Rethinking areas of endemism and barriers: perspectives for a causal historical biogeography and a critique of Schultz and Cracraft (2024)

Historical biogeography faces a persistent conceptual and methodological dilemma concerning the nature of its central analytical units. Using the recent proposal by Schultz and Cracraft (Cladistics 40, 653) as a catalyst, this article critiques the argument that causal inference necessitates the replacement of areas of endemism with barriers, contending that such a forced dichotomy is both artificial and reductionist. It is postulated that modern methodological advances allow areas of endemism to be rigorously treated as dynamic and quantitatively testable hypotheses, thereby overcoming long-standing objections that classify them as mere descriptive constructs. Conversely, an exclusive focus on barriers fundamentally underestimates the multifactorial nature of diversification, neglecting the structural role of dispersal and the complex spatiotemporal dynamism of isolating forces. Effective inference in historical biogeography demands an explicitly pluralistic and process-agnostic perspective, recognizing areas and barriers as complementary, intersecting elements. This integrative approach is essential for accurately capturing the emergent complexity of biogeographic patterns, moving the discipline beyond the limitations of unifocal causal models.