Pool Habitats Research Articles

Influence of dam removal on trichopteran assemblages in the lowland Drzewiczka River, Poland

The aim of this study is to assess the response of Trichoptera in a patchy tailwater stretch of the Drzewiczka River (Poland) to dam removal as compared to the previous pulse discharge disturbance. The study was carried out in the river at the end of a whitewater slalom canoeing track located downstream of the dam reservoir called Drzewieckie Lake (area 0.84 km2). Between February and April 2002, the dam reservoir was gradually emptied before its dredging, and the Drzewiczka River recovered its natural discharge (1.7–4.5 m3 s−1) for several years (temporary renaturisation). Altogether, 120 monthly samples of macroinvertebrates and their environments were collected in two sampling cycles, S1 in 2000–2001 during high discharge fluctuations (2.1–12.0 m3 s−1 daily) and S2 in 2002–2003 during renaturisation after emptying the reservoir, from the following five habitats: HP—pool habitat, HS—stagnant habitat, HM—macrophyte habitat, HB—bank habitat and HR—riffle habitat. On the basis of trichopteran abundance, the patterns in their assemblages were recognised with use of a self-organising map that was a Kohonen artificial neural network. The obtained classification of trichopteran samples was found to be based in general on the spatial criterion, i.e. dependent on habitats, irrespective of which sampling cycle the samples originated from, which clearly showed that the habitat mosaic of the river bed was observed both in S1 and S2. In addition, a very important function was noted for riparian and land plants, which developed intensively at the bottom of the Drzewieckie Reservoir immediately after it was emptied. They restricted extensive transport of reservoir sediments to the downstream river reach, thus reducing differences between S1 and S2 in the tailwater. It is also worth noting that in S1, in comparison to S2, Cyrnus trimaculatus, Mystacides azurea and Lype reducta flowing downstream from the reservoir were observed more frequently in the river, which confirmed that impoundments can be conducive to the presence of certain species downstream of dams. Summing up, although artificial short-term flow fluctuations usually diminish the quality and quantity of benthos, the article presents a case in which they were small and short enough to allow the formation of a mosaic of bed patches and positively affected certain parameters of macrobenthic communities according to the intermediate disturbance hypothesis.

Invertebrate communities in dry-season pools of a large subtropical river: patterns and processes

Dynamics of flooding and drying resulting in fragmentation of lotic habitats are a yearly phenomenon in subtropical floodplain rivers but their ecological significance is not known for invertebrate communities. We studied the response of zooplankton and macroinvertebrate communities in 48 dry-season river pools in the Save-Runde river system (Lowveld, Zimbabwe). Patterns and ecological processes influencing invertebrate communities, taxon richness and macroinvertebrate functional richness were investigated with focus on the role of regional (connectivity) and local processes (habitat characteristics). Local factors accounted for 15% of the variability in the zooplankton community but only 3.4% for the macroinvertebrate community. Important factors affecting zooplankton densities in the pools were depth, vegetation cover and presence of fish (planktivorous and omnivorous). The presence of fish in pools can infer predation risk. Macroinvertebrate abundances were affected by the presence of fish only. Zooplankton densities increased in pools with fish while macroinvertebrate densities declined in the presence of fish. Macroinvertebrates could exert top-down pressure on zooplankton either by competition for resources or predation in pools. Regional factors significantly explained zooplankton but not macroinvertebrate community variability. Connectivity had no significant effect on local pool habitat characteristics. There were no significant differences in water quality variables between flowing river sites and the pools. Zooplankton and macroinvertebrate α- and γ-diversity in dry-season pools was higher than in the flowing river. Species additions rather than species replacements by processes that include dispersal and possibly dormancy may explain increased zooplankton and macroinvertebrate taxon diversity in pools. Functional feeding group (FFG) analysis showed that the proportion of macroinvertebrate predator taxa increased significantly in pools compared to the flowing river. Pools create a more suitable and diverse habitat for these widely dispersing taxa. The other FFG were comparable between the river and pools. The pools are strongly heterotrophic. Our results confirm that habitat fragmentation may actually be beneficial for zooplankton and macroinvertebrate biodiversity in dryland rivers.

Growth, Survival, and Habitat Use of Naturally Reared and Hatchery Steelhead Fry in Streams: Effects of an Enriched Hatchery Rearing Environment

AbstractAfter hatchery‐reared salmonids are released into the wild, their survival and performance are frequently lower than those of wild conspecifics. Additionally, negative effects of hatchery fish on wild fish are cited as factors affecting the recovery of salmonid populations. Alternative hatchery rearing environments and release practices have been proposed to mitigate both problems. We investigated the postrelease growth, survival, habitat use, and spatial distribution of hatchery steelhead Oncorhynchus mykiss fry reared in conventional and enriched environments and compared their performance with that of naturally reared steelhead fry from the same parent population in two streams. Average instantaneous growth rates differed between streams but not among the three rearing groups. The survival of naturally reared fry was significantly greater than that of both types of hatchery fry (relative survival = 0.33) but did not differ between the conventional and enriched environments. Naturally reared fry grew and survived equally well regardless of the type of hatchery fry with which they were stocked. Supplementation increased fry population size in all stream sections but produced hatchery‐biased populations. Steelhead fry preferred pool habitat within stream sections, but pool use was affected by an interaction between rearing environment and stream. Hatchery fry had more clumped spatial distributions than naturally reared fry, which were affected by a significant interaction between rearing type and stream. Hatchery rearing type and stream had no effect on the spatial distribution of naturally reared fry. We conclude that (1) hatchery steelhead fry released in streams grow as well as naturally reared fry but do not survive as well, (2) enriched hatchery environments do not improve postrelease growth or survival, and (3) upon release, fry raised in enriched hatchery environments affect the growth and survival of naturally reared fry in much the same way as fry reared in conventional hatchery environments.

Identification of co‐occurring Branchinecta fairy shrimp species from encysted embryos using multiplex polymerase chain reaction

Morphological identification of many fairy shrimp species is difficult because distinguishing characters are restricted to adults. We developed two multiplex polymerase chain reaction assays that differentiate among three Branchinecta fairy shrimp with distributional overlap in southern California vernal pools. Two of the species are federally listed as threatened. Molecular identification of Branchinecta from cysts allows for species surveys to be conducted during the dry season, expanding the timeframe for population assessment and providing a less intrusive method of sampling sensitive vernal pool habitats.

Landscape genetics and least‐cost path analysis reveal unexpected dispersal routes in the California tiger salamander (Ambystoma californiense)

A major goal of landscape genetics is to understand how landscapes structure genetic variation in natural populations. However, landscape genetics still lacks a framework for quantifying the effects of landscape features, such as habitat type, on realized gene flow. Here, we present a methodology for identifying the costs of dispersal through different habitats for the California tiger salamander (Ambystoma californiense), an endangered species restricted to grassland/vernal pool habitat mosaics. We sampled larvae from all 16 breeding ponds in a geographically restricted area of vernal pool habitat at the Fort Ord Natural Reserve, Monterey County, California. We estimated between-pond gene flow using 13 polymorphic microsatellite loci and constructed GIS data layers of habitat types in our study area. We then used least-cost path analysis to determine the relative costs of movement through each habitat that best match rates of gene flow measured by our genetic data. We identified four measurable rates of gene flow between pairs of ponds, with between 10.5% and 19.9% of larvae having immigrant ancestry. Although A. californiense is typically associated with breeding ponds in grassland habitat, we found that dispersal through grassland is nearly twice as costly as dispersal through chaparral and that oak woodland is by far the most costly habitat to traverse. With the increasing availability of molecular resources and GIS data, we anticipate that these methods could be applied to a broad range of study systems, particularly those with cryptic life histories that make direct observation of movement challenging.

Desiccation of Rock Pool Habitats and Its Influence on Population Persistence in a Daphnia Metacommunity

Habitat instability has an important influence on species' occurrence and community composition. For freshwater arthropods that occur in ephemeral rock pools, the most drastic habitat instabilities are droughts and the intermittent availability of water. However, although the desiccation of a rock pool is detrimental for planktonic populations, it may also bring certain benefits: the exclusion of predators or parasites, for example, or the coexistence of otherwise competitively exclusive species. The commonness of drought resistant resting stages in many aquatic organisms shows the ecological significance of droughts. We measured daily evaporation in 50 rock pools inhabited by three Daphnia species D. magna, D. longispina and D. pulex over one summer. Daily evaporation and ultimately desiccation showed significantly seasonally influenced correlation with pool surface area, presence of vegetation, ambient temperature, wind and standardized evaporation measures. We used the estimates from this analysis to develop a simulation model to predict changes in the water level in 530 individual pools on a daily basis over a 25-year period. Eventually, hydroperiod lengths and desiccation events could be predicted for all of these rock pools. We independently confirmed the validity of this simulation by surveying desiccation events in the 530 rock pools over a whole season in 2006. In the same 530 rock pools, Daphnia communities had been recorded over the 25 years the simulation model considered. We correlated pool-specific occupation lengths of the three species with pool-specific measures of desiccation risk. Occupation lengths of all three Daphnia species were positively correlated with maximum hydroperiod length and negatively correlated with the number of desiccation events. Surprisingly, these effects were not species-specific.

Large Woody Debris and Salmonid Habitat in the Anchor River Basin, Alaska, Following an Extensive Spruce Beetle (Dendroctonus rufipennis) Outbreak

Abstract A widespread and intense spruce beetle outbreak during the 1990s has killed most of the mature white spruce (Picea glauca) trees across many watersheds in south-central Alaska. To investigate the potential habitat impacts in a salmon stream, we characterized the current abundance and species composition of large woody debris (LWD), examined the linkages between LWD and salmonid habitat, and estimated changes in LWD abundance and associated pool habitat over time. LWD abundance was relatively low (97 pieces/km overall) and varied widely according to riparian vegetation typology, ranging from 15 pieces/km at sites with non-forested riparian zones to 170 pieces/km at sites adjacent to cottonwood forest. LWD provided significant fish cover in pools, especially in cottonwood forest stream reaches. LWD-formed pools were relatively rare (15% of total), but LWD abundance explained much of the variation in pool frequency (r2 = 0.86 in spruce forest reaches) and in the proportion of pool habitats (r2 = 0.8...

Systematics of Downingia (Campanulaceae) based on Molecular Sequence Data: Implications for Floral and Chromosome Evolution

Abstract The genus Downingia (Campanulaceae) has been the subject of numerous biosystematic studies, yet little is known of the evolutionary relationships among the 13 currently recognized species. Phylogenetic analyses were undertaken in order to examine the available biosystematic data in a phylogenetic framework. The genus is of particular interest for its extensive chromosomal variation and for its distribution in relatively new, but threatened, vernal pool habitats of western North America. Parsimony analyses of molecular sequence data from the nuclear 18S–26S rDNA internal transcribed spacer region (ITS) and the chloroplast 3’ trnK intron indicate Downingia is monophyletic. Monotypic Porterella is sister to Downingia. Additional close relatives include Legenere and Howellia. Two main clades emerge within Downingia, neither of which have been previously recognized using morphological features. One of the two clades is homogenous in chromosome number (n = 11), and the other heterogenous, with chromoso...

Effects of riparian manipulation on stream communities in small streams: Two case studies

The effects of riparian manipulation in New Zealand are described for two case studies, one a short‐term study of the effects of the removal of riparian vegetation on fish, and the second, a long‐term study of the effect of re‐establishment of riparian vegetation on fish and benthic macro invertebrates. The first case study was an experiment carried out between November 2001 and May 2002. Overhanging bank vegetation and in‐stream wood were removed from short reaches of a small pastoral stream that had intact riparian margins, resulting in a change in stream structure with the formation of shallow uniform runs rather than pool and riffle structures as in unmodified reaches. The removal of bank cover and consequential instream habitat changes reduced inanga (Galaxias maculatus) densities by a factor of four within months of vegetation removal, showing the importance of instream cover and habitat to inanga. Adult longfin eel (Anguilla dieffenbachii) also became less abundant in the cleared reaches, but elvers (Anguilla spp.) became more abundant. In the second case study, pastoral sections in two small streams draining from native forest catchments were restored in 1995/96 by planting riparian vegetation and preventing stock access. After 10 years, the restoration efforts had more than doubled the numbers of giant kokopu (G. argenteus) and redfin bullies (Gobiomorphus huttoni), slightly increased numbers of banded kokopu (G. fasciatus), and decreased shortfin eel (A. australis) numbers by about 40%. The macroinvertebrate communities changed so that they became more similar to those at upstream native forest reference sites. These two case studies show that riparian margins can influence the composition of the fish and macroinvertebrate communities in small streams through the effects on cover, instream habitat and probably water temperature. Riparian restoration was most effective for the fish species that use cover and pool habitat.

Pool Spacing, Channel Morphology, and the Restoration of Tidal Forested Wetlands of the Columbia River, U.S.A.

Abstract Tidal forested wetlands have sustained substantial areal losses associated with human land use, and restoration practitioners lack descriptions of ecosystem structures within these systems, in which surface water is a significant controlling factor on flora and fauna. In particular, the roles of large wood in tidal areas remain poorly described compared to terrestrial and riverine ecosystems. This study documents the role of large wood accumulations in forcing channel morphology in remnant Sitka spruce (Picea sitchensis)–dominated tidal freshwater wetlands (swamps) in the floodplain of the Columbia River, U.S.A., near the Pacific coast. The average pool spacing documented in channel surveys of three swamps near Grays Bay, 2.2–2.8 channel widths per pool, was not significantly different. There were higher numbers of pools on these tidal forested wetland channels (median 2.7 pools/100 m) than on a nearby diked agricultural site prior to restoration. Log jams were common in the swamps and nonexistent in the pasturelands prior to restoration. On the basis of pool spacing and observed sequences of log jams and pools, tidal forested wetland channels were classified consistent with a forced step‐pool channel type. This new classification for tidal systems provides a basis for restoration project design involving placement of large wood and development of pool habitats for aquatic species. Modifications by beaver (Castor canadensis) observed on restoration and reference sites warrant further investigation to explore the interactions between these animals and restoration methods that affect channel structure and hydraulics in tidal forced step‐pool channels.

Hydraulically related hydro‐morphological units: description based on a new conceptual mesohabitat evaluation model (MEM) using LiDAR data as geometric input

AbstractA new conceptual mesohabitat evaluation model was developed and applied to the Kamp River, Austria. The model uses a functional linkage of three parameters (velocity, depth and bottom shear stress) to distinguish six different mesohabitat types (riffle, fast run, run, pool, backwater and shallow water) based on two‐dimensional depth‐averaged hydrodynamic‐numerical modelling. The results clearly revealed the variety and change of mesohabitat‐units under various flow conditions (3.6–89 m3s−1). In particular for low‐energy habitats, a shift from shallow‐ to backwater habitats was recognized at increasing discharges. Fast runs featured a larger percentage of the total wetted area (9–33%) as discharges increased, whereas pool habitats showed low variability (means of around 15%). A velocity‐depth‐bottom shear stress relationship (VDSR) was most suitable to differentiate between mesohabitat patterns; this relationship was compared with Froude numbers and with velocity‐depth ratios using ANOVA statistical analysis. This study also documented that the accuracy of river geometry plays a decisive role in habitat descriptions. Different height tolerances for the computation mesh (0.2 m, 0.5 m, 1 m accuracy) based on LiDAR significantly reduced important mesohabitats. Copyright © 2008 John Wiley & Sons, Ltd.

Relationships between deforestation, riparian forest buffers and benthic macroinvertebrates in neotropical headwater streams

Summary1. Few studies have evaluated the effectiveness of riparian buffers in the tropics, despite their potential to reduce the impacts of deforestation on stream communities. We examined macroinvertebrate assemblages and stream habitat characteristics in small lowland streams in southeastern Costa Rica to assess the impacts of deforestation on benthic communities and the influence of riparian forest buffers on these effects. Three different stream reach types were compared in the study: (i) forested reference reaches, (ii) stream reaches adjacent to pasture with a riparian forest buffer at least 15 m in width on both banks and (iii) stream reaches adjacent to pasture without a riparian forest buffer.2. Comparisons between forest and pasture reaches suggest that deforestation, even at a very local scale, can alter the taxonomic composition of benthic macroinvertebrate assemblages, reduce macroinvertebrate diversity and eliminate the most sensitive taxa. The presence of a riparian forest buffer appeared to significantly reduce the effects of deforestation on benthic communities, as macroinvertebrate diversity and assemblage structure in forest buffer reaches were generally very similar to those in forested reference reaches. One forest buffer reach was clearly an exception to this pattern, despite the presence of a wide riparian buffer.3. The taxonomic structure of macroinvertebrate assemblages differed between pool and riffle habitats, but contrasts among the three reach types in our study were consistent across the two habitats. Differences among reach types also persisted across three sampling periods during our 15‐month study.4. Among the environmental variables we measured, only stream water temperature varied significantly among reach types, but trends in periphyton abundance and stream sedimentation may have contributed to observed differences in macroinvertebrate assemblage structure.5. Forest cover was high in all of our study catchments, and more research is needed to determine whether riparian forest buffers will sustain similar functions in more extensively deforested landscapes. Nevertheless, our results provide support for Costa Rican regulations protecting riparian forests and suggest that proper riparian management could significantly reduce the impacts of deforestation on benthic communities in tropical streams.

Biogeography of Stream Fishes in Connecticut: Defining Faunal Regions and Assemblage Types

Stream fish survey data were analyzed to describe patterns of fish distributions in wadeable streams (primarily 1st–4th order) in Connecticut. Species occurrence within the United States Geological Survey 8-digit hydrologic unit code watersheds were used to aggregate similar watersheds into stream fish faunal regions. Within each identified region, multivariate analyses were used to identify major fish assemblage types and associate stream habitat with assemblage types. The analyses revealed an eastern and western faunal region defined primarily by distribution of a few native species. Native species associated with the western watersheds were: Semotilus atromaculatus (Creek Chub), Exoglossum maxillingua (Cutlips Minnow), and Cottus cognatus (Slimy Sculpin). Native fishes associated with the eastern watersheds were: Erimyzon oblongus (Creek Chubsucker), Esox niger (Chain Pickerel), and Esox americanus (Redfin Pickerel). Inclusion of non-indigenous species in the analyses resulted in a similar east–west grouping of watersheds. Five and four assemblage types were identified in the eastern and western faunal regions, respectively. Both regions harbored 3 fluvial assemblages defined longitudinally from headwater streams to larger wadeable streams and a macro-habitat generalist assemblage inhabiting streams with proportionately more pool habitat, but taxonomic membership and indicator species rankings among assemblages were not necessarily identical between the regions. A distinct assemblage dominated by Redfin Pickerel was recognized only in the eastern region. Streams in the western region were generally higher in elevation and colder in water temperature. The discovery and description of eastern and western fish faunal regions and their fish assemblage types will be useful in stratifying the biological monitoring of streams and other aquatic resource management actions in Connecticut.

Two new protist species, Trypanoplasma ojedae sp. n. (Mastigophora: Kinetoplastida) and Trichodina lascrucensis sp. n. (Ciliophora: Peritrichida) in a blenniid fish, Scartichthys viridis, from the coast of Chile

Two new protistan species were observed in a blenniid fish, Scartichthys viridis, inhabiting tide pools at Las Cruces, central Chile. Trypanoplasma ojedae sp. n. (Mastigophora: Kinetoplastida) in the blood is characterized by its small size (29.8 ± 5.0 x 5.1 +1.2 im), short anterior flagellum (4.9 ± 0.6 im), anterior located kinetoplast (2.4 ± 0.2) and a prominent undulating membrane. All of 18 fish were infected and 67% were parasitized on the gills by an unidentified piscicolid leech that harbored developing and infective biflagellated stages. Trichodina lascrucensis sp. n. (Ciliophora: Peritrichida) parasitized the gill fillaments of all fish. The ciliate is characterized by its body size (70.8 ± 8.4 im), adhesive disc (53 ± 5.4 im), denticular ring (33 ± 3.1 im), mean number of denticles (32.8 ± 3.0), mean number of denticular pins (9.5 ± 1.0) and ovoid micronucleus located near to one of the macronuclear arms. Since none of the two parasites was similar to any species described from marine tide pool habitats as well as from the Pacific Ocean, both are considered new species with the characteristics described herein.

Effects of Summer Drought on Fish and Macroinvertebrate Assemblage Properties in Upland Ouachita Mountain Streams, USA

We sampled fishes and aquatic insects monthly (Jun.–Sept. 2002) from intermittent tributaries of the Alum Fork of the Saline River (Arkansas, U.S.A.) to quantify the response of fish and aquatic insect assemblage properties to seasonal desiccation and habitat fragmentation. We collected a total of 4219 individuals, representing 18 species of fishes and 27 families of aquatic insects. Changes in the composition of fish assemblages were significantly related to temporal variability in pool volume and location in the watershed. Smaller, upstream pools varied in volume more than downstream pools. Fish assemblages were significantly more similar through summer in downstream, larger pool habitats. Changes in the composition of aquatic insect families were related to variation in water quality conditions. Highly eutrophied sites were typically dominated by midge larvae (Chironomidae), resulting in highly similar assemblages over time. Our results support findings at larger space and time scales and call attention to the importance of rapid changes in habitat quality, size and connectivity on stream communities.

Fish Assemblages in a Western Iowa Stream Modified by Grade Control Structures

AbstractOver 400 riprap grade control structures (GCSs) have been built in streams of western Iowa to reduce erosion and protect bridges, roads, and farmland. In conjunction with a companion study evaluating fish passage over GCSs in Turkey Creek, we evaluated the differences in fish assemblage and habitat characteristics in reaches immediately downstream from GCSs (GCS sites) and reaches at least 1 km from any GCS (non‐GCS sites). The GCS sites were characterized by greater proportions of pool habitat, maximum depths, fish biomass, and abundance of juvenile largemouth bass Micropterus salmoides than were non‐GCS sites. Index of biotic integrity (IBI) scores were poor or fair (<43 on a 0–100 scale) and not significantly different between the GCS and non‐GCS sites. Additionally, we investigated both the longitudinal changes in fish assemblages in this GCS‐fragmented stream and the changes in fish assemblages after slope modifications of three GCSs to facilitate fish passage. Thirteen fish species were present throughout the study area, whereas another 15 species exhibited truncated distributions not extending to the most upstream sampling location. After modification of the GCSs, IBI scores increased at seven of nine sites (mean increase = 4.6 points). Also, channel catfish Ictalurus punctatus were detected 7.3 km upstream at sites where, 2 years before GCS modification, they had been absent from collections. Given the number and distribution of GCSs in western Iowa streams, understanding the effects of these structures is vital to the conservation and management of fish assemblages in this and other regions where GCSs or similar structures are used.

Linking scale and diversity partitioning in comparing species diversity of caddisflies in riffle and pool habitats

Assessing and interpreting biodiversity is a key issue of current ecology and sampling is the first and most critical step in biodiversity assessment. We focused on how sampling scale influences the mesohabitat level species diversity components (i.e. alpha, beta, gamma) of caddisflies in a natural submontain stream. We interpreted scale as the relationship between observation unit size (grain), sample size (number of replicates) and total sampled area (sampling effort), and examined in three simulated experiments, how the individual and joint effects of these scale components influence the difference of caddisfly diversity between riffle and pool habitats. Additive partitioning of diversity into within observation unit (a), among observation unit (β) and total diversity components (y) in a scale-dependent manner showed that scale had a fundamental role in (1) quantifying values of diversity components and (2) in detecting differences between assemblages. Although sites showed considerable variability, the study clearly demonstrated that sample size and total sampled area are the most important and critical scale components of sampling, while the size of the observation unit might be indifferent. The analytical method applied here can be used for any aquatic assemblage collected with a sampling device of well defined area (or volume) and at any levels of the habitat hierarchy. The study reveals the importance of the among observation unit component (i.e. small scale beta diversity) in shaping total diversity and calls attention to the careful consideration of scale in environmental assessment and monitoring.

Effects of grazing minnows and crayfish on stream ecosystem structure and function

We compared the effects of 2 common grazers, southern redbelly dace (Phoxinus erythrogaster) and crayfish (Orconectes spp.), on ecosystem structure and function in experimental streams with pool and riffle habitats. Our goal was to identify potentially overlapping roles of these grazers in these systems. Measures of ecosystem structure included algal filament length, particulate organic matter (POM), densities of invertebrate taxa, and algal biomass. Ecosystem function was measured as gross primary productivity (GPP). Biomass-dependent effects of crayfish and dace on ecosystem properties were compared in autumn 2005 when mean water temperature was 12.9°C (range 7.6–27.9°C). Increasing crayfish biomass did not influence ecosystem properties, but increasing dace biomass negatively affected algal filament length and chironomid abundance and positively affected chydorid abundance. Effects of moderately high biomasses of dace and crayfish were compared in spring 2006 when mean water temperature was 21.4°C (range 17.5–29.9°C). Algal filament lengths were generally low relative to values obtained in autumn 2005 in both dace and crayfish treatments. In addition, algal filament length was shorter and chironomid density was lower in crayfish than in dace streams. The contrasting effects of dace and crayfish across sampling days, seasons, and habitats led us to hypothesize that physiological and behavioral traits of these species might limit the redundancy of their effects on ecosystems across broad spatial and temporal scales.

Methods for estimating the amount of vernal pool habitat in the northeastern United States

The loss of small, seasonal wetlands is a major concern for a variety of state, local, and federal organizations in the northeastern U.S. Identifying and estimating the number of vernal pools within a given region is critical to developing long-term conservation and management strategies for these unique habitats and their faunal communities. We use three probabilistic sampling methods (simple random sampling, adaptive cluster sampling, and the dual frame method) to estimate the number of vernal pools on protected, forested lands. Overall, these methods yielded similar values of vernal pool abundance for each study area, and suggest that photographic interpretation alone may grossly underestimate the number of vernal pools in forested habitats. We compare the relative efficiency of each method and discuss ways of improving precision. Acknowledging that the objectives of a study or monitoring program ultimately determine which sampling designs are most appropriate, we recommend that some type of probabilistic sampling method be applied. We view the dual-frame method as an especially useful way of combining incomplete remote sensing methods, such as aerial photograph interpretation, with a probabilistic sample of the entire area of interest to provide more robust estimates of the number of vernal pools and a more representative sample of existing vernal pool habitats.

Conservation of rare species with island‐like distributions: A case study ofLasthenia conjugens(Asteraceae) using population genetic structure and the distribution of rare markers

AbstractCalifornian vernal pools, a patchy, island‐like habitat, are endangered as a result of habitat destruction. Conservation of the remaining vernal pool habitat is essential for the persistence of several endangered species. We present the first study examining DNA‐level genetic diversity within and among populations of a vernal pool plant species. We investigated genetic variation across eight populations of the US federally endangered vernal pool endemicLasthenia conjugens(Asteraceae) using intersimple sequence repeat (ISSR) markers. Genetic diversity within the species was high (Nei's gene diversity estimate was 0.37), with moderate differentiation among populations (BayesianFSTanalog of 0.124). Using anamovaanalysis, we found that the majority of the genetic variation (84%) was distributed within populations. There is a significant relationship between geographical distance and pairwise genetic differentiation as measured by the Bayesian estimate θB. The alternative hypotheses of historic geological processes within the Central Valley and contemporary gene flow are discussed as explanations of the data. Because of the vulnerability of the populations, we calculated a probability of loss for rare alleles (fragments) in the populations. Calculations show that sampling only one of the eight populations forex‐situconservation or restoration will capture approximately 54% of the sampled rare fragments. We believe that one of the sampled populations has become extinct since it was sampled. When removing this population from the above‐mentioned calculations, sampling one population will capture only 41.3% of the sampled rare fragments. We recommend sampling strategies for future conservation and restoration efforts ofL. conjugens.