Vonder Brink Richard H, Vanni Michael J
Department of Zoology, Miami University, 45056, Oxford, OH, USA.
Oecologia. 1993 Mar;95(1):70-80. doi: 10.1007/BF00649509.
Population dynamics, demography and body size of the cladoceranBosmina longirostris were examined in an experimental study in which the abundance of its predator (the cyprind fishPhoxinus eos) was varied in an unproductive lake. Four densities of fish were used, encompassing the biomass of fish in the lake.Bosmina was most abundant at low and medium fish densities (1.06 and 2.12 g fish biomass · m) and less abundant when fish were either absent or present at high density (3.71 g fish biomass · m). The unimodal response to predator abundance resulted from effects on both birth and death rates.Bosmina birth rates increased as fish biomass increased, in response to increasing food (phytoplankton) biomass. Death rates were highest at high fish biomass (because of fish predation) and in the absence of fish (because of predation by the dipteranChaoborus, which was most abundant in the absence of fish). Size-frequency distributions revealed that fish eliminated the larger size classes ofBosmina, and mean carapace length ofBosmina populations was inversely proportional to fish biomass.Bosmina initiated reproduction at smaller size in the presence of fish than in their absence, and size at maturity was inversely proportional to fish biomass. Size at birth also tended to decrease with increasing fish biomass, but this trend was not as strong as that of size at maturity. Decreased size at maturity apparently allowedBosmina individuals to reproduce before becoming vulnerable to fish predation. Flexibility in size at maturity, together with low abundance of invertebrate predators and large herbivores (which were preyed upon by fish), allowedBosmina to become abundant in low and medium fish treatments. In the high fish treatment, mortality due to fish predation was too severe to be offset by decreased size at maturity, andBosmina population density was low. The net response ofBosmina populations to fish predation results from interactive effects of predation on mortality, natality, and life history traits.
在一项实验研究中，对枝角类长吻薄皮溞的种群动态、种群统计学特征和体型进行了研究。该实验在一个贫营养湖泊中进行，改变了其捕食者（鲤科鱼类湖拟鲤）的数量。使用了四种鱼类密度，涵盖了湖泊中鱼类的生物量。薄皮溞在低、中鱼类密度（1.06和2.12克鱼类生物量·平方米）时最为丰富，在无鱼或高鱼类密度（3.71克鱼类生物量·平方米）时数量较少。对捕食者数量的单峰响应是由对出生率和死亡率的影响共同导致的。随着鱼类生物量的增加，薄皮溞的出生率上升，这是对食物（浮游植物）生物量增加的响应。死亡率在高鱼类生物量时最高（由于鱼类捕食），在无鱼时也较高（由于双翅目昆虫幽蚊的捕食，幽蚊在无鱼时最为丰富）。大小频率分布表明，鱼类消除了薄皮溞较大的体型类别，薄皮溞种群的平均头胸甲长度与鱼类生物量成反比。与无鱼时相比，薄皮溞在有鱼时以更小的体型开始繁殖，成熟时的体型与鱼类生物量成反比。出生时的体型也倾向于随着鱼类生物量的增加而减小，但这种趋势不如成熟时的体型那么明显。成熟时体型的减小显然使薄皮溞个体能够在变得易受鱼类捕食之前进行繁殖。成熟时体型的灵活性，加上无脊椎动物捕食者和大型草食动物（它们是鱼类的猎物）数量较少，使得薄皮溞在低、中鱼类处理中数量丰富。在高鱼类处理中，由于鱼类捕食导致的死亡率过高，无法被成熟时体型的减小所抵消，薄皮溞种群密度较低。薄皮溞种群对鱼类捕食的净响应是捕食对死亡率、出生率和生活史特征的交互作用的结果。
