Ecologists have long wondered how plants and algae persist under constant herbivory, and studies have shown that factors like chemical defense and morphology can protect these species from consumption. However, grazers are also highly diverse and exert varying top-down control over primary producers depending on traits such as body size. Moreover, susceptibility of plants and algae to herbivory may vary across life stages and size classes, with juveniles potentially the most vulnerable. Here, we focus on diverse grazing communities within giant kelp forests and compared consumption on two size classes of juvenile giant kelp (Macrocystis pyrifera) across four herbivore species ranging in size. We also integrated field and literature densities to estimate impacts on populations of juvenile kelp. We found that purple sea urchins, a species known for exerting strong control over adult M. pyrifera, had weak per capita impact on microscopic kelp, on par with a much smaller crustacean species. While urchin consumption increased with macroscopic juvenile kelp, it never surpassed the smaller brown turban snail, suggesting that feeding morphology, in addition to herbivore body size, is a predictor of consumption at these small size classes. The smaller herbivores also occurred in high densities in the field, increasing their predicted population-level impacts on juvenile kelp compared to urchins and perhaps other larger, but less abundant, herbivores. This study highlights the variation in species' roles within an herbivore guild and the importance of age-related changes in grazing vulnerability to better understand herbivore control on plant and algae population dynamics.

中文翻译：

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沿海基础物种对草食动物的体型依赖性脆弱性。


生态学家长期以来一直想知道植物和藻类如何在持续的食草下生存，研究表明化学防御和形态等因素可以保护这些物种免遭食用。然而，食草动物也高度多样化，并根据体型等特征对初级生产者施加不同的自上而下的控制。此外，植物和藻类对食草动物的敏感性可能因生命阶段和大小类别而异，其中幼体可能最脆弱。在这里，我们重点关注巨型海带森林内的不同放牧群落，并比较了四种不同大小的食草动物物种对两个大小级别的幼年巨型海带（Macrocystis Pyrifera）的消耗量。我们还整合了实地和文献密度来估计对幼年海带种群的影响。我们发现，紫海胆（一种以对成年紫海胆具有强大控制能力而闻名的物种）对微观海带的人均影响较弱，与较小的甲壳类动物物种相当。虽然海胆的消费随着宏观幼年海带的增加而增加，但它从未超过较小的棕头螺，这表明除了草食动物的体型之外，摄食形态也是这些小尺寸类别消费的预测因素。较小的食草动物也以高密度出现在田间，与海胆和其他较大但数量较少的食草动物相比，增加了它们对幼年海带的预测种群水平影响。这项研究强调了草食动物群体中物种角色的变化以及放牧脆弱性中与年龄相关的变化的重要性，以更好地了解草食动物对植物和藻类种群动态的控制。