Temporal Variation In Environmental Conditions Research Articles

Spatial and temporal variability of algal community dynamics and productivity in floodplain wetlands along the Tanana River, Alaska

AbstractThe boreal landscape is a mosaic of wetlands with distinct ecosystem properties. Algae are important for wetland functioning, but relatively little is known about the structure of algal communities among boreal wetlands. We documented spatial and temporal variability of algal community dynamics and productivity during a growing season in 6 wetlands (1 rich and 1 poor fen, 1 tussock, and 3 riverine marshes) in interior Alaska. Algal biomass and productivity were greater in the poor fen and a riverine marsh than in all other wetlands. Water depth and nutrients were significant predictors of benthic algal biomass and productivity among wetlands and were greatest immediately after the spring thaw and decreased during the growing season. Water depth and nutrients (N and P) explained the most variability in algal community structure. Algal community structure differed among wetlands, and temporal variation in environmental conditions was a significant predictor of the relative abundance of algal genera ...

Changes in community assembly may shift the relationship between biodiversity and ecosystem function.

Can differences in community assemblyalter the relationship between biodiver-sity and ecosystem function? Pholchanet al. (2013) used a variety of manipu-lations to change microbial communityassembly in sludge reactors and exam-ined the subsequent links between diver-sity and a rare function, the removal ofendocrinedisruptingcompounds(EDCs).Interestingly, the authors saw no consis-tent differences between shifts in alphadiversity (e.g., species richness and even-ness) and ecosystem function, observingan increase, decrease and no difference inthe amount of removal of specific EDCswith increases in diversity. They suggestedthat differences in community assemblymay be driving variation in the rela-tionship between biodiversity and func-tion, a fascinating hypothesis that unitesprocesses in community and ecosystemecology.Combinations of four processes affectcommunity assembly: dispersal and diver-sification add new taxa to communitieswhile selection and drift affect their rela-tive abundances (Vellend, 2010; Nemergutet al., 2013). Particular research emphasishas been placed on assembly processesthataredriven bydifferences betweentaxa(“niche”) compared to those in whichany such differences are irrelevant to fit-ness(“neutral”)(Hubbell,2001).Likewise,researchers have focused on the roleof stochasticity, where assembly is moreprobabilistic vs. determinism, in whichrandomness does not affect communitydynamics.Nicheandneutralprocessescanoperateinunison(Adler et al., 2007)andboth can be affected by stochastic anddeterministic forces (Fox, 2012). Indeed,extensive data demonstrate that a varietyof factors, including nutrients, produc-tivity, resource availability, successionalstage, and disturbances may affect the rel-ative importance of different communityassembly mechanisms (Chase, 2007, 2010;Ferrenbergetal.,2013;Kardoletal.,2013).However, to our knowledge, no studieshave directly tested how shifts in com-munity assembly may affect the relation-ship between biodiversity and ecosystemfunction.Of course, a great deal of researchhas focused on pairwise combinationsof the interactions between communityassembly, biodiversity and/or function inisolation. First, a large body of workdemonstrates links between biodiversityand ecosystem function (Cardinale et al.,2011; Hooper et al., 2012), even formicrobial systems (Bell et al., 2005; Hsuand Buckley, 2009; Langenheder et al.,2010; Levine et al., 2011; Jousset et al.,2014). However, the nature and strengthof biodiversity ecosystem function (BEF)relationships have been widely debatedand strongly depend on the type of func-tion and ecosystem examined (Grime,1997; Hooper et al., 2005)andthedegree of redundancy within the com-munity (Reich et al., 2012; Jousset et al.,2014). These complexities may be height-ened for microorganisms due to theextraordinary phylogenetic diversity har-bored within microbial communities, andthe fact that a typical microbial commu-nity contains organisms from within avariety of functional guilds.Second, it is known that differentassemblymechanismsdrivebiodiversityindistinct ways. For example, spatial or tem-poral variation in environmental condi-tions increases biodiversity through nicheprocesses while increases in the diver-sity of the metacommunity or in theratio of immigration/emigration rates canincrease biodiversity through neutral pro-cesses (Vellend, 2010).Finally, a relatively new topic in the lit-erature relates community assembly andecosystem function (Fukami et al., 2010;Nemergut et al., 2013). Vital to such aconsideration is the relationship betweenresponse traits, or traits that can interactwithenvironmentalvariationtodeterminespecies distribution and abundance pat-terns, and effect traits, or traits that deter-mine the functional roles of different taxa(Naeem and Wright, 2003). When com-munities are largely structured by nicheprocesses, variation in the environmentcan directly correlate to effect traits thatare linked to selected response traits(Allison, 2012). However, when commu-nities are structured by neutral processes,ecosystem function will primarily dependon effect trait abundances within themetacommunity, dispersal and ecologicaldrift; thus, relationships between varia-tion in the environment and effect traits

Effects of Biochar on Soil Microbial Biomass after Four Years of Consecutive Application in the North China Plain

The long term effect of biochar application on soil microbial biomass is not well understood. We measured soil microbial biomass carbon (MBC) and nitrogen (MBN) in a field experiment during a winter wheat growing season after four consecutive years of no (CK), 4.5 (B4.5) and 9.0 t biochar ha−1 yr−1 (B9.0) applied. For comparison, a treatment with wheat straw residue incorporation (SR) was also included. Results showed that biochar application increased soil MBC significantly compared to the CK treatment, and that the effect size increased with biochar application rate. The B9.0 treatment showed the same effect on MBC as the SR treatment. Treatments effects on soil MBN were less strong than for MBC. The microbial biomass C∶N ratio was significantly increased by biochar. Biochar might decrease the fraction of biomass N mineralized (K N), which would make the soil MBN for biochar treatments underestimated, and microbial biomass C∶N ratios overestimated. Seasonal fluctuation in MBC was less for biochar amended soils than for CK and SR treatments, suggesting that biochar induced a less extreme environment for microorganisms throughout the season. There was a significant positive correlation between MBC and soil water content (SWC), but there was no significant correlation between MBC and soil temperature. Biochar amendments may therefore reduce temporal variability in environmental conditions for microbial growth in this system thereby reducing temporal fluctuations in C and N dynamics.

Environmental Records from Great Barrier Reef Corals: Inshore versus Offshore Drivers

The biogenic structures of stationary organisms can be effective recorders of environmental fluctuations. These proxy records of environmental change are preserved as geochemical signals in the carbonate skeletons of scleractinian corals and are useful for reconstructions of temporal and spatial fluctuations in the physical and chemical environments of coral reef ecosystems, including The Great Barrier Reef (GBR). We compared multi-year monitoring of water temperature and dissolved elements with analyses of chemical proxies recorded in Porites coral skeletons to identify the divergent mechanisms driving environmental variation at inshore versus offshore reefs. At inshore reefs, water Ba/Ca increased with the onset of monsoonal rains each year, indicating a dominant control of flooding on inshore ambient chemistry. Inshore multi-decadal records of coral Ba/Ca were also highly periodic in response to flood-driven pulses of terrigenous material. In contrast, an offshore reef at the edge of the continental shelf was subject to annual upwelling of waters that were presumed to be richer in Ba during summer months. Regular pulses of deep cold water were delivered to the reef as indicated by in situ temperature loggers and coral Ba/Ca. Our results indicate that although much of the GBR is subject to periodic environmental fluctuations, the mechanisms driving variation depend on proximity to the coast. Inshore reefs are primarily influenced by variable freshwater delivery and terrigenous erosion of catchments, while offshore reefs are dominated by seasonal and inter-annual variations in oceanographic conditions that influence the propensity for upwelling. The careful choice of sites can help distinguish between the various factors that promote Ba uptake in corals and therefore increase the utility of corals as monitors of spatial and temporal variation in environmental conditions.

Temporal and spatial benthic data collection via an internet operated Deep Sea Crawler

Environmental conditions within deep-sea ecosystems such as cold-seep provinces or deep-water coral reefs vary temporally and spatially over a range of scales. To date, short periods of intense ship-borne activity or low resolution, fixed location studies by Lander systems have been the main investigative methods used to investigate such sites.Cabled research infrastructures now enable sensor packages to receive power and transmit data from the deep-sea in real-time. By attaching mobile research platforms to these cabled networks, the investigation of spatial and temporal variability in environmental conditions and/or faunal behaviour across the deep sea seafloor is now a possibility.Here we describe one such mobile platform: a tracked Deep Sea Crawler, controlled in real-time via the Internet from any computer worldwide. The Crawler has been extensively used on the NEPTUNE Canada cabled observatory network at a cold-seep site at ∼890 m depth in the Barkley Canyon, NE Pacific. We present both the technical overview of the Crawler development and give examples of scientific results achieved.

Fluctuating selection and immigration as determinants of the phenotypic composition of a population

It is important to identify the factors that affect the evolutionary potential of populations to respond to environmental changes. Such processes are for example the ones affecting the amount of heritable phenotypic variation in a population. We examined factors explaining the wide phenotypic variation in the genetically determined black-brown dorsal colouration of male pied flycatchers (Ficedula hypoleuca) during a period of >50 years in a northern European breeding population. We demonstrate that the temperature-dependent relative breeding success of brown males predicts the inter-annual change in the proportion of the brown male phenotype. The proportion of brown males also appears to reflect immigration from Central Europe, where the brown type prevails due to local selection pressure. Warm springs in northern Central Europe had a positive effect on the proportion of the brown phenotype in the north in the early part of the study period, which suggests prolonged migration in favourable conditions. However, the association between warm springs and a high proportion of brown males has weakened from the 1950s to the present, which may explain why the proportion of the brown males in our study area decreased by a third during the period 1954 to 2008. This is likely a result of decreasing population size in Central Europe. These results demonstrate that temporal variation in environmental conditions is maintaining variation in the pied flycatcher male phenotype. They also indicate that climate warming has the potential to change the population composition both through temperature-dependent selection and environmental factors affecting long-distance immigration.

Microbial community assembly, theory and rare functions

Views of community assembly have traditionally been based on the contrasting perspectives of the deterministic niche paradigm and stochastic neutral models. This study sought to determine if we could use empirical interventions conceived from a niche and neutral perspective to change the diversity and evenness of the microbial community within a reactor treating wastewater and to see if there was any associated change in the removal of endocrine disrupting compounds (EDCs). The systematic removal of EDCs and micropollutants from biological treatment systems is a major challenge for environmental engineers. We manipulated pairs of bioreactors in an experiment in which “niche” (temporal variation in resource concentration and resource complexity) and “neutral” (community size and immigration) attributes were changed and the effect on the detectable diversity and the removal of steroidal estrogens was evaluated. The effects of manipulations on diversity suggested that both niche and neutral processes are important in community assembly. We found that temporal variation in environmental conditions increased diversity but resource complexity did not. Larger communities had greater diversity but attempting to increase immigration by adding soil had the opposite effect. The effects of the manipulations on EDC removal efficiency were complex. Decreases in diversity, which were associated with a decrease in evenness, were associated with an increase in EDC removal. A simple generalized neutral model (calibrated with parameters typical of wastewater treatment plants) showed that decreases in diversity should lead to the increase in abundance of some ostensibly taxa rare. We conclude that neither niche and neutral perspectives nor the effect of diversity on putative rare functions can be properly understood by naïve qualitative observations. Instead, the relative importance of the key microbial mechanisms must be determined and, ideally, expressed mathematically.

Factors affecting intraspecific variation in home range size of a large African herbivore

Factors affecting intraspecific variation in home range size have rarely been examined using modern statistical and remote sensing methods. This is especially true for animals in seasonal savanna environments in Africa, despite this biome’s importance for both conservation and development goals. We studied the impacts of spatial and temporal variability in environmental conditions, along with individual and social factors, on home range sizes in African buffalo (Syncerus caffer) in northeastern Namibia. Our data set spans 4 years, is derived from 32 satellite tracking collars, and contains over 35,000 GPS locations. We used the local convex hull method to estimate home range size from 31 buffalo captured at 6 sites. We used a variety of remotely sensed data to characterize potential anthropogenic and natural boundaries, as well as seasonal and temporal heterogeneity in environmental conditions. Using an information-theoretic, mixed effects approach, our analyses showed that home ranges varied over two orders of magnitude and are among the largest recorded for this species. Variables relating to vegetation and habitat boundaries were more important than abiotic environmental conditions and individual or social factors in explaining variation in home range size. The relative contributions of environmental, individual, social, and linear boundary variables to intraspecific home range size have rarely been examined and prior to this had not been assessed for any species in seasonal savannas of Africa. Understanding the factors that condition space-use patterns of wildlife in this area will lead to better-informed conservation and sustainable development decisions.

Modelling the skipjack tuna dynamics in the Indian Ocean with APECOSM-E: Part 1. Model formulation

APECOSM-E (Apex-Predator-Ecosystem-Model-Estimation) is a deterministic model that represents the 3D distribution and population dynamics of tropical tuna under the joint effect of environmental conditions and exploitation by fisheries. It is a simplified version of the top predator component of the APECOSM framework, based on a single partial differential equation. The model is structured in 3D space and fish size and considers size dependent reproduction, growth, predation, natural mortality and fishing mortality. Processes are time, space and size-dependent and linked to the environment through mechanistic bioenergetic or behavioral parameterizations. Physiological rates such as growth, reproduction and ageing mortality are derived from the Dynamic Energy Budget (DEB) theory, while horizontal movements and vertical distribution obey a mechanistically derived advection–diffusion formulation driven by habitat gradients and oceanic currents. The effect of fishing is accounted for through the use of fleet-specific size and depth selectivity functions and time-dependent catchability coefficients which relate observed fishing effort to catches and size-frequencies.In this paper we present the mathematical formulations of the physiological and behavioral components of the model, and an application to the skipjack tuna population in the Indian Ocean. The model is run with a daily time step on a 1°×1° horizontal grid and considers 20 vertical layers, reaching a maximal depth of 500m. Results show the effects of spatial and temporal variability of environmental conditions on tuna physiology in terms of growth, reproduction and survival. Moreover, our results suggest that observed trends in reported catches are connected to environmental conditions by means of recruitment dynamics. In addition, the model allows representing the horizontal and vertical distribution of skipjack tuna and assessing the effect of accessibility of the resource to fisheries. The ability of the model to represent the distribution of biomass in accordance with the pattern given by the observed fishing activity was evaluated by comparing the spatial distribution of the simulated biomass with the observed distribution of commercial purse seiners and bait boats catches in the Indian Ocean.The likelihood based method used for estimating the model parameters as well as an analysis of its sensitivity to their values is provided in a companion paper (Dueri et al., 2012).

The influence of habitat fragmentation on genetic diversity of a rare bird species that commonly faces environmental fluctuations

Habitat loss and fragmentation is one of the main causes of biodiversity loss. Rare species are generally thought to be more sensitive to habitat fragmentation than common ones as small populations become even smaller. We did a population genetic study on a rare bird, the Worthen's sparrow Spizella wortheni which is endemic to semi‐arid and arid regions of northeast Mexico. Its population numbers suffer greatly from the transformation of grassland into farmland that leads to a patchy distribution with locally small population sizes. Our data show that its genetic diversity is nevertheless high, few to no differentiation between study localities was found, and gene flow was high. Although we can not exclude that is too early to see an impact on the genetic level, we think that these results might be explained by the species’ biology: like many other birds living in arid areas, the Worthen's sparrow has a nomadic life style; depending on local conditions individuals flexibly move between areas. This behavior could enhance their ability to find suitable habitat patches in a fragmented landscape. Our results imply that nomadic behavior, which is an adaptation to high temporal variability in environmental conditions, may make species more resilient to spatial variability caused by habitat fragmentation. This insight contributes to identifying common factors such as nomadism that predict a species’ sensitivity to habitat fragmentation.

Temporal variations in natural attenuation of chlorinated aliphatic hydrocarbons in eutrophic river sediments impacted by a contaminated groundwater plume

Chlorinated aliphatic hydrocarbons (CAHs) often discharge into rivers as contaminated groundwater baseflow. Biotransformation, sorption and dilution of CAHs in the impacted river sediments have been reported to reduce discharge, but the effect of temporal variations in environmental conditions on the occurrence and extent of those processes in river sediments is largely unknown. We monitored the reduction of CAH discharge into the Zenne River during a 21-month period. Despite a relatively stable influx of CAHs from the groundwater, the total reduction in CAH discharge from 120 to 20cm depth in the river sediments, on average 74±21%, showed moderate to large temporal variations, depending on the riverbed location. High organic carbon and anaerobic conditions in the river sediments allowed microbial reductive dechlorination of both chlorinated ethenes and chlorinated ethanes. δ13C values of the CAHs showed that this biotransformation was remarkably stable over time, despite fluctuating pore water temperatures. Daughter products of the CAHs, however, were not detected in stoichiometric amounts and suggested the co-occurrence of a physical process reducing the concentrations of CAHs in the riverbed. This process was the main process causing temporal variations in natural attenuation of the CAHs and was most likely dilution by surface water-mixing. However, higher spatial resolution monitoring of flow transients in the riverbed is required to prove dilution contributions due to dynamic surface water–groundwater flow exchanges. δ13C values and a site-specific isotope enrichment factor for reductive dechlorination of the main groundwater pollutant vinyl chloride (VC) allowed assessment of changes over time in the extent of both biotransformation and dilution of VC for different scenarios in which those processes either occurred consecutively or simultaneously between 120 and 20cm depth in the riverbed. The extent of reductive dechlorination of VC ranged from 27 to 89% and differed spatially but was remarkably stable over time, whereas the extent of VC reduction by dilution ranged from 6 to 94%, showed large temporal variations, and was often the main process contributing to the reduction of VC discharge into the river.

The Goldilocks effect: intermittent streams sustain more plant species than those with perennial or ephemeral flow

Summary1. Drylands worldwide are typified by extreme variability in hydrologic processes, which structures riparian communities at various temporal and spatial scales. One key question is how underlying differences in hydrology over the length of interrupted perennial rivers influence spatial and temporal patterns in species richness and species composition.2. We examined effects of differences in dry season hydrology on species richness, composition and cover of herbaceous plant communities in the streamside zone (the zone influenced directly by low flows in the channel). Data were collected at ephemeral, intermittent and perennial flow reaches on three rivers of the desert Southwest (Arizona, U.S.A.): Lower Cienega Creek, Hassayampa River and Lower San Pedro River.3. Patterns of species richness varied with temporal scale of analysis, that is between single‐year and multi‐year time frames. At the annual timescale, quadrat species richness (m−2) and herbaceous cover were higher at sites with perennial flow than at either intermittent or ephemeral sites. In contrast to this single‐year pattern, the highest long‐term richness occurred at intermittent sites.4. Quadrat species richness, total species richness at a site (per 18 1‐m2 plots) and cover were more variable year to year at non‐perennial sites than at perennial flow sites. On two of the three rivers, ephemeral sites had the highest inter‐annual compositional variance, while the perennial sites had the lowest.5. Compositional differences between the hydrologic site types were dominated by species turnover, not nestedness. The perennial sites had more wetland and perennial species than the other two site types. The intermittent sites had more annual species than did the other two types.6. High long‐term species richness and distinct species composition of intermittent sites are probably sustained by pronounced temporal variability in environmental conditions (i.e. frequent and persistent flow events, and dry periods). Plants at these sites take advantage of greater moisture than those at ephemeral sites and also experience less competition from resident species than those at perennial sites.7. Conservation of desert riparian diversity depends upon the protection of consistently wet conditions at perennial flow sites, as well as the maintenance of the processes that cause fluctuations in environmental conditions at non‐perennial sites.

Otolith elemental evidence for spatial structuring in a temperate reef fish population

Elemental fingerprints of calcified structures can provide useful insight into dispersal, structure and connectivity of fish and invertebrate populations, but an assumption must be made that fingerprints reflect local physico-chemical conditions at the time of accretion. Physiological control of elemental uptake and temporal variability in environmental conditions can confound interpretation of spatial patterns. Multiple lines of evidence suggest that a commercially important temperate reef fish Parapercis colias (Forster 1801) (Pinguipedidae) in the New Zealand fjords forms discrete subpopulations at the mesoscale (10 to 20 km). We investigate otolith microchemistry as a tool to elucidate population structure and connectivity in the southern fjords. Concentrations of 12 elements (Li, B, Mg, P, S, Ca, Mn, Cu, Zn, Sr, Ba and Pb) were measured at the otolith edge (the most recently accreted region) using laser ablation inductively coupled plasma mass spectrometry (ICP-MS). Demographic and temporal variability were accounted for before spatial patterns were investigated. P:Ca, Sr:Ca and Ba:Ca ratios were positively correlated while Li:Ca was negatively correlated with age. Inter-annual variability in signatures within a single site was widespread. Independent of demography, fingerprints differed between inner and outer fjord subpopulations in Bradshaw-Thompson, Breaksea and Dusky Sounds but not in Doubtful Sound or Long Sound-Preservation Inlet. Solution and laser ablation ICP-MS were similarly able to discriminate between subpopulations of fish in a subset for which one sagitta was analysed by each technique. The assumption that fingerprints represent environmental conditions at the time of accretion is supported by a relocation study between habitats in Doubtful Sound. These results have important implications for temperate reef fish management and support the adoption of spatially explicit measures such as those in place in the New Zealand fjords. © Inter-Research 2011.

Parental migration, climate and thermal exposure of larvae: spawning in southern regions gives Northeast Arctic cod a warm start

Temporal variability in environmental conditions met by early life stages is consid- ered a key driver of fluctuations in recruitment and abundance of fish stocks. Variability in spawn- ing grounds selected by the parental population can change the environmental conditions encountered by the offspring, with consequences for recruitment. We compared how changes in spawning ground distribution and interannual climatic variation influenced the temperature exposure of eggs and larvae of Northeast Arctic cod Gadus morhua along the Norwegian coast. By using a general circulation model and 20 yr of forcing data, we tracked eggs and larvae from various spawning grounds and mapped temperature exposure, potential growth rate and theoret- ical survival probabilities in space and time. We found that the temperature history integrated over the early larval stages decreased by almost 4°C from southern to northern spawning grounds. Thus, variations in spawning ground usage have the potential to outweigh the interannual envi- ronmental variability, and consequently, shifts in spawning grounds may be more important than climatic variability in determining recruitment success. The long-term northbound shift and trun- cation of spawning grounds of the Northeast Arctic cod is thought to be caused by a size-selective trawl fishery in the Barents Sea, which promotes smaller and early maturing individuals to spawn farther north. This selection could increase offspring vulnerability to climatic changes, thereby strengthening the link between climate and recruitment.

Variable offspring size as an adaptation to environmental heterogeneity in a clonal plant species: integrating experimental and modelling approaches

Summary1. The production of variably sized offspring has been hypothesized to be adaptive to temporal variability in environmental conditions.2. This is difficult to verify empirically, and theoretical models are typically generic and not parameterized with data from real populations; studies integrating theoretical and empirical approaches to this problem are rare.3. Here, we present experimental data on the growth of Scirpus maritimus, a clonal aquatic macrophyte that grows through vegetative extensions involving tubers.4. The experiments show that offspring fitness (biomass productivity) is dependent on environmental conditions (water depth).5. Experimental data indicate that variation in offspring (tuber) sizes can be approximated by a lognormal distribution.6. We use these data to develop a different equation model of S. maritimus growth to test whether producing variably sized offspring is adaptive. The model compares fitness under the lognormal strategy to several hypothetical strategies with qualitatively different variance in offspring size.7. The model results suggest that lognormal variation in S. maritimus tuber size may be adaptive to the temporal variation in water levels that characterize its natural Mediterranean environment.8. We illustrate how the underlying principles that lend adaptive value to offspring size variation may apply to other species experiencing similar environmental conditions.9. Synthesis. Close integration of data and theoretical models creates a unique tool for investigating the adaptive value of life‐history traits in clonal aquatic plants.

Bigger or faster? Spring and summer tadpole cohorts use different life‐history strategies

Temporal variation in environmental conditions is a situation faced by prolonged breeders. Yet, few experimental studies provide evidence that such variation may lead to temporal divergence in life-history strategy. The breeding season of a prolonged breeder, the Indian rice frog Fejervarya limnocharis, is interrupted by a mid-summer drainage between the two rice crops, which separates the breeding population into spring and summer cohorts. We used a common garden experiment to test whether tadpoles of the two cohorts have evolved different metamorphic strategies to cope with different environmental temperatures. In a temperature (low and high) by cohort (spring and summer) factorial experiment, we found both spring and summer tadpoles had greater body growth rates, less weight loss before metamorphosis, and thus potentially higher fitness, when raised under their respective field temperatures. The spring tadpoles responded to low temperature with higher body weight at metamorphosis, while the summer tadpoles did not have such a response. On the other hand, while both spring and summer tadpoles responded to high temperature with accelerated developmental rates, summer tadpoles grew significantly faster than the spring ones. In conclusion, the study shows that spring and summer cohorts of Indian rice frog F. limnocharis use different life-history strategies to obtain higher fitness in their respective thermal environments.

Tree-ring width and vessel characteristics of oriental beech (Fagus Orientalis) along an altitudinal gradient in the caspian forests, northern iran

Vessel features of broadleaf trees may contain information about both spatial and temporal variations of environmental conditions. We report quantitative data about annual vessel characteristics for Oriental beech (Fagus orientalis Lipsky) in the Caspian forest in the Alborz Mountains, northern Iran. Time series of tree-ring width and of various vessel variables were constructed over a 50-year period for three sites along an altitudinal gradient from 1260 to 2200 m a.s.l. We evaluated the dependencies between ring width and vessel variables and estimated the influence of altitude and climate on these variables. Mean ring width and average vessel-lumen area decreased towards the high-elevation site whereas total vessel-lumen area was independent from altitude, and vessel density increased. Above-average warm summer and autumn seasons in the year prior to growth were negatively correlated with ring width and average vessel-lumen area whereas precipitation in the current June showed a positive association; vessel density responded exactly opposite to these climatic variables. Total vessel-lumen area was the only variable that reacted differently from site to site, mainly positively to temperature at 1200 m a.s.l. and negatively at 2000 and 2200 m a.s.l., whereas a consistent response to precipitation was lacking. The results indicate that vessel variables are meaningful indicators of changes in dynamics of wood formation in relation to climate along an altitudinal gradient in the Caspian mountains. As for climate reconstruction, we have to conclude that for our study area, vessel variables do not add much to information derived from ring width.

Direct coupling of a genome-scale microbial in silico model and a groundwater reactive transport model

The activity of microorganisms often plays an important role in dynamic natural attenuation or engineered bioremediation of subsurface contaminants, such as chlorinated solvents, metals, and radionuclides. To evaluate and/or design bioremediated systems, quantitative reactive transport models are needed. State-of-the-art reactive transport models often ignore the microbial effects or simulate the microbial effects with static growth yield and constant reaction rate parameters over simulated conditions, while in reality microorganisms can dynamically modify their functionality (such as utilization of alternative respiratory pathways) in response to spatial and temporal variations in environmental conditions. Constraint-based genome-scale microbial in silico models, using genomic data and multiple-pathway reaction networks, have been shown to be able to simulate transient metabolism of some well studied microorganisms and identify growth rate, substrate uptake rates, and byproduct rates under different growth conditions. These rates can be identified and used to replace specific microbially-mediated reaction rates in a reactive transport model using local geochemical conditions as constraints. We previously demonstrated the potential utility of integrating a constraint-based microbial metabolism model with a reactive transport simulator as applied to bioremediation of uranium in groundwater. However, that work relied on an indirect coupling approach that was effective for initial demonstration but may not be extensible to more complex problems that are of significant interest (e.g., communities of microbial species and multiple constraining variables). Here, we extend that work by presenting and demonstrating a method of directly integrating a reactive transport model (FORTRAN code) with constraint-based in silico models solved with IBM ILOG CPLEX linear optimizer base system (C library). The models were integrated with BABEL, a language interoperability tool. The modeling system is designed in such a way that constraint-based models targeting different microorganisms or competing organism communities can be easily plugged into the system. Constraint-based modeling is very costly given the size of a genome-scale reaction network. To save computation time, a binary tree is traversed to examine the concentration and solution pool generated during the simulation in order to decide whether the constraint-based model should be called. We also show preliminary results from the integrated model including a comparison of the direct and indirect coupling approaches and evaluated the ability of the approach to simulate field experiment.

Different Scales of Spatial Segregation of Two Species of Feather Mites on the Wings of a Passerine Bird

The "condition-specific competition hypothesis" proposes that coexistence of 2 species is possible when spatial or temporal variations in environmental conditions exist and each species responds differently to those conditions. The distribution of different species of feather mites on their hosts is known to be affected by intrinsic host factors such as structure of feathers and friction among feathers during flight, but there is also evidence that external factors such as humidity and temperature can affect mite distribution. Some feather mites have the capacity to move through the plumage rather rapidly, and within-host variation in intensity of sunlight could be one of the cues involved in these active displacements. We analyzed both the within- and between-feather spatial distribution of 2 mite species, Trouessartia bifurcata and Dolichodectes edwardsi , that coexist in flight feathers of the moustached warbler Acrocephalus melanopogon. A complex spatial segregation between the 2 species was observed at 3 spatial levels, i.e., "feather surfaces," "between feathers," and "within feathers." Despite certain overlapping distribution among feathers, T. bifurcata dominated proximal and medial regions on dorsal faces, while D. edwardsi preferred disto-ventral feather areas. An experiment to check the behavioral response of T. bifurcata to sunlight showed that mites responded to light exposure by approaching the feather bases and even leaving its dorsal face. Spatial heterogeneity across the 3 analyzed levels, together with response to light and other particular species adaptations, may have played a role in the coexistence and segregation of feather mites competing for space and food in passerine birds.

Repeatability of Female Reproductive Traits in Pigmy Rattlesnakes (Sistrurus miliarius)

The consistency of a trait's expression within individuals reflects both its maximal possible heritability and that trait's susceptibility to the influence of temporal variation in environmental conditions. A lack of repeatability in reproductive traits may also result if there are ontogenetic changes in female reproductive effort. In a decade-long study, we collected data on the reproductive traits (including female SVL, female postpartum condition, litter size, total litter mass, mean offspring mass, and birth date) of free-ranging Pigmy Rattlesnakes in central Florida. We captured and held the study snakes in field enclosures for several weeks before parturition each year. A total of 24 females produced two or more litters during the course of the study. We determined the repeatability for each reproductive trait. Our results indicated that four of the six reproductive traits had high and statistically significant repeatability despite annual variation in environmental conditions. A lack of growth in adult Sistrurus miliarius and the ability of females to skip reproduction in some years appear to foster the high repeatability of reproductive traits. Our research and previous studies indicate that many, but not all, reproductive traits in female snakes are highly repeatable. The repeatability of a few traits, particularly post-partum female condition, is likely to depend strongly on the reproductive mode of the species.