Seasonal patterns of stream macroinvertebrate communities in response to anthropogenic stressors in monsoonal Taiwan

Freshwater ecosystems are affected by a variety of anthropogenic stressors. Temporal variability of biotic communities in these ecosystems makes it difficult to accurately assess the impacts of specific stressors, which has seldom been considered in understudied regions of Asia. We studied the seasonal effects of anthropogenic stressors on stream macroinvertebrates based on sampling every three months over two years at five stream sites in central Taiwan. Several macroinvertebrate metrics (taxon richness, Shannon diversity index, and relative abundance of Trichoptera) were lower during the wet season than the dry season. The presence of dams caused changes in the structure of macroinvertebrate communities, decreased the seasonal variability in relative abundances of Trichoptera, as well as resulted in lower dissolved inorganic nitrogen concentrations and larger substrate size. The presence of urban areas had less or no influence on environmental factors and structural changes. However, significantly lower total abundance, taxon richness, and relative abundance of Trichoptera occurred in the presence of either dams and/or urban areas. One key management implication from the present study is that bioassessment utilizing macroinvertebrates should be facilitated by awareness of the potential role of temporal factors on the effects of anthropogenic stressors, especially in monsoonal Asia.     

A field test for competitive effects of<Emphasis Type="Italic"> Aedes albopictus</Emphasis> on<Emphasis Type="Italic"> A. aegypti</Emphasis> in South Florida: differences between sites of coexistence and exclusion?

We tested whether interspecific competition from Aedes albopictus had measurable effects on A. aegypti at the typical numbers of larval mosquitoes found in cemetery vases in south Florida. We also tested whether the effect of interspecific competition from A. albopictus on A. aegypti differed between sites where A. aegypti either persists or went extinct following invasion by A. albopictus. Similar experiments manipulating numbers of A. albopictus in cemetery vases were conducted at three sites of A. aegypti persistence and three sites where A. aegypti was apparently extinct. The experiments were done using numbers of larvae that were determined by observed numbers of larvae for each site, and with resources (leaf detritus) that accumulated in experimental vases placed into each field site. In both the early rainy season (when number of mosquito larvae was low) and the late rainy season (when number of mosquito larvae was high), there was a significant effect of treatment on developmental progress of experimental A. aegypti. In the late rainy season, when numbers of larvae were high, there was also a significant effect of treatment on survivorship of A. aegypti. However, the competition treatment × site type (A. aegypti persists vs extinct) interaction was never significant, indicating that the competitive effect of A. albopictus on A. aegypti did not differ systematically between persistence versus extinction sites. Thus, although competition from A. albopictus is strong under field conditions at all sites, we find no evidence that variation in the impact of interspecific competition is associated with coexistence or exclusion. Interspecific competition among larvae is thus a viable explanation for exclusion or reduction of A. aegypti in south Florida, but variation in the persistence of A. aegypti following invasion does not seem to be primarily a product of variation in the conditions in the aquatic environments of cemetery vases.     

Using multi-target clustering trees as a tool to predict biological water quality indices based on benthic macroinvertebrates and environmental parameters in the Chaguana watershed (Ecuador)

Macroinvertebrates were sampled in the Chaguana river basin in SW Ecuador in the wet season (March) and the dry season (September) of 2005 and 2006. To assess the robustness of several biological indicators, correlations were calculated between both years and between the wet and the dry season. In addition, it was tested if the indices gave significantly different results for sites with a bad, poor, moderate and good ecological water quality. Composition measures performed poorly in most cases, however, abundance, diversity and richness measures often performed better and tolerance measures, the so-called biotic indices, performed very well, even indices developed for temperate regions. By using pruned multitarget clustering trees, it was possible to predict several well-performing ecological water quality indices simultaneously on the basis of the occurring key macroinvertebrate taxa or, alternatively, on the basis of key environmental variables. In contrast to unpruned trees, which resulted in complex trees that were difficult to interpret and performed inferiorly, pruning resulted in transparent trees. Water quality indices scored high when Hydropsychidae were present and even higher when in addition also Megapodagrionidae were present. When no Hydropsychidae nor Libellulidae were present, the indices reached the lowest scores. However, this model based on key taxa occurrences did not perform well during validation. Water quality indices scored higher with increasing dissolved oxygen concentrations and a strong current velocity. The latter model based on environmental variables also performed well during validation. In the presented study, the ecological water quality could thus be accurately predicted solely on the basis of dissolved oxygen concentration and current velocity. It can therefore be concluded that multitarget clustering trees can be easily used as a practical tool for cost-effective decision support by water quality managers.     

Unravelling the correlates of species richness and ecological uniqueness in a metacommunity of urban pond insects

City ponds have the potential to harbour a rich biodiversity of aquatic insects despite being located in an urban landscape. However, our current knowledge on the correlates of pond biodiversity is limited and even less is known about the factors that influence the ecological uniqueness of urban ponds. The multiple environmental gradients, at different spatial scales, that may affect biodiversity and ecological uniqueness of urban ponds can thus be seen both as an opportunity and as a challenge for a study. In this study, we aimed to fill this gap by focusing on aquatic insect assemblages in 51 ponds in the Swedish city of Stockholm, using a metacommunity perspective. We found that species richness was primarily determined by the density of aquatic insects, water depth and proportion of buildings around the pond. The uniqueness of ponds was estimated as local contributions to beta diversity (LCBD), and it was primarily related to the proportion of arable land and industry around the ponds. With regard to the metacommunity we found two interesting patterns. First, there was a negative relationship between richness and LCBD. Second, biodiversity was spatially independent, suggesting that spatially-patterned dispersal did not structure species richness or LCBD. These last two patterns are important when considering conservation efforts of biodiversity in city ponds. We hence suggest that the conservation of insect biodiversity in urban pond should consider the surroundings of the ponds, and that high-richness ponds are not necessarily those that require most attention because they are not ecologically the most unique.     

Temporal and spatial variation in an index of biological integrity for the middle Wabash River, Indiana

Few studies have addressed within-year temporal variation of IBI scores. We compared index of biotic integrity (IBI) scores for two summer sampling events from a large river during 25 annual periods. The results indicated that IBI scores calculated from June samples were not significantly different from July samples. Spatial autocorrelation was present, such that sites that were closer together produced similar IBI scores and could not be considered independent. Temporal autocorrelation was present, but was not strong. Lower quality sites (low IBI score) did not have higher variation than higher quality sites. Our results show that a single sample of fishes by boat electrofisher during the summer in a large river such as the Wabash River can produce a repeatable estimate of IBI score. Thus, repeated or additional sampling within the summer season to improve the quality of the evaluation is not warranted. Handling editor: J. Trexler     

Saprolegnia strains isolated from river insects and amphipods are broad spectrum pathogens

Saprolegnia species are destructive pathogens to many aquatic organisms and are found in most parts of the world. Reports based on phylogenetic analysis suggest that Saprolegnia strains isolated from aquatic animals such as crustaceans and frogs are close to Saprolegnia strains isolated from infected fish or fish eggs and vice versa. However, it has often been assumed that host specificity occurs for each individual isolate or strain. Here we demonstrate that Saprolegnia spp. can have multiple hosts and are thus capable of infecting different aquatic organisms. Saprolegnia delica, Saprolegnia hypogyna, and 2 strains of Saprolegnia diclina were isolated from aquatic insects and amphipods while S. delica, Saprolegnia ferax, Pythium pachycaule, and a Pythium sp. were isolated from the water of a medium to fast flowing river. The ITS region of the rRNA gene was sequenced for all isolates. In challenge experiments, all four isolates from insects were found to be highly pathogenic to eggs of Atlantic salmon (Salmo salar) and embryos of the African clawed frog (Xenopus laevis). We found that Saprolegnia spp. isolated from salmon eggs were also able to successfully establish infection in nymphs of stonefly (Perla bipunctata) and embryos of X. laevis). These results suggest that Saprolegnia spp. are capable of infecting multiple hosts, which may give them an advantage during seasonal variation in their natural environments.     

Polarization vision in water insects and insects living on a moist substrate

Summary Light polarized by reflection was tested in the field for its attractiveness to flying insects. Attracted insects include bugs: some living in water (Corixidae, Notonectidae, Pleidae), others living on its surface (Gerridae) or near it (Saldidae). Beetles were also attracted: some are aquatic (Hydrophilinae, Dytiscidae, Haliplidae, Hydraenidae), others inhabit moist substrates (Sphaeridiinae). Also included are Chironomidae among other nematocerans. Non-polarized reflected light failed to attract any of these insects even at intensities far higher.Three response groups emerge. One is attracted whenever the degree of polarization is high in the UV-range, irrespectively of the degree of polarization in other wavelength ranges, and irrespectively of colour or brightness of the background beneath the polarizing, reflecting surface. The polarization vision of these insects operates in the UV-range. Another group was attracted only by the reflecting surface over a dark background, where the reflected light was highly polarized at all wave-lengths visible to insects. The third group ranges in between.Some Helophorus species behave in spring like members of the first group; in fall, like members of the second group.The distribution of the above response groups within various taxa is provided. Sensory mechanisms and eco-physiological implications are discussed.Abbreviations B matt black surface - b; y; w; a black, yellow white material and aluminum foil, reflection characteristics as described in the text; - G glass - G/b; G/y; G/w; G/a glass panes on different materials - Gb, y, w; Gb, y, Gb types of animals differing in behavior     

The Conservation of Saproxylic Insects in Tropical Forests: A Research Agenda

Invariably, insects are overlooked when tropical forest management issues are discussed, because there are so many species, they are taxonomically intractable and so poorly known. Often people take the view that if you look after the vegetation and vertebrates, the insects will look after themselves. This may be true for some functional groups, but for saproxylic insects, this seems unlikely. Their study deserves high priority, since they are dependent on the very resource – wood – whose removal from the ecosystem is the usual object of forest management. Given the current international effort to develop 'criteria and indicators' to monitor sustainable forest management for biodiversity values, there is a window of opportunity for sound ecological research on saproxylic insects to influence the formulation of forest policy such that their needs can be taken into account. There is already a large body of knowledge on temperate and boreal region saproxylic insects, and on the effects that logging has on them, but knowledge of the tropical forest situation lags far behind. This paper proposes a research agenda to enable the needs of saproxylic insects to be taken into account in natural forest management in the tropics. Basic questions, such as whether logging has so far had an impact on tropical saproxylic insects, and whether there are workable sampling techniques to investigate this, still remain to be addressed and deserve high priority. The links between the responses of saproxylic insects and more 'charismatic' study species need to be investigated. We also need to know whether there is a correlation between the intensity of logging and the response of saproxylic insects, and, critically, whether we would be justified in measuring some surrogate aspects of forest structure (as potential habitat for saproxylic insects) rather than the saproxylic insects themselves, and modelling this to determine likely impacts of different management regimes. We consider such an ambitious research agenda as justified given the scale of impact that forest use and management is likely to have on tropical forest insects in the future.     

Measuring human disturbance using terrestrial invertebrates in the shrub–steppe of eastern Washington (USA)

Hanford Nuclear Reservation in eastern Washington is an ideal place to study biological responses to diverse human activities because minimally disturbed areas of native shrub–steppe exist in close proximity to areas that have been substantially altered. This range of conditions provides an opportunity to test which attributes of terrestrial invertebrate assemblages change systematically along a gradient of human influence and to select from these a set of biological metrics that can be used for site assessment. We sampled invertebrates at 25 sites at or near the Hanford Reservation: some sites showed past or present influence from agriculture, waste disposal, urbanization, or construction; others had a history of minimal human disturbance.We evaluated 57 attributes of terrestrial invertebrate assemblages to determine if they varied systematically with the intensity of human disturbance. Attributes were measured as taxa richness or percentage relative abundance of key taxonomic, trophic, or ecological groups. Ten attributes were consistently associated with disturbance in 3 years of independent sampling, and another 12 attributes were significant in 2 out of 3 years. Those selected as metrics were total number of invertebrate families (1) number of Diptera families (2) taxa richness of Acarina (3) predators (4) detritivores (5) ground-dwellers (6) and percentage relative abundance of detritivores (7); all declined with increasing disturbance. The percentage relative abundance of Collembola (8) and taxa richness (9) and relative abundance (10) of polyphagous Carabidae increased with disturbance. Two metrics (7 and 10) were excluded from further consideration because they were redundant with other metrics (6 and 9).We transformed the remaining eight metrics to a standard scale and added them to yield a multimetric index—a single value summarizing the biological condition of each site. Undisturbed sites had the highest index values; sites with physical disturbance related to construction or waste disposal ranked next; and agricultural sites had the lowest values, indicating the most severe changes in their resident biota. Index values were lower for more frequently disturbed sites, although the time since last disturbance produced no differences in index values. Repeat sampling at five sites indicated that index values varied little across years and that year-to-year differences were smaller at undisturbed than disturbed sites.This first effort to develop a terrestrial monitoring approach modeled after the aquatic index of biological integrity (IBI) shows promise, but validation of the metrics at other places will be needed before a terrestrial index of biological integrity (T-IBI) can reliably guide management, restoration, or policy decisions.     

Spectral regions in which aquatic insects see reflected polarized light

For diverse water insects (species of Hydrophilidae, Hadraenidae, Dytiscidae, Haliplidae and aquatic Heteroptera), the attractiveness of an artificial water surface was found to vary when the polarization of the reflected light, the property by which these insects identify water, was abolished in different regions of the spectrum. The sensitivity maxima of their reflection-polarization visual systems (max(POL)) thus determined were in various spectral regions, between < 360 nm (UV) and ca. 550 nm (yellow-green). Species with max(POL) at the short-wavelength end of the spectrum would be able to identify bodies of water by polarization regardless of whether the subsurface reflection was bright or dark; nevertheless, this group includes forms that avoid water with a bright subsurface because of the intensity of the reflected light. Species with max(POL) in the long-wavelength region fail to use certain bodies of water with a bright subsurface as habitats because the light they reflect at the longer wavelengths is insufficiently polarized. That the POL system of a species has a large max could affect habitat choice; on the other hand, it could also be that systems operating in the long-wavelength region were produced in the course of adaptation to the light conditions in or above the habitat.Abbreviations max(POL) spectral sensitivity maximum for polarization vision     

Comparability of a regional and state survey: effects on fish IBI assessment for West Virginia,U.S.A.

Probability-based survey designs are now being investigated to allow condition to be assessed for a discrete population of watershed management units and to infer probability of impairment to other unsampled watersheds. Results can be used to focus further monitoring and restoration efforts. Fish community data and index of biotic integrity (IBI) development were compared between the 1993 and 1998 Environmental Monitoring and Assessment Program Mid-Atlantic Integrated Assessment (EMAP-MAIA) survey and a West Virginia Regional EMAP (WV REMAP) survey conducted in 2001–2002. Both designs were based on probability surveys, but the EMAP design treated streams as a continuous linear network comprising an infinite population of points, while the REMAP design used a discrete set of watershed outlets as defined by 12-digit Hydrologic Cataloging Units (HUC12) as the sample population. The comparability of the watershed-based WV REMAP survey design results with the linear network-based EMAP-MAIA survey results for West Virginia was affected by the different size range of watershed areas included in each target population. Once similar watershed area ranges were considered by narrowing the size range included in the West Virginia EMAP-MAIA data set, virtually identical cumulative distribution functions for fish IBI scores were obtained. The reduced variability in reference conditions obtained by applying a restricted range of watershed areas allowed us to detect and correct for ecoregional differences in fish IBI metrics and scores, after excluding the biogeographically distinct Potomac River drainage basin located in the Central Appalachian Ridge and Valley Ecoregion. Handling editor: K. Martens     

A fish-based biotic integrity index for assessment of lowland streams in southeastern Brazil

This study was carried out to develop and apply a fish-based biotic integrity index to assess lowland streams in a highly deforested region of the Upper Paraná River basin. Fifty-six first-order segments were randomly selected for environmental and fish evaluation. Because previous analysis had identified the main type of effect on the streams of the region as physical habitat degradation, 22 qualitatively biological attributes were selected and tested over a physical condition gradient between reference and degraded sites. Sensitivity and redundancy of each attribute revealed that five metrics were adequate for discriminating higher quality from degraded sites. Of the fifty-six streams assessed, one (2%) was classified as good, four (7%) as fair, ten (18%) as poor, and forty-one (73%) as very poor, indicating that, on a regional scale, many aspects of biological integrity are altered, indicative of serious degradation. Considering that first-order segments amount to 11,000 km in total, it is noticeable that 10,000 km of the stream segments have no more than half of the expected conditions, indicative of poor or very poor biotic integrity conditions. Possible strategies of mitigating this scenario are discussed. Handling editor: S. M. Thomaz