Wetland development within the United States is regulated primarily by size. Decisions concerning wetland destruction or conservation are therefore based in part on three inherent assumptions: (1) small wetlands contain water for short portions of the year; (2) small wetlands support few species; and (3) species found in small wetlands are also found in larger wetlands. We tested these assumptions using data on wetland size, relative hydroperiod (drying scores), and relative species richness of amphibians in depression wetlands of the southeastern United States. We found a significant (p = 0.03) but weak (r2 = 0.05) relationship between hydroperiod and wetland size and no relationship (p = 0.48) between amphibian species richness and wetland size. Furthermore, synthetic models of lentic communities predict that short‐hydroperiod wetlands support a unique group of species. Empirical investigations support this prediction. Our results indicate that hydroperiod length should be included as a primary criterion in wetland regulations. We advocate a landscape approach to wetlands regulation, focused in part on conserving a diversity of wetlands that represent the entire hydroperiod gradient.
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.. Ecological Society of America is collaborating with JSTOR to digitize, preserve and extend access to Ecology. Abstract.We used a spatial survey of fish assemblage structure in streams and beaver ponds to: (1) determine the effects of beavers on fish assemblage structure at the reach and drainage basin scales, and (2) assess the influences of pond age, watershed position, and pond environment on fish assemblage structure within beaver ponds. Stream impoundment by beavers affected species richness at the reach scale, but this effect was highly dependent on pond age and drainage area above the pond. In headwater streams, species richness per pond increased to a high in ponds 9-17 yr old and then decreased to a low in ponds >17 yr old. Farther downstream, species richness showed little change with pond age. Assemblage structure varied significantly among unimpounded, impounded, and previously impounded stream reaches, and variation in assemblage structure among ponds was related to pond age and physical habitat. In large ponds there was a shift from lotic to lentic species, and as ponds aged, small-bodied minnows were replaced by larger predators. Because there was high species turnover among impounded and previously impounded reaches, beavers affected patterns of species richness at the drainage basin scale; we collected more species in first-and second-order streams (32 and 38, respectively) than in third-order streams (26). Taken together these results indicate: (1) that beavers have a positive effect on fish species richness in low-order, blackwater streams, but maintenance of this effect requires preservation of both spatial and temporal dynamics of beaver pond creation and abandonment, and (2) the positive relationship between stream fish species richness and drainage area described for many streams may be a recent phenomenon resulting from the extirpation of beavers from much of their historical range.beaver ponds, harsh winter conditions influenced life history characteristics, demographics, and feeding behavior of pumpkinseed sunfish (Lepomis gibbosus) populations (Fox and Keast 1990, 1991), and fishes were predominantly of small body size and partitioned resources among species (Keast and Fox 1990). Schlosser (1995) presented evidence suggesting ponds support "source" populations that provide a supply of immigrants to "sink" populations in adjacent streams, and that the supply of immigrants is controlled by the influence of discharge on boundary characteristics between ponds and streams. Hanson and Campbell (1963) present the only information that compares fish assemblage structure among beaver ponds. In comparing three beaver ponds to other pool habitats in a Missouri stre...
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