrate the importance of testing the sensory abilities of herbivores in realistic multi-sensory settings to understand their function in selective foraging.食物质量是包括植食动物在内所有动物觅食策略中的核心考量因素。能够通过嗅觉、视觉等感官从远距离探测并评估植物营养价值的个体，相较于仅能通过味觉评估食物质量的同类，觅食效率显著更高。选择性觅食不仅会影响植食动物的适合度，还可调控植物群落的结构与组成，但目前学界对嗅觉与视觉线索如何帮助植食动物定位偏好植物的机制仍缺乏深入认知。 本研究以自由活动的广食性哺乳类啃食者——沼泽袋鼠（Wallabia bicolor）为研究对象，测试其利用植物嗅觉与视觉线索，对不同营养条件下培育的细叶桉（Eucalyptus pilularis）幼苗进行定向搜寻或选择性啃食的能力。 低营养组幼苗与高营养组幼苗存在显著表型差异：叶片颜色更浅、茎秆呈红色，且生物量与氮含量更低。在无视觉线索的实验条件下，沼泽袋鼠可通过气味区分放置了剪取幼苗的样本瓶：其对高营养幼苗气味斑块的访问与探查频次最高，其次为低营养幼苗气味斑块，未添加气味的对照斑块频次最低。 然而，当幼苗的视觉与嗅觉线索同时存在时，沼泽袋鼠的觅食偏好发生反转，更倾向于啃食低营养幼苗而非高营养幼苗。当通过将幼苗平贴于地面以削弱其远距离视觉线索时，这种啃食偏好差异便会消失。本研究提示，视觉线索会凌驾于嗅觉线索之上，影响完整幼苗的啃食选择模式。 本研究证实，植食动物能够响应高营养植物的气味信号，但在符合自然生态的真实场景中，它们会综合利用多种视觉与嗅觉线索，其觅食结果并非总是偏向选择高营养食物。本研究结果表明，唯有在具备多感官线索的真实环境中测试植食动物的感官能力，方能明晰其在选择性觅食中的作用机制。