Contrasting effects of functionally distinct tadpole species on nutrient cycling and litter breakdown in a tropical rainforest stream
Contrasting effects of functionally distinct tadpole species on nutrient cycling and litter breakdown in a tropical rainforest stream
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热带雨林溪流中功能不同的蝌蚪物种对养分循环和凋落物分解的对比影响
DOI：
10.1111/fwb.13053
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发表时间：
2018
影响因子：
2.7
通讯作者：
Natuhara Yosihiro
中科院分区：
文献类型：
--
作者：
Ramamonjisoa Noelikanto;Natuhara Yosihiro
人们越来越有兴趣预测物种多样性和丰富度的丧失如何影响生态系统的结构和功能。热带溪流中蝌蚪的多样性和丰度可能非常高，但与其他群体相比，人们对它们的功能作用知之甚少。我们评估了营养生态位，并研究了蝌蚪对溪流中养分循环（排泄和排泄）和垃圾分解的贡献。我们使用了两种生态形态不同的蝌蚪，它们属于马达加斯加拉努马法纳的两个最主要的摄食行会：Boophis quasiboehmei（以下简称 BQ，广义口器，食草动物）和 Mantidactylus melanpleura（以下简称 MM，伞形漏斗口器，悬浮喂食器）。我们进行了田间孵化实验，以量化从排泄和排出中回收的养分，并设置围栏来分析九种处理中蝌蚪对凋落物分解（Pauridianthasp.和Chrysophyllumsp.）的影响：对照（无蝌蚪），单一特异性处理（BQ或MM），三种密度（低、中、高：分别为3、6、12只蝌蚪/0.0625 m2）和混合物种处理（3 BQ + 3 MM、6 BQ + 6 MM）。BQ 和 MM 占据相同的营养级，但碳同位素特征往往不同。 MM 的氮 (N) 和磷 (P) 排泄率较高，但两个物种的 N:P 摩尔排泄比相似。从粪便颗粒（排泄）中回收的营养物质不能立即获得，而是需要矿化：N随着在水柱中的时间而增加，并且在实验结束时（第16天）浓度高出25倍以上，而P浓度呈驼峰状模式，在孵化第4天达到最大值。蝌蚪对垫料分解的影响取决于蝌蚪身份、密度和垫料身份。特别是，在低蝌蚪密度下不会发生分解，并且对质地较软的 Pauridianthasp 叶子的影响通常更强。我们发现蝌蚪多样性对凋落物分解具有累加效应。这些结果表明：（1）具有不同口器的蝌蚪在生态系统中发挥着不同的作用； (2)蝌蚪粪便颗粒是淡水环境中重要的潜在营养来源； (3)蝌蚪丰度对凋落物分解的影响比物种多样性更强，强调了热带溪流中蝌蚪生物量和群落的重要性。养分循环的种间差异和对凋落物分解的不同影响说明了物种特性和生态系统功能之间的密切联系。
There is growing interest in predicting how loss of species diversity and abundance affect the structure and functioning of ecosystems. Tadpole diversity and abundance can be exceptionally high in tropical streams, but, compared to other groups, relatively little is known about their functional roles. We assessed the trophic niches and investigated the contribution of tadpoles to nutrient recycling (excretion and egestion) and litter breakdown in streams.We used two ecomorphologically distinct tadpoles belonging to the two most dominant feeding guilds in Ranomafana, Madagascar:Boophis quasiboehmei(hereafter BQ, generalised mouthpart, grazer) andMantidactylus melanopleura(hereafter MM, umbelliform funnel mouthpart, suspension feeder). We conducted field incubation experiments to quantify nutrients recycled from excretion and egestion, and set enclosures to analyse the effects of tadpoles on litter breakdown (leaves ofPauridianthasp. andChrysophyllumsp.) in nine treatments: control (no tadpoles), monospecific treatment (BQ or MM) at three densities (low, medium, high: 3, 6, 12 tadpoles/0.0625 m2, respectively) and mix‐species treatment (3 BQ + 3 MM, 6 BQ + 6 MM).BQ and MM occupied the same trophic level but tended to differ in their carbon isotopic signatures. MM excreted nitrogen (N) and phosphorus (P) at higher rates, but the two species had similar N:P molar excretion ratio. Nutrients recycled from faecal pellets (egestion) were not immediately available but needed to be mineralised: N increased with time in the water column and was more than 25 times higher in concentration at the end of the experiment (day 16), whereas P concentration showed a hump‐shaped pattern with a maximum value at day 4 of incubation. Effects of tadpoles on litter breakdown depended on tadpole identity, density and litter identity. Particularly, no breakdown occurred at low tadpole density, and effects were generally stronger on the softer texture leavesPauridianthasp. We found additive effects of tadpole diversity on litter breakdown.These findings indicate that (1) tadpoles with different mouthparts play different roles on the ecosystem; (2) tadpole faecal pellets are important latent sources of nutrients in freshwater environments; and (3) tadpole abundance exerted stronger effects than species diversity on litter breakdown, emphasising the importance of tadpole biomass and communities in tropical streams. Interspecific variation in nutrient recycling and differential effects on litter breakdown illustrate a strong linkage between species identity and ecosystem function.