Neville N. Winchester

Arthropod diversity in a tropical forest

Assessing Creepy Crawlies Arthropods are the most diverse group of terrestrial animal species, yet estimates of the total number of arthropod species have varied widely, especially for tropical forests. Basset et al. (p. 1481, see the cover) now provide more reliable estimates of total arthropod species richness in a tropical rainforest in Panama. Intensive sampling of a half hectare of forest yielded just over 6000 arthropod species. Scaling up this result to the whole forest suggests that the total species diversity lies between 17,000 and 40,000 species. Total arthropod species richness in a tropical rainforest can be best predicted by plant diversity. Most eukaryotic organisms are arthropods. Yet, their diversity in rich terrestrial ecosystems is still unknown. Here we produce tangible estimates of the total species richness of arthropods in a tropical rainforest. Using a comprehensive range of structured protocols, we sampled the phylogenetic breadth of arthropod taxa from the soil to the forest canopy in the San Lorenzo forest, Panama. We collected 6144 arthropod species from 0.48 hectare and extrapolated total species richness to larger areas on the basis of competing models. The whole 6000-hectare forest reserve most likely sustains 25,000 arthropod species. Notably, just 1 hectare of rainforest yields >60% of the arthropod biodiversity held in the wider landscape. Models based on plant diversity fitted the accumulated species richness of both herbivore and nonherbivore taxa exceptionally well. This lends credence to global estimates of arthropod biodiversity developed from plant models.

Spatial and environmental factors contributing to patterns in arboreal and terrestrial oribatid mite diversity across spatial scales.

Understanding the conditions under which species traits, species–environment relationships, and the spatial structure of the landscape interact to shape local communities requires quantifying the relative contributions of space and the environment on community composition. Using analogous sampling of arboreal and terrestrial oribatid mite communities across a large spatial scale in a temperate rainforest, we quantified the variation in oribatid mite community structure relating to environmental and spatial factors, and tested whether terrestrial and arboreal communities demonstrated a difference in their patterns of community composition based on the assumption of differences in dispersal potential. The expectation that terrestrial oribatid mite communities are spatially structured while arboreal communities are environmentally structured was supported by our analyses at the level of variation in beta diversity, but not by assessing beta diversity itself. We found that terrestrial oribatid mite communities with active, cursorial dispersal demonstrate spatial constraint consistent with reduced long-distance dispersal opportunities and high environmental dissimilarity among sites. Arboreal communities, which potentially disperse long distances via passive aerial vectors, show a spatial signature associated with patterns in beta diversity and a correlation with environmental dissimilarities among sites. In the arboreal community, moisture content of the substrate, total tree height, and average sampled branch height were significant factors explaining beta diversity patterns. For ground-dwelling species, predator abundance and soil type were important local determinants of community variability. Both communities showed clear spatial structuring, suggesting that dispersal limitation continues to influence community composition across multiple forest watershed locations. Our results provide evidence of dispersal-maintained diversity patterns in response to local environmental factors in arboreal and terrestrial communities. The relative importance of stochastic dispersal assembly may be dependent on strong deterministic effects associated with micro-site and macro-site environmental variation, particularly across large spatial scales.

Environmental and spatial influences upon species composition of a termite assemblage across neotropical forest islands

Patterns of species composition in a neotropical termite assemblage were studied in relation to early effects of forest fragmentation as well as other sources of environmental and spatial heterogeneity. Termite diversity surveys were carried out at three mainland forest sites, and 10 islands of varying size, in an area of lowland tropical forest that had been flooded 4 y earlier, during the creation of the Petit Saut hydroelectric project in French Guiana. The ‘ghost forest’ of dead emergent trees in the flooded zone was also studied for its influence on island termite assemblages. Results suggested that the effects of forest fragmentation upon the total assemblage, and upon soil-feeders in particular, were subordinate to the influence of forest understorey palm density, and the closely associated gradients of soil humus depth and soil pH. Moreover, gradients for these three variables were uncorrelated with forest fragmentation and probably reflected spatial environmental heterogeneity pre-dating inundation events. Nevertheless, factors associated with forest fragmentation appeared to have had a significant effect on changes in termite species composition across the study site, primarily in structuring the wood- and leaf-litter-feeder assemblage. Effects upon the latter were not apparently a result of influx of species from the ghost forest. Purely spatial variation also influenced β-diversity changes in species composition across the site. In conclusion, the effects of forest fragmentation upon termites appear to have been relatively mild compared with other faunal groups, 4 y after flooding. Nevertheless, we predict that the effects of fragmentation on termite assemblages will ultimately be negative. This study also points to the importance of Amazonian understorey palms in structuring a tropical forest termite assemblage.

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.

Arthropod Distribution in a Tropical Rainforest: Tackling a Four Dimensional Puzzle

Quantifying the spatio-temporal distribution of arthropods in tropical rainforests represents a first step towards scrutinizing the global distribution of biodiversity on Earth. To date most studies have focused on narrow taxonomic groups or lack a design that allows partitioning of the components of diversity. Here, we consider an exceptionally large dataset (113,952 individuals representing 5,858 species), obtained from the San Lorenzo forest in Panama, where the phylogenetic breadth of arthropod taxa was surveyed using 14 protocols targeting the soil, litter, understory, lower and upper canopy habitats, replicated across seasons in 2003 and 2004. This dataset is used to explore the relative influence of horizontal, vertical and seasonal drivers of arthropod distribution in this forest. We considered arthropod abundance, observed and estimated species richness, additive decomposition of species richness, multiplicative partitioning of species diversity, variation in species composition, species turnover and guild structure as components of diversity. At the scale of our study (2km of distance, 40m in height and 400 days), the effects related to the vertical and seasonal dimensions were most important. Most adult arthropods were collected from the soil/litter or the upper canopy and species richness was highest in the canopy. We compared the distribution of arthropods and trees within our study system. Effects related to the seasonal dimension were stronger for arthropods than for trees. We conclude that: (1) models of beta diversity developed for tropical trees are unlikely to be applicable to tropical arthropods; (2) it is imperative that estimates of global biodiversity derived from mass collecting of arthropods in tropical rainforests embrace the strong vertical and seasonal partitioning observed here; and (3) given the high species turnover observed between seasons, global climate change may have severe consequences for rainforest arthropods.

Resident corticolous oribatid mites (Acari: Oribatida): Decay in community similarity with vertical distance from the ground

ABSTRACT The decrease in community similarity was examined in corticolous oribatid mites (Acari: Oribatida) sampled along a 36-m vertical profile of 5 western redcedar trees in a temperate rainforest on Vancouver Island, Canada. Samples were collected every 2 m, and all adult oribatid mites were identified to species. When compared to species recorded from previous ground/canopy sampling efforts in the same trees, the 62 corticolous species unequivocally support the separation of these 2 communities at 4m. All sampling heights contained canopy oribatid species, but only 0–4 m communities contained ground-dwelling oribatids. There was significant overall spatial autocorrelation and decay in community similarity with distance originating from species turnover at 4 m, suggesting limited range expansion of ground species into corticolous habitats. Community similarity, richness, and abundance of corticolous oribatid mite assemblages were not autocorrelated after 4 m above ground. Observed patterns at 4 m likely represent an environmental transition zone for ground-dwelling species, such as changes in moisture availability, rather than a physical dispersal barrier for individuals. We conclude that the trunk is not a dispersal corridor for ground species to colonize tree crowns and suggest that low similarity between nearest neighbouring sampling points, combined with the presence of immature and gravid oribatids, supports the assumption that corticolous oribatid mite assemblages are likely dispersal-limited residents.

Oribatid Mite Communities in the Canopy of Montane Abies amabilis and Tsuga heterophylla Trees on Vancouver Island, British Columbia

Abstract To study the oribatid mite community inhabiting microhabitats in the canopy of montane Abies amabilis [(Douglas ex D. Don) Lindl.] and Tsuga heterophylla [(Raf.) Sarg] tree species across five elevational sites, we collected 180 branch tips and 180 foliose/crustose lichen samples over three time periods. Thirty-three species of oribatid mites were identified from the study area. Mite species richness and abundance was significantly affected by microhabitat, and this association was independent of sampling time. At the microhabitat scale, distinct species assemblages were associated with lichen and branch tip habitats, and to a lesser degree, tree species. Conifer specificity was most apparent in the closely related species of Jugatala, where Jugatala tuberosa Ewing was only found on branch tips from A. amabilis and Jugatala sp. was primarily found on branch tips from T. heterophylla. Microhabitat specificity was most pronounced in Dendrozetes sp. where most individuals were found on branch tips and Anachiperia geminus Lindo et al. that occurred primarily on lichens. Principal components analysis of oribatid mite community composition further showed a high degree of association with microhabitat and tree species. Habitat profiles are difficult to discern for many species because tree, microhabitat, and elevation preferences confound distribution patterns. Given the significant tree-microhabitat associations in species composition in this montane canopy study, we suggest that sampling multiple microhabitats across elevations to look for patterns in community structure offers opportunities to explicitly test organizing principles in community ecology.

Out on a limb: microarthropod and microclimate variation in coastal temperate rainforest canopies

Species richness of microarthropods in coastal temperate rainforests of western North America is enhanced by the presence of heterogeneous arboreal habitats (moss mats). We studied the relationship between species traits and microclimate as a structuring mechanism for understanding this high diversity. To examine whether community composition is associated with distinct microclimate zones we used Non‐metric Multidimensional Scaling ordination of environmental and community data. To link the traits of arboreal microarthropod species with observed environmental variables we used a trait‐based approach of RLQ and fourth‐corner analysis. Distinct microclimatic zones were observed in the canopy ecosystem stemming from gradients of moisture, temperature, and climatic stability associated with height in canopy and distance from trunk. Associated with these gradients is the growth and development of epiphytic bryophytes such as moss mats and suspended soils, which in turn, influence canopy microclimates. Microarthropod fauna displayed a community‐level response to microclimate gradients which was mediated and partially explained by a trait‐based analysis. A general decline in species richness was associated with harsher microclimate conditions. While many species possessed desiccation resistance traits under low‐moisture conditions, we posit that other species were able to persist by compensatory movements at very small spatial scales. In conclusion this study highlights the importance of environmental buffering associated with greater epiphytic biomass for preserving canopy microarthropod biodiversity, but also how developing an understanding of the species trait distributional shifts can enhance our understanding of communities under different environmental conditions, and for predicting future communities under global environmental change.

Two new species of oribatid mites (Acari: Oribatida) from Ethiopia, including a key to species of Pilobatella

Abstract Two new oribatid mite species, Austrocarabodes (Uluguroides) kluttzi Ermilov, Winchester, Lowman & Wassie sp. nov. (Carabodidae) and Pilobatella lowmanae Ermilov, Winchester & Wassie sp. nov. (Haplozetidae), are described from Afro-montane forests in the northern highlands of Ethiopia. An identification key to all known species of Pilobatella is given. An annotated checklist of identified oribatid mite taxa sampled in this studyis presented. Fourteen species, six genera and three families are recorded for the first time from Ethiopia.

Ancient Coastal Rainforest Canopies in Western Canada: Issues in Biodiversity and Conservation

As global biodiversity continues to decline, our understanding of species distributions, richness and diversity gradients in concert with broad-scale diversity patterns remain critical issues in conservation biogeography (Dinz-Filho et al. 2010). Evaluation of trends in diversity for insects in general, and soil arthropods in particular, is difficult since distribution patterns for most taxonomic groups remain unknown. However, local-scale diversity patterns have been documented for western coastal Canadian temperate canopy arthropods (e.g. Lindo and Winchester 2008, 2009; Winchester et al. 2008). This ecosystem has many of the features needed to test theories associated with large-scale biogeographical patterns and ecosystem-level conservation initiatives. For example, in combination with experimental approaches and observational studies, canopy arthropod communities may provide opportunities to test evolutionary influences on large-scale diversity patterns in response to climate change (Fig. 38.1). Additionally, factors that influence the geographic variation in soil fauna richness and abundance at different spatial scales can be compared and tested using the unique microhabitats found in the high canopy of intact temperate rainforests of British Columbia, Canada. In general, our research seeks to incorporate fundamental ideas discussed in soil community ecology and understand the factors that generate and maintain patterns of biodiversity.