Valerie M. Behan-Pelletier

Oribatid mite biodiversity in agroecosystems : role for bioindication

The general ecology, biology, life history, and available sources for identification of oribatid mites (including Astigmata), the most numerically dominant arachnid group in the organic horizons of most soils, is reviewed. I use this information as the basis to evaluate data on their role for bioindication in agroecosystems, with the following conclusions: (a) oribatid mites with their low metabolic rates, slow development and low fecundity cannot respond rapidly to resource flushes: astigmatic mites with their contrasting life history traits can respond rapidly; (b) because many agroecosystems represent early successional stages, the oribatid species present are those found in heavily disturbed or early successional habitats, wherever these occur; (c) use of oribatid mites for bioindication must incorporate information on life history traits, and habitat and niche profiles for species.

Global decomposition experiment shows soil animal impacts on decomposition are climate-dependent

Climate and litter quality are primary drivers of terrestrial decomposition and, based on evidence from multisite experiments at regional and global scales, are universally factored into global decomposition models. In contrast, soil animals are considered key regulators of decomposition at local scales but their role at larger scales is unresolved. Soil animals are consequently excluded from global models of organic mineralization processes. Incomplete assessment of the roles of soil animals stems from the difficulties of manipulating invertebrate animals experimentally across large geographic gradients. This is compounded by deficient or inconsistent taxonomy. We report a global decomposition experiment to assess the importance of soil animals in C mineralization, in which a common grass litter substrate was exposed to natural decomposition in either control or reduced animal treatments across 30 sites distributed from 43°S to 68°N on six continents. Animals in the mesofaunal size range were recovered from the litter by Tullgren extraction and identified to common specifications, mostly at the ordinal level. The design of the trials enabled faunal contribution to be evaluated against abiotic parameters between sites. Soil animals increase decomposition rates in temperate and wet tropical climates, but have neutral effects where temperature or moisture constrain biological activity. Our findings highlight that faunal influences on decomposition are dependent on prevailing climatic conditions. We conclude that (1) inclusion of soil animals will improve the predictive capabilities of region- or biome-scale decomposition models, (2) soil animal influences on decomposition are important at the regional scale when attempting to predict global change scenarios, and (3) the statistical relationship between decomposition rates and climate, at the global scale, is robust against changes in soil faunal abundance and diversity.

The Influence of Soil Biodiversity on Hydrological Pathways and the Transfer of Materials between Terrestrial and Aquatic Ecosystems

The boundaries between terrestrial and aquatic ecosystems, known as critical transition zones (CTZ), are dynamic interfaces for fluxes of water, sediment, solutes, and gases. Moreover, they often support unique or diverse biotas. Soils, especially those of riparian zones, have not been recognized as CTZ even though they play a critical role in regulating the hydrologic pathways of infiltration and leaching, or runoff and erosion, which can cumulatively affect biogeochemical processes and human livelihoods at landscape scales. In this review, we show how the processes that regulate hydrologic fluxes across and through soil CTZ are influenced by the activities of soil biota. Our message is fourfold. First, there are a variety of ways in which soil biodiversity, in terms of richness and dominance, can influence hydrological pathways in soil and thus the transfer of materials from terrestrial to aquatic ecosystems. Second, the influence of soil organisms on these hydrological pathways is very much interlinked with other environmental, soil biophysical, and vegetation factors that operate at different spatial and temporal scales. Third, we propose that the influence of soil biodiversity on hydrological pathways is most apparent (or identifiable), relative to other factors, in situations that lead to the dominance of certain organisms, such as larger fauna. Fourth, soils are buffered against environmental change by biophysical properties that have developed over long periods of time. Therefore, the effects of changes in soil biodiversity on hydrological processes at the ecosystem scale might be delayed and become most apparent in the long term.

Changes in abundance and diversity of microarthropods associated with Fescue Prairie grazing regimes

Summary Livestock grazing influences plant community structure, soil quality and health, and is likely to also affect the populations and diversity of soil biota. In our study, we determined the abundance and family level diversity of soil mites under very heavy and light grazing regimes, and a very heavy grazing exclosure, and asked whether there were differences in abundance of mite taxa that reflected the severity of disturbance. The field experiment we sampled was established in 1949 on a Rough Fescue Prairie with Orthic Black Chernozemic (Udic Haploboroll) soils near Stavely Alberta Canada. Soil cores were taken from the light (L)(1.2 AUM (animal unit month) ha –1 ) and very heavy (VH) (4.8 AUM ha –1 ) grazing regimes and the grazing recovery exclosure (Ex) in the very heavy grazing site in June and October 1999. The results showed that the soil temperature, moisture and bulk density varied between the grazing regimes, soil depth and the sampling times. Collembola were not abundant at any of the sites compared with Acari. Among Acari, prostigmatid mites were significantly more abundant in VH site and all the grazing treatments at both depths and sampling times. Oribatida, and to a lesser extent Mesostigmata, were more closely associated with reduced and undisturbed habitats than the Prostigmata, and there was a positive relationship between increased grassland productivity and the abundance and diversity of soil microarthropods. Our results suggest that Acari are sensitive to soil disturbance.

Acari and Collembola biodiversity in Canadian agricultural soils

In Canadian agricultural soils, mites (Acari) are the most diverse and abundant arthropods. In comparison with other arachnids, mites are notable for their small size, diverse feeding habits, often complex life histories, and the range of habitats in which they live. Collembola are also abundant and diverse in soil and litter, they are in the same size range as the Acari, and for that reason the two groups are often combined in soil ecological studies as “microarthropods ”. This paper provides a descriptive overview of the state of our knowledge on the taxonomy of these arthropods. It reviews the literature on biology and ecology of microarthropods in Canadian agroecosystems, especially on implications of various agricultural practices for their diversity and population structure. It discusses the research challenges in taxonomy and ecology to address effective use of this biodiversity in Canadian agroecosystems. Key words: Acari, Collembola, microarthropods, taxonomy, ecology

DOES PLANT SPECIES CO‐OCCURRENCE INFLUENCE SOIL MITE DIVERSITY?

Few studies have considered whether plant taxa can be used as predictors of belowground faunal diversity in natural ecosystems. We examined soil mite (Acari) diversity beneath six grass species at the Konza Prairie Biological Station, Kansas, USA. We tested the hypotheses that soil mite species richness, abundance, and taxonomic diversity are greater (1) beneath grasses in dicultures (different species) compared to monocultures (same species), (2) beneath grasses of higher resource quality (lower C:N) compared to lower resource quality, and (3) beneath heterogeneous mixes of grasses (C3 and C4 grasses growing together) compared to homogeneous mixes (C3 or C4 grasses) using natural occurrences of plant species as treatments. This study is the first to examine the interaction between above- and belowground diversity in a natural setting with species-level resolution of a hyper-diverse taxon. Our results indicate that grasses in diculture supported a more species and phylogenetically rich soil mite fauna than was observed for monocultures and that this relationship was significant at depth but not in the upper soil horizon. We noted that mite species richness was not linearly related to grass species richness, which suggests that simple extrapolations of soil faunal diversity based on plant species inventories may underestimate the richness of associated soil mite communities. The distribution of mite size classes in dicultures was considerably different than those for monocultures. There was no difference in soil mite richness between grass combinations of differing resource quality, or resource heterogeneity.

Global diversity of oribatids (Oribatida: Acari: Arachnida)

Oribatid mites are primarily terrestrial. Only about 90 species (less than 1% of all known oribatid species) from 10 genera are truly aquatic, with reproduction and all stages of their life cycle living in freshwater. Adaptation to aquatic conditions evolved independently in different taxa. However, many terrestrial species can also be found in aquatic habitats, either as chance stragglers from the surrounding habitats, or from periodic or unpredictable floodings, where they can survive for long periods. In spite of their low species richness aquatic oribatids can be very abundant in different freshwater habitats as in lentic (pools, lakes, water-filled microhabitats) or flowing waters (springs, rivers, streams), mainly on submerged plants. The heavily sclerotized exoskeletons of several species enables subfossil or fossil preservation in lakes or bog sediments.

Arboreal oribatid mite diversity: Colonizing the canopy

Abstract Thirty-six species of Oribatida (2596 specimens), representing 29 genera and 21 families were recorded from replicated Malaise traps positioned in the canopy and on the forest floor of old-growth Sitka spruce (Picea sitchensis) on western Vancouver Island, Canada, and in an adjacent clear-cut. Traps were sampled bi-weekly throughout the growing season, and colonization was 100% in the canopy, 91% in the forest floor and 47% in the clear-cut. Nine of the species recovered were not recorded from this site using high gradient extractions of moss from canopy or forest floor. Thirty of these species were Brachypylina, with the families Eremaeidae, Peloppiidae and Ceratozetidae represented by three or more species. Colonizing specimens were predominantly adult, and represent sexual taxa: immatures comprised only 0.9–4.2% of specimens. Ceratoppia spp. , Eporibatula sp.1, Dorycranosus sp.1, Sphaerozetes sp.1 and Oribatella sp.1 had a frequency >50% in the forest floor traps, and Eporibatula sp.1, Sphaerozetes sp.1 and Dendrozetes sp.1 had a frequency >50% in canopy traps. Phoresy as a source of the oribatid fauna in the Malaise traps is unlikely as, of the species represented, only Paraleius sp.1 is modified for this mode of dispersal. The number of species recorded from the traps, and the frequency, relative abundance, and seasonality of many of them, support the hypothesis that active dispersal by random movement is an important mode of colonization of canopy habitats.

Mite (Acari) colonization of vegetated mine tailings near Sudbury, Ontario, Canada

INCO Ltd. near Sudbury, Ontario is rehabilitating nickel- and copper-mine tailings using vegetating techniques that have resulted in habitats of varying age and complexity. Mite (Acari) communities and soil quality characteristics were used to evaluate soil ecosystem development on four tailings sites, 0, 8, 20 and 40 years post rehabilitation in comparison with that on four control sites. Abundance, species richness, diversity (H′) and community structure of soil mites were sensitive indicators of tailings rehabilitation and soil formation. Mite density on older and botanically diverse tailings sites was comparable to that on control sites; however, species richness of oribatids and mesostigmatics was lower than on control sites. Mite species richness and diversity on tailings were lower at less botanically diverse sites regardless of age. Similarity of tailings-mite communities to control-site communities generally increased with age; however, similarities were all less than 60% (Sorensons quantitative index, CN). Mite assemblages on tailings were dominated by a few colonizing species, whereas control sites had a diverse assemblage of species. Soil pH and organic matter (SOM) of rehabilitated tailings improved with age and degree of botanical complexity. Mite density and diversity was positively related to SOM particularily for the Oribatida. SOM and mites were mainly restricted to the 0–5-cm horizon.

Vehicle tracks on high arctic tundra: their effects on the soil, vegetation, and soil arthropods

Examination of the effects of vehicle and pedestrian tracks of known age (13 or more years) and intensity of use (single to multiple passages) on vegetation, soil chemistry, soil arthropods, soil thaw characteristics, and small-scale hydrological changes showed clear and inter-related patterns. In general, all tracks, regardless of age, showed small increases in the depth of thaw beneath them (c. 2.8 cm). Tracks were generally depleted of carbon and to a lesser, but significant extent, of potassium and phosphorus. Slight increases in NO 3 , NH 4 , and calcium were noted. Magnesium and total nitrogen seemed unaffected. On all tracks which had suffered multiple passages vegetation cover was significantly reduced. In a few sites where single passages were recorded, cover increased through proliferation of the sedge, Kobresia myosuroides. Abundance of soil arthropods was significantly reduced on tracks, but the diversity was not. In most sites, soil moisture and over-ground water flow did not seem affected. Only in sedge meadows where compression from a single passage resulted in channelling of water, and where multiple passages removed vegetation and initiated gulley erosion, were effects serious.