The issue of species delimitation has long been confused with that of species conceptualization, leading to a half century of controversy concerning both the definition of the species category and methods for inferring the boundaries and numbers of species. Alternative species concepts agree in treating existence as a separately evolving metapopulation lineage as the primary defining property of the species category, but they disagree in adopting different properties acquired by lineages during the course of divergence (e.g., intrinsic reproductive isolation, diagnosability, monophyly) as secondary defining properties (secondary species criteria). A unified species concept can be achieved by treating existence as a separately evolving metapopulation lineage as the only necessary property of species and the former secondary species criteria as different lines of evidence (operational criteria) relevant to assessing lineage separation. This unified concept of species has several consequences for species delimitation, including the following: First, the issues of species conceptualization and species delimitation are clearly separated; the former secondary species criteria are no longer considered relevant to species conceptualization but only to species delimitation. Second, all of the properties formerly treated as secondary species criteria are relevant to species delimitation to the extent that they provide evidence of lineage separation. Third, the presence of any one of the properties (if appropriately interpreted) is evidence for the existence of a species, though more properties and thus more lines of evidence are associated with a higher degree of corroboration. Fourth, and perhaps most significantly, a unified species concept shifts emphasis away from the traditional species criteria, encouraging biologists to develop new methods of species delimitation that are not tied to those properties.

中文翻译：

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物种概念和物种界定

物种划界问题长期以来一直与物种概念化问题相混淆，导致了半个世纪以来关于物种类别的定义以及推断物种边界和数量的方法的争议。替代物种概念同意将存在视为单独进化的元种群谱系作为物种类别的主要定义属性，但他们不同意在分歧过程中采用谱系获得的不同属性（例如，内在的生殖隔离、可诊断性、单系）作为次要定义属性（次要物种标准）。统一的物种概念可以通过将存在视为单独进化的元种群谱系作为物种的唯一必要属性，将前次要物种标准视为与评估谱系分离相关的不同证据线（操作标准）来实现。这种统一的物种概念对物种划界有几个影响，包括：首先，物种概念化和物种划界问题是明确分开的；以前的次要物种标准不再被认为与物种概念化有关，而只与物种定界有关。其次，以前被视为次要物种标准的所有特性都与物种定界相关，因为它们提供了谱系分离的证据。第三，任何一种特性的存在（如果适当解释）都是物种存在的证据，尽管更多的特性和更多的证据线与更高程度的证实相关联。第四，也许最重要的是，统一的物种概念将重点从传统的物种标准转移，鼓励生物学家开发与这些特性无关的新物种定界方法。