作者:CORINNE LABAUNE、FRÉDÉRIC MAGNIN
DOI:10.1093/mollus/67.4.463
日期:2001.11
It is difficult to define precisely determinant environmental factors that
explain land snail distribution and abundance, and most variables are often
interrelated. In addition, studies have generally examined only a limited
number of environmental variables, yielding a partial and local habitat
description. Recognised determinant factors are: climate, vegetation and soil.
Competitive interactions, historical factors and spatial structure are rarely
included, although they could generate biogeographic patterns on a local or
regional scale. The goal of the present work is to evaluate land snail habitat
complexity by examining a wide range of environmental variables. Land snails
from open environments were studied in a Provence, range, the Grand Luberon,
characterised by low variations in pH and calcium content. Grasslands on the
ridges are maintained by sheep grazing. A stratified sampling was chosen
according to altitude and vegetation structure. Sites were sampled throughout
the range. Different vegetation structure types were analysed, from low
grasslands to shrublands. Thirty-eight environmental variables were noted for
each site. They described: (1) topography and climate, (2) habitat structure,
(3) flora, and (4) spatial structure of snail communities. The main analytical
method used was the partial Canonical Correspondence Analysis which yielded a
partition of species variation into several independent components. The four
environmental variable groups were used separately. We obtained a partition of
ecological variation which emphasised the predominance of habitat structure
over floristic composition and the important role played by environmentally
independent spatial variables. Nevertheless, it remains difficult to
discriminate between the influence of climatic factors s.s., historic
events and/or biotic factors within the altitudinal gradient.
很难精确地定义决定性环境因素,这些因素可以解释陆生蜗牛的分布和丰度,而且大多数变量通常是相互关联的。此外,研究通常只考察有限的环境变量,只能得出局部和局部的栖息地描述。公认的决定性因素包括:气候、植被和土壤。竞争性相互作用、历史因素和空间结构很少被纳入研究,尽管它们可以在局部或区域尺度上产生生物地理格局。本研究的目标是通过考察一系列环境变量来评估陆生蜗牛栖息地的复杂性。普罗旺斯大吕贝隆地区(Grand Luberon)的pH值和钙含量变化较小,我们研究了来自该开阔环境的陆生蜗牛。山脊上的草原由放牧的羊群维护。根据海拔和植被结构选择分层采样。在整个范围内对地点进行采样。分析了从低矮的草原到灌木丛的不同植被结构类型。每个地点记录了38个环境变量。它们描述了:(1)地形和气候,(2)栖息地结构,(3)植物区系和(4)蜗牛群落的空间结构。主要分析方法使用了部分典型对应分析,该方法将物种变异分为几个独立的成分。四个环境变量组分别使用。我们获得了生态变异的分区,强调了栖息地结构对植物区系组成的支配作用,以及环境独立空间变量的重要作用。然而,仍然很难区分气候因素、历史事件和生物因素在海拔梯度中的影响。