Population-level habitat breadth varies with richness in reef fishes

Aim: It has been hypothesized that niche-breadth should decrease with richness, due to interactions such as competition, forcing species to specialize. This hypothesis has been tested at the community-level using species-level niche breadth estimates. However, evidence for changes in niche-breath among populations of the same species are scant. Examining this relationship among populations is crucial for understanding the role of interactions, as opposed to large-scale climate, in altering realized niche breadth.

Location: The Pacific Ocean

Time period: 1996-2010

Methods: We focus on reef fishes along a large-scale richness gradient that is not accompanied by marked environmental changes. Fishes in each site were surveyed in four distinct habitats which allow to estimate the habitat-breadth for each population. We calculated the habitat-breadth of distinct populations of 154 fish species and tested how habitat-breadth varied with richness, while controlling for the effect of abundance. We further tested the effect of traits and trait-distinctiveness on the richness-sensitivity of habitat-breadth.

Results: Habitat-breadth varied with species traits, as large and mobile species were found to be habitat generalists while schooling species habitat specialists. Importantly, habitat-breadth was negatively correlated to richness for 109 out of the 154 species, and, across all species, the relationship was highly significant. As expected from competition being the major driver, we found that species with distinct traits displayed a wider habitat breadth, but that the relationship was sensitive to the type of  trait-distinctiveness index used.

Conclusions: This is the first large-scale evidence that population-level habitat-breadth changes with richness. Results suggest that the realized niche is population specific, and that niche-breadth is reduced by local interactions such as competition. This implies that populations, specifically in rich areas, are far from using their entire fundamental niche. Therefore, the ability to predict habitat preferences in response to global change based on current habitat associations, but without accounting for species interactions, may be limited.

Methods
Underwater visual fish census survey data collected by Michel Kulbicki and Laurent Vigliola.

Data columns are very informative.

'Density' refers to the number of individuals per 100 squared meters.

研究目标：
已有假说提出，受竞争等种间相互作用驱使，物种会发生特化，因此生态位宽度（niche breadth）应随物种丰富度（richness）降低。该假说已通过基于物种水平生态位宽度估算的群落水平检验得到验证，但针对同一物种种群间生态位宽度变化的相关证据仍较为匮乏。探究种群间的这一关联，对于理解种间相互作用（而非大尺度气候）在调控现实生态位宽度（realized niche breadth）变化中所扮演的角色至关重要。

研究区域：
太平洋

研究时段：
1996年—2010年

研究方法：
本研究聚焦于沿大尺度物种丰富度梯度分布且未伴随显著环境变化的礁区鱼类。各调查站点内的鱼类均在四种不同生境中完成调查，以此可估算每个种群的生境宽度。我们计算了154种鱼类不同种群的生境宽度，并在控制种群丰度影响的前提下，检验生境宽度随物种丰富度的变化规律。此外，我们还检验了功能性状及其性状区分度对生境宽度的丰富度敏感性的影响。

研究结果：
生境宽度随鱼类功能性状而异：体型较大、活动能力较强的物种为生境广适种，而集群性物种则为生境特化种。值得注意的是，154个物种中有109个物种的生境宽度与物种丰富度呈负相关关系，且在所有物种中，该关联均具有极高的统计学显著性。正如竞争作为主要驱动因素所预期的那样，我们发现性状区分度更高的物种拥有更宽的生境宽度，但该关联会因所采用的性状区分度指数类型而异。

研究结论：
本研究首次提供了大尺度范围内的证据，证明种群水平的生境宽度随物种丰富度发生变化。研究结果表明，现实生态位具有种群特异性，且诸如竞争等局部种间相互作用会降低生态位宽度。这意味着，尤其是在物种丰富的区域，种群远未完全利用其基础生态位（fundamental niche）。因此，若仅基于当前的生境关联来预测全球变化下的物种生境偏好，却未考虑种间相互作用，其预测能力或存在较大局限。

数据采集与说明：
本研究使用由Michel Kulbicki与Laurent Vigliola采集的水下目视鱼类普查数据。
数据列蕴含丰富的指示信息。
“密度”指每100平方米内的个体数量。