Delineating Freshwater Fish Biogeographic Regions in the Philippine Archipelago
Brian Wade Jamandre, Nico Jose Leander, Rodulf Anthony Balisco, Faith Santiago‐TadeoABSTRACT
Aim
To delineate native freshwater fish biogeographic regions in the Philippine archipelago and identify the contemporary and historical factors that structure freshwater fish diversity, endemism and species turnover.
Location
The Philippine archipelago.
Taxon
Native freshwater fishes.
Methods
We compiled an archipelago‐wide dataset of native freshwater fish occurrences and integrated these with environmental variables and historical biogeographic groupings, including Pleistocene Aggregate Island Complex (PAIC) configurations. Species distributions, diversity and endemism were analysed using cluster analysis of a Simpson's beta (βsim) dissimilarity matrix to delineate provinces, with provincial assignments interpreted in light of the PAIC framework and prior biogeographic evidence. Inventory completeness per province was quantified using coverage‐based rarefaction. Generalised Dissimilarity Modelling (GDM) was used to quantify the relative contributions of geographic, environmental and historical predictors to compositional turnover, with predictor importance and statistical significance assessed by matrix permutation. Indicator species analysis (IndVal) was applied to both the full dataset and the obligate primary‐freshwater (PF) subset, and dendrogram congruence between the two analyses was tested with a Mantel test and cophenetic correlation.
Results
Cluster analysis resolved five freshwater fish biogeographic provinces: Northern Luzon, Central/Southern Luzon, Greater Visayas, Mindanao and Palawan–Mindoro. Geographic distance was the strongest correlate of compositional turnover, while PAIC grouping and contemporary climate variables contributed comparatively little once geographic distance was accounted for. Two patterns stood out. First, the Visayan islands of Leyte and Samar clustered with the rest of the Greater Visayas rather than with Greater Mindanao, despite their conventional PAIC assignment to the latter, a pattern consistent with contemporary marine straits exerting biogeographic influence beyond what Pleistocene land‐bridge predicts. Second, Palawan–Mindoro stood out as a Sundaic outlier within the Philippine archipelago, anchored by obligate primary‐freshwater Cyprinidae of Bornean affinity. By contrast, Greater Visayas lacked any significant obligate‐freshwater indicator and was characterised instead by an estuarine–freshwater interface assemblage, supporting the interpretation of this province as a hydrologically open, marine‐influenced biogeographic system.
Main Conclusions
This study provides the first comprehensive biogeographic framework for Philippine freshwater fishes, clarifying how distance, palaeogeographical history and habitat context are associated with assemblage boundaries in a complex oceanic archipelago. The contrasting biogeographic character of Palawan–Mindoro and Greater Visayas illustrates how a single archipelago can host fundamentally distinct freshwater biogeographic modes shaped by geological origin and contemporary hydrological characteristics. The framework supplies a spatial template for conservation planning in Philippine inland waters and more broadly illustrates the value of integrating historical and contemporary drivers to explain freshwater biogeographic patterns in island systems.