David G. Angeler

Export of nitrogen from catchments: A worldwide analysis

This study reviews nitrogen export rates from 946 rivers of the world to determine the influence of quantitative (runoff, rainfall, inhabitant density, catchment area, percentage of land use cover, airborne deposition, fertilizer input) and qualitative (dominant type of forest, occurrence of stagnant waterbodies, dominant land use, occurrence of point sources, runoff type) environmental factors on nitrogen fluxes. All fractions (total, nitrate, ammonia, dissolved organic and particulate organic) of nitrogen export showed a left-skewed distribution, which suggests a relatively pristine condition for most systems. Total nitrogen export showed the highest variability whereas total organic nitrogen export comprised the dominant fraction of export. Nitrogen export rates were only weakly explained by our qualitative and quantitative environmental variables. Our study suggests that the consideration of spatial and temporal scales is important for predicting nitrogen export rates using simple and easy-to-get environmental variables. Regionally based modelling approaches prove more useful than global-scale analyses.

Landscape structural features control fire size in a Mediterranean forested area of central Spain

Landscape structure may affect fire propagation and fire size. Propagation may be favoured in landscapes that are homogeneous and hindered at places of greater heterogeneity, and where discontinuities occur. We tested whether there is continuity in landscape structure across the edges of 110 fires in the Sierra de Gredos (central Spain). We used Landsat Multispectral Scanner images to map and assess the land-cover composition and other features of fires. Landscape diversity along the pixel row of the fire edge and of the two adjacent ones (burned and unburned) was compared for all fires. Additionally, changes in landscape properties and fuel hazard perpendicular to the fire edge evaluated the degree of discontinuity from inside the burn towards the outside across the edge. Fire size was related to landscape properties and weather conditions using generalized linear regression models. Diversity increased from inside the burn towards the edge and outside the burn. Discontinuity in land-cover types and fuel hazard increased from the inside towards the outside. Modelling confirmed that fire size was in part related to landscape characteristics of the burned area and of the edges of the fire perimeter. We conclude that landscape structure was important in determining fire size in this area.

Microinvertebrate and plant beta diversity in dry soils of a semiarid agricultural wetland complex

The relationship between environmental features and the β diversity of the propagule bank of dry soils of temporary wetlands has relevance to ecological theories of community structure and to the conservation of wetland biodiversity. The correlation of β diversity of microinvertebrates and macrophytes derived from propagules in dry soils with wetland habitat characteristics, catchment land-use, and the distance between wetlands in a remnant pond complex in central Spain was assessed. Redundancy analyses showed that β diversity of both groups correlated with habitat characteristics, whereas associations with catchment agricultural practices were weaker. Nestedness analyses showed that species-poor communities from degraded sites tended to form nested subsets of less degraded ponds with higher species richness. Distance between the ponds had no significant association with community similarity, suggesting that fragmentation did not shape β diversity at the scale of our study area. To maintain high β diversity in this area, ponds with species-rich propagule banks should receive conservation priority. Given the functional dependence by much wildlife on these propagule banks once these wetlands rewet, conservation of this hidden biodiversity is crucial for providing ecosystem services to humans and wildlife.

Can fairy shrimps (Crustacea: Anostraca) structure zooplankton communities in temporary ponds?

Predation and competition are recognised as strong community structuring forces, and these processes are often mediated by keystone species. However, the role of keystone species in the plankton of temporary wetlands has hardly been evaluated. In the present study, the potential structuring role of fairy shrimps (Anostraca, Branchiopoda) on temporary wetland zooplankton communities was assessed. Dry sediments were collected from randomly chosen temporary ponds in the Campo de Calatrava area (Central Spain), and these were rewetted in outdoor microcosms. Zooplankton community dynamics of three wetlands that lacked fairy shrimps (controls) were contrasted with three wetlands that contained Branchinecta orientalis (G. O. Sars) (treatment). ANOVA analyses showed no significant differences in zooplankton community metrics and in taxonomic groups between the controls and treatments. Analyses of similarity (ANOSIM) and similarity percentages (SIMPER) revealed significant differences and a high degree of community dissimilarity within and between treatment levels. The high degree of environmental variability between wetlands compromised the detection of the structuring role of fairy shrimps on zooplankton in the present study. Studies based on manipulative designs could be more appropriate to test for the keystone role of fairy shrimps in temporary wetland food webs. Replicated before-after control-impact (BACI) designs could be especially useful for understanding basic ecological processes and this knowledge could then be used for the development of sound management strategies of ecologically poorly understood temporary ponds.

No diapause prolongation response of Daphnia in the presence of planktivorous mosquitofish (Gambusia holbrooki)

Recent research suggests that planktonic organisms in resting stages can perceive predators chemically and delay hatching to evade predation. Using a co-occurring predator–prey pair (Gambusia holbrooki Girard and Daphnia curvirostris Eylmann) from a Mediterranean floodplain wetland, this study tested for such predator-avoidance behaviour of Daphnia. Results show that hatching patterns of Daphnia were not reduced by the presence of different biomass levels of Gambusia. This could be due to the fact that the density of Gambusia in the wetland is high from late spring to late autumn, suggesting that delayed hatchlings would face increased mortality through consumptive predation.

Application-rate-dependent impacts of a fire retardant on zooplankton community structure of temporary ponds

In the present study, we employed dry sediments in a temporary-pond microcosm experiment to evaluate the response of the zooplankton community after exposure to different application rates of the commercially available fire retardant, Fire-Trol 934. Application rates were selected to reflect ranges used during fire control/prevention operations in grasslands and shrublands in Mediterranean areas. Results show loss of water quality in terms of increased nutrient (total phosphorus and total nitrogen) concentrations, electrical conductivity and water colour. The magnitude of water-quality impact depended on FRC application rate and was most severe in the highest application rate treatment. The zooplankton community was significantly affected by the FRC treatments. In the control, a diverse assemblage of cladocerans, rotifers and ostracods developed, whereas the zooplankton community in all FRC treatments was depauperate, consisting only of a few species of rotifers. The lack of cladocerans, which are effective grazers of phytoplankton, could negatively affect ecosystem functioning and foster eutrophication effects through excessive algal growth, at least during the first weeks after temporary ponds fill with winter rains.

Taxonomic comments on the genus Menoidium (Euglenozoa), with a description of Menoidium intermedium sp. nov.

Summary The genus Menoidium Perty (Rhabdomonadina, Euglenozoa) is currently chaotic as a result of (1) consideration of diagnostic features in several species that are absent in the type species, M. pellucidum Perty, (2) deliberate transfers of species from other genera to Menoidium , and (3) ignorance about the stability/variability of the diagnostic characters under diverse environmental conditions. By comparatively studying several strains of Menoidium in cultures under various environmental conditions, we aimed to investigate morphological plasticity and to identify criteria that could allow for the exact identification of a species. This morphological framework was used to assess the validity of previously described Menoidium species. In conjunction with recent molecular data, we re-evaluated the genus by presenting lists with doubtful (28 taxa) and well-described species (9 taxa), respectively. A new key for identification of species is presented for the latter. On the basis of structural re-examinations of cell structure in cultures, Menoidium intermedium nomen nudum is described and validated.