Hydroperiod Length Research Articles

Influence of agricultural upland habitat type on larval anuran assemblages in seasonally inundated wetlands

Conservation initiatives in agricultural landscapes play an increasingly important role in ensuring the long-term persistence of amphibian biodiversity because native habitats continue to be lost to urban and commercial development. We examined larval anuran structure within seasonally inundated wetlands in four upland habitat types of southcentral Florida differing in degree of upland habitat modification for cattle ranching: native prairie at the Kissimmee Prairie Sanctuary (KPS); and improved pasture, rangeland (semi-native prairie), and woodland habitats at the MacArthur Agro-Ecology Research Center (MAERC). We sampled 24 wetlands monthly for tadpoles using throw-traps and dipnets during the 1999 wet season (June–October), recording 10,126 tadpoles of 10 species. Species richness, mean total abundance, and species abundances differed among upland habitat types. The most heavily modified habitat (pasture) had both species-poor assemblages and low tadpole abundances. Species richness in woodland, rangeland, and native prairie wetlands were similar, but woodland wetlands had higher tadpole abundances. Wetlands in the four habitats differed in the amount of nearby woodland and wetland habitats, length of hydroperiod, and percent cover of aquatic vegetation, which likely contributed to the observed amphibian richness and abundance patterns. Cattle ranches in Florida that retain a large proportion of woodland, rangeland, and temporary wetlands in the landscape are likely to contribute significantly to amphibian conservation initiatives on protected native lands.

Impact of hydroperiod on seasonal dynamics in temporary pool cladoceran communities

We studied seasonal dynamics in cladoceran communities in relation to changing habitat characteristics and biotic interactions in 18 temporary freshwater pools in Kiskunsag (Hungary), with an inundation period varying from less than ten weeks (short) to 10-13 weeks (medium long) and more than 16 weeks (long). Pools were sampled for cladocerans and macroinvertebrates and habitat characteristics were monitored starting two weeks after snow melt (end of March 2005) until July. Analysis of early-season dynamics (March-April), when all three hydroperiod classes were represented, did not reveal differences in cladoceran communities recolonizing pools with a different hydroperiod. Species turnover later in the season (May - July) resulted in the association of some species with the medium and long hydroperiod class. Cumulative species richness increased with hydroperiod length from an average of ten species in short hydroperiod to 15 species in long hydroperiod pools. The longer time available most likely allowed more species to gradually occupy available niches in pools with a longer hydroperiod. With time, feeding and growth conditions became more favorable for predominantly small and/or plant-associated species, while the absence of large Daphnia may have been due to predation risk. A decline of pools with a long inundation cycle, through drainage and/or climate change, may adversely affect cladoceran communities and needs particular attention in the conservation of temporary pools and their inhabitants.

Functional characteristics of macroinvertebrate communities in Mediterranean ponds (Central Italy): Influence of water permanence and mesohabitat type

The macroinvertebrate fauna of twenty-one ponds (thirteen temporary and eight permanent) located in four protected areas in Central Italy were studied in March, May and June 2002, with the aim to bring out relationships between environmental variables and the functional characteristics (functional feeding groups, habits and resistance to drought) of communities. Macroinvertebrates were collected in three mesohabitat types (macrophyte beds, littoral sediments, central sediments). Overall, the functional attributes of temporary and permanent pond communities did not differ greatly. However, at the mesohabitat scale, collector-gatherers, burrowers and permanent residents capable of passive dispersal were more abundant in sediments. Scrapers and shredders, sprawlers and climbers, swimmers and divers, and organisms capable of active dispersal which lack drought resistance were more abundant in macrophyte beds. Although hydroperiod is the main driving factor affecting community structure, our results suggest that it remains an unimportant factor in controlling functional traits, which appeared to be more influenced by substratum types. Moreover, the positive relationship between taxonomic and functional diversity metrics indicates that an increase in taxonomic richness induces a satisfactory partitioning of the ecological resources among taxa, thus maintaining the ecological complexity of the ponds regardless of their hydroperiod length.

Population Structure of Ambystoma tigrinum mavortium in Playa Wetlands: Landuse Influence and Variations in Polymorphism

Playa wetlands are the major habitat for amphibians in the Southern Great Plains, USA. Agricultural cultivation causes playa sedimentation and related hydroperiod reduction in this intensively-farmed region, which in turn affects amphibian community structure. The goals of our study were (1) to investigate the influence of landuse on larval salamander (Ambystoma tigrinum mavortium) occurrence and densities in playas and whether hydroperiod length is an environmental influence on that occurrence, (2) to examine the polymorphic structure (cannibal, intermediate, and typical morphotypes) of larval salamanders and whether the frequency of occurrence of intermediate and typical morphs is associated with the presence of cannibal morphs and variations in hydroperiod length and conspecific density, and (3) to investigate morphological and life history trait differences among morphotypes (i.e., larval periods, growth rates, and body sizes). Cultivation of watersheds negatively affected presence and density of larval salamanders in playas, and this effect was associated with reduced hydroperiods. Although cannibal morphs were rare in playas, their presence negatively influenced presence of intermediate morphs and, thus, in this situation the majority of larvae were typical morphs. When cannibal morphs were absent, intermediate and typical morphs developed in similar proportions among playas with a tendency for intermediate morphs to predominate. Larval density and hydroperiod length were positively associated with the presence of cannibal morphs. Intermediate morphs had distinct growth patterns compared to cannibal and typical morphs and had body size measures (snout-to-vent length and stomach size) in between the two extreme morphs. Cannibal morphs grew faster and reached larger body size at metamorphosis than non-cannibal morphs. When cannibal morphs were absent, intermediate and typical larvae reached larger sizes than when cannibal morphs were present. We conclude that cultivation surrounding playas can negatively influence Ambystoma occurrence in general and especially the cannibal morphotype by reducing wetland hydroperiod. Moreover, a polymorphic community structure in larval amphibians may be important to a properly functioning playa food web.

Macrophyte diversity and physico-chemical characteristics of Tyrrhenian coast ponds in central Italy: implications for conservation

Awareness of pond conservation value is growing all over Europe. Ponds are recognized as important ecosystems supporting large numbers of species and several rare and threatened aquatic plants, macroinvertebrates and amphibians. Notwithstanding ponds, particularly temporary ones, are still neglected in Italy. There are some gaps in our understanding of the macrophyte ecology and the conservation value of Mediterranean small still waters. Therefore, this study investigated the macrophyte communities and physico-chemical characteristics of 8 permanent and 13 temporary ponds along the Tyrrhenian coast near Rome, with the aim to relate the distribution of aquatic plants to environmental variables, and to define the botanical conservation value of ponds. Throughout the study period (Spring 2002), Principal Component Analysis performed on abiotic variables clearly discriminated temporary ponds, smaller and more eutrophic, from permanent ponds, larger and with higher pH and oxygen concentration. A total of 73 macrophyte taxa were collected in the study ponds. Temporary waters hosted a smaller number of plant species than permanent ones. Besides hydroperiod length, the environmental factors related to plant richness were maximum depth, surface area, dissolved oxygen and nitrogen concentration in the water. Moreover, the Non-metric Multidimensional Scaling showed a high dissimilarity in the taxonomic composition of aquatic plants between temporary and permanent ponds. The former contained more annual fast-growing species (Callitriche sp. pl. and Ranunculus sp. pl.), while in the latter species with long life-cycles (i.e. Potamogeton sp. pl.) were more abundant. Our results highlighted that temporary and permanent ponds in central Italy have different macrophyte assemblages, with aquatic species (including some of conservation interest at regional scale) exclusively found in each pond type. This suggested that both type of ponds could give an irreplaceable contribution to the conservation of aquatic plant diversity of these freshwater ecosystems.

The roles of natural temporal and spatial variation versus biotic influences in shaping the physicochemical environment of intermittent ponds: a case study

The importance of top-down and bottom-up mechanisms in lentic systems has largely been explored in stable systems; however, their influence is likely to change along a habitat duration gradient. Using a case study of four intermittent ponds, we test the generality of these paradigms in systems nearing the extreme short end of this gradient. Intermittent ponds fill up with water on a seasonally predictable basis, and are considered more regulated by physicochemical constraints than by biological factors. We found that natural spatial (i.e., pond-to-pond) and temporal variations (i.e., seasonal and annual) were more important than food-web manipulations (i. e., exclusion of aerial colonization, addition of top-predators [beetle larvae and odonate nymphs], and addition versus removal of allochthonous resources [leaf litter] in field enclosures) in shaping the physicochemical environment. Spatial variation included mainly depth-related variables (e. g., conductivity and pH), whereas annual variation included variables associated with hydroperiod length and productivity (e. g., weeks after flooding, pH, nutrients, and chlorophyll-a). Seasonal variation was pronounced but lower in ponds with longer hydroperiod and in mid-season. Enhanced invertebrate predation pressure increased levels of chlorophyll-a. Exclusion of aerial colonizers increased levels of chlorophyll-a and phosphorus, and affected levels of dissolved oxygen (increasing in one pond and decreasing in another). Addition of leaf litter resulted in lower concentrations of dissolved oxygen, higher phosphorus, and lower pH. Leaf litter removal led to increased levels of dissolved oxygen, changed chlorophyll-a (increasing in one pond and decreasing in another), and higher pH (in one pond). We conclude that although pond characteristics, seasonal development, and annual differences were of greater importance than biological factors for shaping the physicochemical characteristics of these intermittent ponds, bottom-up and top-down effects were also influential.

Macroinvertebrate diversity and conservation status of Mediterranean ponds in Italy: water permanence and mesohabitat influence

1. In Italy small water bodies, especially temporary ones, have been little studied. As a consequence, their conservation value as a biodiversity resource is often overlooked despite Mediterranean temporary waters being listed as a priority habitat in the Habitats Directive (92/43/ EEC). 2. A monitoring programme was designed to determine which factors influence pond species richness, and to analyse the variation in macroinvertebrate community structure within and among ponds. Three main contrasting mesohabitats (macrophyte beds, littoral sediments and central sediments) were defined within 21 ponds (8 permanent and 13 temporary) along the Tyrrhenian coast of Italy near Rome, from which invertebrate macrofauna was collected in March, May and June 2002. 3. The main environmental factors influencing the number of species in ponds were hydroperiod length, depth, surface area, dissolved oxygen concentration and macrophyte species richness. Temporary ponds contained a smaller number of taxa than permanent ponds, but both types of ponds supported similar numbers of rare and threatened species. The total number of species, and in particular Coleoptera, Odonata, and Hemiptera, was higher in macrophyte beds than in both littoral and central sediments. 4. Multivariate analysis (non-metric multidimensional scaling) showed that the overall variation in assemblage composition was greater between temporary and permanent ponds than among mesohabitats, suggesting that environmental variables, such as hydroperiod, have a stronger effect on macroinvertebrate communities than substratum type. 5. In terms of species of conservation interest, this study suggests that both pond types and all mesohabitats should be considered in order to obtain a correct evaluation of pond conservation value.

Macroinvertebrate size spectra of Mediterranean ponds with differing hydroperiod length

1. The size spectra of the macroinvertebrate community in ponds with different hydroperiod length were compared along the Tyrrhenian coast of central Italy. Invertebrate sampling was conducted in 21 ponds (8 permanent and 13 temporary) in three different mesohabitats (central sediments, littoral sediments and macrophytes) during spring 2002. Several pond characteristics were also recorded. 2. Density and biomass size spectra were calculated for 123 samples and covered six orders of magnitude in size ranging from 0.126 µg to 0.5 g. The shape of the density size distribution was unimodal, the mode being around 0.05–0.1 mg, with Oligochaeta and Diptera (Chironomidae) numerically dominant in almost all size classes. 3. The periodic drying affected the total biomass per size class, shown by comparing spectra among mesohabitats and pond types. The higher biomass in all size classes showed by permanent ponds and central sediments reflects the major stability of permanent biotopes and, within these, of central sediments. 4. The overall shape of the size spectrum was similar among pond types, mesohabitats and sampling dates. Biomass of larger size classes was linked to variables describing pond stability. 5. We suggest that the biomass size spectrum of benthic macroinvertebrates is a potentially useful tool for quantitative wetland biomonitoring. In small Mediterranean ponds, the regularity of biomass size spectra implies that size-structuring processes are independent of the hydrological stress. Copyright © 2005 John Wiley & Sons, Ltd.

Macroinvertebrate communities in central Platte River wetlands: Patterns across a hydrologic gradient

Wetlands provide critical wildlife habitat in the central Platte River basin of Nebraska, USA, but little is known about their macroinvertebrate communities or how factors such as hydrology affect them. In 1997, we quantified macroinvertebrate abundance, biomass, and community structure and organic matter resources in four natural wetlands that represented a gradient from ephemeral to permanent flooding. All four wetlands had abundant macroinvertebrate communities when flooded, and we observed unique taxa at all sites. Mean annual macroinvertebrate abundance and biomass increased with hydroperiod length, but taxon richness and diversity were greatest in intermittent sites. Non-insect groups, mostly crustaceans, annelids, and mollusks, were important at all sites, and their taxonomic composition shifted across the hydrologic gradient. Insect communities were dominated by dipterans (mostly Chironomidae and Ceratopogonidae) and Coleopterans (mostly Hydrophilidae and Dytiscidae), and these also varied across the hydrologic gradient. Collector-gatherers, scrapers, and predators were the dominant functional groups in terms of biomass, and biomass was most evenly distributed among these groups in intermittent sites. Macroinvertebrate communities in these riparian wetlands vary across natural hydrologic gradients, and diversity peaks in intermittent sites. Patterns of abundance, biomass, and diversity, along with seasonal patterns, suggest that, at a landscape level, a diversity of wetland habitats with different hydrologic regimes will maximize abundance and diversity of freshwater macroinvertebrate communities in this region.

Stochastic variation in reproductive success of a rare frog, Rana sevosa: implications for conservation and for monitoring amphibian populations

Although amphibian populations are thought to be declining in many parts of the world, detailed information on populations in decline are often not available. From 1988 to 2001, we studied temporal variation in the reproductive biology of the only known population of dusky gopher frogs, Rana sevosa Goin and Netting. We found high annual variation in reproductive effort, mortality at the egg and larval stages, and hydroperiod length. No overall trends were apparent in terms of either number of egg masses deposited or in reproductive success, as we found extensive variation among years in the number of egg masses deposited, a high rate of reproductive failure, and no consistent relationship between the number of females present, the number of eggs deposited, and the number of metamorphs emerging. Given the complete isolation of this population from other gopher frogs and the high rate of reproductive failure, the probability of extinction of this population appears to be quite high (0.125–0.316).

Spatially explicit population responses of crayfish Procambarus alleni to potential shifts in vegetation distribution in the marl marshes of Everglades National Park, USA

Hydropattern disturbance has had wide-ranging impacts on wetland communities of the Florida Everglades, especially on the habitats and the aquatic biota of the seasonally flooded marl marshes. We used the Everglades crayfish Procambarus alleni as a model to study the associations among hydrology, vegetation distribution, and population dynamics to assess the potential impacts of hydrological changes on the aquatic faunal community in Everglades National Park. To classify benthic habitats as sources or sinks for the crayfish population, we quantified vegetation community structure using GIS maps in which dominant vegetation types were weighted by local hydroperiod (length of inundation). Regression analysis showed that this habitat classification was associated with crayfish density distribution. We then used a spatially explicit, stage-structured population model to describe crayfish population fluctuations under current environmental conditions and to simulate the potential population-level responses to habitat changes that might occur following hydrological restoration. In habitat that was initially saturated with crayfish, the crayfish population size declined under current environmental conditions and then stabilized at about 13% of the initial density over a 50-year period. A 4-month increase in hydroperiod was then simulated by converting shorter-hydroperiod Muhlenbergia-dominated marsh habitat to longer-hydroperiod Cladium-dominated marshes. The model predicted a rapid 7-fold increase in crayfish density following the simulated habitat restoration. This indicated that several functional effects may result from the restoration of historical hydropatterns in marl marshes: (1) the areal extent of habitat sinks will be reduced to isolated patches, whereas the spatial distribution of aquatic source habitats will expand; (2) crayfish population size will increase and persist over time; (3) the minimum threshold needed to increase secondary aquatic productivity may be a 7-month hydroperiod over 90% of the marl marsh landscape. Restoration of historical hydropatterns could thus have cascading positive effects throughout the Everglades aquatic food web.

HYDROLOGIC INFLUENCES ON INSECT EMERGENCE PRODUCTION FROM CENTRAL PLATTE RIVER WETLANDS

The physical template of freshwater ecosystems has a pervasive influence on biological communities and processes. To examine the influence of hydrology on wetland insect communities, we quantified insect emergence from five riparian sloughs in the central Platte River valley. Annual hydroperiods of the wetlands ranged from 94 to 365 d/yr, and frequency and magnitude of drying events were inversely proportional to hydroperiod length. Three emergence traps were placed in each wetland from April through November 1997. Most insects collected in traps were identified to genus, and individual dry mass (DM) also was determined. Abundance of emerging insects (24 124 individuals/m2) and emergence production (5.1 g DM·m−2·yr−1) were highest from the site with an intermediate hydroperiod of 296 d. Sites with longer and shorter hydroperiods had lower emergence abundance and production. Emergence production from the perennial site, which contained fish year-round, was only 0.26 g DM·m−2·yr−1. Diptera generally dominated emergence trap catches. Chironomidae, Culicidae, and Ceratopogonidae were among the dominant contributors to abundance, whereas Sciomyzidae and Muscidae were important contributors to biomass at most sites. Quadratic equations best described relationships between taxa richness and annual hydroperiod (r2 = 0.78, P < 0.05) or number of drying events/yr (r2 = 0.81, P < 0.05), reflecting a peak in richness at intermediate levels of both. These relationships followed predictions of the intermediate disturbance hypothesis, but specific mechanisms underlying patterns were difficult to discern. Like emergence production, taxa richness was also highest at intermediate hydroperiods. Hence, insect diversity (measured as richness) and emergence production were positively correlated (r2 = 0.85, P < 0.05). Results indicate that the hydrology of central Platte River wetlands exerts a strong influence on insect species richness and emergence production, and that intermittent sites harbor the highest insect diversity and produce more emergent insect biomass. However, trends in seasonal emergence patterns and taxonomic shifts across the hydrologic gradient in this study suggest that a landscape containing a mosaic of hydrologically distinct wetlands will maximize aquatic insect diversity and productivity at larger spatial and temporal scales.

Hydrologic Influences on Insect Emergence Production from Central Platte River Wetlands

The physical template of freshwater ecosystems has a pervasive influence on biological communities and processes. To examine the influence of hydrology on wetland insect communities, we quantified insect emergence from five riparian sloughs in the central Platte River valley. Annual hydroperiods of the wetlands ranged from 94 to 365 d/yr, and frequency and magnitude of drying events were inversely proportional to hydroperiod length. Three emergence traps were placed in each wetland from April through November 1997. Most insects collected in traps were identified to genus, and individual dry mass (DM) also was determined. Abundance of emerging insects (24 124 individuals/m2) and emergence production (5.1 g DM·m−2·yr−1) were highest from the site with an intermediate hydroperiod of 296 d. Sites with longer and shorter hydroperiods had lower emergence abundance and production. Emergence production from the perennial site, which contained fish year-round, was only 0.26 g DM·m−2·yr−1. Diptera generally dominated emergence trap catches. Chironomidae, Culicidae, and Ceratopogonidae were among the dominant contributors to abundance, whereas Sciomyzidae and Muscidae were important contributors to biomass at most sites. Quadratic equations best described relationships between taxa richness and annual hydroperiod (r2 = 0.78, P < 0.05) or number of drying events/yr (r2 = 0.81, P < 0.05), reflecting a peak in richness at intermediate levels of both. These relationships followed predictions of the intermediate disturbance hypothesis, but specific mechanisms underlying patterns were difficult to discern. Like emergence production, taxa richness was also highest at intermediate hydroperiods. Hence, insect diversity (measured as richness) and emergence production were positively correlated (r2 = 0.85, P < 0.05). Results indicate that the hydrology of central Platte River wetlands exerts a strong influence on insect species richness and emergence production, and that intermittent sites harbor the highest insect diversity and produce more emergent insect biomass. However, trends in seasonal emergence patterns and taxonomic shifts across the hydrologic gradient in this study suggest that a landscape containing a mosaic of hydrologically distinct wetlands will maximize aquatic insect diversity and productivity at larger spatial and temporal scales.

Effects of Hydroperiod on Metamorphosis in Rana sphenocephala

Hydroperiod, the time a temporary pond holds water, is an important factor influencing recruitment in amphibian populations and structuring amphibian communities. We conducted an experiment to test the effect of hydroperiod on metamorphic traits of the southern leopard frog (Rana sphenocephala), a common amphibian in the southeastern United States. We reared larval R. sphenocephala in artificial ponds at a density of 32 larvae per tank (initial volume = approximately 650 liter). We dried the tanks according to natural patterns, using three different hydroperiods (60, 75 and 90 d). Experimental hydroperiods had a significant effect on the number of metamorphs and the length of the larval period, but not on overall survival (larvae metamorphs) nor size at metamorphosis. Our findings confirm a pattern observed in field studies and are similar to results of experimental investigations of closely related ranid frogs. Our results demonstrate that relatively small differences in hydroperiod length (i.e., as little as 15 d) may have large effects on juvenile recruitment in R. sphenocephala.

Oral deformities in several species of frogs from the Savannah River Site, USA

AbstractTadpoles of seven species of frogs from 22 wetlands on the Savannah River Site in South Carolina, USA, were examined to assess the prevalence of mouth‐part deformities and axial skeletal deformities. Species examined included southern toad (Bufo terrestris), pine woods treefrog (Hyla femoralis), spring peeper (Pseudacris crucifer), southern chorus frog (P. nigrita), ornate chorus frog (P. ornata), bronze frog (Rana clamitans), and southern leopard frog (R. utricularia). Of the 4,335 tadpoles examined in 1997 and 1998, 6% exhibited mouth‐part deformities and none exhibited axial skeletal deformities. However, significant interspecific differences existed for both prehind‐limb and posthind‐limb developmental stages. The highest percentage of deformities in prehind‐limb stage occurred in spring peeper (27%), ornate chorus frog (29%), and bronze frog (33%), and the lowest percentage occurred in southern toad (5.5%) and southern chorus frog (4.8%). The frequency of mouth deformities decreased from the prehind‐to posthind‐limb developmental stage for six of seven species and was significant for southern toad and ornate chorus frog. Differences existed in the percent of mouth‐part deformities among species in the same wetland and among wetlands for two species (southern toad and southern leopard frog). Among southern toads, mouth‐part deformities increased with increasing hydroperiod length. Oral deformities may lead to lowered feeding success and lowered survival of tadpoles, resulting in a lower percentage of deformities in the posthind‐limb stage.

DEVELOPMENT OF EXPECTATIONS OF LARVAL AMPHIBIAN ASSEMBLAGE STRUCTURE IN SOUTHEASTERN DEPRESSION WETLANDS

We surveyed larval amphibians and fish in 25 relatively pristine depression wetlands on the upper Atlantic coastal plain of South Carolina to examine relationships among hydroperiod length, fish presence/absence and larval amphibian assemblage structure. Our goals were to test the application of general models of lentic community structure to Southeastern depression wetlands and to develop expectations of larval amphibian assemblage structure at reference sites. Amphibian species richness showed a unimodal pattern along a hydroperiod gradient, with wetlands that contained water for 8–10 mo/yr having the highest species richness. Wetlands that contained water for longer periods (i.e., dried only during severe drought) often contained fish and had relatively low amphibian species richness. Most species occurred along a restricted portion of the hydroperiod gradient, and some species were found almost exclusively in wetlands with fish. Associations among the occurrence of species led to relatively discrete breaks in assemblage structure along the hydroperiod gradient. Canonical correspondence analysis of catch-per-unit-effort data identified four groups of wetlands with similar assemblage structure: (1) short (drying in spring), (2) medium (drying in summer), and (3) long (drying in fall or semi-annually) hydroperiod wetlands without fish; and (4) long hydroperiod wetlands with fish. Our results suggest that general models of community structure in lentic systems are applicable to southeastern isolated wetlands and should form the basis for developing expectations of larval amphibian assemblage structure in these systems.

Relationships among Isolated Wetland Size, Hydroperiod, and Amphibian Species Richness: Implications for Wetland Regulations

Abstract: 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.

Influence of Hydroperiod, Isolation, and Heterospecifics on the Distribution of Aquatic Salamanders (Siren and Amphiuma) among Depression Wetlands

We used occurrence data gathered over a four-year period to assess relationships among hydroperiod length (amount of time a wetland holds water during a year), wetland isolation from other aquatic habitats, and the occurrence of sirens (Siren intermedia and S. lacertina) and amphiumas (Amphiuma means) among depression wetlands of the upper Atlantic Coastal Plain. The combined occurrence of sirens and amphiumas was positively correlated with hydroperiod length and negatively correlated with distance to the nearest intermittent aquatic habitat. Occurrences of individual species were negatively correlated with either distance to the nearest intermittent aquatic habitat or elevation difference between wetlands and the nearest permanent aquatic habitat. Siren lacertina showed higher than expected allopatric distribution in relation to other species, suggesting biological interactions may further limit the distribution of sirens and amphiumas among depression wetlands.