Influence of geographical extent on typology- and model-based assessments of taxonomic completeness of river macroinvertebrates

1. River InVertebrate Prediction and Classification System (RIVPACS)‐type predictive models are increasingly used to assess the biological condition of freshwaters, but management schemes may also be based on a priori groupings of similar water bodies (typologies) to control for natural variation in biota. The two approaches may lead to disagreements of the biological status of a site, depending on, for example, the spatial scale at which assessments are conducted. 2. We used data from 96 reference and 134 potentially impacted sites from Western and Central Finland to compare RIVPACS‐type models and a simple size‐based typology of rivers for the assessment of taxonomic completeness (the quotient of the Observed‐to‐Expected number of predicted taxa, O / E) of riffle macroinvertebrates. We specifically examined how geographical extent influences bioassessment performance (accuracy, precision and sensitivity to detect impact) of the two approaches. To fully examine the behaviour of the O / E‐index with the two approaches at differing spatial scales, we performed all assessments with a full range of thresholds for predicted taxa occurrence probabilities (p_t from 0+ to 0.9). 3. Both approaches performed consistently better than the corresponding null models. At the larger extent (i.e. assessment encompassing the whole study area), the RIVPACS‐approach performed in all aspects better than the typology‐approach. However, at the smaller extent (i.e. regional assessments) the RIVPACS‐type models and the typologies showed similar accuracy to predict the actual fauna (mean E), similar precision (SD) of cross‐validated O / E and similar sensitivity to detect sites with human impairment. 4. SD(O / E) decreased (i.e. precision increased) consistently with increasing p_t. However, both approaches were most sensitive at intermediate p_t:s (c. 0.2–0.6) when taxa with low predicted occurrence probabilities were excluded. 5. Our results show that RIVPACS‐type predictive models are less susceptible to variations in spatial scale, whereas the performance of a priori typologies increases with decreasing spatial extent. Thus, RIVPACS‐type models are more efficient for large‐scale bioassessments, but at restricted spatial scales, or with an otherwise biologically meaningful stratification, simple a priori classifications can be equally useful for the assessment of taxonomic completeness of river macroinvertebrates.     

Benzothiadiazole affects the leaf proteome in arctic bramble (Rubus arcticus)

Benzothiadiazole (BTH) induces resistance to the downy mildew pathogen, Peronospora sparsa, in arctic bramble, but the basis for the BTH‐induced resistance is unknown. Arctic bramble cv. Mespi was treated with BTH to study the changes in leaf proteome and to identify proteins with a putative role in disease resistance. First, BTH induced strong expression of one PR‐1 protein isoform, which was also induced by salicylic acid (SA). The PR‐1 was responsive to BTH and exogenous SA despite a high endogenous SA content (20–25 µg/g fresh weight), which increased to an even higher level after treatment with BTH. Secondly, a total of 792 protein spots were detected in two‐dimensional gel electrophoresis, eight proteins being detected solely in the BTH‐treated plants. BTH caused up‐ or down‐regulation of 72 and 31 proteins, respectively, of which 18 were tentatively identified by mass spectrometry. The up‐regulation of flavanone‐3‐hydroxylase, alanine aminotransferase, 1‐aminocyclopropane‐1‐carboxylate oxidase, PR‐1 and PR‐10 proteins may partly explain the BTH‐induced resistance against P. sparsa. Other proteins with changes in intensity appear to be involved in, for example, energy metabolism and protein processing. The decline in ATP synthase, triosephosphate isomerase, fructose bisphosphate aldolase and glutamine synthetase suggests that BTH causes significant changes in primary metabolism, which provides one possible explanation for the decreased vegetative growth of foliage and rhizome observed in BTH‐treated plants.     

The distribution and environmental state of vegetated islands within human‐impacted European rivers

1. Vegetated islands within river corridors are pivotal landscape features and are among the first to disappear as a consequence of flow regulation and channelisation. However, how vegetated islands vary along human‐impacted rivers is poorly understood. 2. We carried out a detailed analysis of the contemporary distribution, diversity and environmental state of vegetated islands within 12 human‐impacted European rivers, using 75 Landsat 7 ETM+ satellite images (1999–2002), historical maps, DEM data and landscape metrics. We tested whether channel fragmentation, catchment land use and the environmental state of fringing floodplains determine the spatial patterns of the islands. We also analysed the historical change of islands within selected sections of the Upper Danube, Upper Rhine and Olt rivers. 3. We identified 2771 islands in the contemporary landscape, varying from 0.06 to 9828 ha. Islands covered up to 21% of the active channel area and contributed up to 32% of the total riparian ecotone length. Island density ranged from 0.06 islands per river‐km (River Sava) to 1.6 islands per river‐km (River Tagliamento). River regulation has led to a marked loss of island density: 94% in the Upper Danube, 93% in the Upper Rhine, and 69% in the Olt. The environmental state of the islands was significantly less altered by human activity than of their fringing floodplains; 93.4% of the vegetated islands exhibited a near‐natural state, while 86% of the fringing floodplains were expansively converted to agricultural and urban land uses. 4. Our results highlight the ubiquitous presence of vegetated islands, their sensitivity to river regulation and their pivotal role for the future restoration and management of river corridors.     

Fish predation and reduction in body size in a Cladoceran population: palaeoecological evidence

SUMMARY. 1 We studied the recent history (1852-1982) of Lake Pyhä-järvi, south-west Finland, using both cladoceran microfossils and independent historical data. The objective of the study was to assess the impact of introduced planktivorous whitefish Coregonus lavaretus s.1. on zooplankton, especially on the main prey species Bosmina coregoni Baird s.str.
2. A size-frequency analysis of carapace remains preserved in the sediments clearly shows a size shift in a Bosmina coregoni population. The carapace length of B. coregoni decreased by 11.0% after the introduction of the size-selective planktivorous whitefish, indicating a parallel body-size reduction.
3.During the study period no changes could be found in the carapace length of Chydorus sphaericus O. F. Müller, which was not preyed upon.     

Impacts of a submerged plant (Elodea canadensis) on interactions between roach (Rutilus rutilus) and its invertebrate prey communities in a lake littoral zone

1. Using 5‐m² field enclosures, we examined the effects of Elodea canadensis on zooplankton communities and on the trophic cascade caused by 4–5 year old (approximately 16 cm) roach. We also tested the hypothesis that roach in Elodea beds use variable food resources as their diet, mainly benthic and epiphytic macroinvertebrates, and feed less efficiently on zooplankton. Switching of the prey preference stabilises the zooplankton community and, in turn, also the fluctuation of algal biomass. The factorial design of the experiment included three levels of Elodea (no‐, sparse‐ and dense‐Elodea) and two levels of fish (present and absent). 2. During the 4‐week experiment, the total biomass of euplanktonic zooplankton, especially that of the dominant cladoceran Daphnia longispina, decreased with increase in Elodea density. The Daphnia biomass was also reduced by roach in all the Elodea treatments. Thus, Elodea provided neither a favourable habitat nor a good refuge for Daphnia against predation by roach. 3. The electivity of roach for cladocerans was high in all the Elodea treatments. Roach were able to prey on cladocerans in Elodea beds, even when the abundance and size of these prey animals were low. In addition to cladocerans, the diet of roach consisted of macroinvertebrates and detrital/plant material. Although the biomass of macroinvertebrates increased during the experiment in all Elodea treatments, they were relatively unimportant in roach diets regardless of the density of Elodea beds. 4. Euplanktonic zooplankton species other than Daphnia were not affected by Elodea or fish and the treatments had no effects on the total clearance rate of euplanktonic zooplankton. However, the chlorophyll a concentration increased with fish in all the Elodea treatments, suggesting that fish enhanced algal growth through regeneration of nutrients. Thus, our results did not unequivocally show that Elodea hampered the trophic cascade of fish via lowered predation on grazing zooplankton. 5. In treatments with dense Elodea beds (750 g FW m^?2), chlorophyll a concentration was always low suggesting that phytoplankton production was controlled by Elodea. Apparently, the top‐down control of phytoplankton biomass by zooplankton was facilitated by the macrophytes and operated simultaneously with control of phytoplankton production by Elodea.