Half a century ago, Janzen and Connell hypothesized that the high tree species diversity in tropical forests is maintained by specialized natural enemies. Along with other mechanisms, these can cause conspecific negative density dependence (CNDD) and thus maintain species diversity. Numerous studies have measured proxies of CNDD worldwide, but doubt about its relative importance remains. We find ample evidence for CNDD in local populations, but methodological limitations make it difficult to assess if CNDD scales up to control community diversity and thereby local and global biodiversity patterns. A combination of more robust statistical methods, new study designs, and eco-evolutionary models are needed to provide a more definite evaluation of the importance of CNDD for geographic variation in plant species diversity.

半个世纪前，Janzen和Connell假设热带森林中高树种的多样性是由专门的天敌维持的。与其他机制一起，它们可能导致特定的负密度依赖性（CNDD），从而保持物种多样性。全世界有许多研究测量了CNDD的代理，但仍对其相对重要性存有疑问。我们发现有足够的证据证明本地人口中的CNDD，但方法的局限性使得很难评估CNDD是否扩大规模以控制社区的多样性，从而控制本地和全球的生物多样性模式。需要结合更强大的统计方法，新的研究设计和生态进化模型，才能更明确地评估CNDD对植物物种多样性地理变异的重要性。