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量化异质景观中的栖息地质量:一种珊瑚礁鱼类的补充

Quantifying site quality in a heterogeneous landscape: recruitment of a reef fish.

作者信息

Shima Jeffrey S, Osenberg Craig W, St Mary Colette M

机构信息

School of Biological Sciences, P.O. Box 600, Victoria University of Wellington, New Zealand.

出版信息

Ecology. 2008 Jan;89(1):86-94. doi: 10.1890/07-0021.1.

Abstract

Heterogeneity in site quality can play an important role in patterns of abundance and population dynamics. Yet, estimating site quality in natural systems can be problematic because site quality can (1) vary through ontogeny for a focal organism, leading to shifts in site quality with age, (2) be confounded with (or masked by) variation in traits of individuals populating the sites, and (3) be correlated with local density. For example, if high-quality sites attract more individuals but vital rates are density dependent, then observed vital rates will be relatively homogeneous in space despite strong heterogeneity in site quality. Here, we operationally define site quality for a reef fish as the mean survival time of juveniles transplanted to sites at a common density and size structure, with random assignment of individuals to sites to remove potential confounding effects of local variation in individual quality and density. Our assays using juvenile age classes of the six-bar wrasse (Thalassoma hardwicke) showed that site quality varied in space (i.e., among patch reefs) but was constant through time. Site quality increased with availability of the branching coral Pocillopora (which is used as a refuge), but decreased with density of a predator, the arc-eye hawkfish, Paracirrhites arcatus (which also uses Pocillopora). We experimentally added colonies of Pocillopora to reefs and (1) increased site quality, (2) enhanced natural settlement rates of six-bar wrasse, but (3) attracted more hawkfish predators, and (4) did not increase survival of juvenile fish under ambient densities. Our results suggest that Pocillopora increases site quality, but attracts greater densities of settlers and predators, resulting in increased density dependence and predation, which mask the underlying effects of Pocillopora on site quality (supporting the hypothesis of "cryptic density dependence"). Variation in site quality and the possible confounding effects of density and individual traits warrant more experimental study.

摘要

栖息地质量的异质性在生物丰度模式和种群动态中可能起着重要作用。然而,在自然系统中估算栖息地质量可能存在问题,因为栖息地质量可能:(1) 对于目标生物而言,会随个体发育而变化,导致栖息地质量随年龄发生变化;(2) 与栖息在这些栖息地的个体特征变化相混淆(或被其掩盖);(3) 与局部密度相关。例如,如果高质量的栖息地吸引了更多个体,但生命率是密度依赖的,那么尽管栖息地质量存在强烈的异质性,观察到的生命率在空间上仍将相对均匀。在此,我们将珊瑚礁鱼类的栖息地质量操作性地定义为以共同密度和大小结构移植到各栖息地的幼鱼的平均存活时间,并将个体随机分配到各栖息地,以消除个体质量和密度的局部变化可能带来的混杂效应。我们使用六带裂唇鱼(Thalassoma hardwicke)幼鱼阶段进行的测定表明,栖息地质量在空间上存在差异(即不同的斑块礁之间),但随时间保持恒定。栖息地质量随着分支珊瑚鹿角杯形珊瑚(用作避难所)的可利用性增加而提高,但随着捕食者弧眼鹰鱼(Paracirrhites arcatus,它也利用鹿角杯形珊瑚)的密度增加而降低。我们通过实验向珊瑚礁添加鹿角杯形珊瑚群体,结果发现:(1) 提高了栖息地质量;(2) 提高了六带裂唇鱼的自然定居率;(3) 吸引了更多的鹰鱼捕食者;(4) 在环境密度下并没有提高幼鱼的存活率。我们的结果表明,鹿角杯形珊瑚提高了栖息地质量,但吸引了更多的定居者和捕食者,导致密度依赖性和捕食作用增加,从而掩盖了鹿角杯形珊瑚对栖息地质量的潜在影响(支持“隐性密度依赖性”假说)。栖息地质量的变化以及密度和个体特征可能产生的混杂效应值得进行更多的实验研究。

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