Groundwater levels in many aquifers are declining due to anthropogenic activities such as increased highcapacity pumping for agriculture or climate-related decreases in natural recharge rates or a combination of factors. At the same time, lake surface temperatures are on the rise in response to a warming climate. As a first step toward evaluating the impacts of declining groundwater levels and warming lake surface temperatures on coupled biophysical processes in lakes, we evaluate the role played by groundwater in circulation and thermal structure within Gull Lake, a deep, dimictic, inland lake in Michigan, USA. A three-dimensional, unstructured grid hydrodynamic model was developed to investigate physical processes in the lake during the summer stratified period. We used high-resolution Acoustic Doppler Current Profiler observations of currents and lake levels as well as temperature data from thermistor chains to test the numerical models. The quality of meteorological forcing fields reconstructed using data from a network of weather stations surrounding the lake were assessed using outputs from a mesoscale numerical weather forecasting model, Weather Research and Forecasting (WRF) and vice versa. Model descriptions of internal heating due to the penetration of shortwave radiation as well as turbulent mixing within the water column were improved using in situ observations. Our results indicate that meteorological forcing fields, carefully reconstructed using WRF model outputs, can provide results comparable to those obtained from a network of weather station data, an important conclusion for modeling lakes in remote parts of the world. The observed low hypolimnetic temperatures could only be explained by taking the groundwater contribution into account and water column temperatures will increase by 8 degrees C or more on average if the groundwater contribution is absent. These results have implications for a number of key biophysical processes that control the structure and function of lake ecosystems including the growth rates of algae, dissolved inorganic nitrogen levels in the lake as well as the depletion of oxygen in deeper layers. (C) 2017 Elsevier Ltd. All rights reserved.

Rising lake temperatures and changing nutrient inputs are believed to favour the spread of a toxic invasive cyanobacterium, Cylindrospermopsis raciborskii (Woloszynska) Seenayya and Subba Raju, in temperate lakes. However, most evidence for these hypotheses is observational or based on physiological measurements in monocultures. We lack clear experimental evidence relating temperature and nutrients to the competitive success of C. raciborskii. To address this, we performed a 2 x 2 factorial laboratory experiment to study the dynamics of mixed phytoplankton communities subjected to different levels of temperature and phosphorus over 51 days. We allowed C. raciborskii to compete with ten different species from major taxonomic groups (diatoms, green algae, cryptophytes, and cyanobacteria) typical of temperate lakes, under low and high summer temperatures (25 and 30 A degrees C) at two levels of phosphorus supply (1 and 25 A mu mol L-1). Cylindrospermopsis raciborskii dominated the communities and strongly decreased diversity under low-phosphorus conditions, consistent with the hypothesis that it is a good phosphorus competitor. In contrast, it remained extremely rare in high-phosphorus conditions, where fast-growing green algae dominated. Surprisingly, temperature played a negligible role in influencing community composition, suggesting that changes in summer temperature may not be important in determining C. raciborskii's spread.

Numerous studies show that increasing species richness leads to higher ecosystem productivity. This effect is often attributed to more efficient portioning of multiple resources in communities with higher numbers of competing species, indicating the role of resource supply and stoichiometry for biodiversity-ecosystem functioning relationships. Here, we merged theory on ecological stoichiometry with a framework of biodiversity-ecosystem functioning to understand how resource use transfers into primary production. We applied a structural equation model to define patterns of diversity-productivity relationships with respect to available resources. Meta-analysis was used to summarize the findings across ecosystem types ranging from aquatic ecosystems to grasslands and forests. As hypothesized, resource supply increased realized productivity and richness, but we found significant differences between ecosystems and study types. Increased richness was associated with increased productivity, although this effect was not seen in experiments. More even communities had lower productivity, indicating that biomass production is often maintained by a few dominant species, and reduced dominance generally reduced ecosystem productivity. This synthesis, which integrates observational and experimental studies in a variety of ecosystems and geographical regions, exposes common patterns and differences in biodiversity-functioning relationships, and increases the mechanistic understanding of changes in ecosystems productivity. StoichFun_SEM_RichnessStoichFun_SEM_EvennessReadme_StoichFun Copyright: CC0 1.0 Universal (CC0 1.0) Public Domain Dedication

Biological diversity depends on the interplay between evolutionary diversification and ecological mechanisms allowing species to coexist. Current research increasingly integrates ecology and evolution over a range of timescales, but our common conceptual framework for understanding species coexistence requires better incorporation of evolutionary processes. Here, we focus on the idea of evolutionarily stable communities (ESCs), which are theoretical endpoints of evolution in a community context. We use ESCs as a unifying framework to highlight some important but under-appreciated theoretical results, and we review empirical research relevant to these theoretical predictions. We explain how, in addition to generating diversity, evolution can also limit diversity by reducing the effectiveness of coexistence mechanisms. The coevolving traits of competing species may either diverge or converge, depending on whether the number of species in the community is low (undersaturated) or high (oversaturated) relative to the ESC. Competition in oversaturated communities can lead to extinction or neutrally coexisting, ecologically equivalent species. It is critical to consider trait evolution when investigating fundamental ecological questions like the strength of different coexistence mechanisms, the feasibility of ecologically equivalent species, and the interpretation of different patterns of trait dispersion.

Rapid evolution in response to environmental change will likely be a driving force determining the distribution of species across the biosphere in coming decades. This is especially true of microorganisms, many of which may evolve in step with warming, including phytoplankton, the diverse photosynthetic microbes forming the foundation of most aquatic food webs. Here we tested the capacity of a globally important, model marine diatom Thalassiosira pseudonana, for rapid evolution in response to temperature. Selection at 16 and 31 degrees C for 350 generations led to significant divergence in several temperature response traits, demonstrating local adaptation and the existence of trade-offs associated with adaptation to different temperatures. In contrast, competitive ability for nitrogen (commonly limiting in marine systems), measured after 450 generations of temperature selection, did not diverge in a systematic way between temperatures. This study shows how rapid thermal adaptation affects key temperature and nutrient traits and, thus, a population's long-term physiological, ecological, and biogeographic response to climate change.

The human gut microbiome develops over early childhood and aids in food digestion and immunomodulation, but the mechanisms driving its development remain elusive. Here we use data curated from literature and online repositories to examine trait-based patterns of gut microbiome succession in 56 infants over their first three years of life. We also develop a new phylogeny-based approach of inferring trait values that can extend readily to other microbial systems and questions. Trait-based patterns suggest that infant gut succession begins with a functionally variable cohort of taxa, adept at proliferating rapidly within hosts, which gradually matures into a more functionally uniform cohort of taxa adapted to thrive in the anoxic gut and disperse between anoxic patches as oxygen-tolerant spores. Trait-based composition stabilizes after the first year, while taxonomic turnover continues unabated, suggesting functional redundancy in the traits examined. Trait-based approaches powerfully complement taxonomy-based approaches to understanding the mechanisms of microbial community assembly and succession.

Mass cultivation of algae for biofuel and other bioproduct production in outdoor, open raceway ponds has some considerable economic advantages. However, these systems would be subject to fluctuations in temperature (among other environmental factors), which can have dramatic effects on the growth rates of algal species and impact the overall productivity and quality of targeted algal crops. This study sought to elucidate the effects of temperature on algal growth rates, biomass accumulation, fatty acid production and composition. We surveyed 26 algal species from 5 different functional groups, growing them at 6 different temperatures between 9 and 32 degrees C. For each surveyed species, we collected eco-physiological trait data including maximum growth rate, thermal optimum (T-opt), thermal niche width, and lower and upper temperature limits for growth (CTmin and CTmax respectively); these data were also pooled for analysis at the functional group level. Responses to temperature varied among species, but at the functional group level we determined that the cyanobacteria have the highest thermal optimum (30.6 +/- 2.3 degrees C), followed by chlorophytes (25.7 +/- 0.1 degrees C) and diatoms (24.0 +/- 0.4 degrees C). Temperature-specific fatty acid (FA) production was mostly controlled by growth rates, though some change in production was attributable to modification of intracellular FA stores. Temperature affected FA profiles in diverse ways, with no consistent trends across species or functional groups. In sum, temperature significantly impacts the overall productivity of algal biofuel systems by influencing species growth rates and fatty acid production. While algal growth rates varied predictably with temperature, we did not find the generalizable trends in temperature dependence of FA composition, suggesting that some aspects of algal cultivation for bioproducts in outdoor, open-air systems may be less predictable. However, a compilation of algal growth and FA composition responses to temperature, such as ours, may be useful for choosing appropriate species for given temperature regimes.

Temperature effects on the fatty acid (FA) profiles of phytoplankton, major primary producers in the ocean, have been widely studied due to their importance as industrial feedstocks and to their indispensable role as global producers of long-chain, polyunsaturated FA (PUFA), including omega-3 (omega3) FA required by organisms at higher trophic levels. The latter is of global ecological concern for marine food webs, as some evidence suggests an ongoing decline in global marine-derived omega3 FA due to both a global decline in phytoplankton abundance and to a physiological reduction in omega3 production by phytoplankton as temperatures rise. Here, we examined both short-term (physiological) and long-term (evolutionary) responses of FA profiles to temperature by comparing FA thermal reaction norms of the marine diatom Thalassiosira pseudonana after ~500 generations (ca. 2.5 years) of experimental evolution at low (16°C) and high (31°C) temperatures. We showed that thermal reaction norms for some key FA classes evolved rapidly in response to temperature selection, often in ways contrary to our predictions based on prior research. Notably, 31°C-selected populations showed higher PUFA percentages (including omega3 FA) than 16°C-selected populations at the highest assay temperature (31°C, above T. pseudonanas optimum temperature for population growth), suggesting that high-temperature selection led to an evolved ability to sustain high PUFA production at high temperatures. Rapid evolution may therefore mitigate some of the decline in global phytoplankton-derived omega3 FA production predicted by recent studies. Beyond its implications for marine food webs, knowledge of the effects of temperature on fatty acid profiles is of fundamental importance to our understanding of the mechanistic causes and consequences of thermal adaptation. 1-FattyAcids_total.measured_molar_05182-FattyAcids_mol.biovolume_raw_05183-FattyAcids_percentages_raw_11184-FattyAcids_MCL_WUnSat_raw_0518 Copyright: CC0 1.0 Universal (CC0 1.0) Public Domain Dedication