Ecology of North American Freshwater Fishes. Stephen T. Ross Ph. D.
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droughts in three years coincided with distinct changes in associations of species or ecospecies. The empirical evidence of Matthews and Marsh-Matthews (2006a) suggests that although some smaller species groups (pairs, triads, or foursomes) might remain consistently in direct contact across years or even decades, there was little evidence that whole assemblage, multispecies associations were constant, or that selection pressures due to such multispecies groups would be consistent across such periods of time.
Persistence, Stability, and Control of Fish Assemblages
As pointed out at the beginning of the chapter, an important reason for trying to understand the levels of persistence and stability in fish assemblages is that assemblages that show high persistence, and particularly those with high stability, may be more influenced by biotic interactions (and have greater likelihood of deterministic control) than by abiotic factors (with greater likelihood of stochastic control). Clearly, the level of physical disturbance can influence the position of a community along a gradient of deterministic to stochastic control, as suggested by various authors, with biotic interactions likely more important in communities with low levels of disturbance and abiotic factors more important in communities with high levels of disturbance (e.g., Grossman et al. 1982; Peckarsky 1983). This is not to say that all assemblages showing stability are deterministically controlled or that all assemblages lacking stability are stochastically controlled. For instance, an assemblage with strong deterministic control based on competitive interactions among species could show a lack of stability because of differential time lags in the effects of species interactions (Strong 1983).
FIGURE 6.6. Persistence of associations among fish taxa in Brier Creek, Oklahoma, based on 19 snorkeling surveys taken over 22 years.
A. A simple example of similarity matrices based on two surveys with three taxa and three pools, where sxy is the similarity of taxa x and y between two pools.
B. Actual data showing the strength of the associations between consecutive samples relative to the time between the surveys; the solid line is the regression line based on the array of Z-scores. Based on Matthews and Marsh-Matthews (2006a).
One way of addressing the question of the degree of deterministic control of fish assemblages would be to follow an assemblage over time in the absence of major disturbance. However, such systems are uncommon in nature, except for some isolated springs. An alternative approach would be to use a seminatural, artificial stream system. If all streams offer essentially the same environments, then deterministic control should result in high similarity among fish assemblages. Matthews and Marsh-Matthews (2006b) stocked seven outdoor artificial streams with identical numbers and kinds of species and then followed assemblage composition for 388 days. Even though the streams were as identical as possible, differences did develop over time in the extent of algal cover and in the level of predation. Different levels of predation were caused by the differential survival of sunfishes among pools. Somewhat surprisingly, even in the absence of natural disturbances, the assemblages diverged significantly in composition, so that the ultimate structure of any of the experimental assemblages “could not be predicted from its initial structure.” In other words, the study did not support predictions of strong deterministic control.
SUMMARY
Fish assemblages change over both ecological and evolutionary time scales. Assemblages controlled primarily by random processes (i.e., primacy of stochastic control) have greater variation in species composition and abundances, compared to those influenced primarily by nonrandom processes (i.e., primacy of deterministic control). Disturbances include any event that disrupts a community or a particular assemblage in some way. Measures of assemblage responses to disturbance include those of persistence (i.e., the presence or absence) of fish species or by stability, a measure that includes the kinds of species and their abundances. Responses of fishes to disturbance 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