Steele M A
Department of Biological Sciences, University of California, Santa Barbara, CA 93106, USA, , , , , , US.
Oecologia. 1997 Sep;112(1):64-74. doi: 10.1007/s004420050284.
Input of individuals dispersing into open populations can be highly variable, yet the consequences of such variation for subsequent population densities are not well understood. I explored the influence of variable input ("supply") on subsequent densities of juveniles and adults in open local populations of two temperate reef fishes, the bluebanded goby (Lythrypnus dalli) and the blackeye goby (Coryphopterus nicholsii). Variable recruitment was simulated by stocking a natural range of densities of young fishes on replicate patch reefs. Density and mortality of the stocked cohorts were followed over time, until the fishes reached maturity. Over the first day of the experiments, mortality of both species was significantly density-dependent; however, there was still a very strong relationship between density on day 1 and density on day 0 (i.e., simulated recruitment was still an excellent predictor of population density). At this point in the study, the main effects of density-dependent mortality were to reduce mean densities and variation about the mean. Over the period from the start of the experiments until the time when maturity was reached by each species (about 1 and 3 months for Lythrypnus and Coryphopterus, respectively), mortality was strongly density-dependent. Such strong density-dependent mortality virtually eliminated any linear relationship between adult density and "recruit" density. However, for both species, the relationship between these two variables was well fit by an asymptotic curve, with the asymptotic density of adults equal to c. 3/m for Coryphopterus, and c. 10/m for Lythrypnus. Natural recruitment (via settlement of larvae) to the reefs over the period of the study (9 months) was above the asymptotic densities of adults for the two species, even though the study did not encompass the periods of peak annual recruitment of either species. This suggests that adult populations of these two gobies may often be limited, and regulated, by post-settlement processes, rather than by input of settlers. Other studies have shown that mortality of the two species is density-independent, or only weakly density-dependent, on reefs from which predators have been excluded. Hence, it appears that predators cause density-dependent mortality in these fishes.
分散进入开放种群的个体输入可能高度可变，然而这种变化对后续种群密度的影响却尚未得到充分理解。我探究了可变输入（“供应”）对两种温带礁鱼——蓝带虾虎鱼（Lythrypnus dalli）和黑眼虾虎鱼（Coryphopterus nicholsii）——开放局部种群中幼鱼和成鱼后续密度的影响。通过在重复的斑块礁上投放自然密度范围的幼鱼来模拟可变补充。对投放群体的密度和死亡率随时间进行跟踪，直至鱼达到成熟。在实验的第一天，两种鱼的死亡率都显著依赖于密度；然而，第1天的密度与第0天的密度之间仍存在非常强的关系（即模拟补充仍然是种群密度的一个极佳预测指标）。在研究的这个阶段，密度依赖死亡率的主要作用是降低平均密度以及围绕平均值的变化。从实验开始到每个物种达到成熟的这段时间（蓝带虾虎鱼约为1个月，黑眼虾虎鱼约为3个月），死亡率强烈依赖于密度。这种强烈的密度依赖死亡率几乎消除了成鱼密度与“补充”密度之间的任何线性关系。然而，对于这两个物种，这两个变量之间的关系都能很好地用一条渐近曲线拟合，黑眼虾虎鱼成鱼的渐近密度约为3条/平方米，蓝带虾虎鱼约为10条/平方米。在研究期间（9个月），通过幼体附着实现的对礁区的自然补充超过了这两个物种成鱼的渐近密度，尽管该研究并未涵盖这两个物种年度补充高峰期。这表明这两种虾虎鱼的成鱼种群可能经常受到定居后过程的限制和调节，而非定居者的输入。其他研究表明，在排除了捕食者的礁区，这两个物种的死亡率与密度无关，或仅微弱地依赖于密度。因此，似乎捕食者导致了这些鱼类的密度依赖死亡率。
