Ecology of North American Freshwater Fishes. Stephen T. Ross Ph. D.
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few studies with suitable data for assessing the temporal persistence and stability of lakes and reservoirs (Table 6.2). However, in an analysis of nine long-term studies (median duration = 15 years; range 11–72) of lentic fish assemblages (eight natural lakes and one impoundment), the levels of persistence and stability were essentially the same as those for lotic systems (Figure 6.5C; Table 6.2). Reduced persistence or stability of assemblages tends to occur in altered habitats and/or in habitats impacted by nonnative plants or animals. In contrast to lotic systems, all but one of the lentic studies had suffered moderate or major human impacts, primarily through commercial fishing pressure, the introduction of nonnative plants and animals, and overall urbanization within the watershed.
Examples of Persistence and Stability in Lentic Systems
Numerous lakes exhibit evidence of negative impacts on persistence and stability. Lake Michigan has received considerable study because of heavy fishing pressure and the introduction of nonindigenous species such as Sea Lamprey (Petromyzon marinus), Alewife (Alosa pseudoharengus), Rainbow Smelt (Osmerus mordax), Coho Salmon, Chinook Salmon, Rainbow Trout, Brown Trout (Salmo trutta), and Brook Trout (Salvelinus fontinalis). Many native species such as Lake Trout, Bloater (Coregonus hoyi), and Cisco (C. artedi), have shown substantial declines and/or increases as numbers of nonindigenous fishes have fluctuated (see also Chapter 15). Although overfishing, Sea Lamprey predation on large fishes, and competitive interactions all contributed to the decline of indigenous fish species, another factor has been predation on early life-history stages (Stewart et al. 1981; Eck and Wells 1987; Miller et al. 1989). Major shifts in species composition of a small Michigan lake after the loss and then reintroduction of Largemouth Bass (Micropterus salmoides) have also been observed (Mittelbach et al. 1995). In Lake Mendota, Wisconsin, which has been impacted by extensive shoreline urbanization and introduction of nonnative vegetation, the fish fauna showed both low temporal persistence as well as low stability (Lyons 1989)
Lentic systems showing greater persistence and stability were generally, but not always, less impacted by habitat alteration or introduction of nonnative species (Table 6.2). In six small Michigan lakes, changes in the fish assemblages were generally low over a four-year period, as determined from a measure of community heterogeneity (based on the average percent dissimilarity over all possible pairs of seine sites within lakes) (Benson and Magnuson 1992). Somewhat surprisingly, heterogeneity among seine hauls within a site (33 m of shoreline) was of the same magnitude as heterogeneity among sites, thus suggesting that fishes were responding to small-scale patchiness of the environment.
In a 15-year study of two depauperate Arctic lakes, Johnson (1994) examined long-term stability of Arctic Char (Salvelinus alpinus) populations. Arctic Char was the sole species in one lake and one of two species in the other. After an initial period of moderate (one lake) and high (the other lake) fishing exploitation, the lakes were allowed to recover for several years. In both lakes, age and size structure of Arctic Char returned to the original condition, indicating population stability.
Using long-term data, Gido et al. (2000) examined stability and persistence of a pelagic reservoir fish assemblage over a 43-year period in Lake Texoma, a large impoundment on the Oklahoma-Texas border. Except for the introduction of two species within the study period, Striped Bass (Morone saxatilis) and Threadfin Shad (Dorosoma petenense), the fauna showed persistence and stability as determined from the rank order of species. Numbers of individuals of each species showed greater fluctuations, with coefficients of variation of the 11 most abundant species ranging from 11–108% over the years.
Persistence and Stability Summary
At the scale of the entire fish assemblage and across a wide range of systems, persistence is fairly common and stability somewhat less so, although both can be impacted by the timing, type, and magnitude of perturbations. Persistence and stability in lentic and lotic systems are generally reduced following severe human disturbances (see also Schlosser 1982; Matthews 1998), and such disturbances occur in both types of systems, although they are more common in lentic (89%) compared to lotic studies (28%). At the population level, rare species, and especially those with limited vagility, recover more slowly or not at all from perturbations, as shown by Albanese et al. (2009) for fishes in the James River drainage, Virginia. Although rare species have less of an effect on most measures of assemblage similarity, there is a greater risk of losing such species either from local habitats or system-wide. Because of this, although responses of assemblages to perturbations indicate generally high stability, postimpact fish assemblages (even if judged highly similar to preimpact assemblages by most measures of assemblage structure) might differ in the loss of rare species.
Although there are fewer lentic compared to lotic studies, those in lentic systems tend to compare longer time intervals (median 15 versus 11 years) and half as many species (mean 10, range 1–20, versus mean 21, range 3–95). Compared to lotic studies, lentic studies were also generally at higher latitudes (mean 49, range 34–64, versus mean 36, range 31–42)—regions that typically have lower fish species diversity. Thus our understanding of persistence and stability in streams, reservoirs, and lakes is incomplete because of relatively few studies and biases in geographic location, species richness, and length of comparisons.
Persistence and Stability of Local Associations
The previous sections dealt with levels of change in species assemblages over time periods of two or more years and over moderate to broad spatial scales. Much less is known about how close contacts of species in associations change over time—for instance how long do multispecies groups remain and do they remain together long enough for reciprocal evolutionary responses (coevolution) to occur? It can be difficult to detect association patterns in species of mobile animals. Individuals found in the same sample may or may not have been in close enough contact to have had direct interactions with each other. The capture of individuals of two species in a sample may not equate to their direct interaction because most survey methods for fishes, or other mobile vertebrates, have fuzzy boundaries and may sample different microhabitats (Ross and Matthews, in press). Also, fishes found together in a relatively long reach of stream (e.g., Marsh-Matthews and Matthews 2002) may, especially in highly structured habitats, occupy different pools or riffles and thus do not encounter each other daily. For mobile animals distributed across a heterogeneous landscape, consistent spatial associations among species could exist because some species (or some life stages within a species) select similar microhabitats totally independent of each other (see also Chapter 13) (Chapman and Chapman 1993; Grossman et al. 1998; Wilson 1999).
TABLE 6.2 Long-Term (≥ 2 years) Studies of North American Lake and Reservoir Fish Assemblages Organized from Low to High Levels of Perceived Stress and from Low to High Latitudes
For a downloadable PDF of all tables, go to ucpress.edu/go/northamericanfishes
Matthews and Marsh-Matthews (2006a) provided one of the clearest studies of the longevity of multispecies associations. Based on 19 snorkeling surveys taken over 22 years, they examined persistence of associations of eight taxonomic species (including minnows, a topminnow, sunfishes, and black basses) and 11 “ecospecies” (with the sunfishes separated into piscivorous adults versus insectivorous juveniles) across 14 adjacent pools within a kilometer reach of Brier Creek, Oklahoma (Figure 6.6). For each completed survey of the 14 pools (Figure 6.6A), species associations were compared by constructing a triangular similarity matrix of species pairs based on relative abundances (Figure 6.6B). Next, the strength of species associations over time was determined by sequentially comparing the 18 matrices using the Mantel test, a statistical procedure for comparing the correlation between matrices (Legendre and Legendre 1998). Concordance (based on Z-scores provided by the Mantel test) declined as the interval between samples increased (Figure 6.6D), so that associations within a year were largely concordant, but associations across years within a season were concordant only in late summer. Overall, species associations were concordant for approximately half of the 18 intervals between snorkeling surveys. Associations were not typically changed by events like floods and droughts,