MCR LTER: Coral Reef: Growth and Survivorship of Dascyllus trimaculatus

The influence of density-dependent and number-dependent processes on individual demographic rates often results in ecological tradeoffs. Because such processes have important implications for individual level fitness and population regulation, they long have been an important topic in ecological research. I used Dascyllus trimaculatus , a site-attached planktivorous coral reef fish, to determine independently the effects of population density and group size on rates of individual growth and mortality. Somatic growth of D. trimaculatus was positively related to the density of D. trimaculatus outplanted to host anenomes, Heteractis magnifica , with nearly twice as much growth observed in individuals living in the highest density treatment. By contrast, survivorship of D. trimaculatus on H. magnifica exhibited a negative relationship with density. There was no significant effect of group size on either the growth or mortality rates of D. trimaculatus . These relationships suggest a tradeoff between density-dependent growth and survival in this species. My analysis of behavioral data indicated that D. trimaculatus living under conditions of higher local population densities displayed decreased rates of intraspecific aggression because of positive feedback between local population density and the foraging distance from an individual’s host anemone. In turn, lower rates of aggression and feeding higher in the water column resulted in increased somatic growth rates due to: (1) a reduced energy expenditure and (2) an increase in prey consumption. These data are part of a Master's Thesis published by ProQuest: Nielsen, Jessica Anne. Effects of density on behaviorally-mediated tradeoffs between growth and survivorship. MA Thesis, University of California Santa Barbara, 2013.密度依赖与数量依赖过程对个体种群统计率的影响，常会引发生态权衡。由于此类过程对个体适合度与种群调控具有重要意义，长期以来均为生态学研究的核心课题之一。本研究以定居性浮游食性珊瑚礁鱼类三斑宅泥鱼（Dascyllus trimaculatus）为实验对象，独立探究种群密度与群体规模对个体生长率及死亡率的影响。 移殖至宿主巨型海葵（Heteractis magnifica）上的三斑宅泥鱼，其躯体生长率与种群密度呈正相关：在最高密度处理组中，个体的生长量近乎为最低密度组的两倍。与之相反，栖息于巨型海葵上的三斑宅泥鱼，其存活率与种群密度呈负相关关系。而群体规模对该物种的生长率与死亡率均无显著影响。上述结果表明，该物种存在密度依赖的生长与存活之间的生态权衡。 对行为数据的分析显示，当局部种群密度较高时，三斑宅泥鱼的种内攻击行为频率会下降，这是由于局部种群密度与个体距宿主海葵的觅食距离之间存在正反馈作用。反过来，更低的攻击行为频率以及在水层更高位置的摄食行为，会通过以下两种途径提升躯体生长率：（1）能量消耗降低，（2）猎物摄取量增加。 本研究数据源自ProQuest收录的一篇硕士学位论文：Nielsen, Jessica Anne. 《密度对行为介导的生长与存活权衡的影响》，加州大学圣巴巴拉分校硕士论文，2013年。