Concordance of species richness patterns among multiple freshwater taxa: a regional perspective

Geographical gradients in species richness and the degree to which different taxa show congruent patterns remain unknown for many taxonomic groups. Here, I examined broad-scale species richness patterns in five groups of freshwater organisms; macrophytes, dragonflies, stoneflies, aquatic beetles and fishes. The analyses were based on provincial distribution records in Denmark, Norway, Sweden and Finland. In general, variation in species richness across provinces was concordant among the groups, but stoneflies showed weaker negative relationships with the other taxonomic groups. Species richness in most groups decreased with increasing latitude and altitude, and a considerable part of the variation was explained by mean July temperature. However, stoneflies showed a reversed pattern, with species richness correlating positively, albeit more weakly, with mean provincial altitude. Nevertheless, combined species richness of all five taxa showed a strong relationship with mean July temperature, accounting for 74% of variation in provincial species richness alone. Such temperature-controlled patterns suggest that regional freshwater biodiversity will strongly respond to climate change, with repercussions for local community organization in freshwater ecosystems in Fennoscandia.     

Biotic homogenisation and differentiation as directional change in beta diversity: synthesising driver–response relationships to develop conceptual models across ecosystems

Biotic homogenisation is defined as decreasing dissimilarity among ecological assemblages sampled within a given spatial area over time. Biotic differentiation, in turn, is defined as increasing dissimilarity over time. Overall, changes in the spatial dissimilarities among assemblages (termed ‘beta diversity’) is an increasingly recognised feature of broader biodiversity change in the Anthropocene. Empirical evidence of biotic homogenisation and biotic differentiation remains scattered across different ecosystems. Most meta-analyses quantify the prevalence and direction of change in beta diversity, rather than attempting to identify underlying ecological drivers of such changes. By conceptualising the mechanisms that contribute to decreasing or increasing dissimilarity in the composition of ecological assemblages across space, environmental managers and conservation practitioners can make informed decisions about what interventions may be required to sustain biodiversity and can predict potential biodiversity outcomes of future disturbances. We systematically reviewed and synthesised published empirical evidence for ecological drivers of biotic homogenisation and differentiation across terrestrial, marine, and freshwater realms to derive conceptual models that explain changes in spatial beta diversity. We pursued five key themes in our review: (i) temporal environmental change; (ii) disturbance regime; (iii) connectivity alteration and species redistribution; (iv) habitat change; and (v) biotic and trophic interactions. Our first conceptual model highlights how biotic homogenisation and differentiation can occur as a function of changes in local (alpha) diversity or regional (gamma) diversity, independently of species invasions and losses due to changes in species occurrence among assemblages. Second, the direction and magnitude of change in beta diversity depends on the interaction between spatial variation (patchiness) and temporal variation (synchronicity) of disturbance events. Third, in the context of connectivity and species redistribution, divergent beta diversity outcomes occur as different species have different dispersal characteristics, and the magnitude of beta diversity change associated with species invasions also depends strongly on alpha and gamma diversity prior to species invasion. Fourth, beta diversity is positively linked with spatial environmental variability, such that biotic homogenisation and differentiation occur when environmental heterogeneity decreases or increases, respectively. Fifth, species interactions can influence beta diversity via habitat modification, disease, consumption (trophic dynamics), competition, and by altering ecosystem productivity. Our synthesis highlights the multitude of mechanisms that cause assemblages to be more or less spatially similar in composition (taxonomically, functionally, phylogenetically) through time. We consider that future studies should aim to enhance our collective understanding of ecological systems by clarifying the underlying mechanisms driving homogenisation or differentiation, rather than focusing only on reporting the prevalence and direction of change in beta diversity, per se.     

The macrophyte, Stratiotes aloides, protects larvae of dragonfly Aeshna viridis against fish predation

Predation could be one force determining which contemporary species occupy a certain habitat. Aeshna viridis is an endangered dragonfly species with a larval distribution strongly associated with lakes where the water plant, water soldier, Stratiotes aloides, occurs. In this study, the larvae were almost exclusively found in patches of S. aloides. To study larval association with S. aloides further, we conducted a series of laboratory experiments. Behavioural experiments indicated that larvae preferred S. aloides. Aeshna viridis larvae were nocturnal and rather inactive. Larvae on S. aloides were less susceptible to predation by the perch, Perca fluviatilis, than larvae on another water plant, Myriophyllum alterniflorum. According to our study it seems that occurrence of S. aloides may limit the distribution of A. viridis, and the protection of refuges may be essential in planning the conservation of this endangered species.     

Functional diversity: a review of methodology and current knowledge in freshwater macroinvertebrate research

Although several studies have examined the functional diversity of freshwater macroinvertebrates, the variety of methodologies combined with the absence of a synthetic review make our understanding of this field incomplete. Therefore, we reviewed the current methodology for assessing functional diversity in freshwater macroinvertebrate research. Our review showed that most papers quantified functional diversity using biological traits, among which feeding habits were the most common traits probably due to the assumed links between feeding and ecosystem functions. A large number of diversity measures have been applied for quantifying functional diversity of freshwater macroinvertebrate assemblages, among which Rao’s quadratic entropy looks like the most frequent. In most papers, functional diversity was positively related to taxon richness, and functional redundancy was a key concept in explaining this correlation. Most studies detected strong influence of the environmental factors as well as human impact on functional diversity. Finally, our review revealed that functional diversity research is biased towards European running waters and is hindered by yet insufficient information on the autecology of macroinvertebrates.     

Ecology and distribution of <Emphasis Type="Italic">Tephroseris longifolia</Emphasis> subsp. <Emphasis Type="Italic">moravica</Emphasis> in relation to environmental variation at a micro-scale

Tephroseris longifolia subsp. moravica is an endemic endangered taxon of European importance. Within the nine recently known populations it occurs in very specific site conditions of ecotone habitats. In our contribution, we try to quantify its realized niche with regard to the measured components of its biotic and abiotic environment. The main aim was to assess the importance of spatial environmental variation on taxon occurrence and performance and to relate the obtained ecological information to data on taxon abundance and demography. Possible reasons of taxon rarity are discussed, too. Comparison of plot pairs indicated that plots containing the taxon had deeper soil and higher soil Na and Mg contents than plots without it. They also contained higher number of species, especially forbs. Several soil parameters were positively correlated with taxon size and density while light parameters played minor role. Negative correlations between cover of vascular plants, especially grasses and taxon size and density suggest its reduced competitive ability. Vascular plant-based ecological indicator values were set for light (6), temperature (5), continentality (4), moisture (5), soil reaction (7) and nutrients (5). The studied sites differed in topography, soil characteristics (pH, soil Na, K, Ca, P and NH₄) and cover of herb litter. Size of taxon populations was negatively related to their finite rate of increase which varied between 1.25 and 2.04 and was most sensitive to demographic parameters related to growth. We conclude, that the studied taxon is not strictly stenotopic as the ranges of several environmental variables were rather wide. We suppose, that the narrow limits of recent taxon occurrence are consequences of its low competitive ability and demographic processes related to germination and seedling establishment. The differing requirements of its ontogenetic stages (seedlings and generative individuals) may define the final limits of its small-scale distribution.     

Volume and acidity of residual gastric fluid after oral fluid ingestion before elective ambulatory surgery.

We studied 211 unselected, healthy, adult patients scheduled to undergo elective ambulatory surgery to determine whether the volume or pH of gastric fluid at induction of anesthesia is correlated with the duration of the preoperative fluid fast. Patients were instructed that they must not eat any solid food after midnight but that they were permitted to drink 150 ml of tea, coffee, apple juice or water until 3 hours before their scheduled time of surgery. Patients with gastric disorders and those taking medications that affect gastric motility or secretion were excluded. No premedicant drugs were given. Following induction of general anesthesia the gastric fluid was aspirated through an orogastric tube, its volume recorded and its pH measured with a calibrated pH meter. The patients were retrospectively assigned to one of four groups according to the interval from last fluid ingestion until induction of anesthesia (less than 3 hours, 3 to 4.9 hours, 5 to 8 hours and nothing after midnight). The mean values and extremes for gastric fluid volume and pH were similar in the four groups. We conclude that healthy patients should be allowed to ingest fluid until 3 hours before elective ambulatory surgery.     

Identification of the sulfur inclusion body inBeggiatoa alba B18LD by energy-dispersive X-ray microanalysis

Dense inclusion bodies were observed under the STEM mode of a scanning electron microscope to occupy peripheral locations in air-dried filaments ofBeggiatoa alba B18LD, and they were determined by energy-dispersive x-ray microanalysis to consist almost entirely of sulfur. These inclusions conform in position and size (220–275 nm in diameter) to bodies seen in thin sections to be both membrane-bounded and enclosed within pockets penetrating the individual cell from the cytoplasmic membrane.