Diatom Assemblages and their Associations with Environmental Variables in Oregon Coast Range Streams, USA

The Oregon Coast Range, rich in natural resources, is under increasing pressure from rapid development. The purpose of this study was to examine diatom species patterns in relation to environmental variables in streams of this region. Diatoms, water quality, physical habitat and watershed characteristics were assessed for 33 randomly selected stream sites. Watershed size, elevation, geology, vegetation and stream morphology varied substantially among sites. Streams were characterized by dilute water chemistry and a low percent of fine substrate. A total of 80 diatom taxa were identified. Taxa richness was low throughout the region (median 15, range 10–26). Assemblages were dominated by two adnate species, Achnanthidium minutissimum and Achnanthes pyrenaicum. Diatoms sensitive to organic pollution dominated the assemblages at all sites (median 85%). Non-metric multidimensional scaling (NMDS) and correlational analysis showed quantitative relationships between diatom assemblages and environmental variables. NMDS axes were significantly correlated with watershed area, watershed geology, conductivity, total nitrogen, total solids and stream width. Diatom-based site classification (Two-way Indicators Species Analysis, (TWINSPAN)) yielded 4 discrete groups that displayed weak correlations with environmental variables. When stream sites were classified by dominant watershed geology, overall diatom assemblages between groups were significantly different (Analysis of Similarity (ANOSIM) global R = 0.19, p < 0.05). Our results suggest that streams in the coastal region are in relatively good condition. High natural variability in stream conditions in the Oregon Coast Range ecoregion may obscure quantitative relationships between environmental variables and diatom assemblages. A bioassessment protocol that classifies sites by major landscape variables and selects streams along the major human disturbance gradient might allow for detection of early signs of human disturbance in environmentally heterogeneous regions, such as the Pacific Northwest.     

A geographically variable model of hemlock woolly adelgid spread

The hemlock woolly adelgid (HWA) (Adelges tsugae) has spread through the range of eastern hemlock (Tsuga canadensis) leaving dead hemlock trees in its wake. We combined county and previously unavailable township level infestation records with geographic variables including plant hardiness zone, elevation, forest cover type, urbanization, precipitation, temperature, and hemlock range in a geographic information system to build models linking HWA spread to the structure and characteristics of the environment. We explored the connections between site variables and spread rate using quantile regression, Tobit regression, a parametric model for heterogeneous error variance, and classification and regression tree modeling. The results show that since 1990 HWA has spread at a rate closer to 12.5 km/yr rather than the 20–30 km/yr previously estimated, however spread rates vary significantly with environmental variables. County-based data show a faster rate of range expansion in the south, 15.6 km/yr, and very slow spread in the northern part of the current range of HWA. The rate of spread based on township records for Pennsylvania and north is 8.13 km/yr. Our study suggests that HWA spreads more slowly in colder areas, with a mean minimum temperature of  − 26.1°C (plant hardiness zone 5B) delineating areas of slower range expansion. HWA also spreads more slowly during cold years, those with lower than average mean January temperatures. Our analysis demonstrates the value of quantile regression, Tobit regression, and classification and regression tree models for understanding the spread of invasive, exotic insects.     

Effect of rock type on the recruitment and early mortality of the barnacle Chthamalus montagui

Discontinuities in distribution of sessile species due to changes in available habitat have rarely been investigated. In the English Channel, soft sedimentary rocks including chalk could potentially present a barrier to eastward range extension of the southern barnacle Chthamalus montagui. To test the effect of rock type on recruitment and mortality, prepared settlement tiles of four calcareous rocks that form important platforms close to existing limits of distribution were fixed to the shore at a site in south-west England, known to have consistently high larval settlement. Prior to fixation, the roughness parameter “R_a” and Potential Settlement Sites (PSS) index was measured. Recruitment was monitored photographically on four occasions during the settlement season and subsequent mortality for 7 months after the settlement season. By the end of the settlement season, recruitment on the hard Kimmeridge Cementstone was significantly less than on the other three rock types and attributed to low surface roughness and fewest Potential Settlement Sites (PSS), yet only 28% of variance could be attributed to PSS. Post-recruitment mortality was more variable, however after 7 months there were significant differences between rock types. Simultaneous surveys of post-recruitment mortality in natural populations showed that although recruitment on chalk can potentially be high, survivorship was relatively low. Thus rock type could be influential in setting species geographical limits.     

A tale of two flatties: different responses of two terrestrial flatworms to past environmental climatic fluctuations at Tallaganda in montane southeastern Australia

Comparative phylogeographic studies of animals with low mobility and/or high habitat specificity remain rare, yet such organisms may hold fine-grained palaeoecological signal. Comparisons of multiple, codistributed species can elucidate major historical events. As part of a multitaxon programme, mitochondrial cytochrome oxidase I (COI) variation was analysed in two species of terrestrial flatworm, Artioposthia lucasi and Caenoplana coerulea. We applied coalescent demographic estimators and nested clade analysis to examine responses to past, landscape-scale, cooling-drying events in a model system of montane forest (Tallaganda). Correspondence of haplotype groups in both species to previously proposed microbiogeographic regions indicates at least four refuges from cool, dry conditions. The region predicted to hold the highest quality refuges (the Eastern Slopes Region), is indicated to have been a long-term refuge in both species, but so are several other regions. Coalescent analyses suggest that populations of A. lucasi are declining, while C. coerulea is expanding, although stronger population substructure in the former could yield similar patterns in the data. The differences in spatial and temporal genetic variation in the two species could be explained by differences in ecological attributes: A. lucasi is predicted to have lower dispersal ability but may be better able to withstand cold conditions. Thus, different contemporary population dynamics may reflect different responses to recent (Holocene) climate warming. The two species show highly congruent patterns of catchment-based local genetic endemism with one another and with previously studied slime-mould grazing Collembola.     

Northern range extension of the seagrasses Halophila johnsonii and Halophila decipiens along the east coast of Florida,USA

The northern geographic limit for Halophila johnsonii and Halophila decipiens has been reported as Sebastian Inlet, within the Indian River Lagoon, Florida. Surveys conducted in August 2007 determined the new northern limit to be 21.5 km north of the previously known limit. This new northern limit is a 10% range extension for H. johnsonii, a federally threatened species. We conclude that these range extensions are recent, based on (1) the small size of patches; (2) unusually good water clarity conditions due to a recent drought; (3) recent mild/warmer winters; and (4) a recent mechanism for transporting propagules, the numerous hurricanes of 2004. Although this recent range extension is considered ephemeral, similar range extensions may have occurred in the past and may occur again in the future under favorable conditions given the high capacity of these two species for dispersal to favorable sites. The northern limits of these species should not be viewed as static locations; rather, they must be considered dynamic features.     

The subterranean genus Niphargus (Crustacea, Amphipoda) in the Middle East: A faunistic overview with descriptions of two new species

The Middle East is at the southeastern borderline of the range of the subterranean amphipod Niphargus. The review of new and published data identified two new species and set the guidelines for the future research in the area. The genus in this part of the world seems to be insufficiently studied. The taxonomic status of Niphargus valachicus, population identified as N. spoeckeri and some populations, identified as N. nadarini, need to be reviewed. According to present data, we expect the highest diversity in Western Turkey. The eventual new records of the genus in the Middle East can be expected from those areas where even the longest periods of drought in the recent geological history did not affect the water supply.