Habitat Use by Migrant Shorebirds in Saline Lakes of the Southern Great Plains

Abstract Shorebirds migrating through the Southern Great Plains of North America use saline lakes as stopovers to rest and replenish energy reserves. To understand how availability of invertebrates, salinity, freshwater springs, vegetation, and water influence the value of saline lakes as migration stopovers, we compared lakes used and not used by migrant shorebirds. Shorebirds used lakes that had freshwater springs, mudflats and standing water, sparse vegetation (≤1% cover), low to moderate salinities (x = 30.87 g/L), and mean invertebrate biomass of 0.79 g/m². Lakes that were not used were generally dry or had hypersaline water (x = 82.56 g/L), lacked flowing springs and vegetation, and had few or no invertebrates (x = 0.007 g/m²). Our results suggest that reduced spring flows and increased salinity negatively affect availability of shorebird habitats and aquatic invertebrates. We recommend preservation of the freshwater springs discharging in the saline lakes. Because the springs are discharged from the Ogallala aquifer, which is recharged through the playa wetlands, the entire complex of wetlands in the Great Plains and the Ogallala aquifer should be managed as an integral system.     

Untangling food‐web structure in an ephemeral ecosystem

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Influence of Solid Surface, Adhesive Ability, and Inoculum Size on Bacterial Colonization in Microcosm Studies

Microcosm studies were performed to evaluate the effect of solid surfaces, bacterial adhesive ability, and inoculum size on colonization success and persistence of Pseudomonas fluorescens and Xanthomonas maltophilia, each with a Tn5 insertion that conferred resistance to kanamycin and streptomycin. Two types of microcosms were used: (i) a simple system that was colonized by Aeromonas hydrophila and a coryneform and (ii) a complex system produced from lake water enrichment cultures. Simple microcosms contained 100 ml of peptone- and yeast extract-supplemented artificial lake water or 60 ml of peptone- and yeast extract-supplemented artificial lake water with 70 g of 3-mm glass beads. Complex microcosms contained 100 ml of lake water with no nutrient additions or 100 ml of lake water with 70 g of glass beads. The microcosms were incubated for 35 days at 20°C. In lake water enrichment microcosms, the presence of beads increased the abilities of P. fluorescens or X. maltophilia to colonize, but their numbers decreased with time in microcosms both with and without beads. The adhesiveness of the bacteria, measured in an in vitro assay, did not relate to colonization success. In simple microcosms, the inoculum size (10, 10², or 10³) of P. fluorescens did not influence colonization success. However, in complex microcosms, an inoculum of 10³ cells was insufficient to ensure colonization by P. fluorescens, while 10⁶ cells resulted in colonization of liquid and beads. Simple microcosm studies, utilizing only a few species, were poor models for complex natural systems. In complex enrichment systems, colonization of surfaces resulted in higher numbers of organisms but did not noticeably promote persistence. Adhesiveness of a particular organism may be a relatively minor factor influencing its ability to colonize solid surfaces in complex natural environments.     

Dried out but alive: how mosquitoes survive 8 months

How malaria mosquitoes persist during the dry season in the Sahel and rapidly rebound at the onset of rains is unclear. Recently, Faiman and colleagues demonstrated that aestivation, a summer dormancy mechanism, is a major persistence strategy of Anopheles mosquitoes, which could be targeted by vector control.     

Tadpole shrimp structure macroinvertebrate communities in playa lake microcosms

Laboratory microcosms were used to assess whether tadpole shrimp, Triops sp., affect community structure of other native macroinvertebrates in playa lakes of the Southern High Plains of Texas. Removal of tadpole shrimp shortly after hatching reduced abundances of many taxa, and decreased subsequent taxonomic richness and diversity. For many invertebrates, the presence of tadpole shrimp in low numbers had a positive effect on mean abundance. Direct effects of tadpole shrimp include the reduction of prey species abundance, which in turn may alter biotic interactions among other taxa. Indirect effects include physical modification of the environment during foraging through surface sediments. Results suggest that tadpole shrimp may be a key species controlling structure of macroinvertebrate communities in playa lakes.     

Molecular Detection of Mycobacterium bovis and Mycobacterium bovis BCG (Pasteur) in Soil

PCR primers specific for the Mycobacterium tuberculosis complex were used to detect the presence of Mycobacterium bovis BCG (Pasteur) in soil microcosms and Mycobacterium bovis in environmental samples taken from a farm in Ireland with a history of bovine tuberculosis. M. bovis genes were detected in soil at 4 and 21 months after possible contamination. Gene levels were found in the range of 1 × 10³ to 3.6 × 10³ gene copies g of soil⁻¹, depending on the sampling area. Areas around badger setts had the highest levels of detectable genes and were shown to have the highest levels of gene persistence. M. bovis-specific 16S rRNA sequences were detected, providing evidence of the presence of viable cells in Irish soils. Studies of DNA turnover in soil microcosms proved that dead cells of M. bovis BCG did not persist beyond 10 days. Further microcosm experiments revealed that M. bovis BCG survival was optimal at 37°C with moist soil (−20 kPa; 30% [vol/wt]). This study provides clear evidence that M. bovis can persist in the farm environment outside of its hosts and that climatic factors influence survival rates.     

Macroinvertebrate abundance, water chemistry, and wetland characteristics affect use of wetlands by avian species in Maine

Our objective was to determine use by avian species (e.g., piscivores, marsh birds, waterfowl, selected passerines) of 29 wetlands in areas with low (<200 μeq l⁻¹) acid-neutralizing capacity (ANC) in southeastern Maine. We documented bird, pair, and brood use during 1982–1984 and in 1982 we sampled 10 wetlands with a sweep net to collect invertebrates. We related mean numbers of invertebrates per wetland to water chemistry, basin characteristics, and avian use of different wetland types. Shallow, beaver (Castor canadensis)-created wetlands with the highest phosphorus levels and abundant and varied macrophyte assemblages supported greater densities of macroinvertebrates and numbers of duck broods (88.3% of all broods) in contrast to deep, glacial type wetlands with sparse vegetation and lower invertebrate densities that supported fewer broods (11.7%). Low pH may have affected some acid-intolerant invertebrate taxa (i.e., Ephemeroptera), but high mean numbers of Insecta per wetland were recorded from wetlands with a pH of 5.51. Other Classes and Orders of invertebrates were more abundant on wetlands with pH > 5.51. All years combined use of wetlands by broods was greater on wetlands with pH ≤ 5.51 (77.4%) in contract to wetlands with pH > 5.51 that supported 21.8% of the broods. High mean brood density was associated with mean number of Insecta per wetland. For lentic wetlands created by beaver, those habitats contained vegetative structure and nutrients necessary to provide cover to support invertebrate populations that are prey of omnivore and insectivore species. The fishless status of a few wetlands may have affected use by some waterfowl species and obligate piscivores.     

Production estimates of the benthic invertebrate community in a small Danish stream

Quantitative samples were used to investigate density, biomass and annual production of the benthic invertebrate fauna in a small Danish stream. Forty-eight taxa were found and the total invertebrate densities varied from 3 810 m^?2 in July to 20 040 m^?2 in December. The total mean annual biomass of the invertebrate fauna was 6.1 g ash-free dry wt m^?2. The annual production of the invertebrates was estimated from their mean annual biomass and their annual P/B ratio. Production of the primary consumers (herbivores and detritivores) was 21.4 g ash-free dry wt m^?2 y^?1 and of secondary consumers (carnivores) 1.1 g m^?2 y^?1. The amount of invertebrate production available to the trout population and the importance of the species as food for trout are discussed.     

Species-specific effects of soil fauna on fungal foraging and decomposition

Decomposer fungi are primary decomposing agents in terrestrial soils. Their mycelial networks play an important role in nutrient mineralisation and distribution, but are also nutritious resources for various soil invertebrates. Global climate change is predicted to alter the diversity and community composition of these soil fauna. To understand whether changes in invertebrate species diversity are likely to affect fungal-mediated decomposition, this study compared the grazing potentials of different invertebrate taxa and functional groups. Specifically, the grazing impacts of seven invertebrate taxa on the growth and spatial distribution of six basidiomycete fungi growing from beech wood blocks in soil microcosms were explored. Wood decay rates by fungi were also compared. The consequences of grazing were both taxon- and species-specific. Generally, macro-invertebrates caused the greatest damage, while meso- and micro-invertebrates often stimulated mycelial growth. Invertebrate size, preferences and population dynamics are likely to influence grazing potentials. Effects of grazing varied between fungi, with mycelial morphology and biochemistry possibly influencing susceptibility. Heavy grazing indirectly increased fungal-mediated wood decomposition. Changes in invertebrate community composition are predicted to have consequences for fungal growth, activity and community structure in woodland soils. Abiotic climate change factors including CO₂ and temperature affect mycelial productivity directly, but the indirect effects, mediated through changes in the soil invertebrate community, may be equally important in controlling ecosystem functioning.     

Heterogeneity in shortgrass prairie vegetation: the role of playa lakes

Abstract. We examined the role of playa lakes in promoting regional heterogeneity on the southern High Plains. The goals of this paper were to: (1) describe vegetation types and zonation patterns within playas, (2) evaluate patterns of species distribution and abundance within and among playas, and (3) assess patterns of heterogeneity within and among playas on a portion of the southern High Plains. Perennial grasses were the most abundant species in playa vegetation. Playa vegetation exhibited distinct and repeatable vegetation zones at the majority of sites, but the number of distinct zones varied from site to site. Agropyron smithii, Buchloë dactyloides, and Panicum obtusum were the most important species of playa interior zones, and Bouteloua gracilis, Buchloë dactyloides, and Schedonnardus paniculatus were important upland species outside of playas. Species distribution and abundance were positively correlated at 38 of 40 sites. The distributions of species occurrences among sites were unimodal both locally and regionally. The degree of heterogeneity varied from playa to playa. Local heterogeneity within playas was found to increase regional heterogeneity; therefore, playas increase both local and regional heterogeneity of vegetation. Long-term monitoring will be necessary to understand the spatial and temporal response of vegetation within and among playas to stochastic climatic factors on the southern High Plains of North America.     

Replacement of native seagrass with invasive algal detritus: impacts to estuarine sediment communities

Biological invasions modify the quality and supply of detrital subsidies to aquatic and terrestrial ecosystems. Where the invader has very different traits to native species, major changes in associated consumer communities may result, as a consequence of differences in their nutritional value and effects on the sedimentary habitat. We assessed how the replacement of seagrasses with the invasive alga Caulerpa taxifolia in modified Australian estuaries influences invertebrate communities of mudflats that are subsidized by detritus from submerged aquatic vegetation. Two months after experimental enrichment of sediments with high (60?g dry weight per 0.25?m² plot) or low (30?g dry weight) quantities of either non-native C. taxifolia or native Posidonia australis or Zostera capricorni detritus, there were positive effects of detrital addition on invertebrate abundance that occurred irrespective of the resource added. By 4?months after addition, however, detritus from invasive C. taxifolia had produced effects on benthic communities that could not be replicated by detritus from either of the native seagrasses. Plots receiving the high loading of C. taxifolia detritus contained fewer invertebrates than plots of the other treatments, perhaps due to the induction of sediment hypoxia. The pattern, however, reversed at low detrital loading, with the plots receiving 30?g of C. taxifolia containing more invertebrates and more taxa than the other plots, presumably due to the greater resource availability for detritivores. Our results demonstrate that replacement of native seagrass with invasive algal detritus can have large impacts on sediment-dwelling communities.     

Competing formate- and carbon dioxide-utilizing prokaryotes in an anoxic methane-emitting fen soil

Methanogenesis in wetlands is dependent on intermediary substrates derived from the degradation of biopolymers. Formate is one such substrate and is stimulatory to methanogenesis and acetogenesis in anoxic microcosms of soil from the fen Schlöppnerbrunnen. Formate dissimilation also yields CO₂ as a potential secondary substrate. The objective of this study was to resolve potential differences between anaerobic formate- and CO₂-utilizing prokaryotes of this fen by stable isotope probing. Anoxic soil microcosms were pulsed daily with low concentrations of [¹³C]formate or ¹³CO₂ (i.e., [¹³C]bicarbonate). Taxa were evaluated by assessment of 16S rRNA genes, mcrA (encoding the alpha-subunit of methyl-coenzyme M reductase), and fhs (encoding formyltetrahydrofolate synthetase). Methanogens, acetogens, and formate-hydrogen lyase-containing taxa appeared to compete for formate. Genes affiliated with Methanocellaceae, Methanobacteriaceae, Acetobacteraceae, and Rhodospirillaceae were ¹³C enriched (i.e., labeled) in [¹³C]formate treatments, whereas genes affiliated with Methanosarcinaceae, Conexibacteraceae, and Solirubrobacteraceae were labeled in ¹³CO₂ treatments. [¹³C]acetate was enriched in [¹³C]formate treatments, but labeling of known acetogenic taxa was not detected. However, several phylotypes were affiliated with acetogen-containing taxa (e.g., Sporomusa). Methanosaetaceae-affiliated methanogens appeared to participate in the consumption of acetate. Twelve and 58 family-level archaeal and bacterial 16S rRNA phylotypes, respectively, were detected, approximately half of which had no isolated representatives. Crenarchaeota constituted half of the detected archaeal 16S rRNA phylotypes. The results highlight the unresolved microbial diversity of the fen Schlöppnerbrunnen, suggest that differing taxa competed for the same substrate, and indicate that Methanocellaceae, Methanobacteriaceae, Methanosarcinaceae, and Methanosaetaceae were linked to the production of methane, but they do not clearly resolve the taxa responsible for the apparent conversion of formate to acetate.     

Aquatic invertebrate assemblages as potential indicators of restoration conditions in wetlands of Northeastern China

Wetland restoration has been implemented widely but evaluation of the effectiveness of wetland restoration has been limited. In this study, we aimed to investigate the utility of aquatic invertebrate assemblages as potential indicators of restoration condition in wetlands of the Sanjiang Plain, Northeastern China. Results from non‐metric multidimensional scaling analysis of invertebrate assemblages showed that study wetlands (n = 16) divided into two groups: natural wetlands and wetlands that have been restored for 4 years were classified as a group, and impaired wetlands and wetlands restored for only 1 year were classified into another group. After 4 years of recovery, 47.9% of invertebrate taxa found at the natural wetlands could also be found at the restored wetlands, primarily insects with aerial dispersal capabilities for rapid colonization. Indicator species analysis identified differences in community composition among wetland types, and Amphiagrion sp. and Bezzia sp. were indicators of the restored wetlands. In Northeastern China, aquatic invertebrate assemblages and certain indicator species may provide robust measures of wetland restoration. It is urgent for further exploration to monitor restored wetlands in the long‐time series and fully assess the efficiency of the restoration.     

黄河三角洲芦苇湿地底栖无脊椎动物与环境因子的关系研究——以石油开采区与淡水补给区为例

分别于2018年5月和8月对黄河三角洲芦苇湿地19(淡水补给区11处,石油开采区8处)处采样点的底栖无脊椎动物和水体理化指标进行调查采样,运用统计方法分析两个区域物种组成、优势种、多样性、群落结构以及与环境因子的关系。结果表明:两季共采集到底栖无脊椎动物54种,主要以水生昆虫、腹足纲和软甲纲为主,淡水补给区和石油开采区各类群组成差异明显。独立样本T检验表明淡水补给区和石油开采区水体理化指标间差异显著(P0.05)。双因子方差分析显示,昆虫纲和腹足纲密度在两区域差异显著(P0.05),软甲纲和腹足纲密度在季节上差异明显(P0.05)。底栖无脊椎动物优势种共10种,淡水补给区指示物种8种,而石油开采区未发现有指示物种。聚类和非参数多维排序(nM DS)显示,底栖无脊椎动物群落结构相似性较低; RDA结果表明:淡水补给区底栖无脊椎动物群落结构主要受Cond,TDS,Sal,pH,Eh,HCO_3~-,SO_4~(2-)等环境因子的影响。石油开采区底栖无脊椎动物群落结构影响较大的环境因子为HCO_3~-、NH_4-N。     

Density of red alder (Alnus rubra) in headwaters influences invertebrate and detritus subsidies to downstream fish habitats in Alaska

We investigated the influence of red alder (Alnus rubra) stand density in upland, riparian forests on invertebrate and detritus transport from fishless headwater streams to downstream, salmonid habitats in southeastern Alaska. Red alder commonly regenerates after soil disturbance (such as from natural landsliding or timber harvesting), and is common along streams in varying densities, but its effect on food delivery from headwater channels to downstream salmonid habitats is not clear. Fluvial transport of invertebrates and detritus was measured at 13 sites in spring, summer and fall during two years (2000–2001). The 13 streams encompassed a riparian red alder density gradient (1–82% canopy cover or 0–53% basal area) growing amongst young-growth conifer (45-yr-old stands that regenerated after forest clearcutting). Sites with more riparian red alder exported significantly more invertebrates than did sites with little alder (mean range across 1–82% alder gradient was about 1–4 invertebrates m^?3 water, and 0.1–1 mg invertebrates m^?3 water, respectively). Three-quarters of the invertebrates were of aquatic origin; the remainder was of terrestrial origin. Aquatic taxa were positively related to the alder density gradient, while terrestrially-derived taxa were not. Streams with more riparian alder also exported significantly more detritus than streams with less alder (mean range across 1–82% alder gradient was 0.01–0.06 g detritus m^?3 water). Based on these data, we predict that headwater streams with more riparian alder will provide more invertebrates and support more downstream fish biomass than those basins with little or no riparian alder, provided these downstream food webs fully utilize this resource subsidy.     

Effects of simulated fire on vesicular-arbuscular mycorrhizae in pinyon-juniper woodland soil

Effects of fire on vesicular-arbuscular mycorrhizal fungi were tested using microcosms constructed from soil, litter, and duff collected beneath canopies of pinyon pine, Utah juniper, and in the open space (interspace). Burning was conducted over wet and dry soils. Soil temperatures were monitored continuously throughout the microcosms during burning. Plants grown in soils burned when dry had a lower VAM colonization than soils burned when wet. Juniper soils demonstrated the greatest reduction, over 95%, compared to their respective controls. Plants grown in interspace soils burned when wet were least affected. There was a positive correlation (r²=0.90) between the decrease in VAM colonization and the soil temperature as a result of the fire. Temperature effects, and associated reductions in VAM, were related to amount of litter burned in each microcosm and the moisture content of the soils.     

Factors influencing macroinvertebrate colonization of seasonal wetlands: responses to emergent plant cover

1. We conducted field experiments to examine factors influencing macroinvertebrate colonization of seasonally flooded marshes. Few macroinvertebrate species were found aestivating in soils within non-flooded wetlands indicating that most taxa colonize these marshes from other flooded habitats.
2. We manipulated amounts of salt grass ( Distichlis spicata ) to examine how emergent plant cover affects aerial colonization by macroinvertebrates. Areas mowed 3 weeks before flooding had low plant cover, areas mowed 5 and 9 weeks before flooding had medium and high plant cover, respectively, and non-mowed control areas had the most plant cover. Macroinvertebrate numbers and biomass were generally higher in mowed treatment areas than in control areas, but overall diversity was generally higher in high plant cover and control areas than in low plant cover areas.
3. Mosquitoes (Culicidae), brine flies (Ephydridae) and hover flies (Syrphidae) were positively correlated with amount of plant cover, and waterboatmen (Corixidae), midges (Chironomidae) and water scavenger beetles (Hydrophilidae) were negatively correlated with plant cover. Species assemblages changed seasonally among treatment areas because these taxa colonize wetlands at different times in the year.
4. These results demonstrate that invertebrate communities may be different within plant stands with heterogeneous amounts of emergent cover, and management practices that alter the structure of wetland vegetation can influence macroinvertebrate communities colonizing seasonal marshes.     

Spatial and seasonal variation in nutrient excretion by benthic invertebrates in a eutrophic reservoir

1. Nitrogen (N) and phosphorus (P) fluxes via excretion by benthic invertebrates were quantified in a eutrophic reservoir (Acton Lake, Ohio, U.S.A.). We quantified variation in nutrient fluxes seasonally (June until November 1997), spatially (three sites) and among taxa (chironomids, tubificid oligochaetes and Chaoborus). 2. The three taxa differed in spatial distribution and contribution to nutrient fluxes. Tubificids were the most abundant taxon at two oxic sites (1.5 and 4 m depth), and were exceedingly rare at an anoxic, hypolimnetic site (8 m). Chironomids were abundant only at the shallowest oxic site. Chaoborus was the only abundant taxon at the anoxic site. Total benthic invertebrate biomass was greatest at the shallowest site and lowest at the anoxic, hypolimnetic site. 3. Mass‐specific excretion rate [μmol NH₄–N or soluble reactive P (SRP) excreted mg dry mass^–1 h^–1] varied among experiments and was influenced by temperature. Differences among taxa were not significant. Thus, nutrient flux through benthic invertebrates was affected more by total invertebrate biomass and temperature than by species composition. 4. Fluxes of N and P via benthic invertebrate excretion (μmol NH₄–N or SRP m^–2 day^–1) were greatest at the oxic sites, where fluxes were dominated by the excretion of tubificids and chironomids. The N and P fluxes at the anoxic site were much lower, and were dominated by excretion by Chaoborus. The ratio of N and P excreted by the benthic invertebrate assemblage varied seasonally and was lowest at the anoxic site. 5. Comparison with other measured inputs shows that excretion by benthic invertebrates could be an important source of nutrients, especially of P. However, the relative importance of nutrient excretion by the benthos varies greatly spatially and temporally.     

Effects of water-level fluctuations on the arbuscular mycorrhizal colonization of Typha latifolia L.

Flooding has been described as one of the primary factors affecting arbuscular mycorrhizal (AM) colonization in wetlands. We investigated the effect of water-level fluctuations on AM colonization of Typha latifolia L. using an experimental wetland in southeastern Idaho, USA that received intermittent flows. Unlike previous research that has examined the effect of flooding on AM fungi using topographic gradients, we replicated flooding in time by sampling across multiple flooding events. AM colonization of T. latifolia occurred during flooded and unflooded periods, but was markedly reduced at drawdown. Both hyphal (R = 0.74, P = 0.015) and arbuscular (R = 0.67, P = 0.033) colonization were positively correlated with the length of the unflooded period. Taken together, the length of the unflooded period and soil moisture explained 83% of the variation in mean hyphal colonization (R² = 0.83, P = 0.001). Overall, the results of this investigation show that drawdown represents a period of reduced AM colonization in T. latifolia.     

Persistent Colonization of Sheep by Escherichia coli O157:H7 and Other E. coli Pathotypes

Shiga toxin-producing Escherichia coli (STEC) is an important cause of food-borne illness in humans. Ruminants appear to be more frequently colonized by STEC than are other animals, but the reason(s) for this is unknown. We compared the frequency, magnitude, duration, and transmissibility of colonization of sheep by E. coli O157:H7 to that by other pathotypes of E. coli. Young adult sheep were simultaneously inoculated with a cocktail consisting of two strains of E. coli O157:H7, two strains of enterotoxigenic E. coli (ETEC), and one strain of enteropathogenic E. coli. Both STEC strains and ETEC 2041 were given at either 10⁷ or 10¹⁰ CFU/strain/animal. The other strains were given only at 10¹⁰ CFU/strain. We found no consistent differences among pathotypes in the frequency, magnitude, and transmissibility of colonization. However, the STEC strains tended to persist to 2 weeks and 2 months postinoculation more frequently than did the other pathotypes. The tendency for persistence of the STEC strains was apparent following an inoculation dose of either 10⁷ or 10¹⁰ CFU. One of the ETEC strains also persisted when inoculated at 10¹⁰ CFU. However, in contrast to the STEC strains, it did not persist when inoculated at 10⁷ CFU. These results support the hypothesis that STEC is better adapted to persist in the alimentary tracts of sheep than are other pathotypes of E. coli.