Mesograzer identity, not host algae, determines consumer stable isotope ratios

Species-specific foraging habits or feeding preferences influence the overall trophic functioning in consumer assemblages. We set out to assess the <i>in situ</i> trophic diversity in a mesograzer assemblage (isopods, amphipods and gastropods) associated with marine littoral macroalgae. More specifically, we set out to establish whether stable isotope ratios of carbon (δ¹³C) and nitrogen (δ¹⁵N) are dependent on primary consumer identity or expressed in relation to the identity of the algal host, i.e<i>.</i> the habitat of the consumer. Consumer locations in bivariate isotope space revealed significant differences among grazer taxa, but no effect of the algal host. This suggests that grazer-specific foraging is more important in driving the qualitative range of feeding in the consumer assemblage than host diversity <i>per se</i> within a macrohabitat, such as a bay or a lagoon. The stable isotope ratios of the mesoherbivores were in line with expectations based on the known feeding ecology of the grazers. However, the trophic diversity suggested by stable isotope analysis implies that even an established concept such as the mesograzer guild may encompass simplifications in terms of functional group membership.

物种特异性觅食习性与取食偏好，会对消费者集合群落的整体营养功能产生影响。本研究旨在评估与海洋潮间带大型藻类共生的中型食草动物类群组合（包含等足类（isopods）、端足类（amphipods）与腹足类（gastropods））的原位（in situ）营养多样性。具体而言，本研究旨在明确碳（δ¹³C）与氮（δ¹⁵N）的稳定同位素比值，究竟是由初级消费者的类群特征决定，还是与消费者的栖息宿主——即藻类宿主——的特征相关联。对双变量同位素空间内消费者分布的分析结果显示，不同食草动物类群间存在显著差异，但未观测到藻类宿主的影响效应。这表明，在海湾或潟湖这类大生境中，相较于宿主本身的多样性，物种特异性的食性模式对消费者集合群落取食的定性范围的塑造作用更为关键。中型草食动物的稳定同位素比值与基于已知食草动物取食生态学的预期结果一致。然而，稳定同位素分析所揭示的营养多样性意味着，即便诸如中型食草动物功能群这类已被广泛认可的概念，其功能群归属的划分也可能存在过度简化的问题。