UFZ-Helmholtz Centre for Environmental Research, Department of System Ecotoxicology, Permoserstrasse 15, D-04318 Leipzig, Germany.
Aquat Toxicol. 2010 Apr 1;97(1):15-22. doi: 10.1016/j.aquatox.2009.11.018. Epub 2009 Dec 2.
Ecotoxicological field studies have shown that total abundance and biomass often recover shortly after pulsed toxicant stress. In contrast, population structure showed comparatively long-term alterations before reaching pre-treatment conditions. We investigated two mechanisms that may explain the prolonged recovery of population structure: latent toxicant effects on life-history traits on the individual level and competition on the population level. To test these hypotheses we exposed populations of Daphnia magna to a pulse of the pyrethroid Fenvalerate. For several generations the populations were kept at two different degrees of competition: strong competition at carrying capacity and reduced competition maintained by simulated predation. After disturbance due to Fenvalerate exposure, biomass recovered after 14-17 days. In contrast, size structure characterised by a lack of large and dominance of small organisms recovered after 43 days in populations with strong competition. Size structure recovered twice faster in populations with reduced competition. We explain this as follows: due to toxicant induced mortality, food availability and consequently birth rate increased and populations were dominated by small individuals. In populations without predation, these cohorts grew and eventually exerted high intraspecific competition that (i) stopped further growth of juveniles and (ii) increased mortality of adults. These demographic processes were mainly responsible for the prolonged recovery of size structure. In contrast, for populations with predation, the regular harvest of individuals reduced competition. Juveniles developed continuously, allowing a fast recovery of size structure in these dynamic populations. In risk assessment the duration for populations to recover from (toxicant) stress, is crucial for the determination of ecological acceptable effects. We conclude that competition needs to be considered in order to understand and predict recovery of size structure.
生态毒理学野外研究表明，在脉冲毒物胁迫后，总丰度和生物量通常会迅速恢复。相比之下，种群结构在达到处理前的条件之前会发生长期的变化。我们研究了两种可能解释种群结构恢复时间延长的机制：个体水平上的潜在毒物对生活史特征的影响和种群水平上的竞争。为了检验这些假设，我们将大型溞（Daphnia magna）种群暴露于拟除虫菊酯 Fenvalerate 的脉冲中。在几代中，种群保持在两种不同程度的竞争下：在承载能力下的强竞争和通过模拟捕食维持的弱竞争。在 Fenvalerate 暴露引起的干扰之后，生物量在 14-17 天后恢复。相比之下，在强竞争的种群中，缺乏大型生物且小型生物占主导地位的大小结构在 43 天后恢复。在竞争较弱的种群中，大小结构的恢复速度快了两倍。我们这样解释：由于毒物诱导的死亡率，食物供应增加，出生率相应增加，种群由小型个体主导。在没有捕食的种群中，这些群体生长，最终产生强烈的种内竞争，这导致（i）幼体进一步生长停止，（ii）成体死亡率增加。这些人口过程是大小结构恢复时间延长的主要原因。相比之下，对于有捕食的种群，个体的定期收获降低了竞争。幼体持续发育，使这些动态种群的大小结构快速恢复。在风险评估中，种群从（毒物）胁迫中恢复的持续时间对于确定生态可接受的影响至关重要。我们的结论是，为了理解和预测大小结构的恢复，需要考虑竞争。
