The Swire Institute of Marine Science and the School of Biological Sciences, The University of Hong Kong, Pokfulam Road, Hong Kong, Hong Kong SAR.
Department of Biology, University of Florence, via Madonna del Piano 6, 50019, Sesto Fiorentino, Italy.
BMC Ecol. 2018 Feb 15;18(1):8. doi: 10.1186/s12898-018-0164-1.
The spatial distribution of mangrove crabs has been commonly associated with tree zonation and abiotic factors such as ground temperature and soil granulometry. Conversely, no studies were designed to investigate the role of competition for resources and predation in shaping crab distribution in mangroves, despite these biotic factors are recognised as key determinants for spatial patterns observed in the communities colonising rocky and sandy intertidal habitats.We studied floral and faunal assemblages in two zones of a Sri Lankan mangrove, a man-made upper intertidal level and a natural eulittoral, mid-shore one. Leaf choice experiments were designed to study both feeding rate and intra and inter-specific interactions for food of sesarmid crabs in the two habitats in order to better understand crab spatial distribution.
The two intertidal belts differed in terms of floral composition and crab species abundance. The eulittoral zone was strongly dominated by Neosarmatium smithi, while within the elevated littoral fringe four sesarmids (N. smithi, N. asiaticum, N. malabaricum and Muradium tetragonum) were more evenly distributed. At both levels, all sesarmids showed to collect significantly more Bruguiera spp. and Rhizophora apiculata leaves than Excoecaria agallocha ones. There was no temporal segregation in feeding activity among the four species, resulting in a high interference competition for leaves. Regardless of the habitat, N. smithi was always successful in winning inter-specific fights.
Our results showed that the elevated littoral fringe was more crowded with crabs, but was less favourable in terms of food availability and environmental conditions. The dominance of N. smithi in gathering mangrove leaves suggests that this species may segregate the other sesarmids into less favourable habitats. The present data strongly suggest for the first time that interference competition for food can contribute to shape mangrove crab spatial distribution.
红树林蟹的空间分布通常与树木的分布带以及地面温度和土壤粒度等非生物因素有关。然而，尽管这些生物因素被认为是塑造红树林中栖息在岩石和沙质潮间带生物群落空间格局的关键决定因素，但没有研究旨在调查资源竞争和捕食在塑造蟹类在红树林中的分布中的作用。我们研究了斯里兰卡红树林的两个区域的植物和动物群集，一个是人为的高潮带，另一个是自然的中潮带。设计了叶片选择实验，以研究两种生境中 sesarmid 蟹的摄食率以及种内和种间相互作用，以便更好地了解蟹的空间分布。
两个潮间带带在植物组成和蟹类物种丰度方面存在差异。中潮带主要由 Neosarmatium smithi 占据，而在升高的潮间带边缘，有四种 sesarmid 蟹（N. smithi、N. asiaticum、N. malabaricum 和 Muradium tetragonum）分布更为均匀。在两个水平上，所有 sesarmid 蟹都明显更多地收集 Bruguiera spp. 和 Rhizophora apiculata 的叶子，而不是 Excoecaria agallocha 的叶子。在四种物种中，没有在摄食活动方面出现时间上的隔离，导致对叶片的强烈干扰竞争。无论在哪个栖息地，N. smithi 总是能够在种间战斗中获胜。
我们的结果表明，升高的潮间带边缘有更多的螃蟹，但在食物可用性和环境条件方面不太有利。N. smithi 在收集红树林叶片方面的优势表明，该物种可能会将其他 sesarmid 蟹类驱赶到较不利的栖息地。本研究首次强烈表明，食物的干扰竞争可以有助于塑造红树林蟹的空间分布。
