Spatial and ontogenetic variation in isotopic niche among recovering fish communities revealed by Bayesian modeling

Exploitation and changing ocean conditions have resulted in altered species interactions and varied population dynamics within marine fish communities off northeast Newfoundland and southern Labrador, Canada. To understand contemporary species interactions, we quantified the isotopic niches, niche overlap, and ontogenetic niche change among seven dominant fish species using stable isotope analyses. Analyses used fishes from three regions differing in fish and prey diversities. Differences in fish and diet composition diversity among regions were found using Simpson’s inverse diversity index. The regions of lowest diversities had higher instances of niche overlap and higher percentage of niche overlap area. The region of highest diversity had the widest spread of niches with greater distances from the community centroid. Ontogenetic shifts were observed such that larger individuals shifted towards the community centroid with the exception of Atlantic cod. Atlantic cod in particular was found to consistently be the top predator of the analyzed species. Our results reveal: (a) overlap in isotopic niches and spread within niche space was correlated with fish and diet diversity; (b) ontogenetic shifts are important when considering a species’ niche and quantifying spatial variation in community niche profiles.

人类捕捞活动与持续变化的海洋环境，已导致加拿大纽芬兰东北部及拉布拉多南部近海海洋鱼类群落内的物种相互作用发生改变，种群动态亦呈现多样化特征。为厘清当前的物种相互作用机制，本研究通过稳定同位素分析（stable isotope analysis），对7种优势鱼类的同位素生态位（isotopic niche）、生态位重叠（niche overlap）及个体发育生态位变化（ontogenetic niche change）进行了定量分析。本研究采集了三个鱼类与猎物多样性存在差异的区域的鱼类样本开展分析。通过辛普森逆多样性指数（Simpson’s inverse diversity index）分析，发现不同区域的鱼类组成与食性组成多样性存在显著差异。多样性水平最低的区域，其生态位重叠发生频率更高，生态位重叠区域占比也更大。多样性水平最高的区域，其生态位分布范围最广，且各生态位距群落质心（community centroid）的平均距离更大。研究观察到个体发育生态位偏移现象：除大西洋鳕鱼（Atlantic cod）外，体型更大的个体其生态位均向群落质心偏移。尤其值得注意的是，大西洋鳕鱼在所有被分析物种中始终处于顶级捕食者的生态位。本研究结果表明：(1) 同位素生态位重叠程度与生态位空间分布范围，均与鱼类组成及食性多样性显著相关；(2) 在探讨物种生态位特征、量化群落生态位轮廓的空间变异时，个体发育生态位偏移是不可忽视的重要因素。