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Melvin L. Warren, Jr. Center for Bottomland Hardwoods Research Southern Research Station

Fish Faunal Regions of the Southern United States: Isolation by Distance as a Structuring Mechanism. Melvin L. Warren, Jr. Center for Bottomland Hardwoods Research Southern Research Station USDA Forest Service Oxford, MS USA fswarren@olemiss.edu. North America ~1100+ freshwater fishes.

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Melvin L. Warren, Jr. Center for Bottomland Hardwoods Research Southern Research Station

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  1. Fish Faunal Regions of the Southern United States:Isolation by Distance as aStructuring Mechanism Melvin L. Warren, Jr. Center for Bottomland Hardwoods Research Southern Research Station USDA Forest Service Oxford, MS USA fswarren@olemiss.edu

  2. North America ~1100+ freshwater fishes Two salient features of southern U.S. fish fauna: High Diversity Range-restricted taxa

  3. >50% of North American Freshwater Fishes

  4. Range Extent of Fish Taxa High numbers of range restricted taxa

  5. Objectives Delimit fish faunal regions objectively and test for distinctiveness Determine importance of isolation-by-distance (i.e., drainage interconnectivity) in the geo-spatial structuring of the fauna

  6. 51 drainage units THE DATABASE All native fish taxa (685) assigned as present or absent in each drainage unit. • NATIVE SUBSETS • Darter taxa (218) • Minnow taxa (209) • Catfish taxa (46) • Sucker taxa (44)

  7. Methods • 5 pairwise faunal distance matrices of drainage units (Jaccards distance, UPGMA clustering): • all native fishes • subsets of the native fauna (darters, minnows, suckers, catfishes) • NMS (Non-metric Multidimensional Scaling) as independent test of adequacy of cluster-derived faunal regions (Sorenson distance) • Internodal drainage distance matrix • Mantel tests to test structural similarity between distance matrices

  8. 13 Internodal Distances Between Drainages Min 1, Max 34 nodes

  9. Atlantic Drainages & Florida Peninsula Gulf Drainages & Mississippi River Drainage Similarity All Native Fishes (chaining= 3.59%)

  10. Atlantic Drainages & Florida Peninsula Lower Mississippi River & tribs, Ohio mainstem, Gulf drainages Ohio R. tribs, Tenn-Cumb-Missouri Rivers Drainage Similarity All Native Fishes

  11. Drainage Similarity (Jaccards) All Native Fishes Atlantic Slope (North) Atlantic Slope (South) Florida Peninsula & Panhandle Mobile Basin & Middle Gulf Slope Mississippi R. & tribs Ohio River mainstem Western Gulf Slope Tennessee R., Cumberland R., Ohio R. tribs Missouri R. & tribs, Illinois-Neosho R.

  12. Atlantic N ‘Missouri R.’ ‘Tenn-Cumb Ohio tribs’ ‘Mississippi R’ Atlantic S ‘Mobile Basin’ West Gulf Slope Fla Peninsula

  13. Axis 1: 72.3% Axis 2: 13.8% Axis 3: 10.3% Final Stress = 4.8, “excellent” Instability= 0.00352, “low” Gulf Drainages & Mississippi River Basin Atlantic Drainages & Florida Peninsula

  14. NMS All Native Fishes Missouri R. & tribs, Illinois-Neosho R. Tenn-Cumberland-Ohio tribs Miss. R. & tribs & Ohio R. mainstem Atlantic North Western Gulf Slope Atlantic South Florida Peninsula & Panhandle Mobile Basin & Middle Gulf Slope

  15. NMS All Native Fishes Western Gulf Slope Missouri R. & tribs Illinois-Neosho R. Florida Peninsula & Panhandle Mobile Basin & Middle Gulf Slope Atlantic South Tenn-Cumberland-Ohio tribs Atlantic North Axis 1: 72.3% Axis 2: 13.8% Axis 3: 10.3%

  16. All Natives & Subsets(Mantel tests) All significant p < 0.001

  17. Fish & Internodal Drainage Distance Matrices

  18. Summary • A set of highly distinctive faunal regions emerged from the analyses-. • Faunal geo-spatial structure is highly congruent with drainage interconnectivity across the entire fauna and all major families. • Simple model of hierarchical, isolation-by-distance accounts for most of the faunal structure.

  19. Summary • Geo-spatial structuring in the native fauna is very strong, producing highly distinct faunal regions. • Structure is highly congruent with drainage interconnectivity for all major families. • Drainage faunas are “samples of regional faunas,” appear “undersaturated,” and likely are strongly affected by increased isolation from regional faunas.

  20. Drainage- and Regional-scale Diversity How is drainage-scale native fish diversity related to regional-scale fish diversity?

  21. Theoretical Expectations for Regional Richness and Local Richness

  22. Drainage & Regional Diversity

  23. How is drainage-scale native fish diversity related to regional-scale fish diversity? • Drainage-scale diversity related linearly, positively, and strongly to regional-scale diversity. • So what? • Implications for increased extinction risk from natural or human-induced fragmentation and isolation (e.g., coastal systems, dams, water quality) (Sheldon, 1987; Matthews and Robison 1998). • Implications for faunal ‘undersaturation’ such that biotic and/or abiotic interactions have not limited drainage level fish diversity (e.g., Cornell, 1993). • Implications for establishment of non-indigenous fishes. • Emphasizes strong role of ‘historical contingency’ in assembling the fauna.

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