Continuous benthic community change along a depth gradient in Antarctic shallows: evidence of patchiness but not zonation

Many shallow water polar communities demonstrate considerable change along a bathymetric gradient. However, it is currently unclear whether community change is generally continuous or discrete. To determine the nature of community change with depth, extensive photographic surveys at three sites at Adelaide Island, West Antarctic Peninsula, were conducted along a bathymetric gradient of 5–35 m depth. Macroalgae were largely absent at the sites, so only distinguishable macrofauna were counted and analysed. Faunal abundance was greatest at the shallowest stations of the depth transects, whilst richness at both species and phylum level increased with depth. Variability in community structure between replicate transects decreased with depth, so that assemblages at >25 m depth were more homogenous. Depth had a highly significant effect on total abundance, species richness and community structure, and it is likely that the frequency of ice disturbance, which also decreases with depth, drives this pattern. Overall, high variability between transects at each site was recorded, which suggested considerable patchiness at the scale of tens of meters. Community change along the bathymetric gradient was continuous and no evidence of discrete zones of assemblages was recorded.     

Community composition of root‐associated fungi in a Quercus‐dominated temperate forest: “codominance” of mycorrhizal and root‐endophytic fungi

In terrestrial ecosystems, plant roots are colonized by various clades of mycorrhizal and endophytic fungi. Focused on the root systems of an oak‐dominated temperate forest in Japan, we used 454 pyrosequencing to explore how phylogenetically diverse fungi constitute an ecological community of multiple ecotypes. In total, 345 operational taxonomic units (OTUs) of fungi were found from 159 terminal‐root samples from 12 plant species occurring in the forest. Due to the dominance of an oak species (Quercus serrata), diverse ectomycorrhizal clades such as Russula, Lactarius, Cortinarius, Tomentella, Amanita, Boletus, and Cenococcum were observed. Unexpectedly, the root‐associated fungal community was dominated by root‐endophytic ascomycetes in Helotiales, Chaetothyriales, and Rhytismatales. Overall, 55.3% of root samples were colonized by both the commonly observed ascomycetes and ectomycorrhizal fungi; 75.0% of the root samples of the dominant Q. serrata were so cocolonized. Overall, this study revealed that root‐associated fungal communities of oak‐dominated temperate forests were dominated not only by ectomycorrhizal fungi but also by diverse root endophytes and that potential ecological interactions between the two ecotypes may be important to understand the complex assembly processes of belowground fungal communities.     

Biofouling communities on test panels coated with TBT and TBT-free copper based antifouling paints

Abstract

Formation of biofouling communities on the surfaces of steel panels coated with two different TBT-free copper-based and one TBT-based antifouling paint was examined following submersion for periods of 3, 6, 9 and 12 months in Kastela Bay, Croatia. Test panels coated with Shopprimer and anticorrosive paint were used as control panels. Thirty five taxa of benthic algae and 32 taxa of benthic animals were found. Diatomeae dominated by frequency and abundance on test panels coated with antifouling paints, while the animal species Serpula vermicularis, Mytilus galloprovincialis and Balanus amphitrite amphitrite dominated the fouling communities on control panels. On panels protected by antifouling paints, low values of biomass were found compared to the very high values associated with control panels.     

Assessing the impacts of imperfect detection on estimates of diversity and community structure through multispecies occupancy modeling

Detecting all species in a given survey is challenging, regardless of sampling effort. This issue, more commonly known as imperfect detection, can have negative impacts on data quality and interpretation, most notably leading to false absences for rare or difficult‐to‐detect species. It is important that this issue be addressed, as estimates of species richness are critical to many areas of ecological research and management. In this study, we set out to determine the impacts of imperfect detection, and decisions about thresholds for inclusion in occupancy, on estimates of species richness and community structure. We collected data from a stream fish assemblage in Algonquin Provincial Park to be used as a representation of ecological communities. We then used multispecies occupancy modeling to estimate species‐specific occurrence probabilities while accounting for imperfect detection, thus creating a more informed dataset. This dataset was then compared to the original to see where differences occurred. In our analyses, we demonstrated that imperfect detection can lead to large changes in estimates of species richness at the site level and summarized differences in the community structure and sampling locations, represented through correspondence analyses.     

Arthropod communities on creosote bush (<Emphasis Type="Italic">Larrea tridentata</Emphasis>) in desert patches of varying degrees of urbanization

The goal of the present study was to investigate the influence of urbanization on the richness, abundance and composition of arthropod communities associated with creosote bush, Larrea tridentata [DC] Cov., in Phoenix, Arizona. Arthropod communities were sampled in two desert types varying in degree of urbanization including fringe deserts (relatively undisturbed expanses of desert outside of Phoenix) and urban deserts (patches of desert within the urban core of Phoenix). Two studies were conducted including (1) a seasonal study (conducted at two fringe desert and two urban desert sites over a nine-month period), and (2) a snapshot study (conducted at multiple fringe desert and urban desert sites over an eight-day period). Results from both studies demonstrated that overall richness and abundance of creosote bush arthropod communities were lower in urban deserts than in fringe deserts. Additionally, creosote bush arthropod community composition varied greatly, both temporally and spatially. These differences in richness and abundance between fringe deserts and urban deserts suggest that the creosote bush arthropod community may be a useful focal biotic community to monitor when assaying for environmental change due to urbanization in arid habitats.     

Effects of sedimentation from water-based drill cuttings and natural sediment on benthic macrofaunal community structure and ecosystem processes

In this study, we aim at investigating the role of physical disturbance in effects of water-based drill cuttings on benthic ecosystems. Today, most of the cuttings discharged from oil and gas installations contain water-based drilling muds, rather than oil-based or synthetic muds. Drill cuttings with water-based muds are assumed to cause only marginal effects on the benthos, mainly resulting from sedimentation. However, this statement has not been experimentally tested, which is the purpose of the present work. Natural sediment particles and water-based drill cuttings were added to benthic communities in layer thicknesses of 3-24 mm in a mesocosm set-up. During the following 6 months, changes in benthic community structure and fluxes of oxygen and nutrients across the sediment water interface were studied. There was a significant reduction in number of taxa, abundance, biomass and diversity of macrofauna with increasing thickness of drill cuttings, which was not observed for the natural sediment particles. The drill cuttings also influenced oxygen consumption and oxygen penetration depth in the sediment, and it was concluded that an organic compound in the drill cuttings initiated a typical eutrophication response. Fluxes of phosphate and silicate were, however, similarly affected by the two types of particles, and maximum fluxes occurred in sediments treated with thin layers (3-6 mm) of particles. As the response of water-based drill cuttings in the present study was a result of factors other than physical disturbance, we recommend a reconsideration of the assumption that water-based drill cuttings only cause sedimentation (burial) effects.     

Ecotone delimitation: Epigean–hypogean transition in cave ecosystems

Abstract The ecotone zone between epigean and hypogean environments has been delimited for two limestone caves using a new method proposed herein. The richness and the diversity of the ecotone, epigean and hypogean environments and their similarities have also been determined. The ecotones were delimited using a similarity matrix between the inner and outer sectors of each cave. The ecotone of Dona Rita's cave was estimated to be 12 m long and the ecotone of Retiro's cave 16 m. The richness (S) of arthropods in Dona Rita's cave was higher in the ecotone (S = 131), intermediate in the epigean environment (S = 75) and lower in the hypogean system (S = 45). The invertebrate diversity (H′) was lower in the hypogean environment (H′ = 2.89) and not statistically different between the epigean environment and the ecotone (H′ = 3.56 and H′ = 3.76, respectively). The richness in Retiro's cave was higher in the ecotone (S = 86), intermediate in the epigean environment (S = 39) and lower in the hypogean system (S = 12). The invertebrate diversity was lower in the hypogean environment (H′ = 0.48), intermediate in the ecotone (H′ = 3.02) and higher in the epigean region (H′ = 3.29). Species migration patterns, differential environmental barriers and determination of accidental versus trogloxenes/troglophylous species are topics that are primarily approached by establishing ecotone zones in caves. The aim of the present paper is to establish the delimitation of theses zones.     

Heart rot hotel: fungal communities in red-cockaded woodpecker excavations

Tree-cavity excavators such as woodpeckers are ecosystem engineers that have potentially complex but poorly documented associations with wood decay fungi. Fungi facilitate cavity excavation by preparing and modifying excavation sites for cavity excavators. Associations between fungi and endangered red-cockaded woodpeckers (RCWs) are particularly interesting because these are the only birds that specialize in excavating into the heartwood of living pines, a process that takes years to complete. Using molecular methods, we examined fungal communities in complete and incomplete RCW excavations, and non-cavity control trees. In addition to finding a high diversity of fungi, we found three groupings of fungal communities corresponding to the three groups of trees sampled. We show that trees selected for cavity excavation by RCWs are infected by distinct fungal communities, and propose two hypotheses to explain this outcome: the bird facilitation hypothesis and the tree selection hypothesis.     

Thyme travels: 15N isoscapes of Thymus vulgaris L. invasion in lightly grazed pastoral communities

Alterations to ecosystem nitrogen (N) cycling by introduced plant species may increase the invasibility of habitat providing a positive feedback for the introduced species to become invasive. Spatial patterns of foliar and soil δ¹⁵N ratios reflect variation in rates and process of N‐cycling across invaded landscapes and provide insight into N‐source uptake and utilization strategies of invasive plant species. To evaluate invasion‐associated changes in soil and foliar δ¹⁵N at different scales: regional (among different sites), local (between north‐ and south‐facing aspect at the same site), and microsite (within populations in the same community), we measured foliar and soil δ¹⁵ N, animal faeces cover (as a proxy for grazing intensity) and N₂‐fixing species cover from inside to outside Thymus vulgaris L. (thyme)‐invaded lightly grazed pastoral communities in Central Otago, southern South Island, New Zealand. Mean thyme foliar δ¹⁵N were near‐zero across the invaded landscape, and did not change across the advancing edge of invasion or with aspect. There was no evidence that associations with N₂‐fixing species provide a potential N source. Soil δ¹⁵N was lower inside of thyme compared to at the edge or outside of thyme and was varied between aspects at some sites. Animal faeces cover as a proxy for grazing intensity explained only 23% of this observed variation of soil δ¹⁵N. Thyme invasion may result in lowered soil δ¹⁵N reflecting alterations to N dynamics. Associated invasion‐related impacts of animal grazing may also impact soil δ¹⁵N. Further studies are required to distinguish the underlying mechanism responsible for the observed patterns of foliar and soil δ¹⁵N values across thyme‐invaded Central Otago landscapes.     

Twenty years of understorey bird extinctions from Amazonian rain forest fragments: consistent trends and landscape-mediated dynamics

Aim We analysed presence/absence data for understorey bird species in rain forest fragments sampled from 1979 through 2001. Here we consider extinctions between 1992, when most fragments had been isolated for at least 8 years, and 2001. Our objectives were to determine whether high extinction rates documented soon after isolation continued through up to 20 years after isolation, and to examine fragment size and landscape effects on extinction. Location Biological Dynamics of Forest Fragments Project, near Manaus, Brazil. Methods Through 1992, birds were surveyed with standardized mist net sampling in ten 1‐ to 100‐ha fragments. We repeated the mist net protocol in 2000–01. We also added remote taping of the dawn chorus and tape playback surveys for species captured in 1991–92 but not in 2000–01. Results Between 1992 and 2001, 37 species went extinct in at least one fragment. As expected, extinction rate decreased with increasing fragment size. Over 30% of species went extinct in 1‐ha fragments, compared to about 5% in 100‐ha fragments. Extinction followed a predictable pattern: most species lost from 100‐ha fragments between 1992 and 2001 had already gone extinct in smaller fragments before 1992. Despite extinctions, fragments gained species between 1992 and 2001, apparently due to species moving through the developing second growth matrix. Fragments surrounded by old second growth had lower extinction rates than predicted based on fragment size alone. Main conclusions Sequential extinctions occurred for at least 20 years. Some additional species previously lost from smaller fragments may continue to go extinct in 100‐ha fragments. At the same time, species assemblages in 1‐ and 10‐ha fragments mostly reflect second‐growth dynamics by 20 years after isolation. High species loss predicted from the first few years after isolation has not occurred, almost certainly because of recolonization.