Holyoak M, Lawton J H
Department of Biology, Imperial College at Silwood Park, SL5 7PY, Ascot, Berks, UK.
NERC Centre for Population Biology, SL5 7PY, Ascot, Berks, UK.
Oecologia. 1992 Sep;91(3):425-430. doi: 10.1007/BF00317633.
A variety of techniques were used to test for density dependence in 32 time series from bracken-feeding insects. Seventeen taxa (primarily species, but including some pooled data from two or more closely related species whose larvae could not be distinguished in frond surveys) occurred on an open site; a woodland site held 15 taxa. For series of 12 years, collected on the open habitat, direct density dependence was detected by one or more of the techniques in 10 (58.8%) of 17 taxa, compared to only 5 (33.3%) of 15 taxa with time series of 8 years in length from the woodland habitat. Delayed density dependence was detected in 6 cases for the open site and in no cases at the woodland site. Either direct or delayed density dependence was found in 13 (76.5%) of 17 taxa for the open site and 13 (86.7%) of the 15 taxa which occurred on both sites. Although these results suggest a high frequency of density dependence in the species making up the bracken insect community, results from individual tests were extremely variable. Density dependence was detected least often by Vickery and Nudds' (1984) test, and most frequently by Varley and Gradwell's (1960) test, although the latter is prone to high rates of detecting spurious density dependence. Direct density dependence was detected most frequently in taxa that were univoltine and did not have delayed diapause, i.e. in those taxa whose life-histories conform most closely to the assumptions of the models underlying the analyses. Delayed density dependence occurred more frequently in species with more complex life-histories at the open site (taxa that were either bivoltine or multivoltine, or had delayed diapause). The results are consistent with the view that that the bracken herbivore assemblage consists of populations which are independently regulated by density dependent processes, although the present analyses suggest that we cannot rely on these tests to firmly show whether density dependence is present or not in an individual time series of the lengths considered here.
运用了多种技术来检测32个来自以蕨类为食的昆虫的时间序列中的密度制约。17个分类单元（主要是物种，但包括一些来自两个或更多密切相关物种的汇总数据，其幼虫在叶调查中无法区分）出现在一个开阔地带；一个林地有15个分类单元。对于在开阔栖息地收集的12年时间序列，17个分类单元中有10个（58.8%）通过一种或多种技术检测到直接密度制约，相比之下，来自林地栖息地的8年时间序列的15个分类单元中只有5个（33.3%）检测到。在开阔地带检测到6例延迟密度制约，在林地未检测到。在开阔地带的17个分类单元中有13个（76.5%）以及在两个地点都出现的15个分类单元中有13个（86.7%）发现了直接或延迟密度制约。尽管这些结果表明构成蕨类昆虫群落的物种中密度制约频率较高，但单个测试的结果差异极大。Vickery和Nudds（1984年）的测试检测到密度制约的频率最低，而Varley和Gradwell（1960年）的测试检测到的频率最高，尽管后者容易出现检测到虚假密度制约的高比率。直接密度制约在单化性且没有延迟滞育的分类单元中检测到的频率最高，即在那些生活史最符合分析基础模型假设的分类单元中。延迟密度制约在开阔地带生活史更复杂的物种中出现得更频繁（双化性或多化性的分类单元，或有延迟滞育的分类单元）。这些结果与以下观点一致，即蕨类食草动物组合由受密度制约过程独立调节的种群组成，尽管目前的分析表明，我们不能依靠这些测试来确凿地表明在此处考虑的长度的单个时间序列中是否存在密度制约。
