Entities on a Temporal Scale

Empirical and philosophical problems with the subspecies rank

Species-level taxonomy derives from empirical sources (data and techniques) that assess the existence of spatiotemporal evolutionary lineages via various species "concepts." These concepts determine if observed lineages are independent given a particular methodology and ontology, which relates the metaphysical species concept to what "kind" of thing a species is in reality. Often, species concepts fail to link epistemology back to ontology. This lack of coherence is in part responsible for the persistence of the subspecies rank, which in modern usage often functions as a placeholder between the evolutionary events of divergence or collapse of incipient species. Thus, prospective events like lineages merging or diverging require information from unknowable future information. This is also conditioned on evidence that the lineage already has a detectably distinct evolutionary history. Ranking these lineages as subspecies can seem attractive given that many lineages do not exhibit intrinsic reproductive isolation. We argue that using subspecies is indefensible on philosophical and empirical grounds. Ontologically, the rank of subspecies is either identical to that of species or undefined in the context of evolutionary lineages representing spatiotemporally defined individuals. Some species concepts more inclined to consider subspecies, like the Biological Species Concept, are disconnected from evolutionary ontology and do not consider genealogy. Even if ontology is ignored, methods addressing reproductive isolation are often indirect and fail to capture the range of scenarios linking gene flow to species identity over space and time. The use of subspecies and reliance on reproductive isolation as a basis for an operational species concept can also conflict with ethical issues governing the protection of species. We provide a way forward for recognizing and naming species that links theoretical and operational species concepts regardless of the magnitude of reproductive isolation.

Areas of endemism: to overlap or not to overlap, that is the question

The concept of "areas of endemism", and the assumption that these patterns are always a consequence of vicariant events, are reviewed. This assumption is related to the idea that areas of endemism have well-defined limits and never share any surface with other areas of endemism because they must represent sister areas supported by sister taxa. Based on this idea, overlapping areas have been considered rarely, or ignored completely. Using a data set of mammals of North America, we test here whether the overlapping areas are indeed sister areas supported by sister taxa, thus evaluating whether vicariant events are commonly the factor producing areas of endemism.

Establishing a Framework for a Natural Area Taxonomy

The identification of areas of endemism is essential in building an area classification, but plays little role in how natural areas are discovered. Rather area monophyly, derived from cladistics, is essential in the discovery of natural area classifications or area taxonomy. We propose Area Taxonomy to be a new sub-discipline of historical biogeography, one that can be revised and debated, and which has its own area nomenclature. Separately to area taxonomy, we outline how natural areas may be discovered by transcribing the concepts of homology and monophyly from biological systematics to historical biogeography, in the form of area homologues, area homologies and area monophyly.