Evolution of Delphacidae (Hemiptera: Fulgoroidea): combined‐evidence phylogenetics reveals importance of grass host shifts

The planthopper family Delphacidae is a speciose lineage of phloem‐feeding insects, with many species considered as pests of economic significance on essential world food commodities (including rice, maize, wheat, barley and sugar cane). Despite their economic importance, evolutionary relationships among delphacids, particularly those within the speciose tribe Delphacini, are largely unknown. Presented here are the results of a phylogenetic investigation of Delphacidae based on DNA nucleotide sequence data from four genetic loci (18S rDNA, 28S rDNA, wingless and cytochrome oxidase I) and 132 coded morphological characters. The resulting topologies are used to test the higher classification of Delphacidae and to examine evolutionary patterns in host–plant associations. Our results generally support the higher classifications of Delphacidae proposed by Asche, Emeljanov and Hamilton, and suggest that the rapid diversification of the Delphacini was associated with host shifts to, and within, Poaceae, and specifically from C3 to C4 grasses.     

Land clearing reduces gene flow in the granite outcrop‐dwelling lizard,Ctenophorus ornatus

An important question for the conservation of species dwelling in fragmented habitats is whether changes to the intervening landscape create a barrier to gene flow. Here, we make use of the spatial distribution of the granite outcrop‐dwelling lizard, Ctenophorus ornatus, to compare inferred levels of gene flow between outcrops in a nature reserve with that between outcrops in the adjacent agricultural land. Genetic variation, relatedness and subdivision were compared within groups of individuals from different outcrops similar in size and distance apart at each site. In the agricultural land, we found significantly lower genetic variation within outcrops and greater genetic differentiation between outcrops than in the reserve. Further, the rate at which genetic divergence between outcrops increased over geographical distance was significantly greater in the agricultural land than in the reserve. We also found that individuals were more closely related within outcrops but more distantly related between outcrops in the cleared land. These effects occur over a small spatial scale with an average distance between outcrops of less than five kilometres. Thus, even though land clearing around the outcrops leaves outcrop size unchanged, it restricts gene flow, reducing genetic variation and increasing population structure, with potentially negative consequences for the long‐term persistence of the lizards on these outcrops.     

Population genetic data suggest a role for mosquito‐mediated dispersal of West Nile virus across the western United States

After introduction, West Nile virus (WNV) spread rapidly across the western United States between the years 2001 and 2004. This westward movement is thought to have been mediated by random dispersive movements of resident birds. Little attention has been placed on the role of mosquito vectors in virus dispersal across North America. The mosquito vector largely responsible for WNV amplification and transmission of WNV in the western USA is Culex tarsalis. Here we present population genetic data that suggest a potential role for C. tarsalis in the dispersal of WNV across the western USA. Population genetic structure across the species range of C. tarsalis in the USA was characterized in 16 states using 12 microsatellite loci. structure and geneland analyses indicated the presence of three broad population clusters. Barriers to gene flow were resolved near the Sonoran desert in southern Arizona and between the eastern Rocky Mountains and High Plains plateau. Small genetic distances among populations within clusters indicated that gene flow was not obstructed over large portions of the West Coast and within the Great Plains region. Overall, gene flow in C. tarsalis appears to be extensive, potentially mediated by movement of mosquitoes among neighbouring populations and hindered in geographically limited parts of its range. The pattern of genetic clustering in C. tarsalis is congruent with the pattern of invasion of WNV across the western United States, raising the possibility that movement of this important vector may be involved in viral dispersal.     

Is proximity to the North Atlantic Drift and the Continental Shelf Current sustaining freshwater European eel populations in western Scotland?

1. We report on freshwater resident eel numbers in western Scotland based on two time series of data, independent of each other, spanning 28 years and that do not rely upon fisheries information. 2. Data from eel captures on trash screens of a pumping station (1982–2003) on Loch Lomond and electrofishing data from a stream in Lochaber, the Allt Coire nan Con (1989–2010), are compared with similar time series eel population data from elsewhere in the British Isles and more widely in Europe. 3. Over the period of the study, indices of eel numbers from across Europe declined by between 72 and 95%; in stark contrast, neither time series from western Scotland showed evidence for decline between 1982 and 2010. 4. We provisionally conclude that freshwater populations in western Scotland are being maintained by regional processes directly related to the proximity of the leading edge of the North Atlantic Drift and the Continental Shelf Current and the direction of prevailing winds.     

Determining adequate trapping effort and species richness using species accumulation curves for environmental impact assessments

Abstract Environmental impact assessments (EIA) require that the proponent indicates the potential impact that a development will have on the biodiversity of the area. As part of this assessment it is normal practice to inventory the vertebrate species in the area. We show here how species accumulation curves can be used as a tool by environmental consultants to indicate the adequacy of their trapping effort and predict species richness for a disturbance site. The shape of a species accumulation curve is influenced by the number of species in an assemblage and the proportional number of singletons (rarely caught species) in the survey sample. We provide guidelines for the number of individuals that need to be caught in a trapping program to achieve 80% and 90% of the species in a habitat, and we indicate how this number can be adjusted to accommodate variations in relative species abundance.     

Variation in abundance across a species' range predicts climate change responses in the range interior will exceed those at the edge: a case study with North American beaver

The absence of information about how abundance varies across species' ranges restricts most modeling and monitoring of climate change responses to the range edge. We examine spatial variation in abundance across the northeastern range of North American beaver ( Castor canadensis ), evaluate the extent to which climate and nonclimate variables explain this variation, and use a species–climate envelope model that includes spatial variation in abundance to predict beaver abundance responses to projected climate change. The density of beaver colonies across Québec follows a roughly logistic pattern, with high but variable density across the southern portion of the province, a sharp decline in density at about 49°N, and a long tail of low density extending as far as 58°N. Several climate and nonclimate variables were strong predictors of variation in beaver density, but 97% of the variation explained by nonclimate variables could be accounted for by climate variables. Because of the peak and tail density pattern, beaver climate sensitivity (change in density per unit change in climate) was greatest in the interior and lowest at the edge of the range. Combining our best density–climate models with projections from general circulation models (GCM) predicts a relatively modest expansion of the species' northern range limit by 2055, but density increases in the range interior that far exceed those at the range edge. Thus, some of the most dramatic responses to climate change may be occurring in the core of species' ranges, far away from the edge-of-the-range focus of most current modeling and monitoring efforts.     

Hydrological and biogeochemical controls on the timing and magnitude of nitrous oxide flux across an agricultural landscape

Anticipated increases in precipitation intensity due to climate change may affect hydrological controls on soil N₂O fluxes, resulting in a feedback between climate change and soil greenhouse gas emissions. We evaluated soil hydrologic controls on N₂O emissions during experimental water table fluctuations in large, intact soil columns amended with 100 kg ha^?1 KNO₃‐N. Soil columns were collected from three landscape positions that vary in hydrological and biogeochemical properties (N= 12 columns). We flooded columns from bottom to surface to simulate water table fluctuations that are typical for this site, and expected to increase given future climate change scenarios. After the soil was saturated to the surface, we allowed the columns to drain freely while monitoring volumetric soil water content, matric potential and N₂O emissions over 96 h. Across all landscape positions and replicate soil columns, there was a positive linear relationship between total soil N and the log of cumulative N₂O emissions (r²= 0.47; P= 0.013). Within individual soil columns, N₂O flux was a Gaussian function of water‐filled pore space (WFPS) during drainage (mean r²= 0.90). However, instantaneous maximum N₂O flux rates did not occur at a consistent WFPS, ranging from 63% to 98% WFPS across landscape positions and replicate soil columns. In contrast, instantaneous maximum N₂O flux rates occurred within a narrow range (?1.88 to ?4.48 kPa) of soil matric potential that approximated field capacity. The relatively consistent relationship between maximum N₂O flux rates and matric potential indicates that water filled pore size is an important factor affecting soil N₂O fluxes. These data demonstrate that matric potential is the strongest predictor of the timing of N₂O fluxes across soils that differ in texture, structure and bulk density.     

Agrarian legacy in soil nutrient pools of urbanizing arid lands

Today's worldwide expansion of dry land cities consumes cultivated and native ecosystems, providing laboratories for investigating imprints of former land use in places where people now live. Around Phoenix, USA, we compared soil nutrient pools in residential yards converted from farms with nutrient pools in yards developed on native desert. Organic matter, carbon (C), nitrogen (N), and soluble ions were >2-fold greater in yards that were previously agrarian than in yards that were not. These pools remain elevated 40 years after land conversion to residential use. Present N accumulation (1.5 g m⁻² yr⁻¹) is not affected by prior land use, suggesting that rates of residential fertilizer application and retention are not affected by antecedent soil fertility. Bioavailable, inorganic phosphorus (P_av) is elevated in soil with a recent agrarian past, but this signal disappears after 10–30 years of residential use owing to an accumulation of P_av in never-farmed yards. Our results indicate a 'direct agrarian legacy,' wherein agrarian amendment of nutrient pools endures urbanization, more so than an 'indirect legacy,' wherein present land management is molded by former land use. Agriculture in dry lands thus sequesters material in soils, and—as we also found higher material contents in residential soils than in contemporary agrarian soils—residential land use simply adds to the agrarian legacy these soils already bear. Intense human use of arid lands may cause increases in material pools in soils, a condition with potential global consequence.     

Effects of wildfire and permafrost on soil organic matter and soil climate in interior Alaska

The influence of discontinuous permafrost on ground‐fuel storage, combustion losses, and postfire soil climates was examined after a wildfire near Delta Junction, AK in July 1999. At this site, we sampled soils from a four‐way site comparison of burning (burned and unburned) and permafrost (permafrost and nonpermafrost). Soil organic layers (which comprise ground‐fuel storage) were thicker in permafrost than nonpermafrost soils both in burned and unburned sites. While we expected fire severity to be greater in the drier site (without permafrost), combustion losses were not significantly different between the two burned sites. Overall, permafrost and burning had significant effects on physical soil variables. Most notably, unburned permafrost sites with the thickest organic mats consistently had the coldest temperatures and wettest mineral soil, while soils in the burned nonpermafrost sites were warmer and drier than the other soils. For every centimeter of organic mat thickness, temperature at 5 cm depth was about 0.5°C cooler during summer months. We propose that organic soil layers determine to a large extent the physical and thermal setting for variations in vegetation, decomposition, and carbon balance across these landscapes. In particular, the deep organic layers maintain the legacies of thermal and nutrient cycling governed by fire and revegetation. We further propose that the thermal influence of deep organic soil layers may be an underlying mechanism responsible for large regional patterns of burning and regrowth, detected in fractal analyses of burn frequency and area. Thus, fractal geometry can potentially be used to analyze changes in state of these fire prone systems.