Predicting how food webs will respond to global environmental change is difficult because of the complex interplay between the abiotic forcing and biotic interactions. Mechanistic models of species interactions in seasonal environments can help understand the effects of global change in different ecosystems. Seasonally ice-covered lakes are warming faster than many other ecosystems and undergoing pronounced food web changes, making the need to forecast those changes especially urgent. Using a seasonally forced food web model with a generalist zooplankton grazer and competing cold-adapted winter and warm-adapted summer phytoplankton, we show that with declining ice cover, the food web moves through different dynamic regimes, from annual to biennial cycles, with decreasing and then disappearing winter phytoplankton blooms and a shift of maximum biomass to summer season. Interestingly, when predator-prey interactions were not included, a declining ice cover did not cause regime shifts, suggesting that both are needed for regime transitions. A cluster analysis of long-term data from Lake Baikal, Siberia, supports the model results, revealing a change from regularly occurring winter blooms of endemic diatoms to less frequent winter bloom years with decreasing ice cover. Together, the results show that even gradual environmental change, such as declining ice cover duration, may cause discontinuous or abrupt transitions between dynamic regimes in food webs.

Predicting how food webs will respond to global environmental change is difficult because of the complex interplay between the abiotic forcing and biotic interactions. Mechanistic models of species interactions in seasonal environments can help understand the effects of global change in different ecosystems. Seasonally ice-covered lakes are warming faster than many other ecosystems and undergoing pronounced food web changes, making the need to forecast those changes especially urgent. Using a seasonally forced food web model with a generalist zooplankton grazer and competing cold-adapted winter and warm-adapted summer phytoplankton, we show that with declining ice cover, the food web moves through different dynamic regimes, from annual to biennial cycles, with decreasing and then disappearing winter phytoplankton blooms and a shift of maximum biomass to summer season. Interestingly, when predator-prey interactions were not included, a declining ice cover did not cause regime shifts, suggesting that both are needed for regime transitions. A cluster analysis of long-term data from Lake Baikal, Siberia, supports the model results, revealing a change from regularly occurring winter blooms of endemic diatoms to less frequent winter bloom years with decreasing ice cover. Together, the results show that even gradual environmental change, such as declining ice cover duration, may cause discontinuous or abrupt transitions between dynamic regimes in food webs.

The spread of an enteric pathogen in the human gut depends on many interacting factors, including pathogen exposure, diet, host gut environment, and host microbiota, but how these factors jointly influence infection outcomes remains poorly characterized. Here we develop a model of host-mediated resource competition between mutualistic and pathogenic taxa in the gut that aims to explain why similar hosts, exposed to the same pathogen, can have such different infection outcomes. Our model successfully reproduces several empirically observed phenomena related to transitions between healthy and infected states, including (1) the nonlinear relationship between pathogen inoculum size and infection persistence, (2) the elevated risk of chronic infection during or after treatment with broad-spectrum antibiotics, (3) the resolution of gut dysbiosis with fecal microbiota transplants, and (4) the potential protection from infection conferred by probiotics. We then use the model to explore how host-mediated interventions-namely, shifts in the supply rates of electron donors (e.g., dietary fiber) and respiratory electron acceptors (e.g., oxygen)-can potentially be used to direct gut community assembly. Our study demonstrates how resource competition and ecological feedbacks between the host and the gut microbiota can be critical determinants of human health outcomes. We identify several testable model predictions ready for experimental validation.

Body size is an important trait of any organism, including phytoplankton, because it affects physiological and morphological performance, reproduction, population growth rate and competitive interactions. Understanding how interacting top-down and bottom-up factors influence phytoplankton cell size in different aquatic environments is still a challenge. Structural equation modeling (SEM) is a comprehensive multivariate statistical tool for detecting cause-effect relationship among different variables and their hierarchical structure in complex networks (e.g. trophic interactions in ecosystems). Here, several SEM models were employed to investigate the direct and indirect interaction pathways affecting the phytoplankton size structure in 44 mostly eutrophic and hypereutrophic permanent lakes in western Turkey. Among the 15 environmental variables tested, only rotifers and Carlson's Trophic Index (TSI) had significant direct positive effect on the mean phytoplankton size and size variance, respectively. The results indicate that both bottom-up and top-down factors significantly affect phytoplankton community size structure in eutrophic and hypereutrophic lakes in warm climates. Rotifer grazing increased the abundance of large-sized phytoplankton species, such as filamentous and colonial cyanobacteria and TSI affected phytoplankton size variance, with a higher size variance in hypereutrophic lakes.

This dataset reports the elemental composition of phytoplankton communities from multivariate mesocosm experiments conducted with a natural phytoplankton community from Narragansett Bay, RI. These data were assessed in Anderson et al. The Interactive Effects of Temperature and Nutrients on a Spring Phytoplankton Community (in prep). For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/848587 Copyright: https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0

This dataset represents microscopy cell counts from multivariate mesocosm experiments conducted with a natural phytoplankton community from Narragansett Bay, RI. These data were assessed in Anderson et al. The Interactive Effects of Temperature and Nutrients on a Spring Phytoplankton Community (in prep). For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/848977 Copyright: https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0

Despite increasing interest in winter limnology, few studies have examined under-ice zooplankton communities and the factors shaping them in different types of temperate lakes. To better understand drivers of zooplankton community structure in winter and summer, we sampled 13 lakes across a large trophic status gradient for crustacean zooplankton abundance, taxonomic and functional community composition and C/N stable isotopes. Average winter zooplankton densities were one-third of summer densities across the study lakes. Proportionally, cladocerans were more abundant in summer than winter, with the opposite pattern for calanoids and cyclopoids. In green (eutrophic) lakes, zooplankton densities were higher under the ice than in brown (dystrophic) and blue (oligotrophic) lakes, suggesting better conditions for zooplankton in productive lakes during winter. Overall, zooplankton communities were more similar across lakes under the ice than during the open water season. Feeding group classification showed a decrease in herbivore abundance and an increase in predators from summer to winter. C/N stable isotope results suggested higher lipid content in overwintering zooplankton and potentially increased reliance on the microbial loop by winter zooplankton. Our results show substantial variation in the seasonality of zooplankton communities in different lake types and identify some of the factors responsible for this variation.

As groundwater depletion becomes a global phenomenon, inland lake ecosystems are being impacted by decreasing groundwater supply. While the current trend of rapid surface warming of inland lakes continues, the deep waters can resist changes, depending on the nature of surface water - groundwater interactions. However, the effects of these interactions on lake processes are not fully understood. Here we investigate the role of groundwater on coupled biophysical processes in a deep, dimictic, groundwater-fed lake using mechanistic models combined with data from field observations. Although excess nutrient inputs are the most commonly cited reason for algal blooms, here we show that algal blooms in inland lakes can also appear due to a decreasing groundwater supply while all other factors remain the same. Results indicate that decreasing groundwater supply to lakes leads to elevated hypolimnetic temperatures, enhanced algal growth rates and algal blooms, and oxygen depletion, thus exacerbating the negative effects of surface warming. Our work suggests that globally declining groundwater supplies may have a significant negative effect on water quality of inland lakes by accelerating water column warming and stimulating algal growth, especially when the groundwater contribution to the lake system is significant compared to riverine discharge. The work provides insights for management efforts to improve the resilience of groundwater-dependent ecosystems in the face of external stressors.

Phytoplankton are key players in global biogeochemical cycles, and the effects of ocean warming on their carbon-nitrogen-phosphorus (CNP) stoichiometry, photosynthesis, size, morphology, growth rates, and other traits are of great ecological consequence. The physiological mechanisms of adaptation to temperature in phytoplankton are poorly understood, as are the consequences of the evolution of these processes (e.g., nutrient uptake, photosynthesis) for global biogeochemistry. In general, high temperatures favor smaller cells with higher surface area-to-volume ratios, but repeatable patterns in cellular CNP stoichiometry across temperature remain elusive. Here, we compared thermal reaction norms for cellular C, N, P, and chlorophyll a (Chl a) content and for carbon assimilation rate in replicate populations of the marine diatom Thalassiosira pseudonana evolved for 500 generations at 16 degrees C and 31 degrees C. We also examined the thermal reaction norms for cell volume and morphological traits. T. pseudonana has a cylindrical frustule and likely primarily exchanges materials with the environment through the round valve faces. We found that the 31 degrees C-selected T. pseudonana populations had smaller cells and higher per-biovolume densities of nutrients and Chl a than the 16 degrees C-selected populations across assay temperatures but there were no detectable patterns in CNP stoichiometry. The 31 degrees C-selected populations also had higher valve surface area-to-cell volume ratio that increased more with temperature, suggesting better nutrient uptake capabilities than in the 16 degrees C-selected populations. Our study demonstrates that temperature-dependent physiological plasticity may evolve differently at different temperatures and suggests that future phytoplankton communities will consist of smaller, more nutrient-dense cells.