Dunic Jillian C, Baum Julia K
Department of Biology, University of Victoria, PO Box 1700 STN CSC, Victoria, BC, V8W 2Y2, Canada.
J Anim Ecol. 2017 May;86(3):577-589. doi: 10.1111/1365-2656.12637. Epub 2017 Mar 20.
Temperate marine fish communities are often size-structured, with predators consuming increasingly larger prey and feeding at higher trophic levels as they grow. Gape limitation and ontogenetic diet shifts are key mechanisms by which size structuring arises in these communities. Little is known, however, about size structuring in coral reef fishes. Here, we aimed to advance understanding of size structuring in coral reef food webs by examining the evidence for these mechanisms in two groups of reef predators. Given the diversity of feeding modes amongst coral reef fishes, we also compared gape size-body size allometric relationships across functional groups to determine whether they are reliable indicators of size structuring. We used gut content analysis and quantile regressions of predator size-prey size relationships to test for evidence of gape limitation and ontogenetic niche shifts in reef piscivores (n = 13 species) and benthic invertivores (n = 3 species). We then estimated gape size-body size allometric scaling coefficients for 21 different species from four functional groups, including herbivores/detritivores, which are not expected to be gape-limited. We found evidence of both mechanisms for size structuring in coral reef piscivores, with maximum prey size scaling positively with predator body size, and ontogenetic diet shifts including prey type and expansion of prey size. There was, however, little evidence of size structuring in benthic invertivores. Across species and functional groups, absolute and relative gape sizes were largest in piscivores as expected, but gape size-body size scaling relationships were not indicative of size structuring. Instead, relative gape sizes and mouth morphologies may be better indicators. Our results provide evidence that coral reef piscivores are size-structured and that gape limitation and ontogenetic niche shifts are the mechanisms from which this structure arises. Although gape allometry was not indicative of size structuring, it may have implications for ecosystem function: positively allometric gape size-body size scaling relationships in herbivores/detritivores suggests that loss of large-bodied individuals of these species will have a disproportionately negative impact on reef grazing pressure.
温带海洋鱼类群落通常具有大小结构，随着捕食者的生长，它们会捕食越来越大的猎物，并处于更高的营养级。口裂限制和个体发育过程中的食性转变是这些群落中出现大小结构的关键机制。然而，对于珊瑚礁鱼类的大小结构，人们了解甚少。在这里，我们旨在通过研究两组珊瑚礁捕食者中这些机制的证据，来增进对珊瑚礁食物网中大小结构的理解。鉴于珊瑚礁鱼类的摄食方式多种多样，我们还比较了各功能组之间口裂大小与身体大小的异速生长关系，以确定它们是否是大小结构的可靠指标。我们使用肠道内容物分析以及捕食者大小与猎物大小关系的分位数回归，来检验珊瑚礁食鱼动物（n = 13种）和底栖食无脊椎动物（n = 3种）中口裂限制和个体发育生态位转变的证据。然后，我们估计了来自四个功能组的21个不同物种的口裂大小与身体大小的异速生长比例系数，其中包括草食性/碎屑食性动物，预计它们不会受到口裂限制。我们发现了珊瑚礁食鱼动物中大小结构的这两种机制的证据，最大猎物大小与捕食者身体大小呈正相关，并且个体发育过程中的食性转变包括猎物类型和猎物大小范围的扩大。然而，底栖食无脊椎动物中几乎没有大小结构的证据。在所有物种和功能组中，正如预期的那样，食鱼动物的绝对口裂大小和相对口裂大小最大，但口裂大小与身体大小的比例关系并不能表明存在大小结构。相反，相对口裂大小和口部形态可能是更好的指标。我们的结果提供了证据，表明珊瑚礁食鱼动物具有大小结构，并且口裂限制和个体发育生态位转变是这种结构产生的机制。虽然口裂异速生长并不表明存在大小结构，但它可能对生态系统功能有影响：草食性/碎屑食性动物中口裂大小与身体大小呈正异速生长比例关系，这表明这些物种中大型个体的丧失将对珊瑚礁的啃食压力产生不成比例的负面影响。
