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Common Taxa (common + taxa)
Selected AbstractsA field-based microcosm method to assess the effects of polluted urban stream sediments on aquatic macroinvertebratesENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 1 2005Vincent Pettigrove Abstract A method using field-based microcosms was developed to determine the effects of contaminated sediments on aquatic macroinvertebrates. Fine sediments from nonpolluted, moderately polluted, and severely polluted bodies of water were placed in microcosms positioned within the littoral zone of a nonpolluted wetland near Melbourne (Victoria, Australia). In three experiments, 47 taxa, including 18 Chironomidae, 6 taxa from other Diptera families, and 7 Hemiptera taxa, colonized the microcosms, mostly via eggs deposited by flying adults. The effects of sediment type on the presence and abundance of common taxa were considered statistically. Pollution levels in sediments (indexed either by a principal components analysis or by the concentration of zinc, the predominant metal) resulted in reduced occurrence and abundance of eight taxa but had no effect on another five taxa. These findings were validated with an extensive field database for the distribution of macroinvertebrates and associated concentrations of zinc in sediments from streams and wetlands in the Melbourne region. The occurrence of eight taxa and the abundance of two taxa varied at similar zinc concentrations in sediments from both the microcosms and the field. Patterns for another two species did not match the microcosm results, but these groups contained multiple species with potentially diverse responses. The present results suggest that contaminant levels in sediments probably have a direct effect on the occurrence and abundance of macroinvertebrates in bodies of water in urban areas. The microcosm method can be used to gather information regarding the effects of sediment quality on macroinvertebrates in lentic habitats, particularly for indigenous species that cannot be easily reared or tested in laboratory conditions. Because almost all macroinvertebrates in microcosms develop from eggs, the most sensitive life stages (i.e., first and second instars) are exposed to polluted sediments. [source] Effects of floods versus low flows on invertebrates in a New Zealand gravel-bed riverFRESHWATER BIOLOGY, Issue 12 2006ALASTAIR M. SUREN Summary 1. Floods and low flows are hydrological events that influence river ecosystems, but few studies have compared their relative importance in structuring invertebrate communities. Invertebrates were sampled in riffles and runs at eight sites along 40 km of a New Zealand gravel-bed river every 1,3 months over 2.5 years, during which time a number of large flood and low flow events occurred. Flows were high in winter and spring, and low in summer and autumn. Four flow-related variables were calculated from hydrological data: flow on the day of sampling (Qsample), maximum and minimum flow between successive samples (Qmax and Qmin, respectively), and the number of days since the last bed-moving flood (Ndays). 2. The invertebrate community was summarised by relative densities of the 19 most abundant taxa and four biotic metrics [total abundance, taxon richness, the number of Ephemeroptera, Plecoptera and Trichoptera taxa (i.e. EPT richness), and per cent EPT]. Invertebrate density fluctuated greatly, and was high in summer and autumn, and low during winter and spring. Stepwise multiple regression (SMR) analysis was used to investigate relationships between the invertebrate community and season, flow, habitat and water temperature. 3. Seasonal variables were included in almost 50% of the SMR models, while flow-related variables were included in >75% of models. Densities of many taxa were negatively correlated to Qmin and Qmax, and positively correlated to Ndays, suggesting that while high flows reduced invertebrate densities, densities recovered with increasing time following a flood. Although season and flow were confounded in this study, many of the taxa analysed display little seasonal variation in abundance, suggesting that flow-related variables were more important in structuring communities than seasonal changes in density associated with life-cycles. 4. Five discrete flood and low flow events were identified and changes to invertebrate communities before and after these events examined. Invertebrate densities decreased more commonly after floods than after low flows, and there was a significant positive relationship between the number of taxa showing reductions in density and flood magnitude. Densities of most invertebrates either remained unchanged, or increased after low flow events, except for four taxa whose densities declined after a very long period (up to 9 months) of low flow. This decline was attributed to autogenic sloughing of thick periphyton communities and subsequent loss of habitat for these taxa. 5. Invertebrate communities changed more after floods and the degree of change was proportional to flood magnitude. Community similarity increased with increasing time since the last disturbance, suggesting that the longer stable flows lasted, the less the community changed. These results suggest that invertebrate communities in the Waipara River were controlled by both floods and low flows, but that the relative effects of floods were greater than even extended periods of extreme low flow. 6. Hydraulic conditions in riffles and runs were measured throughout the study. Riffles had consistently faster velocities, but were shallower and narrower than runs at all measured flows. Invertebrate density in riffles was expressed as a percentage of total density and regressed against the flow-related variables to see whether invertebrate locations changed according to flow. Significant negative relationships were observed between the per cent density of common taxa in riffles and Qsample, Qmax and Qmin. This result suggests either that these animals actively drifted into areas of faster velocity during low flows, or that their densities within riffles increased as the width of these habitats declined. [source] Effects of sand sedimentation on the macroinvertebrate fauna of lowland streams: are the effects consistent?FRESHWATER BIOLOGY, Issue 1 2006BARBARA J. DOWNES Summary 1. In lowland streams sand sedimentation can produce sand slugs: very slow moving, discrete volumes of sand that are created episodically. Hypothetically, such sedimentation causes losses of habitat and fauna but little is known about the effects of sand slugs. In south-eastern Australia sand slugs are widespread, especially in streams with granitic catchments. 2. This study in north-central Victoria was centred on three streams that rise in the Strathbogie Ranges and flow out onto lowland plains, where they contain sand slugs. Below the sand slugs, the streams are slow-flowing ,chains of ponds' with a clay streambed. To correct for potential upstream-downstream confounding of comparisons, two unsanded, nearby streams were included as potential controls. Habitat measurements and faunal samples were taken in Spring 1998, from three sites in the sand slug and three sites in the clay-bed, downstream sections of each impacted stream, as well as from three sites in commensurate upstream and downstream sections of the control streams. 3. The sand-slugged sections had significantly higher velocities, shallower depths and less coarse woody debris than the unsanded downstream sections. Macroinvertebrate taxon richness and abundance showed some significant differences between the sand and clay sections compared with commensurate up- and downstream locations in the control streams. Effects were not uniform, however. In Castle Creek there were no significant differences between the sand and clay sections, in Pranjip-Ninemile Creek taxon richness and abundances were higher in sand than in the clay sections, whereas in Creightons Creek the ,expected' results of lower taxon richness and abundance in the sand were found. 4. Of the 40 most common taxa, only eight provided a clear signal related to sand and, of these, one (Slavina sp.) occurred only in the sand slugs, whereas the other seven had significantly higher numbers in the clay sections. Of these taxa, three were ostracods, three were chironomids and one was a tubificid oligochaete, all taxa that live in detritus-rich environments. Overall faunal composition did not show a clear distinction though, between sandy and clay sites. The sand slug community of Creightons Creek was very different from the other communities in all of the streams. There were clear differences in community composition between the sand-affected and the control streams, even for downstream, clay sections, suggesting they cannot act as controls for the impacted sections of the sand-slugged streams. 5. Differences between streams within categories (particularly between sand-slugged streams) and between sites in the same section of stream accounted for most of the variability in species richness and the abundances of each of the 40 most common taxa. That finding was repeated when data were examined at the family level, for both numbers of families per sample and collated lists of families occurring across sites. These results strongly suggest that the effects of sedimentation by sand slugs do not overwhelm background variation in macroinvertebrate density and diversity. Overall the results suggest that many taxa may respond individually, and that there is much variation between sand-affected streams even over relatively small (approximately <10 km) spatial scales. [source] Local disturbance history affects patchiness of benthic river algaeFRESHWATER BIOLOGY, Issue 9 2003Christoph D. Matthaei Summary 1.,Recent research has shown that high-flow events in streams leave a small-scale mosaic of bed patches that have experienced scouring, sediment deposition (fill), or remained stable. Few studies have investigated if this ,local disturbance history' contributes to the patchy distribution of benthic organisms in streams and rivers. 2.,In the present research, we demonstrate that local disturbance history in a mid-sized river can have both short- and long-term effects on epilithic algae. Chains buried vertically in the substratum of the river bed (236 in a 800-m reach) indicated that two floods (return periods ,1 year) caused a mosaic of bed patches with different disturbance histories. Once after the first and twice after the second flood, we sampled epilithic algae (mainly diatoms) in replicate patches that had been scoured, filled, or remained stable during the respective event. Algal biomass and cell density per substratum area were determined. 3.,Three months after the first flood, algal biomass, total diatom density, diatom taxon richness, and densities of six of nine most common taxa were highest in fill patches. Six days after the second flood, biomass was highest in stable patches, indicating a refugium function of these patches. The refugium patches consisted of average-sized stones, in contrast to previous studies of flood refugia for benthic algae in which these refugia were always large and/or immobile substrata. Four weeks after the second flood, diatoms tended to be most abundant in scour patches. With one exception, these differences between patch types could not be attributed to differences in local near-bed current velocity or water depth. 4.,The effects of disturbance history were more complex than a simple refugium function of stable patches because algal patterns changed with time since the last disturbance, possibly depending on the successional state of the algal mats. [source] Fallowing did not disrupt invertebrate fauna in Philippine low-pesticide irrigated rice fieldsJOURNAL OF APPLIED ECOLOGY, Issue 3 2010Kenneth G. Schoenly Summary 1.,Fallowing, a type of rotation where no crop is grown, deprives insect pests of food. In tropical irrigated rice, it is not known whether fallow periods deplete natural enemy populations and reduce their pest control effectiveness in post-fallow crops. We tested the null hypothesis that small-scale synchronous cropping (embedded in asynchronously planted rice landscapes) does not significantly increase pest densities during post-fallow periods in the presence of a large, diverse natural enemy complex undisrupted by insecticides. We tested this null hypothesis by comparing the invertebrate fauna before and after fallowing. 2.,In six molluscicide-only fields at the International Rice Research Institute (IRRI) in southern Luzon and at Zaragoza in central Luzon, Philippines, canopy and floodwater invertebrates were vacuum-sampled over two cropping seasons, dry and wet. 3.,Thirty-three of the ubiquitous common taxa dominated the samples in both seasons at each site. Most species were natural enemies of rice pests and recyclers of organic matter in the floodwater and waterlogged sediments; some were rice pests. 4.,Fallowing depleted populations of more ubiquitous taxa at Zaragoza (four natural enemies, one detritivore) than at IRRI (one herbivore, one natural enemy). At both sites, only green leafhoppers, Nephotettix virescens and Nephotettix nigropictus, had consistently higher post-fallow densities than pre-fallow densities. 5.,At both sites, fallowing did not affect rice-invertebrate faunas differently between seasons with regard to community structure, trajectories and accumulation rates of guild members. 6.,Synthesis and applications.,In tropical irrigated rice fields, small-scale synchronous fallowing combined with low-pesticide inputs and pest-resistant rice varieties did not induce pest outbreaks or notably diminish populations of natural enemies when embedded in asynchronous cropping on larger, regional scales. Our results suggest that small-scale synchronous fallowing, when embedded in asynchronously planted landscapes, does little harm to biological regulation of the invertebrate faunal community and may be adopted as part of integrated pest management when it serves other purposes. [source] Rarity, specialization and extinction in primatesJOURNAL OF BIOGEOGRAPHY, Issue 4 2002A. H. Harcourt Aim To determine and explain biological traits that distinguish rare from common primate taxa. Location Africa, Americas, Asia, Madagascar. Methods We compare the biology of rare primate taxa with the biology of common taxa. Rarity is defined by (1) small size of geographic range; (2) small geographic range plus low local population density; and (3) small geographic range plus low local density plus narrow habitat specificity. After a linear comparison of size of geographic range with various biological traits, globally and by realm, extremes of rarity and commonness per realm are identified, and then combined for a global analysis. Tests are done both with genera treated as independent data points (n=62), and also with phylogenetic control by use of an independent contrasts test. Extinction risk in vertebrates, including primates, often correlates with high resource requirements, slow population recovery rate, and specialization. The three indices of rarity are therefore compared with these three general traits. Measures of resource use are body mass, local density, annual range size, and group size; of recovery rate, interbirth interval, and maximum intrinsic rate of natural population increase; and of degree of specialization, variety of diet, of habitats, maximum latitude, and morphological variety. All data come from the literature. Because several measures are compared, probabilities are Bonferroni corrected. Results If rarity in primates correlates with any biological attribute, it consistently correlates with only measures of specialization, and not with measures of high resource use, or slow population recovery rate. Without phylogenetic correction, the first two indices of rarity associate significantly with all four measures of specialization, and the third with maximum latitude. With phylogenetic correction, the first index still associates with all four, the second with two (maximum latitude, number of species per genus), and the third shows no significant associations. While the four measures of specialization are strongly interrelated, stepwise regressions on geographic range indicate that maximum latitude has the strongest effect, followed by dietary variety and number of species per genus and, finally, habitat variety. Main conclusions The most commonly demonstrated traits of susceptibility to extinction are those of high resource use, slow recovery rate, and specialization. Yet, while rarity (almost however, it is defined) is an inevitable precursor to extinction, specialization is the only trait found to correlate with rarity in this study. We cannot explain this apparent contradiction. [source] | ||||||||||