Do natural enemies mediate conspecific negative distance- and density-dependence of trees? A meta-analysis of exclusion experiments
Song, Xiaoyang; Corlett, Richard (2022), Do natural enemies mediate conspecific negative distance- and density-dependence of trees? A meta-analysis of exclusion experiments, Dryad, Dataset, https://doi.org/10.5061/dryad.jq2bvq89c
Conspecific negative distance- and density-dependence is believed to be one of the most important mechanisms controlling forest community assembly and species diversity globally. Plant pathogens, and insect and mammalian herbivores, are the most common natural enemy types that have been implicated in this phenomenon, but their general effects at different plant life stages are still unclear. Here, we conduct a meta-analysis of studies that involved robust manipulative experiments, using fungicides, insecticides, or exclosures, to assess the contributions of different natural enemy types to distance- and density-dependent effects at seed and seedling stages. We found that conspecific negative distance- and density-dependence was more common at the seedling stage. Only 30% of studies showed significant conspecific negative distance- and density-dependence. Among those studies, applying fungicides significantly reduced the effect of conspecific negative distance -dependent mortality. Excluding large mammals reduced the effect of conspecifics, but with only marginal significance (p < 0.1). Our study confirms that plant pathogens have a significant impact on distance -dependent mortality and suggests that the impacts of herbivores on seedlings have been understudied. At the seed stage, large and small mammals, respectively, appear to weaken and enhance negative conspecific distance-dependent mortality. Future research should identify specific agents of mortality, investigate the interactions among different enemy types, and assess how global change may affect natural enemies and thus influence the strength of conspecific distance- and density-dependence.