Ecology of North American Freshwater Fishes. Stephen T. Ross Ph. D.
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1970). The times of egress of fishes from these refugia differed because of the earlier retreat of ice from coastal refugia and from the Missouri Refugium of Great Plains compared to the Mississippi Refugium. What these examples suggest is that the fish assemblages in formerly glaciated regions experienced a steplike increase in potential colonizers over time as passage from the various refugia became possible. In addition, as emphasized by Figure 3.6, regional faunas were established by colonizers from potentially a number of different refugia and thus have experienced different evolutionary histories and faunal associates.
The impact of postglacial dispersal is also illustrated by fishes occupying the Chehalis River valley, a small coastal drainage in western Washington that provided a refugium for lowland fishes of Puget Sound drainages and the Olympic Peninsula (McPhail 1967; McPhail and Taylor 1999). During the last advance of the Wisconsinan glaciation, the Puget Lobe of the Cordilleran ice sheet penetrated south to cover what is now Puget Sound (Figure 3.7) (Porter and Swanson 1998). South of the ice sheet, the Chehalis River valley remained unglaciated over much of its area, as did the larger lower Columbia River farther south (McPhail 1967; Pielou 1991). Although early faunal exchange occurred between the Chehalis and Columbia rivers, during the middle to late Pleistocene these faunas remained distinct. Drainages north of the Chehalis River that now flow into Puget Sound were ice covered for approximately 900–1,000 years (Porter and Swanson 1998). The Puget Lobe reached its maximum southern extent 16,950 years ago and then began receding 16,850 years ago (Porter and Swanson 1998). As it began to recede, flow was to the south into the Chehalis River and thence to the Pacific Ocean. The Chehalis River fish fauna, comprising eight species of primary freshwater fishes, gradually dispersed northward as the ice withdrew, especially species such as the Longnose Dace (Rhinichthys cataractae) that are adapted to swiftly flowing water (McPhail 1967). The farthest northward penetration of fishes from the small Chehalis River Refugium was achieved by the Nooksack Dace (Rhinichthys cataractae ssp.) and the Salish Sucker (Catostomus catostomus ssp.), which reached the Fraser River system of southern British Columbia (Figure 3.7) (McPhail 1997; Pearson 2000; Hutchings and Festa-Bianchet 2009). As the ice sheet receded past what is now the mouth of the Snohomish River (Figure 3.7), sea water from the Strait of Juan de Fuca poured into the large proglacial lakes that had expanded to occupy the Puget Sound Basin, quickly changing the basin from fresh water to sea water and limiting further northward distribution of primary freshwater fishes (McPhail 1967).
FIGURE 3.7. Modern and Pleistocene features of western Washington showing the location of the Chehalis River Refugium, modern-day Puget Sound (medium gray), the maximum southward penetration of the Puget Lobe of the Cordilleran ice sheet (light gray), early proglacial lakes, and other place names mentioned in the text. Based on McPhail (1967) and Porter and Swanson (1998).
Because glaciers are currently retreating, it is also possible to study postglacial colonization as it is now occurring. Cluster analysis of observed plant and animal taxa from newly developing streams in Glacier Bay, Alaska, results in three categories (Milner 1987). Newly emergent, meltwater streams support a limited biota consisting of algae and insects. Clearwater streams that are supported by runoff and snowmelt from the watershed have a greater diversity of insects compared to meltwater streams and also support a few Pink and Chum salmon (Oncorhynchus gorbuscha and O. keta). Clearwater streams fed from lakes, resulting in increased buffering of water quality, have extensive growth of algae and mosses, as well as a higher diversity of invertebrates and fishes.
SUMMARY
Biotic assemblages in general have undergone a continual cycle of breakup and rearrangement over geological time. As shown by this chapter, it is clear that fishes are no exception to this general pattern. Populations of freshwater fishes in most of North America have, through various means, been subjected to periodic fragmentation and restriction of their ranges. In some cases, as with typically lowland groups such as mooneyes and catfishes in western North America, their extirpation subsequent to the Oligocene was complete throughout the region. In other cases, range restriction and fragmentation was followed by population and range expansion, such as in Flannelmouth Sucker or in numerous species that recolonized northern North America following the retreat of the Pleistocene ice sheets. Recolonization of faunas most likely occurred as a mosaic, with specific faunal elements added over time from specific source regions. Especially in formerly glaciated regions of northern North America, recolonization of postglacial habitats occurred from often multiple refugia, greatly adding to the historical complexity of species and assemblages. Regions that remained free of ice and were otherwise less impacted by tectonic or climatic changes, such as the southeastern United States, support the greatest diversity of freshwater fishes.
The dynamic history of North American fish assemblages also carries an important conservation message. The goal of conservation of fishes should not only be to preserve species and assemblages in a “snapshot” of time but to conserve the full biodiversity of species and assemblages so that they have the potential to respond to natural (as well as anthropogenic) changes in their environments. This is clearly a challenging but critically important objective.
SUPPLEMENTAL READING
Pielou, E. C. 1991. After the Ice Age, the return of life to glaciated North America. University of Chicago Press, Illinois. An important general reference on the recolonization of formerly glaciated areas of North America.
Powell, J. L. 2005. Grand Canyon, solving the earth’s grandest puzzle. Penguin Group, New York, New York. A fascinating account of the untangling of formation of the Grand Canyon, beginning with the work of John Wesley Powell.
Sada, D. W., and G. L. Vinyard. 2002. Anthropogenic changes in biogeography of Great Basin aquatic biota. Smithsonian Contributions to the Earth Sciences 33:277–93. Details the multiple ways that humans (including native hunters and gatherers, the first European settlers, and modern society) have interacted and impacted aquatic faunas in the Great Basin.
Smith, G. R., C. Badgley, T. P. Eiting, and P. S. Larson. 2010. Species diversity gradients in relation to geological history in North American freshwater fishes. Evolutionary Ecology Research 12: 693–726. A recent and thorough synthesis of factors shaping the North American freshwater fish fauna.
WEB SOURCES
Desert Fishes Council. 2012. Species tracking. http://www.desertfishes.org/?page_id=327.
Reheis, M. 1999. Extent of Pleistocene Lakes in the western Great Basin: U.S. Geological Survey Miscellaneous Field Studies Map MF-2323. U.S. Geological Survey, Denver, CO. http://geo-nsdi.er.usgs.gov/metadata/map-mf/2323/metadata.faq.html.
PART TWO
Formation, Maintenance, and Persistence of Local Populations and Assemblages
Chapters in Part 1 show how fish populations and assemblages are shaped by broadscale geological and climatic factors over broad temporal and spatial scales. The focus now turns to how local fish assemblages and populations are influenced by regional faunas, by the general nature of the landscape in which they occur, and by the interplay of temporal and spatial habitat heterogeneity (see the following figure). Instead of the mega- and macroscale domains (sensu, Delcourt and Delcourt 1988) that span temporal and spatial scales from 10,000 to billions of years and 100s to thousands of kilometers, the focus now is on meso- and microscale domains of 1–10,000 years and meters to tens of kilometers.
Examples of filters affecting the formation of local fish assemblages from a regional species pool and their associated chapters.
FOUR
Responses of Populations and Assemblages to Biotic and Physical Factors
CONTENTS