Leonardsson Kjell
Department of Animal Ecology, University of Umeå, S-901 87, Umeå, Sweden.
Oecologia. 1994 Feb;97(1):26-34. doi: 10.1007/BF00317905.
Possible mechanisms for differences in population densities and dynamics were investigated in the amphipod Monoporeia affinis at two deep sites in the northern Bothnian Sea. The two sites were sampled yearly for 10 years. Average sizes, growth and mortality of the different age-classes were estimated from the cohort structure of the two populations. Laboratory experiments also investigated the ability of the common predatory isopod Saduria entomon to cause densitydependent (DD) mortality of the prey M. affinis. At site A, 43 m depth, the average density of M. affinis was twice as high as at site B, 81 m depth. The fluctuations in density were asynchronous between the two sites. Recruitment and subadult sizes of Monoporeia affinis were density dependent at both sites. The main functional difference between the two populations seemed to be the DD mortality of the 1 + cohort that occurred only at the low-density site B. A corresponding DD mortality was found in the predation experiments at densities of 1 + m. affinis corresponding to those found at site B. The potential importance of the predator was also indicated by a significant negative correlation between the biomass of S. entomon and the rate of change in M. affinis density in the field. The similarities in the abiotic factors between the two sites suggested that differences in carrying capacity should be small. The results could be explained by the predation regulation hypothesis for the low-density population at site B, while at site A M. affinis seemed to be regulated by intra-specific competition and limited by predation. It is suggested that in this simple predator-prey system there is potential for the existence of alternative equilibria.
在波的尼亚湾北部的两个深海站点，对近螯虾（Monoporeia affinis）种群密度和动态差异的可能机制进行了研究。这两个站点每年采样，持续了10年。根据两个种群的年龄结构估算了不同年龄组的平均大小、生长和死亡率。实验室实验还研究了常见捕食性等足类动物萨氏真蛇尾（Saduria entomon）对猎物近螯虾造成密度依赖性（DD）死亡的能力。在43米深的A站点，近螯虾的平均密度是81米深的B站点的两倍。两个站点的密度波动并不同步。两个站点的近螯虾补充量和亚成体大小均与密度有关。两个种群之间的主要功能差异似乎在于仅在低密度的B站点出现的1 +年龄组的DD死亡。在捕食实验中，当近螯虾密度与B站点的密度相当时，也发现了相应的DD死亡。野外萨氏真蛇尾的生物量与近螯虾密度变化率之间存在显著负相关，这也表明了捕食者的潜在重要性。两个站点非生物因素的相似性表明，承载能力的差异应该很小。研究结果可以用B站点低密度种群的捕食调节假说来解释，而在A站点，近螯虾似乎受种内竞争调节，并受捕食限制。研究表明，在这个简单的捕食者 - 猎物系统中，存在替代平衡的可能性。
