There is a growing consensus that traits offer a powerful way to examine the relationship between the environment, organismal strategies, species interactions, and ecological success. To date, trait-based research has largely been focusing on individual trophic levels and not on cross-level interactions. Looking at traits not only within but across trophic levels and identifying traits that together define trophic interactions holds a great potential for understanding the mechanisms of interactions. Here, we outline the conceptual foundation for cross-trophic trait-based frameworks, using planktonic food webs as an example. First, we compile a list of traits important within different individual trophic levels and show that there are traits that are common across trophic levels ("universal" traits), as well as trophic level-specific traits. Next, we focus on traits that characterize interactions across trophic levels, focusing on two types of interaction-grazer-primary producer and host-parasite, identifying the similarities and differences between these interactions. We outline the trait hierarchies that define possible and realized intertrophic interactions and their strengths. We then highlight the importance of trade-offs among those traits in shaping interactions and explaining general patterns in the structure and function of food webs. Finally, we discuss the environmental influences on traits, their eco-evolutionary responses to changing conditions and how those responses may alter trophic interactions. The extension of trait-based approaches from individual trophic levels to food webs and different trophic interactions should stimulate further conceptual development, enrich the field of aquatic sciences, and provide a framework to better predict global change effects on ecosystems.

Hydrolab and nutrient data collected from Gull Lake, Michigan, USA during years 2014-15 and reported in the paper below:Safaie, A., Litchman, E., and Phanikumar, M.S., Decreasing Groundwater Supply Can Exacerbate Lake Warming and Trigger Algal Blooms, Journal of Geophysical Research - Biogeosciences (2021)

A complex interplay of environmental variables impacts phytoplankton community composition and physiology. Temperature and nutrient availability are two principal factors driving phytoplankton growth and composition, but are often investigated independently and on individual species in the laboratory. To assess the individual and interactive effects of temperature and nutrient concentration on phytoplankton community composition and physiology, we altered both the thermal and nutrient conditions of a cold-adapted spring phytoplankton community in Narragansett Bay, Rhode Island, when surface temperature was 2.6 degrees C and chlorophyll > 9 mu g L-1. Water was incubated in triplicate at -0.5 degrees C, 2.6 degrees C, and 6 degrees C for 10 d. At each temperature, treatments included both nutrient amendments (N, P, Si addition) and controls (no macronutrients added). The interactive effects of temperature and resource availability altered phytoplankton growth and community structure. Nutrient amendments resulted in species sorting and communities dominated by larger species. Under replete nutrients, warming tripled phytoplankton growth rates, but under in situ nutrient conditions, increased temperature acted antagonistically, reducing growth rates by as much as 33%, suggesting communities became nutrient limited. The temperature-nutrient interplay shifted the relative proportions of each species within the phytoplankton community, resulting in more silica rich cells at decreasing temperatures, irrespective of nutrients, and C : N that varied based on resource availability, with nutrient limitation inducing a 47% increase in C : N at increasing temperatures. Our results illustrate how the temperature-nutrient interplay can alter phytoplankton community dynamics, with changes in temperature amplifying or exacerbating the nutrient effect with implications for higher trophic levels and carbon flux.

Mathematica code for "A general framework for species-abundance distributions: linking traits and dispersal to explain commonness and rarity", Ecology Letters. Requires: Wolfram Mathematica (tested on v13.1) EcoEvo package (tested on v1.6.4) This research was supported by the Simons Foundation grant 343149, NSF grant DEB 17-54250 and NASA grant 80NSSC18K1084. Copyright: Creative Commons Attribution 4.0 International Open Access

Mathematica code for "A general framework for species-abundance distributions: linking traits and dispersal to explain commonness and rarity", Ecology Letters. Requires: Wolfram Mathematica (tested on v13.1) EcoEvo package (tested on v1.6.4) This research was supported by the Simons Foundation grant 343149, NSF grant DEB 17-54250 and NASA grant 80NSSC18K1084. Copyright: Creative Commons Attribution 4.0 International Open Access

Dental microwear consists of microscopic damage features on the occlusal surfaces of tooth enamel and reflects physical properties of the diet, as well as enamel structure and post- mortem history of the tooth. Microwear analysis has been used to infer the diets of extinct mammals through comparison of features on fossil teeth with those on teeth of living mammals with known diets. A method for documenting microwear of large mammals using a light microscope was developed as an alternative to approaches based on scanning electron microscopy. We adapted this method for investigating microwear features on squirrel teeth. Both modern and fossil squirrels occur in diverse terrestrial habitats and eat a range of herbivorous to omnivorous diets.

Dental microwear consists of microscopic damage features on the occlusal surfaces of tooth enamel and reflects physical properties of the diet, as well as enamel structure and post-mortem history of the tooth. Microwear analysis has been used to infer the diets of extinct mammals through comparison of features on fossil teeth with those on teeth of living mammals with known diets. A method for documenting microwear of large mammals using a light microscope was developed as an alternative to approaches based on scanning electron microscopy. We adapted this method for investigating microwear features on squirrel teeth. Both modern and fossil squirrels occur in diverse terrestrial habitats and eat a range of herbivorous to omnivorous diets. We compared microwear features from upper molars of several modern species of frugivorous tree squirrels and omnivorous ground squirrels. We also examined fossil sciurids from the Miocene Siwalik sequence of Pakistan and a Pliocene locality in the central plains of the United States. We found significant differences in microwear features among modern squirrels of different diets and habitats, suggesting that microwear features can be used to infer the diets or preferred habitats of extinct species. Microwear features were preserved on some of the fossil specimens. A comparison of Pliocene Spermophilus rexroadensis to modern Spermophilus suggests a diet similar to that of the modern species examined. Microwear of Miocene Eutamias differed from the pattern in any of the living squirrels examined. The approach presented here holds strong potential for illuminating the trophic ecomorphology of small-mammal fossils.

The principal objections to the proposition that organic agriculture can contribute significantly to the global food supply are low yields and insufficient quantities of organically acceptable fertilizers. We evaluated the universality of both claims. For the first claim, we compared yields of organic versus conventional or low-intensive food production for a global dataset of 293 examples and estimated the average yield ratio (organic: non-organic) of different food categories for the developed and the developing world. For most food categories, the average yield ratio was slightly < 1.0 for studies in the developed world and > 1.0 for studies in the developing world. With the average yield ratios, we modeled the global food supply that could be grown organically on the current agricultural land base. Model estimates indicate that organic methods could produce enough food on a global per capita basis to sustain the current human population, and potentially an even larger population, without increasing the agricultural land base. We also evaluated the amount of nitrogen potentially available from fixation by leguminous cover crops used as fertilizer. Data from temperate and tropical agroecosystems suggest that leguminous cover crops could fix enough nitrogen to replace the amount of synthetic fertilizer currently in use. These results indicate that organic agriculture has the potential to contribute quite substantially to the global food supply, while reducing the detrimental environmental impacts of conventional agriculture. Evaluation and review of this paper have raised important issues about crop rotations under organic versus conventional agriculture and the reliability of grey-literature sources. An ongoing dialogue on these subjects can be found in the Forum editorial of this issue.

When aerobic microbes deplete oxygen sufficiently, anaerobic metabolisms activate, driving losses of fixed nitrogen from marine oxygen minimum zones. Biogeochemical models commonly prescribe a 1-10 mu M critical oxygen concentration for this transition, a range consistent with previous empirical and recent theoretical work. However, the recently developed STOX sensor has revealed large regions with much lower oxygen concentrations, at or below its 1-10 nM detection limit. Here, we develop a simplified metabolic model of an aerobic microbe to provide a theoretical interpretation of this observed depletion. We frame the threshold as O*(2), the subsistence oxygen concentration of an aerobic microbial metabolism, at which anaerobic metabolisms can coexist with or outcompete aerobic growth. The framework predicts that this minimum oxygen concentration varies with environmental and physiological factors and is in the nanomolar range for most marine environments, consistent with observed concentrations. Using observed grazing rates to calibrate the model, we predict a minimum oxygen concentration of order 0.1-10 nM in the core of a coastal anoxic zone. We also present an argument for why anammox may be energetically favorable at a higher oxygen concentration than denitrification, as some observations suggest. The model generates hypotheses that could be tested in the field and provides a simple, mechanistic, and dynamic parameterization of oxygen depletion for biogeochemical models, without prescription of a fixed critical oxygen concentration.