Low species turnover of upland Amazonian birds in the absence of physical barriers

Aim: One of the oldest and most powerful ways for ecologists to explain distinct biological communities is to invoke underlying environmental differences. But in hyper-diverse systems, which often display high species richness and low species abundance, these sorts of community comparisons are especially challenging. The classic view for Amazonian birds posits that riverine barriers and habitat specialization determine local and regional community composition. We test the tacit, complementary assumption that similar bird communities should therefore permeate uniform habitat between major rivers, regardless of distance.

Location: Upland (terra firme) rainforests of central Amazonia.

Results: In all, we detected 244 forest-dependent birds, with an average of 190 species (78%) per plot. Species turnover was negligible, no unique indicator species were found among plot pairs, and all documented species were already known from a complete inventory at one of the three sites.

Main conclusions: Our study corroborates the classic biogeographical pattern and suggests that turnover contributes little to regional avian diversity within upland forests. Using a grain size of 100 ha, this implies that upland birds perceive the environment as uniform, at least over distances of ~60 km. Therefore, to maximize both local species richness and population persistence, our findings support the conservation of very large tracts of upland rainforest. Our analyses also revealed that the avifauna at Reserva Ducke, encroached by urban sprawl from the city of Manaus, shows the hallmarks of a disturbed community, with fewer vulnerable insectivores. This defaunation signals that even an enormous preserve (10 × 10 km) in lowland Amazonia is not insulated from anthropogenic degradation within the surrounding landscape.

Methods
We conducted intensive whole-community surveys of birds in three pairs of 100-ha plots, separated by 40-60 km. We then used dissimilarity indices, cluster analysis, and ordination to characterize differences among the six avian communities.

研究目的：生态学家解释不同生物群落的经典且最具说服力的方法之一，便是依托其背后的环境差异。但在超多样化生态系统中——这类系统往往兼具极高的物种丰富度与极低的物种个体多度——这类群落对比研究往往极具挑战。针对亚马孙鸟类的经典理论认为，河流屏障与生境特化决定了局域及区域的群落组成。本研究将检验一项默认的补充性假设：即无论距离远近，大型河流之间的均质生境中，鸟类群落应趋于一致。

研究区域：亚马孙中部的高地（terra firme）雨林。

研究结果：本次研究共记录到244种森林依赖型鸟类，每个样地平均记录190种，占总物种数的78%。物种更替率极低，样地对之间未发现特有指示物种，且所有记录到的物种均已在三个研究样地之一的完整调查名录中被收录。

主要结论：本研究验证了经典的生物地理学模式，并表明在高地雨林中，物种更替对区域鸟类多样性的贡献极小。以100公顷为样地尺度，这意味着高地鸟类至少在60公里左右的范围内，会将环境视为均质的。因此，为最大化局域物种丰富度与种群存续能力，本研究结果支持对大片高地雨林进行保护。本研究同时发现，受马瑙斯市城市扩张侵蚀的杜克自然保护区（Reserva Ducke）的鸟类区系呈现出受干扰群落的特征，其脆弱食虫鸟类的数量更少。这种鸟类区系退化现象表明，即便亚马孙低地的巨型保护区（面积达10×10公里），也无法免受周边景观中人为活动带来的生境退化影响。

研究方法：我们在三对间距为40~60公里的100公顷样地中开展了高强度的鸟类全群落调查。随后通过群落相异性指数、聚类分析与排序分析，对六个鸟类群落之间的差异进行表征。