Combining Traits and Density to Model Recruitment of Sessile Organisms

We propose an integrative approach that explains patterns of recruitment to adult populations in sessile organisms by considering the numbers of individuals and their body size. A recruitment model, based on a small number of parameters, was developed for sessile organisms and tested using the barnacle Semibalanus balanoides, a marine invertebrate inhabiting North Atlantic intertidal shores. Incorporating barnacle body size improved model fit beyond that based on density alone, showing that growth played an important role in how resource limitation affected survival. Our approach uncovered the following: First, changes in the shape of the recruitment curve resulted from the balance between individual growth and mortality. Second, recruitment was limited by the least plastic trait used to characterise body size, operculum area. Basal area, a trait that responded to increases in barnacle density, did not contribute significantly to explain patterns of recruitment. Third, some temporal variation is explained by changes in the amount of space occupied by shells of dead barnacles: at high cover barnacles are densely packed and these shells remain long after death. Fourth, seasonal variation and spatial variation in survival can be separated from that resulting from resource limitation; survival was predicted for two different shores and four sampling times using a single recruitment model. We conclude that applying this integrative approach to recruitment will lead to a considerable advance in understanding patterns of mortality of early stages of sessile organisms.本研究提出一种整合性研究方法，通过考量个体数量与体型大小，阐释固着生物（sessile organisms）成种种群的种群补充模式。针对固着生物，本研究构建了基于少量参数的种群补充模型，并以栖息于北大西洋潮间带的海洋无脊椎动物纹藤壶（Semibalanus balanoides）为对象开展模型验证。纳入藤壶体型参数后，模型拟合效果优于仅以密度为自变量的模型，表明个体生长在资源限制影响种群存活的过程中发挥了重要作用。本研究方法揭示了如下结论：其一，种群补充曲线的形态变化源于个体生长与死亡率之间的动态平衡；其二，种群补充受到表征体型的可塑性最低的性状——鳃盖面积（operculum area）的限制，而随藤壶密度升高而发生变化的基底面积（basal area），则对种群补充模式的解释无显著贡献；其三，部分时间变异可通过死亡藤壶壳体占据的空间变化得到解释：当藤壶盖度较高时，个体间排布紧密，死亡后的壳体会长时间留存于栖息地；其四，可将存活的季节变异与空间变异与资源限制引发的变异区分开来，本研究通过单一种群补充模型，即可预测两处潮间带、四个采样时间点的种群存活情况。综上，将该整合性研究方法应用于种群补充研究，将极大推动我们对固着生物早期阶段死亡模式的认知。