Identification of Fine-Scale Marine Benthic Ecoclines by Multiple Parallel Ordination

The species-environment relationship is a fundamental structural property of natural ecosystems. Marine sedimentary macrofauna is known to be structured by a range of environmental variables; however, the mechanisms by which environmental variables covary to form complex-gradients (i.e., groups of intercorrelated environmental variables), and how these are related to coenoclines (i.e., gradients in species composition), remain poorly understood. We classified our study area into geomorphological features that were used for stratified sampling of macrofaunal polychaetes, molluscs, and echinoderms. The resulting species-by-site matrix was subjected to indirect gradient analysis by a multiple parallel ordination strategy, using detrended correspondence analysis and nonmetric multidimensional scaling. One major and one minor coenocline were identified. Based on the correlation between complex-gradients and the main coenocline we hypothesise the existence of two ecoclines that we have termedPeriodic hypoxiaandPeriodic physical forcing. We conclude that a combination of recurrent (periodical) and extreme events is likely to determine the variation found in the species composition of marine sedimentary ecosystems. Based on the results of our study, we conclude that indirect gradient analysis is a useful tool for enhancement of our basic mechanistic understanding of the processes governing the compositional structure of marine sediment communities.

Influence of Environmental Gradients on the Abundance and Distribution of Mycobacterium spp. in a Coastal Lagoon Estuary

ABSTRACT Environmental mycobacteria are of increasing concern in terms of the diseases they cause in both humans and animals. Although they are considered to be ubiquitous in aquatic environments, few studies have examined their ecology, and no ecological studies of coastal marine systems have been conducted. This study uses indirect gradient analysis to illustrate the strong relationships that exists between coastal water quality and the abundance of Mycobacterium spp. within a U.S. mid-Atlantic embayment. Mycobacterium species abundance and water quality conditions (based on 16 physical and chemical variables) were examined simultaneously in monthly samples obtained at 18 Maryland and Virginia coastal bay stations from August 2005 to November 2006 (n = 212). A quantitative molecular assay for Mycobacterium spp. was evaluated and applied, allowing for rapid, direct enumeration. By using indirect gradient analysis (environmental principal-components analysis), a strong linkage between eutrophic conditions, characterized by low dissolved-oxygen levels and elevated nutrient concentrations, and mycobacteria was determined. More specifically, a strong nutrient response was noted, with all nitrogen components and turbidity measurements correlating positively with abundance (r values of >0.30; P values of <0.001), while dissolved oxygen showed a strong negative relationship (r = −0.38; P = 0.01). Logistic regression models developed using salinity, dissolved oxygen, and total nitrogen showed a high degree of concordance (83%). These results suggest that coastal restoration and management strategies designed to reduce eutrophication may also reduce total mycobacteria in coastal waters.

Habitat structure and small mammals abundances in one semiarid landscape in the Brazilian Caatinga

Studies conducted under a major project sponsored by the Brazilian Academy of Sciences in the 1970's concluded that the small mammal fauna of the semiarid Caatinga region of Brazil is impoverished and highly restricted to mesic granite outcroppings due to the lack of water conserving physiological capabilities in its species. This work focuses the abundance of small mammals in five typical Caatinga habitats. Indirect gradient analysis shows that three theoretical environmental variables explain most of the variance present in the community abundance matrix. Direct analysis of gradients show that none of these variables is highly correlated to availability of granite outcroppings. Our data also suggest that the abundances in Caatinga are not particularly low when compared to neighbor biomes and that underlying factors of habitat use by Caatinga small mammals are more complex than previously supposed.

Indirect gradient analysis of the Mangal formation of Gazi bay (Kenya)

(1) Based on vegetation relevés of sample units along transects perpendicular to the coastline, the mangal ecosystem of Gazi Bay (Kenya) has been investigated. (2) An indirect gradient analysis is performed by the ordination method Detrended Correspondence Analysis. (3) The first ordination axis can be interpreted in terms of resistance of the different species to flooding. (4) A similar zonation pattern is found as described by WALTER &amp; STEINER (1936). (5) Zonation is closely connected with morphological and ecophysiological features of the mangrove species. Therefore stomatal density has been measured. Sonneratia has by far the lowest stomatal density, Lumnitzera the highest.

High elevation vegetation of the Enchantment Lakes Basin, Washington

The vegetation of the Enchantment Lakes Basin, which is located at and above timberline on the slopes of Mount Stuart, Washington, was examined by classification and ordination methods. A vegetation map relates the 21 recognized community types to physiographic and topographic features. Vegetation was divided into plots with and without trees. The 11 forested communities include those dominated by Larix lyallii and Cassiope mertensiana on moist slopes, L. lyallii and Phyllodoce glanduliflora on steep north-facing slopes, Abies lasiocarpa and Vaccinium inyrtillus on low elevation, moist sites, and several communities dominated by Pinus albicaulis on dry, exposed slopes. The 10 alpine communities include dry fell-fields dominated by Lupinus lepidus with a variety of forbs, communities dominated by Cassiope mertensiana and Phyllodoce glanduliflora and by P. empetriformis, and lush and wet meadow communities dominated by Lupinus polyphyllus and Carex nigricans. These communities are related to those identified by other workers in the Pacific Northwest. Keys to the vegetation of this area are presented. Indirect gradient analysis using reciprocal averaging revealed both vegetation and species patterns. In the subalpine, moisture appears to be the dominant operational gradient, while inferred temperature is a secondary factor. In the alpine vegetation, a combined gradient of moisture and exposure is indicated by reciprocal averaging. Special ordinations derived from reciprocal averaging reflect these interpretations and identify indicator species for particular habitats in both subalpine and alpine. The patterns are summarized with a mosaic diagram. The use of multivariate methods provided means to summarize primary survey data quickly and efficiently. The pattterns thus revealed are comparable to other studies in the Pacific Northwest and thus engender confidence in the use of indirect gradient analysis as a valuable tool for primary survey in these ecosystems. A vegetation map, keys to vegetation types, community and species patterns, and the relationship between classifications and ordinations emerged from this study.