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The stream continuum concept suggests that the physical structure of the stream channel coupled with the hydrological cycle and energy inputs results in a consistent pattern of community structure and function along a stream. I evaluated this concept in a headwater fish community along two physical gradients: upstream to downstream and riffle to pool.Habitat diversity and volume increased from upstream to downstream, and from riffle to pool. Temporal variation in habitat diversity was greater upstream. Upstream, and in riffles, habitat volume tended to vary more with time. Fluctuations in rainfall regime caused annual variation in habitat, especially in volume. Benthic insect density was highest from autumn (October-November) through spring (May-June). Following emergence of adults in late spring, invertebrate densities were low in summer in areas with riparian vegetation, but were not lower where riparian vegetation was absent and stable substrates were present. Along a gradient of substrates from silt-sand to gravel-rock, insect production increased, as indicated by adults and pupae in the drift. Peak resource availability for insectivore-piscivore fishes occurred in late summer and autumn, due to increased abundance of young-of-the-year fish.Pool and raceway-pool habitat guilds and insectivore and insectivore-piscivore trophic guilds contained the largest number of species. Increases in species richness were primarily associated with the addition of deeper habitats. Species richness of the pool insectivore-piscivore guild was especially variable over time. Biomass in shallow areas consisted predominantly of generalized insectivores. In deep, stable habitats, generalized insectivores were replaced as the predominant trophic group by insectivore-piscivores and large benthic insectivores. Immigration of fish occurred in spring and autumn, the periods of highest resource availability. Immigration between midriver and headwater regions primarily involved older age classes (III+), and was associated with changes in flow regime, habitat structure, and seasonal dynamics of the resource base of particular trophic groups. Flow regime and habitat volume appeared to be important factors limiting immigration in autumn, especially in pool species.Habitat diversity (depth, current, and substrate; DCS) was significantly correlated with fish species diversity (FSD). However, considerable variation occurred in the relationship between the two variables, including: (I) FSD decreased in winter in shallow, less diverse habitats due to emigration, and increased in spring due to recolonization; (2) FSD increased in spring and autumn when resource availability increased; (3) FSD was least predictable from DCS in autumn, when flow regimes were low and large numbers of fish recruits were present; and (4) DCS did not predict FSD as accurately in temporally variable upstream areas where large numbers of small fish dominated the community, especially in areas with human disturbance.Young age groups (O-Il) were primarily found in shallow, ...

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org. Abstract.I examined the effects of age and body size on intra-and interspecific habitat relationships for 15 species of fishes in a natural second-order warm water stream. Juveniles (age 0) of all taxa and adults (>age 0) of taxa with small maximum body size (darters and cyprinids) were at high densities predominantly in shallow riffle and raceway habitats. Adults of taxa with large maximum body size (catastomids and centrarchids) were at low densities predominantly in deep pool habitats. Based on the complementarity in depth distribution of large and small fishes, controlled experiments were conducted in a seminatural experimental stream to assess (1) the effect of large centrarchid piscivores in pools on the habitat use of small fishes, (2) the influence of structural complexity of pool habitats on the interaction between centrarchid predators and their prey, and (3) the effectiveness of centrarchid predators at capturing small fishes when shallow refugia exist. In the ex? periments, juvenile hornyhead chub, white sucker, and smallmouth bass were allowed to select one of four physical habitats in the presence and absence of adult smallmouth bass: riffle, raceway, structurally simple pool, or structurally complex pool. Predators were re? stricted to pool habitats so that riffles and raceways were effective refugia. Predation by bass occurred even though effective refugia were present. However, the taxa exhibited considerable variation in susceptibility to predation; white suckers were most vulnerable and smallmouth bass least vulnerable. In the absence of bass, juveniles of all taxa preferred structurally complex or structurally simple pools, even though benthic insect densities were higher in riffles than pools. In the presence of bass, juveniles of all taxa were largely restricted to shallow riffle or raceway refugia, with the extent of the shift in distribution to shallow habitats related to the vulnerability ofthe taxa to predation. If juvenile fishes occurred in pools with centrarchid predators, juveniles were at low densities and only in pools with high structural complexity. These results suggest that the high density and extensive overlap in habitat use of small fishes in shallow habitats of small warm water streams is related to the increased risk of predation by centrarchids in pools.

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. Abstract. We sampled riffle and pool habitats of small streams in Minnesota, Illinois, and Panama to examine variation in species-area relationships within and between the respective fish faunas. For six of the seven steams studied, habitat volume was a better predictor of species richness than was habitat area, and number of individuals was a better predictor of species richness than habitat volume. Slopes of species-volume relationships were similar among regions, but the number of species per unit volume was greater in Panama. Multiple regression analyses indicated that knowledge of habitat complexity and volume did not enhance appreciably the capability of linear models to predict species richness from number of individuals in the sample. These results support the hypothesis that species-area relationships may often be epiphenomena stemming from the more comprehensive community "samples" intercepted by larger habitat patches. Although number of individuals was the best single predictor of species richness, habitat structure and type clearly influenced species' distributions in some streams, thereby indicating that speciesarea relationships were not strictly sampling phenomena. An index of habitat complexity based on depth, current, and bottom type was correlated with species richness in two Panama streams. Also, the abundance of individual species was more likely to be correlated with habitat volume in Panama than in Illinois or Minnesota, and species relative abundances were more similar between years in Panama than in Illinois or Minnesota streams, especially in pools. These patterns suggest that in streams subject to strong seasonal and annual environmental variation, habitat features are poorer predictors of fish distribution and abundance than in streams subject to less environmental variability. We speculate that annual variability in reproductive success and harsh winters interact to maintain imbalance between the fish assemblages and their habitat in Minnesota. Weak relationships between species richness and habitat volume or complexity may be indicative of population variability and the predominance of extinction/recolonization processes in community organization. Ecological Society of America

/ Fishes in midwestern streams of the United States experience strong upstream-downstream gradients in natural environmental variability. Upstream fishes experience greater temporal variability in physical-chemical conditions than downstream fishes, particularly in intermittent streams. Associated with these changes in environmental variability, basic changes occur in life history attributes and temporal variation in community structure of stream fishes. As a whole, upstream species have a shorter life-span, smaller body size, and earlier sexual maturity than downstream species. Descriptive studies also suggest upstream species exhibit more rapid recolonization after severe physical disturbance than downstream species, and fish community structure is temporally more variable in upstream than downstream areas. These longitudinal differences in life history characteristics suggest that upstream fish communities will exhibit more rapid recovery from severe anthropogenic disturbances than downstream fish communities. The greater temporal variability of fish community structure in upstream areas also suggests it will be more difficult in upstream than downstream areas to use fish-based indices to distinguish whether subtle changes in environmental quality are due to natural or anthropogenic disturbances. Long-term monitoring of fishes throughout drainage basins is critically needed to establish more precisely the natural range of variation in community structure. Such monitoring will allow regulatory agencies to distinguish, with greater confidence, the influence of anthropogenic disturbances on stream fishes from the influence of natural environmental variation.Stream fish ecologists have long recognized the effect of both abiotic (Starrett 1951, Larimore and others 1959, Horwitz 1978, Coon 1987, Finger and Stewart 1987 and biotic (Mendelson 1975, Power andMatthews 1983) factors on stream fishes. However, there have been few attempts to integrate how the relative influence of these factors changes longitudinally along streams and, perhaps more importantly, the implications of these changes for environmental management and resource assessment procedures. In light of this, my objectives are, first, to summarize briefly the patterns of upstream-downstream environmental variation in natural lotic ecosystems. I then illustrate how life history characteristics and temporal variation in community structure of fishes changes along upstream-downstream gradients. Finally, I examine the implications of these results for the potential rate of recovery of upstream vs downstream fish communities from anthropogenic disturbances and the current use of fishes to monitor resource degradation from these disturbances.