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
Relating Assemblages to the Environment
Multivariate Statistics and Fish Assemblages
Local versus Regional Effects on Assemblages
FISHES ARE CONFRONTED by an environment that is complex and heterogeneous, with components of their habitat changing on multiple temporal and spatial scales. For instance, water temperature or turbidity might change on an hourly or daily frequency, altering the suitability of certain habitats; in contrast, substrata might change over a longer time period of days, months, years, or decades, and basic structures, such as shoreline characteristics in lakes or riffle–pool sequences in streams, might vary on a scale of many months to tens or hundreds of years.
Various approaches
