Is Erica tetralix abundance on wet heathlands controlled by nitrogen deposition or soil acidification?

Erica tetralix is the key species on NW European wet heathlands, where it is often found to be the dominating plant species. Consequently, it is of considerable concern that the species has decreased significantly in cover from 28% to 18% over a six-year period. In order to understand the underlying causes, a structural equation modeling (SEM) approach was applied on ecological data from 1130 wet heathland plots. Both atmospheric N deposition and soil acidification were included in the SEM. The most important causal effect revealed by the SEM was a significant negative effect of N deposition on the cover of E. tetralix, whereas soil acidity tended to have a negative effect of relatively less importance. There was no significant effect of N deposition on soil pH, which indicates that there are no major indirect effects of N deposition on the cover of E. tetralix mediated by soil acidification.

The effect of glyphosate on the growth and competitive effect of perennial grass species in semi-natural grasslands

Biodiversity within European semi-natural biotopes in agro-ecosystem is declining, and herbicide drift from neighbouring fields is considered as an important factor for the decline. The aim of the present study was to investigate whether the growth and competitive interactions in a model system of two perennial grass species, Festuca ovina and Agrostis capillaris, are affected by sub-lethal doses of glyphosate in field margins. In a glasshouse experiment with ample nitrogen, the interspecific competitive interactions were found to be significantly affected by glyphosate; the competitive effect of F. ovina on A. capillaris increased and the competitive effect of A. capillaris on F. ovina decreased with increasing doses of glyphosate. Furthermore, the importance of interspecific competition increased with the glyphosate dose. The results of the study of competitive interactions are in agreement with the observed plant community dynamics at the field site where F. ovina was found to be more dominant in plots treated with a relatively high dose of glyphosate. Importantly, the effects of glyphosate on the plant community dynamics critically depended on the effect of glyphosate on the plant competitive interactions. The study concludes that the current practice in the environmental risk assessment of non-target effects of herbicides, where single species are tested in the greenhouse, may be inadequate for assessing the effect of herbicides in semi-natural plant communities. The presented methods can be used for assessing the importance of competitive interactions for the sensitivity of non-target plants to herbicides in risk assessment.

Interaction between density and Cu toxicity for Enchytraeus crypticus--comparing first and second generation effects

Density of organisms varies considerably in nature depending e.g. on seasonality or food availability. A recent investigation on interaction between Cu and density using Enchytraeus crypticus showed that density itself (5-50 per 20 gr dry soil) had an impact on population and individual growth [up to 3000 individuals per test vessel], but the interaction between density and Cu toxicity was not significant. Here, a follow-up study was performed, in which the interactions between density and Cu-exposure were investigated along a two-generation exposure using E. crypticus (three factorial: 1. density (5-50), 2. Cu (0-300 mg/kg) and generation (G1-G2)). After G1, the juveniles were retrieved and further exposed under the same conditions along a G2 (using a refined density set - 10 and 50). Results showed an interaction between density and Cu in the reproduction of E. crypticus, this being significant in G2, showing lower toxicity for higher density of organisms whereas in the 1st generation the opposite occurred. Hence, there was an interaction seen along G1 to G2, i.e. animals from density 50 in G1 when further exposed at density 50 in G2 had lower Cu toxicity compared to when further exposed at density 10. Possible explanations include the hydra effect (overcompensation in G2 due to stress in G1) or that for density 50 the organisms are exposed to less Cu than at lower densities, this by e.g. (1) organisms avoid exposure by lumping/clustering which would limit exposure to Cu and (2) there would be less available Cu contaminated soil per individual at high density hence less exposure.

Gene flow and population structure of a common agricultural wild species (Microtus agrestis) under different land management regimes

The impact of landscape structure and land management on dispersal of populations of wild species inhabiting the agricultural landscape was investigated focusing on the field vole (Microtus agrestis) in three different areas in Denmark using molecular genetic markers. The main hypotheses were the following: (i) organic farms act as genetic sources and diversity reservoirs for species living in agricultural areas and (ii) gene flow and genetic structure in the agricultural landscape are influenced by the degree of landscape complexity and connectivity. A total of 443 individual voles were sampled within 2 consecutive years from two agricultural areas and one relatively undisturbed grassland area. As genetic markers, 15 polymorphic microsatellite loci (nuclear markers) and the central part of the cytochrome-b (mitochondrial sequence) were analysed for all samples. The results indicate that management (that is, organic or conventional management) was important for genetic population structure across the landscape, but that landscape structure was the main factor shaping gene flow and genetic diversity. More importantly, the presence of organically managed areas did not act as a genetic reservoir for conventional areas, instead the most important predictor of effective population size was the amount of unmanaged available habitat (core area). The relatively undisturbed natural area showed a lower level of genetic structuring and genetic diversity compared with the two agricultural areas. These findings altogether suggest that political decisions for supporting wildlife friendly land management should take into account both management and landscape structure factors.

The effect of nitrogen and glyphosate on survival and colonisation of perennial grass species in an agro-ecosystem: does the relative importance of survival decrease with competitive ability?

The ecological success of a plant species is typically described by the observed change in plant abundance or cover, but in order to more fully understand the fundamental plant ecological processes, it is necessary to inspect the underlying processes of survival and colonization and how they are affected by environmental conditions. A general ecological hypothesis on the effect of environmental gradients on demographic parameters is proposed and tested. The hypothesis is that decreasing fitness or competitive ability along an environmental gradient is associated with an increasing importance of survival for regulating the abundance of the species. The tested hypothesis is related to both the stress gradient hypothesis and whether the importance of competition increases along productivity gradients. The combined effect of nitrogen and glyphosate on the survival and colonization probability of two perennial grass species, Festuca ovina and Agrostis capillaris, which are known to differ in their responses to both glyphosate and nitrogen treatments, is calculated using pin-point cover data in permanent frames. We found that the relative importance of survival increased with the level of glyphosate for the glyphosate sensitive A. capillaris and decreased for the glyphosate tolerant F. ovina. Likewise, increasing levels of nitrogen increased the importance of survival for the relative nitrophobic F. ovina. Consequently, the proposed hypothesis was corroborated in this specific study. The proposed method will enable predictions of the effects of agricultural practices on community dynamics in a relatively simple setup eliminating the need to quantify all the interaction among the species in the plant community. The method will be immediately useful for the regulation of non-cultivated buffer strips between agricultural fields and semi-natural and natural biotopes such as hedgerows and waterways.

Evidence for acidification-driven ecosystem collapse of Danish Erica tetralix wet heathland

We report observations of disappearance of Erica tetralix in wet heathland, which is unlikely to be caused by competition, as E. tetralix is dying before its place is taken up by other species. To investigate the causes, we used both old and new data. Results showed that presence of Molinia caerulea and Calluna vulgaris were substantial in the former E. tetralix dominated areas. Measurements of the C/N ratio in the morlayer were between 21 and 26 under the E. tetralix stands. As the expected C/N ratio in a healthy nutrient poor ecosystem like the E. tetralix wet heathland is around 30, this indicates that the ratio is probably decreasing and, correspondingly, the probability of nitrogen leaching from the ecosystem is increasing. The morlayer pH was extremely low-between 3.03 and 3.78. This represents a pH decline since the 1960s, where pH values generally were above 4. This supports the hypothesis that the decrease in morlayer pH is the major factor explaining the disappearance of E. tetralix and that measures to increase pH should be considered as part of the recommendations for relevant future management.

A native species with invasive behaviour in coastal dunes: evidence for progressing decay and homogenization of habitat types

A new species has recently invaded coastal dune ecosystems in North West Europe. The native and expansive inland grass, Deschampsia flexuosa, progressively dominating inland heaths, has recently invaded coastal dunes in Denmark, occasionally even as a dominant species. A total of 222 coastal locations with 5,000 random sample plots have been investigated. These findings are in contrast to historical records, and D. flexuosa has never been considered belonging to coastal dune ecosystems. The occurrence of the typical inland grass in the coastal dunes is a strong indication of increase in nutrient level and that human influences may cause a native species to be invasive in new ecosystems. This could be a radical example of change in species composition due to a long lasting exceedance of critical load of nitrogen. The investigation also showed a general increase in cover of the most dominant species.

Quantitative historical change in bumblebee (Bombus spp.) assemblages of red clover fields

Background

Flower visiting insects provide a vitally important pollination service for many crops and wild plants. Recent decline of pollinating insects due to anthropogenic modification of habitats and climate, in particular from 1950's onwards, is a major and widespread concern. However, few studies document the extent of declines in species diversity, and no studies have previously quantified local abundance declines. We here make a quantitative assessment of recent historical changes in bumblebee assemblages by comparing contemporary and historical survey data.

Methodology/Principal Findings

We take advantage of detailed, quantitative historical survey data from the 1930's on bumblebee (Bombus spp.) abundances and species composition in red clover (Trifolium pratense) fields, an important floral resource and an attractant of all bumblebee species. We used the historical survey data as a pre-industrialization baseline, and repeated the same sampling protocol at nearly the same localities at present, hence setting up a historical experiment. We detected historical changes in abundances (bees/m²) of both workers (the “pollinatory units”) and queens (effective population size), in addition to species composition. In particular, long-tongued bumblebee species showed consistent and dramatic declines in species richness and abundances throughout the flowering season of red clover, while short-tongued species were largely unaffected. Of 12 Bombus species observed in the 1930's, five species were not observed at present. The latter were all long-tongued, late-emerging species.

Conclusions/Significance

Because bumblebees are important pollinators, historical changes in local bumblebee assemblages are expected to severely affect plant reproduction, in particular long-tubed species, which are pollinated by long-tongued bumblebees.

Maxillary sagittal growth evaluated on dry skulls from children and adolescents

OBJECTIVE

The hypothesis of the present study is that the inter-relationship between the greater palatine foramen (stable structure) and the first maxillary molar, which is located in the growing and forward-moving maxilla, expresses the longitudinal growth of the maxilla.

MATERIALS AND METHODS

The material comprised 25 human anthropological maxillae, normally developed and without tooth agenesis. The material was sub-grouped according to dental stages. Each sample was photographed in the occlusal view and two transverse reference lines were constructed, one connecting the palatine foramina and another connecting the lingual interlobal incisions in the first permanent molars. The perpendicular distance (T) between these two lines expressed the distance between the foramen and the first molar.

RESULTS

The T-distance increased markedly between the stages where the first, second and third molars had erupted. The study also showed that the greater palatine foramen was located palatally to the first molar in the stage where only the first molar had erupted, palatally to the second molar when this molar had erupted and palatally to the third molar when this molar had erupted.

CONCLUSION

This study shows that the greater palatine foramen is located close to the most posterior located and erupted permanent molar in normally developed dentitions without agenesis. This information may be valuable for dentists when applying local anesthetics. Furthermore, the study revealed a growth pattern in the maxilla, which may reflect the etiology behind crowding in the maxillary molar region.

The effect of nitrogen deposition on the species richness of acid grasslands in Denmark: a comparison with a study performed on a European scale

The effect of atmospheric nitrogen deposition on the species richness of acid grasslands was investigated by combining data from a large Danish monitoring program with a large European data set, where a significant non-linear negative effect of nitrogen deposition had been demonstrated (Stevens et al., 2010). The nitrogen deposition range in Denmark is relatively small and when only considering the Danish data a non-significant decrease in the species richness with nitrogen deposition was observed. However, when both data sets were combined, then the conclusion of the European survey was further corroborated by the results of the Danish monitoring. Furthermore, by combining the two data sets a more comprehensive picture of the threats to the biodiversity of acid grasslands emerge; i.e., species richness in remnant patches of acid grassland in intensively cultivated agricultural landscapes is under influence not only from nitrogen deposition, but also from current and historical land use.

Genetic adaptation of earthworms to copper pollution: is adaptation associated with fitness costs in Dendrobaena octaedra?

Exposure to copper pollution affects reproduction, growth and survival of earthworms. It is known that earthworms can cope with high copper burdens, but the distinction between physiological acclimation and evolutionary heritable changes and associated fitness consequences of the adaption to long-term copper exposure has rarely been studied. To investigate adaptation of earthworm populations of Dendrobaena octaedra to copper contamination, three populations from polluted soil were studied and compared to three unpolluted reference sites. Adult worms were collected at all six sites and cultured in uncontaminated control soil in the laboratory, where life-history traits were studied and F1-generations were produced. The newly hatched F1-generation worms were placed in uncontaminated control or copper-spiked soil to study if the adaptation was due to acclimation or genetic inheritance. This experiment showed that populations from polluted areas generally had a higher individual growth rate, reduced time to maturity, increased reproduction, and also increased mortality compared to the reference populations in both control and copper-spiked soil. The differences in life-history traits indicate that natural selection has resulted in genetic adaptation to copper pollution in the exposed populations. The population growth rates suggest a weak detrimental effect on population growth rate of being exposed to copper for both type of populations, but no sign of cost. On the contrary, estimates of population growth rates integrating all life-history traits showed that copper adapted populations perform on average relatively better than reference populations in both uncontaminated and copper-spiked soil.

Impacts of heavy metals, polyaromatic hydrocarbons, and pesticides on freeze tolerance of the earthworm Dendrobaena octaedra

Previous studies have shown that the interactions between chemicals and climatic stressors can lead to synergistically increased mortality. In the present study, we investigated the effect of seven common environmental contaminants on survival at -6 and 15°C as well as on reproduction at 15°C in the earthworm Dendrobaena octaedra. Three classes of chemicals were considered: Heavy metals (nickel, lead, and mercury), polycyclic aromatic hydrocarbons (pyrene and phenanthrene), and pesticides (abamectin and carbendazim). Phenanthrene interacted antagonistically with freezing temperatures, whereas no interaction was observed with any of the tested pesticides. Two of the three tested metals (nickel and mercury) reduced the freeze tolerance synergistically (mercury was especially potent). This suggests that traditional laboratory studies, in which organisms are exposed to increasing concentrations of a single compound under otherwise optimal conditions, may underestimate the toxicity of some metals to field populations living in cold areas.

Changes in membrane phospholipids as a mechanistic explanation for decreased freeze tolerance in earthworms exposed to sublethal copper concentrations

At low temperature, cell membrane functionality depends on adjustments of membrane phospholipid fatty acid (PLFA) composition. We here test the hypothesis that previous exposure to copper (Cu) may deteriorate tolerance to freezing temperatures because of Cu-induced changes of PLFA composition of cell membranes in the freeze-tolerant earthworm Dendrobaena octaedra. Cu levels and freezing temperatures were varied in a full factorial design. We measured PLFA composition and lipid peroxidation. A highly significant interaction was observed between subzero temperatures and Cu concentrations above 120 mg/kg dry soil. Lipid peroxidation increased slightly in worms exposed to Cu. In particular, the analysis showed that Cu had a significant negative effect on the polyunsaturated PLFA, linoleic acid (18:2omega6,9), which has previously been reported to correlate positively (R2 = 0.92) with freeze tolerance in D. octaedra. This supports our hypothesis that reduced tolerance to freezing temperatures in Cu-exposed worms may be due to membrane damage.

Exposure to mercury reduces heat tolerance and heat hardening ability of the springtail Folsomia candida

We investigated the combined effects of mercury (HgCl(2)) and acute heat on survival of the springtail Folsomia candida. The springtails were exposed to a range of aqueous concentrations (0-48 mg Hg(2+)/L) of HgCl(2) for 24 h. Subsequently, the same individuals were exposed to a range of high temperatures, from 20 to 35.5 degrees C. We found a highly significant synergistic interaction between effects of mercury and heat, with a reduced tolerance to heat after exposure to sublethal concentrations of mercury. Further, the heat hardening ability of F. candida was studied at sublethal concentrations of mercury. F. candida was able to heat harden (exposure to a mild heat treatment increasing survival of subsequent severe heat); however, when the springtails experienced a previous exposure to as little as 1 mg Hg(2+)/L, heat hardening failed to improve survival of heat shock at 34.5 degrees C, even though this was much lower than concentrations affecting survival without heat stress. Mild heat stress is known to induce the heat shock protein, HSP70, and real-time quantitative PCR confirmed that pre-acclimation to 32 degrees C did indeed cause >5-fold up-regulation of HSP70 expression. This up-regulation was not affected by previous exposure to 1 mg Hg(2+)/L.