Wolf B O, del Rio C Martínez
Department of Biology, The University of New Mexico, 167 Carstetter Hall, Albuquerque, NM 87131-1091, USA.
Isotopes Environ Health Stud. 2003 Mar;39(1):53-67. doi: 10.1080/1025601031000102198.
Succulent CAM plants, such as columnar cacti, are important physiognomic elements of many arid lands. Although, these plans are often ecologically important because they provide abundant resources in the form of nectar and fruit, their contribution to the energy, nutrient and water budgets of consumes has not been quantified. We describe an isotopic approach that allows quantifying the ecological importance of CAM succulents. We first briefly review our work on the interaction between saguaros, an archetypical CAM succulent, and the desert doves that feed on its fruit. We then describe the potential importance of saguaro fruit as a function of its abundance, macronutrient composition, and seasonal availability. We argue that the resources provided by saguaros do much to satisfy the energy and water requirements of the birds that reside in hot subtropical deserts during the summer. We then describe the carbon isotope composition of saguaros and of the plant community in which they are imbedded and use two species of desert doves to illustrate how stable isotopes can reveal the importance of a single plant as a source of carbon and water for consumers. The second section of this review presents new data on the importance of saguaros for the entire community of birds that inhabit the Sonoran Desert during the summer. We show how the resources of saguaro reach across dietary guilds and account for a large proportion of the diet of many insectivorous species as well as that of granivorous and frugivorous species. We demonstrate that many of these species probably obtain significant water as well as nutrients from saguaro fruit. Finally, we point out the current limitations of using deuterium as a water tracer in animal systems.
肉质景天酸代谢（CAM）植物，如柱状仙人掌，是许多干旱地区重要的外貌特征元素。尽管这些植物通常具有重要的生态意义，因为它们以花蜜和果实的形式提供丰富的资源，但它们对消费者的能量、营养和水分预算的贡献尚未得到量化。我们描述了一种同位素方法，可用于量化CAM多肉植物的生态重要性。我们首先简要回顾一下我们关于一种典型的CAM多肉植物——巨人柱与以其果实为食的沙漠鸽之间相互作用的研究。然后，我们描述了巨人柱果实作为其丰度、常量营养素组成和季节性可用性的函数的潜在重要性。我们认为，巨人柱提供的资源在很大程度上满足了夏季栖息在炎热亚热带沙漠中的鸟类的能量和水分需求。然后，我们描述了巨人柱及其所嵌入的植物群落的碳同位素组成，并使用两种沙漠鸽来说明稳定同位素如何揭示单一植物作为消费者碳和水来源的重要性。本综述的第二部分展示了关于巨人柱对夏季栖息在索诺兰沙漠的整个鸟类群落重要性的新数据。我们展示了巨人柱的资源如何跨越不同的食性群体，并在许多食虫物种以及食谷和食果物种的饮食中占很大比例。我们证明，这些物种中的许多可能从巨人柱果实中获取大量的水分和营养。最后，我们指出了在动物系统中使用氘作为水示踪剂目前存在的局限性。
