Ecology of North American Freshwater Fishes. Stephen T. Ross Ph. D.
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New World genera of the Cyprinodontidae began diverging in the Miocene (7–9 mya)—dates that are earlier than those proposed by Miller (1981) based largely on geological inferences. Some species within the family are of much more recent origin, dating to less than one million years (Echelle et al. 2005).
COTTIDAE (30 SPECIES) In terms of the diversity of genera, the sculpins are primarily a marine family. However, the genus Cottus is well represented in North American fresh waters with 28 species, and there are at least two freshwater species of Myoxocephalus. The oldest fossils of the genus Cottus are from late Miocene (ca. 11 mya) deposits of North America in what is now Oregon (Linder 1970; Cavender 1986). Freshwater forms in both genera are derived from marine species (Gilbert 1976; Burr and Mayden 1992). In contrast to the Miocene age of Cottus, freshwater species of Myoxocephalus are more recent, likely invading freshwater habitats in the early to middle Pleistocene around the beginning of the major continental glaciations (ca. 0.9 mya) (Kontula and Väinölä 2003).
ATHERINOPSIDAE (39 SPECIES) The New World silversides are primarily a marine family, although there are five genera that occur widely in freshwater habitats. Fossil silversides are known from Pliocene formations (ca. 4–5 mya)—one in what is now Arizona and the other from the Mesa Central of the Mexican Plateau (Cavender 1986). The Arizona fossils were most likely from a marine or brackish water habitat and have been assigned to the modern species Colpichthys regis (Todd 1976). The Mexican material also represented modern species of the genus Menidia (formerly placed in Chirostoma) (Barbour 1973; M. L. Smith 1981). Freshwater silversides are derived from marine ancestors, with perhaps several independent invasions of fresh water by species groups occupying the Mexican Plateau and those found in more northern regions of North America (Barbour 1973; Gilbert 1976; Burr and Mayden 1992).
SUMMARY
Fish evolution began in the early Paleozoic, perhaps 500–470 million years ago (mya). Modern bony fishes, the teleosts, appeared by the lower Mesozoic (230–206 mya), and by the middle Mesozoic (195 mya), representatives of most major groups of fishes were present. The distribution of marine and freshwater fishes worldwide, and the occurrence and distribution of North American freshwater fishes, have been strongly shaped by the movements of landmasses—plate tectonics.
The diverse fish fauna of North America came to occupy North America over a span of hundreds of millions of years, from as early as the late Paleozoic through the Pleistocene, and continuing into the present as populations respond to changing environmental conditions. Over two-thirds of the fauna, in terms of family origins, has occupied North America since the Paleogene (ca. 24 mya) or earlier, whereas ages of particular species can be much more recent. The minnows and darters, the two most speciose North American families, are also among the more recent (Miocene and Oligocene) arrivals.
Lineages of fishes in North America have various origins as well. Half of North American freshwater fishes have a marine origin, followed by those originating in North America (or in ancient landmasses of Pangea and Laurasia), Central and South America, and Eurasia. Because of the long and varied histories of fish lineages, contemporary assemblages of fishes should be viewed as being composed of suites of species with potentially widely differing histories, with adaptations that have likely been shaped to a greater or lesser extent by interactions in fish assemblages that were greatly different from those they are currently occupying.
SUPPLEMENTAL READING
Cavender, T. M. 1986. Review of the fossil history of North American freshwater fishes, 699–724. In The zoogeography of North American freshwater fishes. C. H. Hocutt and E. O. Wiley (eds.). John Wiley and Sons, New York, New York. An important reference to the fossil history of North American fishes.
Grande, L. 2001. An updated review of the fish faunas from the Green River Formation, the world’s most productive freshwater Lagerstätten, 1–38. In Eocene biodiversity: Unusual occurrences and rarely sampled habitats. G. F. Gunnell (ed.). Kluwer Academic/Plenum Publishers, New York, New York. A comprehensive review of one of the most complete series of fossil fish faunas.
Smith, A. G., D. G. Smith, and B. M. Funnell. 1994. Atlas of Mesozoic and Cenozoic coastlines. Cambridge University Press, Cambridge, United Kingdom. An important reference for understanding continental margins during the Mesozoic and Cenozoic.
WEB SOURCES
Scotese, C. R. Paleomap Project. http://www.scotese.com/Earth.htm.
Paleogeography and Geologic Evolution of North America. http://jan.ucc.nau.edu/∼rcb7/nam.html.
THREE
Reshaping North American Fish Faunas
THE ROLE OF LATE CENOZOIC CLIMATIC AND TECTONIC EVENTS
CONTENTS
Tertiary and Quaternary Events
Examples from Western North America
Examples from Northern and Eastern North America
Changes in Drainage Patterns and Stream Connections in Eastern North America
Changes in Drainage Patterns and Stream Connections in Northern and Northwestern North America
FISH ASSEMBLAGES AND POPULATIONS are continually challenged by changes in their local and regional environments. These changes could be relatively minor, such as local shifts in stream habitats caused by alterations in pools or riffle structure, or changes in access to habitats caused by shifts in the distribution of large piscivores. More extreme changes might include annual shifts in water level and/or flow rates caused by variation in precipitation. On an even larger scale, changes could reflect long-term climatic shifts, such as the onset of the Pleistocene Ice Ages, or major tectonic events, such as the uplift of the Colorado Plateau in the late Cretaceous that resulted in major alterations of stream connections and drainage patterns (G. R. Smith et al. 2010). Examples of some of the large-scale events that characterized the middle to late Cenozoic and their impacts on fishes are the topic of this chapter.
TERTIARY AND QUATERNARY EVENTS
From the previous chapter it is apparent how North American fish assemblages have been shaped by large-scale geologic and climatic events, with some fish lineages, such as lampreys, having experienced events as far back as the late Paleozoic. Such climatic and geologic events have, over time, shaped the pattern of fish diversity that characterizes North America (Figure 1.5). In addition, fish assemblages, like other biotic assemblages, have undergone continual breakup and rearrangement (Jablonski and Sepkoski 1996). In this section the emphasis is on events occurring during the Cenozoic, particularly the late Tertiary and early Quaternary Periods, while still recognizing that many of the long-term climatic and geological impacts are part of continual processes shaping our planet.
Examples from Western North America
In the early Paleozoic (Cambrian), western regions of North America subsided and were covered by seas that lasted, to varying extents, into the Jurassic (Stokes 1986). The exposed continental margin of North America cut through portions of Alberta, Montana, and Utah, essentially following the