生境面积大小对Janzen-Connell效应中密度和距离制约的影响

Influences of Habitat Size on Density- and Distance- dependence of Janzen-Connell Effects

关键词:  Janzen-Connell效应，密度制约，距离制约，生境破碎化，生物多样性

Key words:  Janzen-Connell effect  density-dependence  distance-dependence  habitat fragmentation  biodiversity

摘要:

全球变化和人为干扰导致生境破碎化日益严重，生境面积的减小导致了生物多样性的降低，如何维持生境破碎化下的植物多样性的问题亟待解决。本研究选择探究生境面积大小对Janzen-Connell效应中密度和距离制约的影响，以及密度和距离制约的驱动机制，旨在为生境破碎化背景下植物多样性的维持机制提供科学参考依据。通过在Web of Science数据库中收集并筛选出的1970年至2019年全球50个森林地点为数据基础，采用荟萃分析法，分析在密度和距离制约实验中不同类型驱动者的效应值大小，并用分段回归和非分段回归分别模拟分析密度和距离制约效应值大小与生境大小的关系。结果表明：在67项研究161项实验中，病原菌和无脊椎动物的效应值大小在距离制约实验中显著小于0（存在JC效应），而在密度制约实验中不显著。相反，脊椎动物的效应值大小仅在密度制约实验中显著小于0。虽然只有距离制约效应值随生境面积的减小呈先增大后减小趋势，但密度制约趋势线的拟合转折点在距离制约之前，表明生境面积的减小会先影响密度制约。本研究阐明了密度和距离制约的主要驱动者分别是密度型驱动者（脊椎动物）和距离型驱动者（病原菌和无脊椎动物），而密度制约比距离制约对生境面积的减少更敏感，可能是两种驱动者对生境面积的需求不同所导致。因此，在不同生境面积的片段中关注不同类型的驱动者有利于生物多样性的维持。

Abstract:

Habitat fragmentation is becoming more and more serious due to global change and anthropogenic disturbance, and the decrease of habitat area leads to the decrease of biodiversity. The problem of how to maintain plant diversity under habitat fragmentation needs to be solved urgently. In this study, we explored the effects of habitat area on density- and distance-dependence of the Janzen-Connell effect, as well as the driving mechanism of it, that can provide a scientific reference for the mechanism of plant diversity maintenance in habitat fragmentation. We conducted a meta-analysis of data from 1970 to 2019 including 50 forest locations worldwide which were collected and filtered from the Web of Science database. The effect size of different drivers in the density- and distance-dependent experiments were analyzed, and the relationship between the density- and distance-dependent effect size and the habitat size was simulated by piecewise regression and non-piecewise regression, respectively. Across 161 experiments (67 studies), we found that effect sizes of pathogen and invertebrate were significantly less than 0 in distance-dependent experiments (JC effect), but not in density-dependent experiments. In contrast, the effect sizes of vertebrate were only significantly negative in density-dependent experiments. Although only the distance-dependence effect size increased first and then decreased with the decrease of habitat area, the inflection point of the density-dependence trend appeared before than the distance-dependence, indicating that the decrease of habitat area would first affect the density- dependence. Our study demonstrates that different enemies are the main drivers of density- and distance-dependence, respectively. Density-dependence is more sensitive to the decrease of habitat area than the distance-dependence, which may be caused by the different demands of the two drivers on habitat area. Therefore, focusing on different types of drivers in different sizes of fragments can help to biodiversity maintenance.