An Exploration of Hypotheses that Explain Herbivore and Pathogen Attack in Restored Plant Communities

Many hypotheses address the associations of plant community composition with natural enemies, including: (i) plant species diversity may reduce enemy attack, (ii) attack may increase as host abundance increases, (iii) enemy spillover may lead to increased attack on one host species due to transmission from another host species, or enemy dilution may lead to reduced attack on a host that would otherwise have more attack, (iv) physical characteristics of the plant community may influence attack, and (v) plant vigor may affect attack. Restoration experiments with replicated plant communities provide an exceptional opportunity to explore these hypotheses. To explore the relative predictive strengths of these related hypotheses and to investigate the potential effect of several restoration site preparation techniques, we surveyed arthropod herbivore and fungal pathogen attack on the six most common native plant species in a restoration experiment. Multi-model inference revealed a weak but consistent negative correlation with pathogen attack and host diversity across the plant community, and no correlation between herbivory and host diversity. Our analyses also revealed host species-specific relationships between attack and abundance of the target host species, other native plant species, introduced plant species, and physical community characteristics. We found no relationship between enemy attack and plant vigor. We found minimal differences in plant community composition among several diverse site preparation techniques, and limited effects of site preparation techniques on attack. The strongest associations of community characteristics with attack varied among plant species with no community-wide patterns, suggesting that no single hypothesis successfully predicts the dominant community-wide trends in enemy attack.

多项假说旨在阐释植物群落组成（plant community composition）与天敌（natural enemies）之间的关联，具体包括：（一）植物物种多样性（plant species diversity）可降低天敌危害（enemy attack）；（二）天敌危害程度随宿主（host）植物多度升高而增加；（三）天敌溢出效应（enemy spillover）可能因跨宿主物种传播，导致某一宿主物种的危害程度升高，而天敌稀释效应（enemy dilution）则可降低原本危害程度更高的宿主的受危害水平；（四）植物群落物理特征（physical characteristics of the plant community）可影响天敌危害；（五）植物活力（plant vigor）会对天敌危害产生影响。采用重复设置植物群落（replicated plant communities）的修复实验（restoration experiments），为验证上述假说提供了绝佳契机。为探究上述相关假说的相对预测能力，并解析多种修复场地预处理技术（restoration site preparation techniques）的潜在影响，本研究针对某修复实验中的六种最常见本土植物物种（native plant species），调查了节肢动物植食者（arthropod herbivore）与真菌病原菌（fungal pathogen）的危害情况。多模型推断（multi-model inference）结果显示，植物群落整体的病原菌危害与宿主多样性间存在微弱但稳定的负相关关系（negative correlation），而植食程度（herbivory）与宿主多样性则无显著关联。本研究的分析还揭示，不同宿主物种的天敌危害程度，分别与目标宿主植物多度、其他本土植物物种多度、外来植物物种（introduced plant species）多度以及群落物理特征存在物种特异性关联（host species-specific relationships）。未发现天敌危害与植物活力间存在关联。多种差异化场地预处理技术间的植物群落组成差异极小，且此类技术对天敌危害的影响有限。群落特征与天敌危害间关联最强的变量因植物物种而异，未出现全群落层面的统一模式，这表明尚无单一假说能够准确预测天敌危害在全群落尺度的主导性趋势。