Random patch dynamics of larval Chironomidae (Diptera) in the bed sediments of a gravel stream

• 1 The larval chironomid community of the sediment surface and the hyporheic inters titial was investigated in two longitudinal transects of an alpine gravel stream between September 1984 and August 1985. Eighty larval species and species groups were identified, most of which belonged to the subfamily Orthocladiinae. Of all larval individuals 51.1% inhabited the first 10cm of the bed sediments, and 93.2% occurred between the surface and 40cm depth.
• 2 The spatial species turnover showed marked variations between horizontally adjacent sampling sites in each of the four sediment depth layers. In both transects the species composition showed a significantly lower turnover in the upper 10cm of the bed sediments than in the deeper layers.
• 3 Spatial community stability showed an oscillating pattern between all sampling sites due to density shifts of larvae between depth layers. Temporal differences in resilience (local stability) were significantly and positively related to changes in the cumulative discharge pattern in the gravel brook, thus indicating the apparent ability of the community to recover quickly following disturbances.
• 4 The five abundant species, Corynoneura lobata, Synorthocladius semivirens, Tvetenia calvescens, Micropsectra atrofasciata and Rheotanytarsus nigricauda, exhibited significant differences in their sediment depth distribution, with density maxima shifting between depth layers. Spatial autocorrelations suggest that these larvae form patches between neighbouring sampling sites with varying sizes and inter-patch distances in each of four sediment layers. A simulation test, in which individuals of each species were randomly permuted between microhabitats of each depth layer separately, indicated that the patches might have arisen by chance.
• 5 To evaluate the significance of observed spatial resource overlap values amongst these five chironomid species, neutral models were developed based on 300 randomizations of each possible species pair-wise association of individuals and patches of species. The spatial organization of a larval chironomid assemblage in the stream Oberer Seebach seemed to be governed by coexistence due to random patch formation and dispersal patterns within the interstitial habitats, which reduce the probability of strong competitive interactions.

     

Population dynamics and resource utilization by larval Chironomidae (Diptera) in a backwater area of the River Danube

1. The five most abundant species of the larval chironomid community in a backwater area of the River Danube were analysed in terms of population dynamics and utilization of space from July 1985 to July 1986. The life histories of Prodiamcsa olivacea (Meigen), Cryptochironomus defectus (Kieffer), Harnischia curtilamellata (Malloch), Polypedilum laetum (Meigen) and Polypedilum scalaenum Schrank were described; the number of estimated generations per year was two for P. olivacea, H. curtilamellata, P. laetum and P. scalaenum and three for C. defectus. A decline in larval densities of P. olivacea and P. scalaenum was significantly correlated with increasing cumulative water discharge in an area close to a dam (P<0.01). 2. Spatial overlap and resource width were estimated for these chironomid species across four ranges of water depth, in three sections of the River Danube. An increasing mean spatial overlap between larval species coincided significantly with higher mean resource utilization in all cross-sections during the sampling period. Simulations of spatial overlap between randomized species associations were conducted for analyses of coexistence and dispersion between larval populations. On the basis of comparison with a neutral model, in which patches of individuals were randomly reassigned to habitat units, spatial segregation was significantly (P<0.05) different from chance for seventy-three out of 263 species pairs examined through the year. 3. An analysis of the spatial dispersion of each chironomid species (using the standardized Morisita index) suggested temporally and spatially varying patterns of dispersion, whereas the mean spatial segregation between patches of larval species might have resulted from temporary formations of random patches in this backwater area of the River Danube. 4. Spatial stability estimated as the minimum positive eigenvalue of the species matrix was significantly positively related to mean spatial segregation, indicating that a lower habitat segregation between patches of larval species pairs may lead to a destabilization of the larval species assemblage.     

Phenology and bathymetric distribution of the profundal chironomid fauna in Starnberger See (F.R. Germany)

Results of the first long-term investigation of the profundal chironomid fauna of Starnberger See, a prealpine lake are reported. Data are presented on the qualitative and quantitative composition of the chironomid fauna in the profundal of Starnberger See, on the spatial variation, and on the phenology of the dominant species, based on pupal occurrence and the seasonal distribution of larval instars. Twenty-five distinct chironomid taxa could be recorded in the profundal zone. Typical inhabitants of the profundal zone of Starnberger See are the larvae of the genus Micropsectra. The maximum abundance of Micropsectra larvae were found at 60 m with 5644 Ind.m⁻². Abundance, distribution and phenology of the dominant chironomid species are discussed in comparison with other lakes.     

Predation on meiobenthic assemblages: resource use of a tanypod guild (Chironomidae, Diptera) in a gravel stream

1. Three predatory chironomid species constituted numerically 8.8% (± 95% CL 2.2) of the macro- and meiobenthic community at the sediment surface and in the hyporheic zone of Oberer Seebach, a gravel stream in Lower Austria. Larvae of Thienemannimyia geijskesi (Goetghebuer) and Nilotanypus dubius (Meigen) occurred in higher densities in sediment depths between 10 and 40 cm, whereas Conchapelopia pallidula (Meigen) achieved higher densities at the sediment surface. The three species completed one generation in a year. 2. A total of ninety-seven prey species and instars were identified by gut analyses, of which forty-one benthic rotifer species constituted 69.5% of individuals and twenty-three chironomid species and their instars, 22.9%. The three tanypod species showed shifts from mainly rotifer species in early instars to chironomids and diverse other meio- and macrofaunal taxa in later instars. Rather than shifting towards larger prey sizes, growing predators expanded their upper size thresholds and continued to include smaller prey species in their diet. The extent to which tanypod instars fed on similar prey size classes declined with increasing larval size. Predation by tanypods amounted to 2.2% (± 95% CL 0.1) of the combined prey densities and prey consumption averaged 1.32 (bootstrap 95% CL 1.26–1.39) individuals per predator individual. 3. Preferences for microhabitat flow differed between predator species and in the prey assemblage. Prey densities and densities of T. geijskesi and C. pallidula were highest in pool areas, whereas N. dubius achieved high densities in riffle sites. 4. Tanypod larvae fed non-selectively among prey types. To test the significance of observed size(instar)-specific spatial and dietary overlap values amongst tanypod species, simulations were generated from random models for pairs of intra- and interspecific associations of individuals and groups of prey and predator species. Groups and individuals of tanypod instars fed near randomly on groups of prey types and a high proportion (P > 0.60) of prey individuals are quasi-randomly chosen by tanypods in those patches. Tanypod instar-pairs did not show a sustained trophic resource partitioning in time, thus reducing the degree of competitive interactions for food in this predator guild. Spatially segregated and non-segregated tanypod instars formed random aggregations independent of each other at different flow microhabitats. 5. Species-rich prey assemblages such as benthic rotifers and larval chironomids increased the probability of non-selective feeding upon a wide spectrum of prey species by tanypods. Prey choice was governed by prey availability and tanypod individuals fed on many species at rather even proportions independent of each other.     

湖南省阳明山山顶苔藓矮林优势种空间分布格局

山顶苔藓矮林是亚热带山地常绿阔叶林区在极端气候与环境条件下发育的一种群落变型,通过研究优势植物的分布格局与规模,可以有效地指导植被保护与管理活动。在湖南阳明山国家级自然保护区的山顶苔藓矮林区设置3个样地,应用相邻格子法对优势种云锦杜鹃(Rhododendron fortunei)进行每木调查,在不同取样尺度(面积)上采用方差/均值比率法(v/m)、负二项参数(k)、丛生指数(I)、平均拥挤度(m~*)、聚块性指数(m~*/m)、聚集指数(C_a)和格林指数(GI)等聚集强度指数对云锦杜鹃种群分布格局进行分析。结果表明:阳明山山顶苔藓矮林优势种云锦杜鹃种群在北、南、东三个方位上的空间分布格局总体上为聚集分布,随着取样尺度的增大,聚集格局强度和规模依次减弱;而山顶苔藓矮林优势种群不同年龄阶段的空间分布特征为随着种群年龄的增大,其空间分布格局呈聚集强向聚集弱、以至于向随机分布发展;阳明山山顶苔藓矮林优势种群及其分布格局形成的主要原因是云锦杜鹃种群本身的种子繁殖及传播方式和类营养繁殖等生物学特性及方位、坡向等环境因子影响所致。     

Why do traditional dispersion indices used for analysis of spatial distribution of plants tend to become obsolete?

It is common to characterize the spatial distribution of plant patterns as random, aggregate, or uniform. In this context, a major challenge for the researcher is the choice of the method to identify the spatial pattern correctly as well as the factors related to it. The vast literature on the subject is not recent, especially regarding the dispersion indices. The aim of this review was to conduct a critical and temporal analysis of these dispersion indices and test their effectiveness in determining the spatial distribution of Paepalanthus chiquitensis Herzog (Eriocaulaceae). This species is a meaningful model due to its occurrence in specific sites. The Lexis, Charlier, dispersion, relative variance, aggregation, Green, inverse of k of the negative binomial, Morisita, and standardized Morisita indices were limited to indicating that the individuals of the species are aggregate and did not provide information on neither spatial dimension (scale) where the aggregation occurs, nor the factors related to this aggregation. Although they have distinct magnitudes, the algebraic expressions of dispersion, relative variance, aggregation, Green, inverse of k, Morisita, and standardized Morisita indices exhibited a close relationship with each other and little progress from their precursors Lexis and Charlier. By disregarding the possibility of spatial dependence, these indices make it impossible to generate important hypotheses for the investigation of factors related to spatial structure. Therefore, they became obsolete and are falling into disuse. It should be noted that these measurements accomplished their role and contributed to science in times of limited technologies for spatial data.     

Structure,dynamics and production of the benthic fauna in Lake Manitoba

The structure and diversity, including seasonal variation, and the energy budget of the benthic fauna in southern Lake Manitoba were studied and related to physical and chemical properties of the water and sediment. A total of 47 taxa were identified but 90 percent of individuals were represented by seven taxa (Candona rawsoni, Cytheromorpha fuscata, Pisidium spp., Amnicola limosa, Harnischia curtilamellata, Procladius freemani and Chironomus sp.). The spatial and temporal dynamics, dispersion patterns and life cycles of these abundant species are described.The net production was 5.05 Kcal/m²/yr for the only carnivorous species (Procladius freemani) and 28.53 Kcal/m²/yr for non-carnivorous species. The gastropod Amnicola limosa and the chironomid Chironomus sp. appear to be the most important contributors to the total biomass and net production of the community. Annual turnover rate (P/B) for all seven taxa aver-aged 2.82, with the chironomid species having the highest value and the gastropod species the lowest (3.7 and 1.75 respectively).Contribution No. 52 of the University of Manitoba Field Station (Delta Marsh).     

Assembly mechanisms shaping tropical litter ant communities

Community ecology seeks to unravel the mechanisms that allow species to coexist in space. Some of the contending mechanisms may generate tractable signatures in the amount of trait and phylogenetic dispersion among co‐existing species. When a community presents a pattern with reduced trait or phylogenetic dispersion, mechanisms based on ecological filters are brought into consideration. On the other hand, limiting similarity mechanisms such as competitive exclusion are proposed when communities present patterns of trait or phylogenetic even‐dispersion. The strength of these mechanisms likely varies with the spatial scale of an observed sample. I surveyed species‐rich tropical litter ant communities in a spatially nested design that allowed me to explore the spatial scales, fine (0.25 m²), intermediate (9 m²), and broad (361 m²) at which these mechanisms act. I then assessed the relationship between observed ant communities and potential species pools ranging in size, from plot, site, and island‐wide areas. Patterns of phylogenetic dispersion within ant communities suggested that ant communities were composed of species that were more closely related than expected by a random sampling of phylogenetic pools. The magnitude of phylogenetic ‘clustering’ increased with the size of the species pool but was similar among communities assembled from different spatial scales. Patterns of dispersion of one ecological trait (i.e. body size) within ant communities also showed clustering of body sizes, and most communities were composed of ant species that were smaller than expected by a random sampling of trait pools. Trait clustering increased with the size of the species pool but decreased at broad spatial scales. Together, these results suggest that ecological filters, not interspecific interactions, are structuring tropical ant communities, favoring clades with small worker sizes. The larger dependency on the size of regional pools than on the spatial scale suggests that environmental heterogeneity is greater among than within the study sites.     

Accounting for spatial autocorrelation in null models of tree species association

A commonly used null model for species association among forest trees is a well‐mixed community (WMC). A WMC represents a non‐spatial, or spatially implicit, model, in which species form nearest‐neighbor pairs at a rate equal to the product of their community proportions. WMC models assume that the outcome of random dispersal and demographic processes is complete spatial randomness (CSR) in the species’ spatial distributions. Yet, stochastic dispersal processes often lead to spatial autocorrelation (SAC) in tree species densities, giving rise to clustering, segregation, and other nonrandom patterns. Although methods exist to account for SAC in spatially‐explicit models, its impact on non‐spatial models often remains unaccounted for. To investigate the potential for SAC to bias tests based upon non‐spatial models, we developed a spatially‐heterogeneous (SH) modelling approach that incorporates measured levels of SAC. Using the mapped locations of individuals in a tropical tree community, we tested the hypothesis that the identity of nearest‐neighbors represents a random draw from neighborhood species pools. Correlograms of Moran's I confirmed that, for 50 of 51 dominant species, stem density was significantly autocorrelated over distances ranging from 50 to 200 m. The observed patterns of SAC were consistent with dispersal limitation, with most species occurring in distinct patches. For nearly all of the 106 species in the community, the frequency of pairwise association was statistically indistinguishable from that projected by the null models. However, model comparisons revealed that non‐spatial models more strongly underestimated observed species‐pair frequencies, particularly for conspecific pairs. Overall, the CSR models projected more significant facilitative interactions than did SH models, yielding a more liberal test of niche differences. Our results underscore the importance of accounting for stochastic spatial processes in tests of association, regardless of whether spatial or non‐spatial models are employed.     

辽东山区次生林乔木幼苗分布格局与种间空间关联性

在辽东山区次生林建立4 hm^2样地(200 m×200 m),研究0~50 m尺度范围内乔木幼苗分布格局及种间空间关联性.结果表明:在完全随机零模型下,0~20 m尺度上,95%的树种呈现聚集分布格局;0~16 m尺度上,19个树种呈现聚集分布;随着尺度的增加,聚集分布树种的比例逐渐减少,50 m尺度上,随机分布成为树种分布的主要形式;在异质性泊松过程零模型下,0~24 m尺度上,5%的树种呈现聚集分布,26~50 m尺度上,42%和58%的树种呈现随机和均匀分布.在完全随机零模型下,正相关树种对比例最高,且在50 m尺度下呈现正相关、负相关、无相关3种相关性的树种对比例相同;在异质性泊松过程零模型下,树种对主要呈现负相关,且随尺度增大,负相关的树种对比例逐渐升高.种子扩散限制和生境异质性在某种程度上解释了乔木幼苗的聚集分布格局,乔木幼苗强烈的聚集分布又促使种间空间关联性密切,更新群落稳定性较差.     

Instar distribution and biomass of Chironomidae larvae in Lago El Junco, Isla San Cristobal, the Galápagos

The distribution, abundance and standing crop biomass of chironomid larvae were determined at one-meter depth intervals along three radial transects. Samples were collected by coring soft sediments while diving. Three genera were found in the lake: Chironomus sp. (collector-filtering larvae), Ablabesmyia sp. (predatory larvae) and Goeldichironomus sp. (collector-filtering larvae). Standing crop densities of chironomids, averaged over the entire lake, varied from 30,594 larvae/m² to 11,428 larvae/m² at different depths. No statistically significant zonation in density was found for the two most common taxa, Chironomus sp. (87.8% of specimens) and Ablabesmyia sp. (9.0%), however the deepest zones (>4 m) had the lowest estimated densities. Significant differences in standing crop biomass were detected, with the 6 m depth having greatest biomass. The increase in standing crop biomass was a function of (1) lower frequency of first instars of Chironomus sp. and Ablabesmyia sp. at 6 m (2) higher average larval biomass of both species at 6 m and (3) very significant increase in average biomass of fourth instars of Chironomus sp. at 6 m compared to fourth instars at shallower depths. These results indicate that the lentic chironomids of this isolated oceanic habitat consist of a small number of species that are ecological generalists and tolerant of low oxygen concentrations.     

Stochastic approach to determine spatial patterns of lizard community on a desert island

One of the principal sources of error in identifying spatial arrangements is autocorrelation, since nearby points in space tend to have more similar values than would be expected by random change. When a Markovian approach is used, spatial arrangements can be measured as a transition probability between occupied and empty spaces in samples that are spatially dependent. We applied a model that incorporates first-order Markov chains to analyse spatial arrangement of numerical dominance, richness, and abundance on a lizard community at different spatial and temporal scales. We hypothesized that if a spatial dependence on abundance and richness exists in a diurnal desert community, then the Markov chains can predict the spatial arrangement. We found that each pair of values was dependent only on its immediate predecessor segment. In this sense, we found intergeneric differences at temporal and spatial scales of recurrence estimates. Also, in desert scrub, species show higher spatial aggregation and had lower species richness than at the island level; the inverse pattern occurred on rocky hillsides. At the species level, Uta stansburiana is the most abundant species in desert scrub, while Sauromalus slevini is the most abundant species on rocky hillsides. This report attempts to understand, using Markovian spatial models, the effect of nearby samples on local abundance and richness on different scales and over several seasons.     

Distributional Patterns of Diatoms and Limnodrilus Oligochaetes in a Kenyan Dry Streambed Following the 1999–2000 Drought Conditions

Drought is a natural phenomenon experienced by many intermittent and also seasonal lotic systems. It has diverse effects on the structure and distribution of biological communities through habitat transition from wetted to terrestrial conditions. The Njoro River, a tropical stream, was drought‐stressed between late 1999 and mid 2000, providing an opportunity to sample and describe the distributional patterns of diatoms and Limnodrilus oligochaetes in the vertical sediment profile. The dispersion of Limnodrilus oligochaetes with sediment depth profile varied from quasi‐random (i.e. exponent k of the negative binomial distribution >2.0 or <0) at the surface to strong aggregation (0 < k < 1.0) in the deeper sediments. Diatoms were heterogenous, with most species contributing less than 1% of all the diatoms collected from the riverbed. Contagious dispersion was a common feature among the diatom species. The distribution of Fragilaria ulna was largely quasi‐random in all sites, with Nitzschia amphibia and Cocconeis placentula demonstrating quasi‐random distribution in the Kerma vertical sediment profile. Escape from stranding to deeper sediment strata as the drought progressed was not a universal response among the diatom species. Our results showed that drought‐stress altered the structure of biological assemblages and also emphasized the need for the management of tropical lotic systems and their catchments for flow permanence. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Spatial indicators of plant community assembly from a 453-year sand-dune chronosequence

Background : We explored evidence for spatial patterning in vegetation across a sand-dune chronosequence spanning 453 years of primary succession to test for indications of a temporal signature of niche versus neutral processes during community assembly.

Methods : The study was conducted on a series of dune-capped beach ridges located in Wilderness State Park in Emmet County of northern Lower Michigan, United States (45° 43′ N, 84° 56′ E). Nearest-neighbour survey data were subjected to species dispersion and association analyses.

Results : Both species richness and species evenness showed the classic ‘hump-shaped’ relationship across successional time, suggesting that competition is an important force in structuring this community. However, the only evidence of intra-specific aggregation occurred in the youngest dune. Older dunes displayed random spatial structure and the oldest dunes tended toward a mix of random patterns and intra-specific segregation, i.e. with nearest neighbours more likely than by chance to be inter-specific. In addition, the frequency of species having lower neighbour-species richness than expected by chance was higher in younger, not older dunes. Species with significantly low neighbour richness (based on absolute nearest neighbours) on later dunes tended to have a high proportion of nearest neighbours that were intra-specific.

Conclusions : The data provided no evidence that resident species in later succession have greater intra-specific aggregation or more niche differentiation based on horizontal niche space. The data are more consistent with theories of community assembly involving competitive equivalence and/or effects of facilitation.     

Seasonal dynamics and spatial distribution of chydorid cladocerans in relation to chironomid larvae in the sandy littoral zone of an oligo-mesotrophic lake

The seasonal variation of the principal macro- and meiobenthic taxa in the sandy littoral zone of the oligomesotrophic Dutch Lake Maarsseveen I was studied during two years. Population peaks of the different taxa were clearly separated in time. In early spring there were chironomid density peaks of Stictochironomus sticticus, in one year followed by a Polypedilum maximum. From June–July chydorid cladocerans dominated, with a peak of Monospilus dispar followed by a peak of Rhynchotalona falcata. In autumn the chironomid Cladotanytarsus mancus became dominant, remaining so throughout the winter.To study the spatial heterogeneity of the major macro- and meiofaunal taxa, samples were taken in a grid of 2.5 × 10 m. Distributions of all but one taxon were significantly different from random, with Morisita indices varying from 1.23 (chironomids) to 2.10 (the chydorid Monospilus dispar). Wind-induced disturbance presumably had strong and species-specific effects on littoral macro- and meiobenthic taxa. Chydorid heterogeneity increased immediately following the first autumn storm of the season; this may be explained by the tendency of these organisms to remain attached to detritus particles.Temporal and spatial correlation coefficients between macro- and meiobenthic taxa were generally low, suggesting that interactions between these groups are weak, with distribution patterns that are independent of each other. Among the meiofaunal taxa, positive spatial and temporal correlation coefficients were found; apparently, the similarity in both seasonal dynamics and spatial distribution is larger among the meiofaunal taxa than between macro- and meiofaunal taxa. Also among most of the chironomid species significant positive temporal correlations were found, except for Stictochironomus sticticus and Polypedilum sp.; these species have similar life-cycles, but were during one year temporally separated by several alternating settlement peaks. In the next year, Polypedilum disappeared completely following an extremely strong Stictochironomus settlement peak.     

Spatial distribution of subfossil Chironomidae in surface sediments of a large, shallow and hypertrophic lake (Taihu, SE China)

Spatial heterogeneity of benthic communities has clear implications for estimating lake production, biodiversity as well as identifying representative sites for palaeolimnological studies. This study investigates chironomid variability and the controlling factors (i.e., environmental and spatial variables) in surface sediments from Taihu Lake (2,338 km²), a hypertrophic lake in the Yangtze delta in eastern China. The spatial distribution of chironomids shows distinct heterogeneity. Microchironomus tabarui-type and Tanypus dominate the midge communities around the estuaries, while Cricotopus sylvestris-type and Polypedilum nubifer-type are the predominant taxa in the East Bays and the East Taihu Lake. Redundancy analysis was used for exploring the relationships between chironomid variability and environmental and spatial stressors. Four variables were identified as significant factors that influence chironomid community structures. The high nutrient concentrations around the estuarial areas favor the development of nutrient-tolerant taxa. Water depth-related oxygen depletion in the open lake during algae blooms prohibits the survival of many organisms, except for a few hypoxic-resistant species. High transparency in the East Bays and the East Taihu Lake indirectly creates a favorite microhabitat for macrophyte-associated chironomid species through aquatic plants. Space per se is a significant forcing factor for organism community and distribution at scales of >1,000 km². It might be important to consider spatial variables more explicitly in future studies of chironomids in large lakes where multiple stressors make the interactions within the ecosystem more complicated. This study aims to illustrate the ecological characteristics of specific chironomid taxa related to a “microecosystem” which is contributed by the multiple environmental gradients within a large lake, and to provide empirical support for interpretation of palaeochironomid data.     

Multi-scale heterogeneity in a macrobenthic epifauna community

A quantitative study, based on monthly samples taken by divers with 0.1m² quadrats, was conducted on a benthic community settling coarse sediments in an area exposed to strong water currents.The richness of the community was high both in terms of biomass (270±107 g m^–2 in ash-free dry weight) and diversity (ten zoologicals groups for a total of 98 species). Three suspension feeding species were dominant: Ophiothrix fragilis, Urticina felina and Alcyonium digitatum accounted for more than 95% of the total biomass at all sampling periods.Spatial heterogeneity analysis confirmed the role of these three dominant species. Heterogeneity revealed at a scale of 0.1 m² by dendrograms (qualitative similarity index) or by Factor Correspondence Analysis (FCA) (on biomasses) was due to the strong dispersion of rare species.The influence of the observation scale was visualised by building Rank-Frequency Diagrams using progressively aggregated replicates. The distribution of relative biomasses and the rank of the dominant species always stabilized at scale of 0.4 or 0.5 m².The three dominant species were overdispersed at a scale of 0.1 m² compared with a Poisson distribution. Spatial competition among the three species was suggested by their dispersion in the plane of the FCA. Calculation of a multiple linear regression (at the scale of 0.8 m²) showed negative relationships among these dominant species.Temporal homogeneity was indicated (at a scale of 0.8 m²) by dendrograms of species similarities among samples and by FCA performed on total biomasses.     

The structure of diversity in an epiphytic chironomid community

The structure of diversity in a chironomid community inhabiting submerged macrophytes was analysed, including the relationship between predation/competition and chironomid diversity. Diversity as expressed by the Shannon functionH was found to be strongly associated with equitabilityJ but not with species richnessS in this community. Chironomid species richness was correlated with the abundance of diatoms. DiversityH and equitabilityJ were significantly correlated with chironomid density through the year. Invertebrate predators were generally rare and occurred sporadically throughout the year in this habitat, with only three species (Chaetogaster diaphanus, Rhyacophila dorsalis andZavrelimyia sp.) attaining >25% habitat occupancy. Neither these predators nor non-chironomid competitors encountered in the same habitat (Stylaria lacustris, Ophidonais serpentina, Hydroptila sp.,Simulium spp. andHydropsyche siltalai) appeared to affect diversity measures of the chironomid community under study, apart from a weak tendency of highSimulium density negatively affecting the total chironomid abundance. In conjunction with other analyses, this chironomid community seemed to be stochastically dynamic and was little influenced by biotic factors such as predation and competition.     

Swimming Behaviour of <Emphasis Type="Italic">Chironomus acerbiphilus</Emphasis> Larvae in Lake Katanuma

We conducted a seasonal survey of the swimming behaviour of Chironomus acerbiphilus larvae in volcanic Lake Katanuma from April 1998 to December 2001. Swimming C. acerbiphilus density was much higher than other chironomid species in lakes. All C. acerbiphilus larvae (1st through 4th instars) swam, but the earlier instars (especially the 1st) had the greatest densities and fluctuations. First instars were never found in the benthic population. This result indicates that the 1st-instar larvae are planktonic. Low water temperature (below about 10 °C) resulted in the seasonal disappearance of swimming chironomid larvae. Chemical factors – oxygen depletion or presence of hydrogen sulfide – also restricted the distribution of swimming and benthic larvae. Larvae were distributed only in the oxygen-rich part of the lake bottom and swam only in the oxygen-rich layer of the water column. The density of older swimming C. acerbiphilus (3rd and 4th instars) tended to increase with increasing benthic larval densities. The chemical stress of oxygen depletion or presence of hydrogen sulfide during holomixis within and after the stratification period leads to conspicuous swimming behaviour of benthic C. acerbiphilus larvae. Almost all C. acerbiphilus larvae died on this occasion.     

Temperature change as a driver of spatial patterns and long‐term trends in chironomid (Insecta: Diptera) diversity

Anthropogenic activities have led to a global decline in biodiversity, and monitoring studies indicate that both insect communities and wetland ecosystems are particularly affected. However, there is a need for long‐term data (over centennial or millennial timescales) to better understand natural community dynamics and the processes that govern the observed trends. Chironomids (Insecta: Diptera: Chironomidae) are often the most abundant insects in lake ecosystems, sensitive to environmental change, and, because their larval exoskeleton head capsules preserve well in lake sediments, they provide a unique record of insect community dynamics through time. Here, we provide the results of a metadata analysis of chironomid diversity across a range of spatial and temporal scales. First, we analyse spatial trends in chironomid diversity using Northern Hemispheric data sets overall consisting of 837 lakes. Our results indicate that in most of our data sets, summer temperature (T_jul) is strongly associated with spatial trends in modern‐day chironomid diversity. We observe a strong increase in chironomid alpha diversity with increasing T_jul in regions with present‐day T_jul between 2.5 and 14°C. In some areas with T_jul > 14°C, chironomid diversity stabilizes or declines. Second, we demonstrate that the direction and amplitude of change in alpha diversity in a compilation of subfossil chironomid records spanning the last glacial–interglacial transition (~15,000–11,000 years ago) are similar to those observed in our modern data. A compilation of Holocene records shows that during phases when the amplitude of temperature change was small, site‐specific factors had a greater influence on the chironomid fauna obscuring the chironomid diversity–temperature relationship. Our results imply expected overall chironomid diversity increases in colder regions such as the Arctic under sustained global warming, but with complex and not necessarily predictable responses for individual sites.