can be in the form of resistance to environmental stressors or through resilience—a measure of the ability of populations and assemblages to recover following the disturbance.
Studies of persistence and stability of fish assemblages are challenged because of greatly varying turnover rates in assemblages from different parts of North America. In addition, metrics used to determine stability form a hierarchical series of increasing sensitivity to change, such that the choice of analysis also influences the outcome. Furthermore, studies should be cognizant of biases. For example, studies on lotic systems are biased toward lowlatitude, southeastern regions, in contrast to those on lentic systems, which are biased toward higher latitudes.
SUPPLEMENTAL READING
Albanese, B. W., P. L. Angermeier, and J. T. Peterson. 2009. Does mobility explain variation in colonization and population recovery among stream fishes? Freshwater Biology 54:1444–60. Shows the variation in resilience, through recolonization ability, across streams and species.
Grossman, G. D., J. F. Dowd, and M. Crawford. 1990. Assemblage stability in stream fishes: a review. Environmental Management 14:661–71. A review of data on fish assemblage stability using coefficients of variation.
Grossman, G. D., P. B. Moyle, and J. O. Whitaker, Jr. 1982. Stochasticity in structural and functional characteristics of an Indiana stream fish assemblage: A test of community theory. The American Naturalist 120:423–54. An important paper that stimulated much research and discussion on the relative stability of fish assemblages.
Matthews, W. J., R. C. Cashner, and F. P. Gelwick. 1988. Stability and persistence of fish faunas and assemblages in three midwestern streams. Copeia 1988:945–55. Comparisons of fish assemblage persistence and stability using resemblance measures.
Matthews, W. J., and E. Marsh-Matthews. 2006. Temporal changes in replicated stream fish assemblages: Predictable or not? Freshwater Biology 51:1605–22. A test of stability of non-perturbed fish assemblages using an outdoor, experimental stream system.
PART THREE
Form and Function
The previous parts dealt with how fishes respond to their environments and to each other at small and large spatial and temporal scales. However, this has been largely a “phenomenological” approach (sensu, Koehl 1996), where species and individuals have been treated as “black boxes” that perform certain functions. The chapters in this part take more of a “mechanistic” approach in exploring the interactions of morphology, ecology, and evolution, and the resultant impacts on fish populations and assemblages.
SEVEN
Morphology and Functional Ecology of the Fins and Axial Skeleton
CONTENTS
Body Shape, Fin Location, and Maneuverability
Gaits, Maneuverability, and Specialization
Loss of Gaits and Specialization in Water-Column Fishes
Loss of Gaits and Specialization in Substratum Fishes
Evolutionary Trends in Form and Function
Natural Selection, Phenotypic Plasticity, Body Form, and Function
Lake Waccamaw
Sticklebacks
Sunfishes
Trade-Offs in Form and Function
Does Morphology Predict Ecology?
Tests of the Ecomorphological Hypothesis
Studies Assuming Validity of the Ecomorphological Hypothesis
VERTEBRATE EVOLUTION BEGAN in an aquatic environment in the early Paleozoic (500+ mya), followed by the evolution of tetrapods and then the evolution of terrestriality in the middle Devonian (390 mya) (Clack 2002; Nelson 2006). The aquatic and terrestrial environments occupied by vertebrate organisms offer their own sets of challenges and opportunities. For instance, unlike air, water is incompressible for all practical purposes and has much greater viscosity (the resistance of a fluid to deformation because of internal friction). Viscosity becomes increasingly significant as body size decreases and so is an especially important issue for larval stages of fishes (Webb and Weihs 1986). Because the viscosity and density of water are much greater than in air, movement in water must overcome greater drag compared to terrestrial vertebrates moving over land or flying. As a consequence, aquatic organisms, other than those where speed is not an issue, have streamlined body shapes to reduce the energy requirements of locomotion. Also, volume for volume, oxygen content in water is about a thirtieth of that in air (Kramer 1987), and obtaining oxygen from water is additionally challenging by the need to move a viscous medium across respiratory surfaces. Compared to movement on land, the lack of a solid surface to push against reduces the resultant force, although water is a much more efficient medium to push against compared to air. In contrast to terrestrial vertebrates, because their density is close to that of water, aquatic vertebrates gain all or a majority of their bodily support from water rather than having to invest in a skeletal system that can carry the weight of the body. In addition, little energy is required to move vertically. In a now-classic study, Schmidt-Nielsen (1972) provided a way of comparing some of the costs and benefits of movement in water, air, and on land. He determined that the net energetic cost of powering 1 gram of vertebrate over 1 km relative to body size was lowest for swimming, intermediate for flying, and greatest for running. The disciplines of fish biomechanics and hydrodynamics are presently very active, due in part to new technologies allowing the precise quantification of water flow patterns around swimming fishes (Lauder and Tytell 2006). This chapter explores the interaction of morphological evolution in fishes with their success in various freshwater habitats.
BASICS OF FISH PROPULSION
The body of a fish essentially consists of a compression resistant notochord or vertebral column, surrounded by lateral musculature, and wrapped in a complex arrangement of connective tissue and skin (Danos et al. 2008). In contrast to terrestrial locomotion, where the limbs involved in locomotion must also support the body, fishes can use a variety of mechanisms for locomotion, both independently and in concert, and can employ a variety of control surfaces such as scales, body projections, and fins to affect their posture and position in the water column (Webb 1994, 2006).
Forces to Overcome
To achieve forward motion, the force generated by a swimming fish must equal (constant swimming speed) or exceed (acceleration) the resistance to movement caused by drag (Webb 1975; Blake 1983a). The two components of drag
