Interspecific interactions, such as competition, are among the key factors that determine the distribution, abundance and diversity of organisms in natural communities of aquatic ecosystems. However, a marked reduction in the environmental integrity of streams may lead to modifications of the natural dynamics of these communities, including co-occurrence patterns and body size. In the Amazon, the replacement of forests by production systems is one of the leading causes of alterations to riverine ecosystem. The insects of the order Odonata (dragonflies and damselflies) are predators known to compete for environmental resources but are also sensitive to environmental changes such as those caused by shifts in land use. In this scenario, the present study evaluated species co-occurrence and body size patterns in adult odonates found at preserved and altered Amazonian streams, to determine whether there are morphological differences among the species that enable their coexistence. During the study, 98 streams in the eastern Amazon region were sampled, and a habitat integrity index (HII) was used to evaluate the integrity of each stream (based on variables such as the condition of the riparian vegetation and channel, and land use). Ten male individuals were selected from each species, and nine morphometric measurements were taken from each individual. A total of 3588 specimens were collected and distributed in nine families, 49 genera and 134 species. We found a non-random pattern of co-occurrence in the species of the odonate suborder Zygoptera and a random pattern in the suborder Anisoptera, in both preserved and altered streams. We found morphological divergence between pairs of zygopteran species, in the whole sample and both categories of stream integrity separately. No such morphological divergence was found in the pairs of anisopteran species. The distribution patterns of odonate species are limited by specific environmental processes, especially in preserved environments and in specialists, such as most zygopterans. Zygopteran species have more specific microhabitat requirements, which could explain this pattern, whereas anisopterans prefer open environments, which usually have a greater supply of resources, although there tends to be less microhabitat heterogeneity, which leads to reduced competition. Given this, future studies should use limiting similarity (e.g. morphological attributes) in addition to environmental and spatial factors to better understand the factors structuring these communities. Among these mechanisms, the effects of common ancestry (phylogenetic inertia) and biogeography are important factors that should also be considered in future studies.

中文翻译：

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保存和改变的亚马逊河流中蜻蜓和豆娘（昆虫纲：蜻蜓目）的共生模式和体型

种间相互作用，例如竞争，是决定水生生态系统自然群落中生物的分布、丰度和多样性的关键因素之一。然而，溪流环境完整性的显着降低可能会导致这些群落的自然动态发生改变，包括共生模式和体型。在亚马逊，生产系统取代森林是河流生态系统改变的主要原因之一。蜻蜓目昆虫（蜻蜓和豆娘）是众所周知的掠食者，它们会争夺环境资源，但也对环境变化（例如土地利用变化引起的环境变化）很敏感。在这种情况下，本研究评估了在保存和改变的亚马逊河流中发现的成虫的物种共生和体型模式，以确定物种之间是否存在形态差异，从而能够共存。在研究过程中，对亚马逊东部地区的98条溪流进行了采样，并使用了栖息地完整性指数（HII）来评估每条溪流的完整性（基于诸如河岸植被和河道状况以及土地利用等变量） . 从每个物种中选择 10 个雄性个体，并从每个个体中进行 9 次形态测量测量。总共收集了3588个标本，分布在9个科，49属和134种中。我们在保存和改变的溪流中发现了齿翅亚目 Zygoptera 的非随机模式和异翅目亚目中的随机模式。我们分别在整个样本和两类河流完整性中发现了成对的合翅目物种之间的形态差异。在成对的翅翅目物种中没有发现这种形态差异。齿类物种的分布模式受特定环境过程的限制，特别是在保存环境和专家中，例如大多数合翅目。合翅目物种有更具体的微生境要求，这可以解释这种模式，而异翅目则更喜欢开放环境，通常有更多的资源供应，尽管微生境异质性往往较少，这导致竞争减少。鉴于此，除环境和空间因素外，未来的研究还应使用有限的相似性（例如形态属性），以更好地了解构成这些群落的因素。在这些机制中，共同祖先（系统发育惰性）和生物地理学的影响是未来研究中也应考虑的重要因素。