Schleuning Matthias, Matthies Diethart
Philipps-Universität Marburg, Fachbereich Biologie, Pflanzenökologie, Karl-von-Frisch-Str. 8, D-35043 Marburg, Germany.
Conserv Biol. 2009 Feb;23(1):174-83. doi: 10.1111/j.1523-1739.2008.01054.x. Epub 2008 Sep 25.
An important aim of conservation biology is to understand how habitat change affects the dynamics and extinction risk of populations. We used matrix models to analyze the effect of habitat degradation on the demography of the declining perennial plant Trifolium montanum in 9 calcareous grasslands in Germany over 4 years and experimentally tested the effect of grassland management. Finite population growth rates (lambda) decreased with light competition, measured as leaf-area index above T. montanum plants. At unmanaged sites lambda was <1 due to lower recruitment and lower survival and flowering probability of large plants. Nevertheless, in stochastic simulations, extinction of unmanaged populations of 100 flowering plants was delayed for several decades. Clipping as a management technique rapidly increased population growth because of higher survival and flowering probability of large plants in managed than in unmanaged plots. Transition-matrix simulations from these plots indicated grazing or mowing every second year would be sufficient to ensure a growth rate > or =1 if conditions stayed the same. At frequently grazed sites, the finite growth rate was approximately 1 in most populations of T. montanum. In stochastic simulations, the extinction risk of even relatively small grazed populations was low, but about half the extant populations of T. montanum in central Germany are smaller than would be sufficient for a probability of survival of >95% over 100 years. We conclude that habitat change after cessation of management strongly reduces recruitment and survival of established individuals of this perennial plant. Nevertheless, our results suggest extinction processes may take a long time in perennial plants, resulting in an extinction debt. Even if management is frequent, many remnant populations of T. montanum may be at risk because of their small size, but even a slight increase in size could considerably reduce their extinction risk.
保护生物学的一个重要目标是了解栖息地变化如何影响种群动态和灭绝风险。我们使用矩阵模型分析了栖息地退化对德国9个钙质草原上多年生植物山地车轴草（Trifolium montanum）种群统计学的影响，并通过实验测试了草地管理的效果。有限种群增长率（λ）随着光照竞争的增加而降低，光照竞争以山地车轴草植株上方的叶面积指数来衡量。在未管理的地点，由于大型植株的补充率较低、存活率和开花概率较低，λ小于1。然而，在随机模拟中，100株开花植物的未管理种群的灭绝被推迟了几十年。作为一种管理技术，修剪迅速提高了种群增长率，因为与未管理地块相比，管理地块中大型植株的存活率和开花概率更高。来自这些地块的转移矩阵模拟表明，如果条件保持不变，每隔一年放牧或割草足以确保增长率≥1。在频繁放牧的地点，大多数山地车轴草种群的有限增长率约为1。在随机模拟中，即使是相对较小的放牧种群，其灭绝风险也较低，但德国中部现存的山地车轴草种群中约有一半小于100年内生存概率>95%所需的规模。我们得出结论，停止管理后栖息地的变化强烈降低了这种多年生植物成年个体的补充率和存活率。然而，我们的结果表明，多年生植物的灭绝过程可能需要很长时间，从而导致灭绝债务。即使管理频繁，许多残留的山地车轴草种群可能因其规模较小而面临风险，但即使规模略有增加也可能大大降低其灭绝风险。
