Changes In Invertebrate Communities Research Articles

Context-dependent responses of terrestrial invertebrates to anthropogenic nitrogen enrichment: A meta-analysis.

Anthropogenic increases in nitrogen (N) concentrations in the environment are affecting plant diversity and ecosystems worldwide, but relatively little is known about N impacts on terrestrial invertebrate communities. Here, we performed an exploratory meta-analysis of 4365 observations from 126 publications reporting on the richness (number of taxa) or abundance (number of individuals per taxon) of terrestrial arthropods or nematodes in relation to N addition. We found that the response of invertebrates to N enrichment is highly dependent on both species' traits and local climate. The abundance of arthropods with incomplete metamorphosis, including agricultural pest species, increased in response to N enrichment. In contrast, arthropods exhibiting complete or no metamorphosis, including pollinators and detritivores, showed a declining abundance trend with increasing N enrichment, particularly in warmer climates. These contrasting and context-dependent responses may explain why we detected no overall response of arthropod richness. For nematodes, the abundance response to N enrichment was dependent on mean annual precipitation and varied between feeding guilds. We found a declining trend in abundance with N enrichment in dry areas and an increasing trend in wet areas, with slopes differing between feeding guilds. For example, at mean levels of precipitation, bacterivore abundance showed a positive trend in response to N addition while fungivore abundance declined. We further observed an overall decline in nematode richness with N addition. These N-induced changes in invertebrate communities could have negative consequences for various ecosystem functions and services, including those contributing to human food production.

Potential propagation of agricultural pesticide exposure and effects to upstream sections in a biosphere reserve.

In the last decades, several studies have shown that pesticides frequently occur above water quality thresholds in small streams draining arable land and are associated with changes in invertebrate communities. However, we know little about the potential propagation of pesticide effects from agricultural stream sections to least impacted stream sections that can serve as refuge areas. We sampled invertebrates and pesticides along six small streams in south-west Germany. In each stream, the sampling was conducted at an agricultural site, at an upstream forest site (later considered as "refuge"), and at a transition zone between forest and agriculture (later considered as "edge"). Pesticide exposure was higher and the proportion of pesticide-sensitive species (SPEARpesticides) was lower in agricultural sites compared to edge and refuge sites. Notwithstanding, at some edge and refuge sites, which were considered as being least impacted, we estimated unexpected pesticide toxicity (sum toxic units) exceeding thresholds at which field studies suggested adverse effects on freshwater invertebrates. We conclude that organisms in forest sections within a few kilometres upstream of agricultural areas can be exposed to ecologically relevant pesticide levels. In addition, although not statistically significant, the abundance of pesticide-sensitive taxa was slightly lower in edge compared to refuge sites, indicating a potential influence of adjacent agriculture. Future studies should further investigate the influence of spatial relationships, such as the distance between refuge and agriculture, for the propagation of pesticide effects and focus on the underlying mechanisms.

Vegetation shapes aboveground invertebrate communities more than soil properties and pollution: a preliminary investigation on a metal-contaminated site

Pollution with trace metals (TM) has been shown to affect diversity and/or composition of plant and animal communities. While ecotoxicological studies have estimated the impact of TM contamination on plant and animal communities separately, ecological studies have widely demonstrated that vegetation is an important factor shaping invertebrate communities. It is supposed that changes in invertebrate communities under TM contamination would be explained by both direct impact of TM on invertebrate organisms and indirect effects due to changes in plant communities. However, no study has clearly investigated which would more importantly shape invertebrate communities under TM contamination. Here, we hypothesized that invertebrate communities under TM contamination would be affected more importantly by plant communities which constitute their habitat and/or food than by direct impact of TM. Our analysis showed that diversity and community identity of flying invertebrates were explained only by plant diversity which was not affected by TM contamination. Diversity of ground-dwelling (GD) invertebrates in spring was explained more importantly by plant diversity (27% of variation) than by soil characteristics including TM concentrations (8%), whereas their community identity was evenly explained by plant diversity and soil characteristics (2-7%). In autumn, diversity of GD invertebrates was only explained by plant diversity (12%), and their identity was only explained by soil characteristics (8%). We conclude that vegetation shapes invertebrate communities more importantly than direct effects of TM on invertebrates. Vegetation should be taken into account when addressing the impacts of environmental contamination on animal communities.

Effect of entomopathogenic fungus Metarhizium robertsii on non-target organisms, water bugs (Heteroptera: Corixidae, Naucoridae, Notonectidae)

The influence of the fungus Metarhizium robertsii Bischoff, Rehner and Humber on the mortality of four water bug species, Cymatia coleoptrata (Fabricius), Sigara assimilis (Fieber), Ilyocoris cimicoides cimicoides (Linnaeus), and Notonecta reuteri Hungerford, and bloodsucking mosquito Anopheles messeae Falleroni, was investigated under various concentrations of conidia and different treatment types. We found that the mortality of adults of the water bug species was similar or higher than that of A. messeae, with C. coleoptrata and S. assimilis being more susceptible to M. robertsii than N. reuteri, I. c. cimicoides, and the mosquito A. messeae. Treatment with dry conidia at concentrations of 5 × 104 and 5 × 105 conidia/ml caused higher mortality of the water bug species than did treatment at the same concentrations with conidia in an aqueous suspension. In contrast, higher concentrations (5 × 106 conidia/ml) led to higher mortality after treatment with the aqueous suspension, relative to treatment with dry conidia. Our studies showed that water bugs exhibited the classical development of a mycosis with hemocoel colonization, mummification, and conidia formation on cadavers directly on the surface of the water. Possible changes in invertebrate communities in aquatic ecosystems after treatment with Metarhizium are discussed.

Species at Risk (SPEAR) index indicates effects of insecticides on stream invertebrate communities in soy production regions of the Argentine Pampas.

We investigated relationships among insecticides and aquatic invertebrate communities in 22 streams of two soy production regions of the Argentine Pampas over three growing seasons. Chlorpyrifos, endosulfan, cypermethrin, and lambda-cyhalothrin were the insecticides most frequently detected in stream sediments. The Species at Risk (SPEAR) pesticide bioassessment index (SPEARpesticides) was adapted and applied to evaluate relationships between sediment insecticide toxic units (TUs) and invertebrate communities associated with both benthic habitats and emergent vegetation habitats. SPEARpesticides was the only response metric that was significantly correlated with total insecticide TU values for all three averaged data sets, consistently showing a trend of decreasing values with increasing TU values (r2=0.35 to 0.42, p-value=0.001 to 0.03). Although pyrethroids were the insecticides that contributed the highest TU values, toxicity calculated based on all insecticides was better at predicting changes in invertebrate communities than toxicity of pyrethroids alone. Crustaceans, particularly the amphipod Hyalella spp., which are relatively sensitive to pesticides, played a large role in the performance of SPEARpesticides, and the relative abundance of all crustaceans also showed a significant decreasing trend with increasing insecticide TUs for two of three data sets (r2=0.30 to 0.57, p-value=0.003 to 0.04) examined. For all data sets, total insecticide TU was the most important variable in explaining variance in the SPEARpesticides index. The present study was the first application of the SPEAR index in South America, and the first one to use it to evaluate effects of pesticides on invertebrate communities associated with aquatic vegetation. Although the SPEAR index was developed in Europe, it performed well in the Argentine Pampas with only minor modifications, and would likely improve in performance as more data are obtained on traits of South American taxa, such as pesticide sensitivity and generation time.

Habitat disruption by a coastal invader: local community change in Atlantic Canada sedimentary habitats

While digging and foraging, the non-indigenous green crab (Carcinus maenas) creates a landscape of distinctive pits or depressions in the sediment. Despite their visibility and widespread occurrence in Atlantic Canada and elsewhere, the community influence and persistence of this disturbance remain undocumented. This study addressed this gap in our knowledge using two approaches. First, in both sandy and muddy habitats, we monitored fresh feeding pits (disturbed sediments) for up to 9–11 days after their formation, recording their sediment properties and diversity and density of invertebrate fauna, and comparing these characteristics to those of ambient (undisturbed) sediments in similar habitat. Second, we quantified local-scale invertebrate diversity and density in feeding pits and ambient sediments in muddy habitat only, at three other sites within a Marine Protected Area (MPA). Grain size did not differ between disturbed and ambient sediments and did not change over time within habitats. We also found no significant differences in invertebrate diversity and density between disturbed and undisturbed sandy sediments. In contrast, the invertebrate fauna differed significantly between disturbed and ambient muddy sediments, particularly during the first 4 days after disturbance. Feeding pits in muddy sediments also took twice longer to fill up than pits in sandy sediments. These results were consistent with the comparison of disturbed and undisturbed muddy sediments in the MPA: at least at the local scale, the foraging by this invader significantly altered community structure. Ambient sediments had a higher number of species and nearly twice as many invertebrates compared to disturbed sediments. Overall, our results suggest that visual evidence of green crab feeding pits in muddy sediments can be used as a fairly reliable predictor of local-scale changes in invertebrate communities. The persistence of these local-scale changes depends on the type of habitat in which the disturbance takes place.

Estimating the effects of land use at different scales on high ecological status in Irish rivers

High ecological status at river sites is an indicator of minimal disturbance from anthropogenic activities and the presence of ecologically important species and communities. However, a lack of clarity on what factors cause sites to lose high ecological status is limiting the ability to maintain the quality of these sites. Examination of ecological status records at 508 high status river sites throughout the Republic of Ireland revealed that 337 had fallen below high status at some point between 2001 and 2012 due to changes in invertebrate communities. A geographical information system was used to characterise land use and environmental variables in the catchment, riparian and reach areas upstream of the sites. The relationships between these variables at the three spatial scales and whether or not river sites had maintained high ecological status were then estimated by multiple logistic regression and propensity modelling. The results indicated that grassland at either catchment or riparian scales had a greater negative impact on high ecological status than at the reach scale. This effect appeared to be strongest for upland, steeply sloping rivers that are subject to high rainfall, possibly due to the presence of sensitive biota and/or a greater potential for erosion. These results highlighted the need for better management of grassland upstream of the high status sites, with a focus on river alterations and critical source areas of nutrients, sediments and pesticides that are hydrologically connected to the river. Sustainable management practices and land use planning in those areas will need to be considered carefully if the aim of maintaining high ecological status at river sites is to be achieved.

Re-engineering buried urban streams: Daylighting results in rapid changes in stream invertebrate communities

Stream daylighting is a radical form of restoration which aims to improve morphological, chemical and ecological condition through the re-creation of an open channel from a buried or piped channel. Whilst empirical assessments of its efficacy are lacking, it is hypothesised that the substantial changes in habitat, channel form and energy supply arising from daylighting would lead to a significant changes in stream invertebrate communities, particularly where source populations of macroinvertebrates exist upstream. In this first published study of the ecological outcomes arising from a daylighting project, changes in the invertebrate community were assessed in two reaches of an urban stream catchment in Auckland, New Zealand's largest city, which were daylighted in early 2013. The two reaches allowed a paired assessment, where one of the reaches had a large area of intact native forest in its headwaters. Stream macroinvertebrates were sampled monthly pre- and post-daylighting to assess changes in stream macroinvertebrate communities.Community composition significantly changed pre- to post-daylighting (PERMANOVA Pseudo-F=2.0978, P=0.0018), where communities in different reaches changed by 58% and 71%, respectively. Taxonomic richness did not change with daylighting; however taxa replacements were apparent with 44 new taxa being collected in daylighted reaches and 11 taxa disappearing. Daylighting resulted in marked changes in energy resources and improved habitat in the short-term which altered invertebrate communities from biofilm feeding collector-browser communities to algal grazer communities. Although daylighting did not fully restore these streams from the effects of urbanisation, it is one practical option for the management of urban streams. Further, the presence of a local source population was an important determinant of stream community structure. Where source populations existed upstream community responses to daylighting were greater, including increased abundances of sensitive taxa.

Predicting the effect of invertebrate regime shifts on wading birds: Insights from Poole Harbour, UK

Regime shifts in benthic invertebrates within coastal ecosystems threaten the survival of wading birds (Charadrii). Predicting how invertebrate regime shifts will affect wading birds allows conservation management and mitigation measures to be implemented, including protection of terrestrial feeding areas. An individual-based model was used to investigate the impact of regime shifts on wading birds through their prey (marine worms and bivalves) in the estuarine system Poole Harbour, (UK). The model predicted the number of curlew (Numenius arquata), oystercatcher (Haematopus ostralegus), black-tailed godwit (Limosa limosa), redshank (Tringa totanus) and dunlin (Calidris alpina) supported in the Harbour during the non-breeding season (autumn and winter months). The most dramatic declines in bird numbers were for regime shifts that reduced the abundance of the largest invertebrates, particularly marine worms. The least adaptable bird species (those with the most restrictive diets) were unable to compensate by consuming other prey. Generally, as birds adapt to changes by switching to alternative prey species and size classes, changes in invertebrate size and species distribution do not necessarily affect the number of birds that the Harbour can support. Our predictions reveal a weakness in using birds as indicators of site health and invertebrate regime shifts. Differences in bird populations would not necessarily be detected by standard survey methods until extreme changes in invertebrate communities had occurred, potentially beyond the point at which these changes could be reversed. Therefore, population size of wading birds should not be used in isolation when assessing the conservation status of coastal sites.

Dynamics of Invertebrate Diversity in a Tropical Stream

Regional studies of biotic communities are important for characterising their normal spatial and temporal variation, but there are few such studies of tropical streams. This paper describes changes in invertebrate communities in Yuccabine Creek, a seasonal upland rainforest stream in tropical Australia, over three-year and decadal periods. Invertebrate abundance, richness and evenness were temporally stable, except after major drying or wet-season flows, from which they recovered quickly; however, three wet seasons contrasted in abundance patterns. Species’ responses to flood or drought varied depending on life-histories and habitat dynamics. Communities showed contrasts between wet, early-dry and late-dry seasons, with different characteristic species. Current velocity, leaf litter and substratum particle size were the main environmental correlates with species abundances and multivariate scores. Between-decade contrasts were due to antecedent rainfall and loss of canopy cover. Trophic composition varied seasonally, driven by abundances of predators and detritivores. Yuccabine Creek differs from comparable temperate streams in its high diversity of invertebrates, continual recruitment and spring-dominated continual leaf fall; and from some other tropical streams in its seasonal flow regime. Interpretation of invertebrate metrics in these streams needs to account for historical, antecedent and current conditions, but biannual samples would adequately characterise the fauna.

Evaluating the success of managed realignment for the restoration of salt marshes: Lessons from invertebrate communities

Studying successional processes and related factors in salt marshes encompasses both fundamental (community structuration) and applied (biodiversity conservation and restoration) issues. Current managed realignment projects and sites where, in the past, large storm events led to breaches in embankments create unique experimental conditions for such challenges by re-instating tidal inundation and salt-marsh development. We conducted a pair-matched approach using natural and recreated (either accidentally or managed) salt marshes and studied changes in invertebrate communities over time during a field experiment (Essex, UK). Trophic guild was assigned to all invertebrates, and detailed analyzes conducted on most abundant (amphipods, Orchestia sp., 9666 individuals) and diversified (spiders, 43 species) groups. A total of 27,180 invertebrates (almost all arthropods: 99% of specimens) was collected in 2005. The conservation equivalency was achieved quickly (which was shown here with spider assemblages), but that did not translate into a complete functional equivalency. Indeed neither the structure of trophic guilds, nor the potential role of marine enrichment and fish nursery, estimated through the population size of amphipods, was achieved by managed realignments. We finally argue that the study of invertebrates brings information complementary to those brought by plants, and underline that functional and conservation equivalency have to be assessed separately.

Effects of Didymosphenia geminata removal on river macroinvertebrate communities

Periphyton blooms dominated by Didymosphenia geminata have been reported from hundreds of rivers. D. geminata blooms consist of thick mats that cover kilometers of riverbed. Benthic habitat conditions are altered when large areas of sediment and native periphyton are replaced by D. geminata mats and these habitat changes may lead to changes in the composition and abundance of benthic invertebrates. Mensurative studies have provided circumstantial evidence of changes in invertebrate communities in response to D. geminata blooms. However, those studies may have confounded the effects of D. geminata and other environmental variables. To identify direct effects of D. geminata on invertebrate communities, we conducted a paired before–after, control-impact (BACIP) experiment in three D. geminata-infested rivers. The experimental impact was the removal of D. geminata mats from 35–50 m2 areas of riverbed. We tested for effects of D. geminata removal on macroinvertebrate community metrics, including total density, taxon richness, and the prevalence of Ephemeroptera, Plecoptera, and Trichoptera (EPT) and trophic groups. The BACIP analysis indicated that D. geminata removal caused a decrease in total density at two rivers, a decrease in the density of dipterans and an increase in % EPT invertebrates at one river, and an increase in % algivorous invertebrates at another river. A multivariate analysis indicated that there was more variation in invertebrate community structure among rivers than between treatments within rivers. The limited effects of D. geminata removal on invertebrate communities were probably related to the composition of colonist pools and the relatively small cleared areas; cleared areas were surrounded by large areas of D. geminata-covered habitat and the colonist pools were dominated by taxa that inhabit D. geminata mats.

Functional traits of soil invertebrates as indicators for exposure to soil disturbance

We tested a trait-based approach to link a soil disturbance to changes in invertebrate communities. Soils and macro-invertebrates were sampled in sandy soils contaminated by long-term wastewater irrigation, adding notably organic matter and trace metals (TM). We hypothesized that functional traits of invertebrates depict ways of exposure and that exposure routes relate to specific TM pools. Geophages and soft-body invertebrates were chosen to inform on exposure by ingestion or contact, respectively. Trait-based indices depicted more accurately effects of pollution than community density and diversity did. Exposure by ingestion had more deleterious effects than by contact. Both types of exposed invertebrates were influenced by TM, but geophages mainly responded to changes in soil organic matter contents. The trait-based approach requires to be applied in various conditions to uncorrelate specific TM impacts from those of other environmental factors.

Interactive effects of chemical and biological controls on food-web composition in saline prairie lakes

Salinity is restricting habitatability for many biota in prairie lakes due to limited physiological abilities to cope with increasing osmotic stress. Yet, it remains unclear how salinity effects vary among major taxonomic groups and what role other environmental parameters play in shaping food-web composition. To answer these questions, we sampled fish, zooplankton and littoral macroinvertebrates in 20 prairie lakes (Saskatchewan, Canada) characterized by large gradients in water chemistry and lake morphometry. We showed that salinity thresholds differed among major taxonomic groups, as most fishes were absent above salinities of 2 g L-1, while littoral macroinvertebrates were ubiquitous. Zooplankton occurred over the whole salinity range, but changed taxonomic composition as salinity increased. Subsequently, the complexity of fish community (diversity) was associated with large changes in invertebrate communities. The directional changes in invertebrate communities to smaller taxa indicated that complex fish assemblages resulted in higher predation pressure. Most likely, as the complexity of fish community decreased, controls of invertebrate assemblages shifted from predation to competition and ultimately to productivity in hypersaline lakes. Surprisingly, invertebrate predators did not thrive in the absence of fishes in these systems. Furthermore, the here identified salinity threshold for fishes was too low to be a result of osmotic stress. Hence, winterkill was likely an important factor eliminating fishes in low salinity lakes that had high productivity and shallow water depth. Ultimately, while salinity was crucial, intricate combinations of chemical and biological mechanisms also played a major role in controlling the assemblages of major taxonomic groups in prairie lakes.

Coqui frog invasions change invertebrate communities in Hawaii

The Puerto Rican coqui frog (Eleutherodactylus coqui) invaded Hawaii in the late 1980s. Because the coqui reaches high densities and consumes large quantities of invertebrates, it was hypothesized to change invertebrate communities where it invades. Previous research found that coquis can change invertebrate communities, but these studies used highly manipulative, small-scale experiments. The objective of this research was to determine whether coquis create community-level changes in invertebrate communities at the landscape scale. We collected leaf litter, flying, and foliage invertebrates on both sides of 15 coqui invasion fronts across the island of Hawaii. Multivariate analyses show that coquis are associated with changes in leaf-litter communities, primarily reductions in Acari, but are not associated with overall changes in flying or foliage communities. Across sites, coquis reduced the total number of leaf-litter invertebrates by 27%, specifically by reducing Acari by 36%. Across sites, coquis increased flying Diptera by 19%. Changes were greater where coqui densities were higher. We suggest that coquis changed leaf-litter communities primarily through direct predation, but that they increased Diptera through the addition of frog carcasses and excrement. Results support previous studies conducted in more controlled settings, but add to our understanding of the invasion by showing that coqui effects on invertebrate communities are measurable at the landscape scale.

Downstream changes in spring-fed stream invertebrate communities: the effect of increased temperature range?

Reduced thermal amplitude has been highlighted as a limiting factor for aquatic invertebrate diversity in springs. Moving downstream water temperature range increases and invertebrate richness is expected to change accordingly. In the present study temperature patterns were investigated in seven spring-fed streams, between April 2001 and November 2002, and compared to five run-off-fed streams to assess the degree of crenic temperature constancy. Temperature and physico-chemical characteristics of the water, and food resource levels were measured, and the invertebrate fauna collected at 4 distances (0, 100, 500 m and 1 km) from seven springs in the North and South Islands of New Zealand. Temperature variability was greater for run-off-fed streams than for springs, and increased in the spring-fed streams with distance from the source. Periphyton and physico-chemical characteristics of the water did not change markedly over the 1 km studied, with the exception of water velocity and organic matter biomass, which increased and decreased, respectively. The rate of increase in temperature amplitude differed greatly for the studied springs, probably being affected by flow, altitude, and the number and type of tributaries (i.e., spring- or run-off-fed) joining the spring-fed stream channel. Longitudinal changes in the number and evenness of invertebrate taxa were positively correlated to thermal amplitude (rs = 0.8). Moving downstream, invertebrate communities progressively incorporated taxa with higher mobility and taxa more common in nearby run-off-fed streams. Chironomids and non-insect taxa were denser at the sources. Chironomid larvae also numerically dominated communities 100 and 500 m downstream from the sources, together with Pycnocentria spp. and Zelolessica spp., while taxa such as Hydora sp. and Hydraenidae beetles, the mayflies Deleatidium spp. and Coloburiscus humeralis, and the Trichoptera Pycnocentrodes spp., all had greater abundances 1 km from the sources. In conclusion, water temperature range was highly correlated with number of taxa, although other factors, such as substratum composition, stability and invertebrate drift, may also play an important role in the determination of longitudinal changes in invertebrate community composition and structure along spring-fed streams.

The structure of soil mesopopulation bearing on climatic changes and anthropogenic impact on geosystems at the taiga-steppe contact in the Baikal region

The paper gives landscape-ecological analysis of soil population in steppe and forest geosystems of the Baikal region and specific Baikalian climate. The changes in invertebrate communities under anthropogenic impact against the background of increased air and soil temperatures have been characterized.

Relationships between soil fauna communities and humus forms: Response to forest dynamics and solar radiation

This study investigated the responses of soil animal communities, soil functioning and humus forms to forest dynamics and solar radiation. We examined changes in invertebrate communities and soil features in two subalpine spruce forests (Eastern Italian Alps, Trento) growing on a calcareous bedrock, with different sun exposures (north and south), each forming a chronosequence of three developmental phases: clearing, regeneration stand (25-year-old trees) and mature stand (170-year-old trees). Our results indicate that the two forest sites differed in solar energy input, soil chemical properties and the relationships between forest dynamics and animal communities. In the north-facing site, soil fauna communities were very similar in the three forest developmental phases. Conversely, in the south-facing site, the composition of invertebrate communities and the diversity of zoological groups varied greatly among developmental phases. The highest abundance of total invertebrates, and mites in particular, occurred in the south-facing mature stands while the south-facing regeneration stand was characterised by higher densities of Collembola, Chilopoda, Symphyla, Protura and Aranea. The structure of communities in clearings was the same as in regeneration stands but with lower invertebrate abundance. Humus forms and soil features changed with developmental phases in both the south- and north-facing sites, although variations were more pronounced in the southern exposure. Mature stands were characterised by high levels of soil organic carbon and nitrogen, C/N values and low pH, the clearings and regeneration stands being characterised by a greater release of mineral nitrogen. The diversity of zoological groups (Shannon–Wiener index) was linearly correlated to soil pH, Humus Index, the amount of organic carbon and the species richness of herbaceous plants. Our results about the composition and the diversity of invertebrate communities are consistent with the observations of other authors studying south-exposed forests growing on different bedrock types, indicating that such relationships are widespread. The higher densities of invertebrates in the south-facing site may be attributed to higher solar radiation, and the positive correlation observed between total soil fauna abundance and solar energy supports the “more individuals” hypothesis that assumes a positive relationship between the number of individuals and energy availability. Possible ways by which forest dynamics control soil invertebrate communities are discussed.

Changes in humus forms and soil animal communities in two developmental phases of Norway spruce on an acidic substrate

This study focuses on the relationships between forest dynamics and changes in humus forms and animal communities in three areas of spruce forest at two developmental phases: two areas with 24-year-old trees (mean age) and one area with 136-year-old trees located in the Italian Alps. Mesofauna and macroarthropods were identified at the level of zoological group, order, super-family or family, when possible. They were then classified into morphotypes on the basis of features observable under a magnifying glass. The humus form varied from amphimull to dysmull in the 24-year-old spruce stands (regeneration), and was a dysmoder under the 136-year-old trees (adult). Results of correspondence analysis and ANOVA indicated that soil pH was higher in regeneration stands, where animal communities were mainly characterized by high densities of collembola, centipedes, and macrofauna. The diversity of zoological (and functional) groups was also higher in regeneration stands. The two regeneration stands differed only in the abundance of gamasids and Protura. Soil carbon and nitrogen contents increased in the mature spruce stand, as did the C/N ratio. The abundance of animals increased due to higher densities of mites, particularly oribatids while collembola, macrofauna, zoological diversity and the rate of disappearance of the litter decreased. The comparison of morphotype assemblages by hierarchical agglomerative clustering indicated that the shift between 24-year-old and 136-year-old trees, observed for humus forms, also occurred for animal communities. Differences in soil characteristics and animal communities between the two phases of the forest cycle corresponded to those generally observed between mull and moder, except for collembola which are generally more abundant in the thick organic layers of moder soils. Our findings confirm the change in humus form previously noted by other authors in the French Alps, but are inconsistent with data on humus forms and collembola and oribatid mite populations from Northern Europe. We conclude that changes in invertebrate communities, particularly arthropods, with the growth phases of spruce may be attributed to (1) soil impoverishment, due to the increased rate of nutrients and water uptake by growing trees; and (2) increase in recalcitrant litter input, mostly transformed by oribatid mites. Our data indicated that animal communities and humus forms could be a reliable means of assessing functional characteristics of the ecosystem corresponding to each growth phase of spruce.

Effects of riparian grazing and channelisation on streams in Southland, New Zealand. 2. Benthic invertebrates

Abstract A survey of benthic invertebrate faunas in riparian‐protected, riparian‐grazed, and channelised reaches of five Southland streams with catchment sizes of 3–37 km2 was carried out. It was part of a wider investigation to assess the effects of riparian grazing and channelisation on stream habitat and biota. In small streams (catchment areas 3–10 km2 ; widths 1–4 m), channelisation or intensive grazing by cattle greatly reduced shading by riparian vegetation, resulting in substantial increases in daily maximum temperatures during summer. Channelisation also caused gross changes in channel morphology and intensive grazing of a reach with moist streamside soils was associated with increased bed sedimentation and bank damage. Marked changes in invertebrate communities were associated wilh these habitat modifications. In general, taxa favoured by cool water and low periphyton abundance (e.g., Plecoptera, Paraleptamphopus caeruleus, Deleatidium sp., and Helicopsyche albescens) decreased in density, whereas densities of taxa favoured by an abundance of periphyton (e.g., Chironomidae and Oxyethira albiceps) increased. In contrast, differences in physical habitat and invertebrate communities were minor between paired grazed and riparian‐protected reaches of the larger streams (catchment areas 10–33 km2 ; median widths 6–16 m) where grazing had little or no effect on stream shading. These results indicate that in small streams, with median natural channel widths below c. 6 m, the effects on benthic invertebrates decrease in the following order, channelisation > intensive grazing by cattle > extensive grazing by cattle and/or sheep. Shade provided by riparian vegetation appears to play a vital role in maintaining cool, headwater, stream habitats for benthic invertebrate communities in these streams.