Determinants of Reef Fish Assemblages on Tropical Oceanic Islands

ABSTRACT Diversity patterns are determined by biogeographic, energetic, and anthropogenic factors, yet few studies have combined them into a large-scale framework in order to decouple and compare their relative effects on fish faunas. Using an empirical dataset derived from 1527 underwater visual censuses (UVC) at 18 oceanic islands (five different marine provinces), we determined the relative influence of such factors on reef fish species richness, functional dispersion, density and biomass estimated from each UVC unit. Species richness presented low variation but was high at large island sites. High functional dispersion, density, and biomass were found at islands with large local species pool and distance from nearest reef. Primary productivity positively affected fish richness, density and biomass confirming that more productive areas support larger populations, and higher biomass and richness on oceanic islands. Islands densely populated by humans had lower fish species richness and biomass reflecting anthropogenic effects. Species richness, functional dispersion, and biomass were positively related to distance from the mainland. Overall, species richness and fish density were mainly influenced by biogeographical and energetic factors, whereas functional dispersion and biomass were strongly influenced by anthropogenic factors. Our results extend previous hypotheses for different assemblage metrics estimated from empirical data and confirm the negative impact of humans on fish assemblages, highlighting the need for conservation of oceanic islands. Keywords: species richness, functional dispersion, density, fish biomass, biogeographic factors, energetic factors, anthropogenic factors, marine provinces.

摘要
生物多样性格局由生物地理、能量与人为因素共同塑造，但鲜有研究将这三类因素整合至大尺度分析框架中，以拆解并对比它们对鱼类群落的相对影响。本研究依托18个大洋性岛屿（隶属于5个不同海洋生物地理区）的1527次水下目视调查（underwater visual censuses, UVC）所获的实测数据集，量化了上述因素对每个调查单元所估算的珊瑚礁鱼类物种丰富度、功能分散度、种群密度及生物量的相对影响。
物种丰富度的变异程度较低，但在大型岛屿样点中数值较高。本地物种种库庞大且距离最近礁体较远的岛屿，其功能分散度、种群密度与生物量均处于较高水平。初级生产力对鱼类物种丰富度、种群密度及生物量均产生正向影响，这证实了初级生产力更高的海域能够支撑更大的种群规模，并在大洋性岛屿上形成更高的生物量与物种丰富度。
人类人口稠密的岛屿，其鱼类物种丰富度与生物量均更低，这体现了人为活动的负面影响。物种丰富度、功能分散度与生物量均与距离大陆的距离呈正相关关系。
总体而言，物种丰富度与鱼类种群密度主要受生物地理与能量因素的调控，而功能分散度与生物量则显著受到人为因素的影响。本研究结果拓展了此前基于实测数据估算不同群落指标的相关假说，证实了人类活动对鱼类群落的负面影响，并凸显了保护大洋性岛屿生态系统的必要性。
关键词：物种丰富度，功能分散度，种群密度，鱼类生物量，生物地理因素，能量因素，人为因素，海洋生物地理区。