Stochastic population dynamics in populations of western terrestrial garter snakes with divergent life histories

Comparative evaluations of population dynamics in species with temporal and spatial variation in life-history traits are rare because they require long-term demographic time series from multiple populations. We present such an analysis using demographic data collected during the interval 1978-1996 for six populations of western terrestrial garter snakes (Thamnophis elegans) from two evolutionarily divergent ecotypes. Three replicate populations from a slow-living ecotype, found in mountain meadows of northeastern California, were characterized by individuals that develop slowly, mature late, reproduce infrequently with small reproductive effort, and live longer than individuals of three populations of a fast-living ecotype found at lakeshore locales. We constructed matrix population models for each of the populations based on 8-13 years of data per population and analyzed both deterministic dynamics based on mean annual vital rates and stochastic dynamics incorporating annual variation in vital rates. (1) Contributions of highly variable vital rates to fitness (lambda(s)) were buffered against the negative effects of stochastic variation, and this relationship was consistent with differences between the meadow (M-slow) and lakeshore (L-fast) ecotypes. (2) Annual variation in the proportion of gravid females had the greatest negative effect among all vital rates on lambda(s). The magnitude of variation in the proportion of gravid females and its effect on lambda(s) was greater in M-slow than L-fast populations. (3) Variation in the proportion of gravid females, in turn, depended on annual variation in prey availability, and its effect on lambda(s) was 4 23 times greater in M-slow than L-fast populations. In addition to differences in stochastic dynamics between ecotypes, we also found higher mean mortality rates across all age classes in the L-fast populations. Our results suggest that both deterministic and stochastic selective forces have affected the evolution of divergent life-history traits in the two ecotypes, which, in turn, affect population dynamics. M-slow populations have evolved life-history traits that buffer fitness against direct effects of variation in reproduction and that spread lifetime reproduction across a greater number of reproductive bouts. These results highlight the importance of long-term demographic and environmental monitoring and of incorporating temporal dynamics into empirical studies of life-history evolution.     

The evolution of marmot sociality: II. Costs and benefits of joint hibernation

Summary Social groups of alpine marmots (Marmota marmota) were studied for 7 years. The groups consisted of a territorial pair and up to 18 lower ranking animals of various ages, mostly the pair's offspring (Tables 1, 2). Group members lived in a common home range and always hibernated together in one hibernaculum. Groups with older, subordinate animals experienced slightly higher summer mortality but significantly reduced winter mortality (Fig. 1). Infant winter mortality was further decreased if most older subordinates were potentially their full sibs (Fig. 2). Subordinate group members lost less mass during winter with increasing size of the hibernating group, but this trend was reversed when infants were present. Furthermore, augmented mass loss due to low hibernaculum quality became evident (Fig. 3). Apart from these effects, the presence of infants caused additional mass loss in potential full sibs. The opposite was found in subordinates certainly descending from other parents than those of the infants (Table 3).Winter mortality and mass loss data revealed (i) a general benefit of joint hibernation, (ii) an unavoidable cost of infants' presence to other group members, (iii) that only potential full sibs helped in warming infants, (iv) that helping was energetically expensive and increased infant survival. The evolution of postponed dispersal in ground-dwelling squirrels has been attributed to the direct fitness gained by enhanced reproductive chances of offspring when not expelled from the natal territory (Armitage 1981, 1987, 1988). This study shows that group living in alpine marmots has benefits during winter and indicates the additional importance of kin selection in marmot social evolution.     

Geolocation of free-ranging fish on the European continental shelf as determined from environmental variables

Demersal fish cannot readily be tracked using satellite-based or light-based geolocation techniques. As an alternative, we describe the tidal location method, which uses tidal data recorded by electronic data storage tags (DSTs), to determine geoposition. Times of high water (H) and tidal ranges (R) recorded by DSTs moored at known locations, and from free-swimming tagged plaice, Pleuronectes platessa, were compared with a North Sea tidal database to identify all positions with matching values of H and R. Within the recording precision of the tag (ǂ.2 m, ᆞ min) and the predicted accuracy of the model generated tidal data (ǂ.15 m, ᆨ min), geolocations over much of the North Sea and eastern English Channel were predicted to be accurate to within 40 km, sometimes to within 10 km. Positional estimates of the moored tags were within 15.7Dž.5 km of the actual locations. Geolocations made from tagged plaice within 5 days of release and 5 days pre-recapture were within 35ᆬ km and 37ᆫ km of release and recapture positions respectively. Our results demonstrate the ability of this method to accurately describe the migrations of North Sea plaice throughout their geographical range with a level of accuracy unattainable using light-based geolocation. The method could equally be applied to any shelf-dwelling demersal fish that periodically rests on the sea-bed for the duration of a tidal cycle. In fisheries management, the method has clear potential application in defining the movements and migrations of other commercial species.     

Moisture effects on eolian particle entrainment

In wind tunnel experiments, we study the effects of soil moisture on the threshold condition to entrain fine grain sand/silt into eolian flow and the near-bed concentration of airborne particles. To study the effect of particle shape on moisture bonding, we use two types of particles nearly equal in size: spherical glass beads $(d_{50} = 134\,\upmu \mathrm{m})$ and sieved quartz sand $(d_{50} = 139 \,\upmu \mathrm{m})$ . Both are poorly graded soils. We conducted these experiments at low moisture contents $({<}1\,\%)$ . We found that the spherical particles were more sensitive to changes in moisture than the sand, attributable to the large differences in specific surface area of the two particles. The larger specific surface area for sand is due to the surface roughness of the angular sand particle. Consequently, sand “stores” more moisture via surface adsorption, requiring higher soil moisture content to form liquid bridges between sand particles. Based on these findings, we extend the concept of a threshold moisture content, $w^{\prime }$ —originally proposed for clayey soils—to soils that lack any measureable clay content. This allows application of existing models developed for clayey soils that quantify the moisture effect on the threshold friction velocity to sand and silty soils (i.e., clay content $=$ 0). Additionally, we develop a model that quantifies the moisture effects on near-surface airborne particulate concentration, using experimental observations to determine the functional dependence on fluid and particle properties, including soil specific area. These models can be applied to numerical simulation of particulate plume formation and dispersion.     

Referencing of street-level flows measured during the DAPPLE 2004 campaign

Street-level mean flow and turbulence govern the dispersion of gases away from their sources in urban areas. A suitable reference measurement in the driving flow above the urban canopy is needed to both understand and model complex street-level flow for pollutant dispersion or emergency response purposes. In vegetation canopies, a reference at mean canopy height is often used, but it is unclear whether this is suitable for urban canopies. This paper presents an evaluation of the quality of reference measurements at both roof-top (height = H) and at height z = 9H = 190 m, and their ability to explain mean and turbulent variations of street-level flow. Fast response wind data were measured at street canyon and reference sites during the six-week long DAPPLE project field campaign in spring 2004, in central London, UK, and an averaging time of 10 min was used to distinguish recirculation-type mean flow patterns from turbulence. Flow distortion at each reference site was assessed by considering turbulence intensity and streamline deflection. Then each reference was used as the dependent variable in the model of Dobre et al. (2005) which decomposes street-level flow into channelling and recirculating components. The high reference explained more of the variability of the mean flow. Coupling of turbulent kinetic energy was also stronger between street-level and the high reference flow rather than the roof-top. This coupling was weaker when overnight flow was stratified, and turbulence was suppressed at the high reference site. However, such events were rare (<1% of data) over the six-week long period. The potential usefulness of a centralised, high reference site in London was thus demonstrated with application to emergency response and air quality modelling.     

Removal and formation of chlorinated triclosan derivatives in wastewater treatment plants using chlorine and UV disinfection

Triclosan, a common antimicrobial agent, may react during the disinfection of wastewater with free chlorine to form three chlorinated triclosan derivatives (CTDs). This is of concern because the CTDs may be photochemically transformed to tri- and tetra-chlorinated dibenzo-p-dioxins when discharged into natural waters. In this study, wastewater influent, secondary (pre-disinfection) effluent, and final (post-disinfection) effluent samples were collected on two occasions each from two activated sludge wastewater treatment plants, one using chlorine disinfection and one using UV disinfection. Concentrations of triclosan and three CTDs were determined using ultra performance liquid chromatography-triple quadrupole mass spectrometry with isotope dilution methodology. Triclosan and the CTDs were detected in every influent sample at levels ranging from 453 to 4530 and 2 to 98 ng L⁻¹, respectively, though both were efficiently removed from the liquid phase during activated sludge treatment. Triclosan concentrations in the pre-disinfection effluent ranged from 36 to 212 ng L⁻¹, while CTD concentrations were below the limit of quantification (1 ng L⁻¹) for most samples. In the treatment plant that used chlorine disinfection, triclosan concentrations decreased while CTDs were formed during chlorination, as evidenced by CTD levels as high as 22 ng L⁻¹ in the final effluent. No CTDs were detected in the final effluent of the treatment plant that used UV disinfection. The total CTD concentration in the final effluent of the chlorinating treatment plant reached nearly one third of the triclosan concentration, demonstrating that the chlorine disinfection step played a substantial role in the fate of triclosan in this system.