The degree of dietary specialization has a fundamental impact on the ecological function and interactions of suspension feeders. While niche differentiation by food particle size is common among obligate suspension feeders, its role is not evident in facultative ones. In this study, we aimed at providing new insights on the matter by focusing on sympatric mysid species. As mysids use different mechanisms for raptorial and filter-feeding, they represent a more adequate model system than e.g., the more extensively studied copepods. We made morphological measurements on the four coexisting invasive Ponto Caspian mysid species to determine the areas and mesh sizes of their filters. We also quantified their clearance rates on the microalga Cryptomonas sp. in a laboratory experiment to reveal how morphological differences manifest in their overall filtering capacity. We found relatively small but consistent differences in the primary filter area among the species, indicating that morphological constraints due to the enclosed position of the setae might limit the possibility for differentiation. The primary filter mesh sizes were small in all four species (0.69–2.73 μm) with moderate but consistent intraspecific differences, suggesting that the benefit of being able to capture small particles might outweigh the pressure for differentiation. The observed clearance rates were in accordance with the morphological characteristics of the species, highlighting that auxiliary filters (present in one of the species, Limnomysis. benedeni) are needed to increase filtering capacity considerably. Our study confirmed that food particle size can contribute to the niche differentiation of facultative filter feeders, but also indicated that they can tolerate a higher overlap than obligate ones. The observed differences were related to the habitat preferences and predatory potentials of the species, suggesting that complementarity among the different niche axes might further facilitate their coexistence.

中文翻译：

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兼性滤食动物的生态位分化：来自入侵性滨里海糠虾的见解

饮食的专业化程度对悬浮饲养者的生态功能和相互作用有着根本性的影响。虽然食物颗粒大小的生态位分化在专性悬浮饲养者中很常见，但其作用在兼性悬浮饲养者中并不明显。在这项研究中，我们旨在通过关注同域糠虾物种来提供关于这一问题的新见解。由于糠虾使用不同的猛禽和滤食机制，因此它们代表了比研究更广泛的桡足类更合适的模型系统。我们对四种共存的滨里海糠虾物种进行了形态学测量，以确定其过滤器的面积和网格尺寸。我们还量化了它们对微藻隐藻的清除率。在实验室实验中揭示形态差异如何体现在其整体过滤能力中。我们发现各物种之间的初级过滤面积存在相对较小但一致的差异，表明由于刚毛的封闭位置而导致的形态限制可能会限制分化的可能性。所有四个物种的初级过滤网目尺寸都很小（0.69-2.73 μm），具有适度但一致的种内差异，这表明能够捕获小颗粒的好处可能超过分化的压力。观察到的清除率与该物种的形态特征一致，突出表明需要辅助过滤器（存在于其中一种物种 Limnomysis. benedeni 中）来显着提高过滤能力。我们的研究证实，食物颗粒大小有助于兼性滤食动物的生态位分化，但也表明它们比专性滤食动物可以容忍更高的重叠。观察到的差异与物种的栖息地偏好和捕食潜力有关，这表明不同生态位轴之间的互补性可能进一步促进它们的共存。