Den Boer P J
Biological Station LUW, Kampsweg 27, 9418PD, Wijster, The Netherlands.
Oecologia. 1990 May;83(1):38-46. doi: 10.1007/BF00324631.
When testing census data of insect populations for regulation, and/or for overall density dependence in the course of numbers over years, certain conditions, which follow from the testing models, should be fulfilled. Even if the series of densities may be considered a piece of first-order Markov chain (a necessary condition) significant test results need not obviously point to regulation of numbers by dominant density-dependent processes. Such a case is presented by the pine looper population at "Hoge Veluwe" studied by Klomp. A drastic drop in density from 1952 to 1953, which takes 78-97% of the log-density range (LR) over all years, most probably wrongly causes significant test results. This is supported by some simulation experiments. Moreover, we cannot be sure that the population was sufficiently isolated, i.e. that dispersal of adults from surrounding populations did not importantly influence population numbers. Among 6 Panolis-populations studied by Schwerdtfeger during 17 years a single one scored significantly with all tests. This resulted, however, from such a drastic drop in density that it covered the entire log-density range (LR=9.39), which therefore is wider than in any of the other (non-significant) populations. Another Panolis-population that maintained itself during 60 years, and which also scored significantly, most probably was kept within limits by supplementation of very low densities with immigrants, on the one hand, and by restriction of high densities by defoliation caused by other species, on the other. It is discussed whether this can be considered "regulation", or results from spreading of risk. It is concluded that the range stability of particular populations must be considered generally to be the result of stabilization by both internal and external processes among which both density-dependent and density-independent processes play a significant part, and from which the contribution of the density-dependent processes need not be separated. The most interesting aspect of the stabilization of animal numbers is its relationship with the expected survival time of the population.
在检验昆虫种群普查数据以进行调控，和/或检验多年数量变化过程中的总体密度依赖性时，应满足检验模型所推导的某些条件。即使密度序列可被视为一阶马尔可夫链（一个必要条件），显著的检验结果也不一定明显表明数量受主要密度依赖性过程的调控。克伦普研究的“霍赫维卢韦”地区的松尺蠖种群就是这样一个例子。1952年至1953年密度急剧下降，占所有年份对数密度范围（LR）的78 - 97%，很可能错误地导致了显著的检验结果。一些模拟实验支持了这一点。此外，我们不能确定该种群是否足够隔离，即周围种群的成虫扩散是否没有对种群数量产生重要影响。施韦特费格在17年里研究的6个松夜蛾种群中，只有一个在所有检验中都得到显著结果。然而，这是由于密度急剧下降以至于涵盖了整个对数密度范围（LR = 9.39），因此比其他任何（不显著的）种群的范围都要宽。另一个持续了60年且也得到显著结果的松夜蛾种群，很可能一方面是通过移民补充极低密度个体而维持在一定范围内，另一方面是通过其他物种造成的落叶限制高密度个体。文中讨论了这是否可被视为“调控”，还是风险扩散的结果。得出的结论是，特定种群的范围稳定性通常必须被视为内部和外部过程稳定作用的结果，其中密度依赖性和密度独立性过程都起着重要作用，而且密度依赖性过程的贡献无需单独区分。动物数量稳定最有趣的方面在于它与种群预期生存时间的关系。
