Dudas Sarah E, Dower John F, Anholt Bradley R
Department of Biology, University of Victoria, Victoria, British Columbia, Canada.
Ecology. 2007 Aug;88(8):2084-93. doi: 10.1890/06-1216.1.
Marine invaders have become a significant threat to native biodiversity and ecosystem function. In this study, the invasion of the varnish clam (Nuttallia obscurata) in British Columbia, Canada, is investigated using a matrix modeling approach to identify the life history characteristics most crucial for population growth and to investigate population differences. Mark-recapture analyses and field collections from 2003 to 2004 were used to determine individual growth, survival rates, and fecundity for two sites. A multi-state matrix model was used to determine population growth rates and to conduct sensitivity and elasticity analyses. A life table response experiment was also used to determine what life history stage contributed most to observed differences in population growth rates. Population survey data were used in conjunction with the matrix model to determine plausible recruitment levels and to investigate recruitment scenarios. Both populations are currently declining but are likely sustainable because of the pulsed nature of large recruitment events. Survival of larger clams (>40 mm) is the most important for population growth based on elasticity and sensitivity analyses. Adult survival also had the largest influence on observed differences between site-specific population growth rates. The two populations studied differed in recruitment dynamics; one experiencing annual recruitment with higher post-settlement mortality and the other, episodic recruitment and lower post-settlement mortality. The most influential factor for the successful invasion of the varnish clam appears to be survival of the larger size classes. Therefore, any process that decreases adult survival (e.g., predation, commercial harvest) will have the greatest impact on population growth.
海洋入侵物种已对本地生物多样性和生态系统功能构成重大威胁。在本研究中，运用矩阵建模方法对加拿大不列颠哥伦比亚省油彩蛤（Nuttallia obscurata）的入侵情况展开调查，以确定对种群增长最为关键的生活史特征，并研究种群差异。利用2003年至2004年的标记重捕分析和实地采集数据，确定了两个地点的个体生长、存活率和繁殖力。采用多状态矩阵模型来确定种群增长率，并进行敏感性和弹性分析。还运用了生命表响应实验来确定哪个生活史阶段对观察到的种群增长率差异贡献最大。将种群调查数据与矩阵模型结合使用，以确定合理的补充水平并研究补充情景。目前两个种群数量都在下降，但由于大量补充事件的脉冲性质，它们可能具有可持续性。基于弹性和敏感性分析，较大蛤蜊（>40毫米）的存活对种群增长最为重要。成体存活率对特定地点种群增长率之间观察到的差异也有最大影响。所研究的两个种群在补充动态方面存在差异；一个经历年度补充，定居后死亡率较高，另一个则是间歇性补充且定居后死亡率较低。油彩蛤成功入侵的最有影响因素似乎是较大尺寸类别的存活。因此，任何降低成体存活率的过程（如捕食、商业捕捞）都将对种群增长产生最大影响。
