Biology subjects

Kremer, C. T.

Publications and source records attributed to Kremer, C. T..

7 recordsLinked to original sources

bioRxiv2026

Phenotypic plasticity affects species packing in seasonally fluctuating environments

Environmental variability influences the evolution of phenotypic plasticity and the ecological interactions among species in communities, but it is unclear how these processes interact to affect ecological systems across scales. We investigate models describing how plasticity evolves in competitive communities exposed to seasonal variation in abiotic conditions. We conducted eco-evolutionary analyses to identify communities of coexisting species with evolutionarily stable plasticity traits. These analyses revealed that the presence of interspecific competitors constrained the evolution of plasticity in some species, which instead evolved to be specialists. Plasticity often impaired species coexistence by allowing individual species to control more niche space. Communities containing plastic species were usually less species-rich but more productive and less variable. Similar results were obtained when plasticity rate was evolutionarily labile, but plasticity rate altered the patterning of temporal niche partitioning. This work shows how plasticity and competition combine to shape ecological and trait responses to environmental variability.

ecology↗

bioRxiv2025

Warm-loving species perform well under limiting resources:trait combinations for future climate

Ecosystems are warming alongside shifts in other abiotic factors, leading to interactive effects on populations and communities. This underscores the importance of studying how organisms respond to multiple environmental changes simultaneously. In aquatic ecosystems, as surface waters of lakes and oceans warm, longer and stronger periods of thermal stratification lead to changes in resource (light and nutrient) availability. We investigate the combined effect of temperature and resource availability on 19 populations (comprising 17 species) of freshwater phytoplankton to examine how temperature influences the minimum resource requirements (and Monod parameters) for light, nitrogen, and phosphorus. We also evaluate how resource availability affects each populations thermal traits (i.e. thermal performance curve -TPC-parameters). When averaged across all populations, the requirements for light and phosphorus tended to display a U-shaped relationship along temperatures. Individual populations varied greatly in their responses to temperature, leading to shifts in the identity of the best competitor across the thermal gradient, particularly for nitrogen and phosphorus. TPC responses to resource limitation were highly variable, but thermal optima and maxima of individual populations often decreased with resource limitation, and thermal breadths (range where growth is 80% or more of its maximum) often increased due to a flattening of TPCs. Across all populations and resource types, the maximum optimum temperature across resource levels (maximum Topt) tended to be positively correlated with the temperature at which they had the lowest resource requirements (minimum R*). However, the temperature at which populations were the best competitors tended to be [~]5 {degrees}C colder on average than the temperature at which they grew the fastest. The populations with the highest thermal optima also had the lowest minimum resource requirements. Our findings reveal trait associations suggesting that some taxa already exhibit trait combinations that would support high performance under future warm and resource-limited conditions.

ecology↗

bioRxiv2025

Trait and Growth Responses to Sequential Environmental Change linked to Sensitivity in Synechococcus populations

O_LIEnvironmental change often occurs as a sequence of stressors rather than as isolated events. While the individual and combined effects of multiple stressors are well studied, the ecological consequences of sequential environmental change remain poorly understood. Such sequences, for example, a marine heatwave followed by seasonal herbicide runoff, are increasingly common under global change. C_LIO_LIWe investigated how legacy effects (the imprint of past environmental conditions) influence subsequent population performance and functional traits, and how these effects are mediated by strain-specific sensitivities. C_LIO_LIUsing a fully factorial design, we exposed six strains of the globally abundant pico-phytoplankton Synechococcus sp. to three environmental conditions: warming, herbicide exposure, and a control, under both chronic (same condition across time) and sequential (different conditions across time) regimes. We measured population performance (per-capita growth rate, maximum density) and key functional traits (cell size, chlorophyll content). C_LIO_LIPopulation responses diverged significantly between chronic and sequential exposures, revealing a strong legacy effect. Trait changes were often decoupled from growth metrics, suggesting independent response axes. Strain identity and its interaction with past conditions explained substantial variation in both growth and trait responses. C_LIO_LIWe identify and conceptualise four distinct mechanisms of legacy effects during sequential change: overcompensation, amplification, constraint and depression, each linked to strain-specific responses. Consequently, incorporating legacy effects into predictions of biodiversity dynamics and ecosystem function under global change is therefore both feasible and essential. C_LI

ecology↗

bioRxiv2024

Unexpected levels of antibiotic resistance in marine bacterial communities not solely explained by urban river discharge

Driven by anthropogenic pressures, antibiotic resistance has become more prevalent within urban bacterial communities over recent decades. In general, resistance is expected to spread from highly impacted areas into surrounding environments as the spatial patterns of resistance reflect the balance between the ability of dispersal and horizontal gene transfer to spread resistance, and the effects of dilution or selection driven by other environmental or ecological factors that change along these gradients. However, the strength and scale of this effect is less clear, especially in coastal environments. We investigated antibiotic resistance of bacterial communities along a transect from a freshwater site in the Los Angeles River (surrounded by high-density urban development) out into the San Pedro Basin in the Pacific Ocean. We determined the minimum concentration of twelve different antibiotics needed to inhibit the growth of bacterial communities across eight sites. We also examined community composition and the prevalence of known genes related to antibiotic resistance from anthropogenic sources in each sample using 16S rRNA sequencing and qPCR. In contrast to our expectations, marine bacteria communities displayed higher resistance than the freshwater LA River community. Rather than the presence of known resistance genes or proximity to urban impacts, patterns of resistance were more strongly associated with the higher species diversity found in marine communities. These unexpected results open new opportunities to determine why marine bacterial communities possess high resistance and the repercussions for potentially pathogenic bacteria and their impacts on the health of humans and wildlife.

microbiology↗

bioRxiv2024

How interactions between temperature and resources scale from populations to communities

Temperature and resources are fundamental factors that determine the ability of organisms to function and survive, while influencing their development, growth, and reproduction. Major bodies of ecological theory have emerged, largely independently, to address temperature and resource effects. It remains a major challenge to unite these ideas and determine the interactive effects of temperature and resources on ecological patterns and processes, and their consequences across ecological scales. Here, we propose a simple, physiologically motivated model capturing the interactive effects of temperature and resources (including inorganic nutrients and light) on the growth of microbial ectotherms over multiple ecological scales. From this model we derive a set of key predictions. At the population level, we predict (i) interactive effects of resource limitation on thermal traits, (ii) consistent differences in the temperature sensitivity of auto- and heterotrophs, and (iii) the existence of specific tradeoffs between traits that determine the shape of thermal performance curves. At the community level, we derive predictions for (iv) how limitation by nutrients and light can change the relationship between temperature and productivity. All four predictions are upheld, based on our analyses of a large compilation of laboratory data on microbial growth, as well as field experiments with marine phytoplankton communities. Collectively, our modeling framework provides a new way of thinking about the interplay between two fundamental aspects of life -- temperature and resources -- and how they constrain and structure ecological properties across scales. Providing links between population and community responses to simultaneous changes in abiotic factors is essential to anticipating the multifaceted effects of global change.

ecology↗

bioRxiv2020

Dual thermal ecotypes detected within a nearly genetically-identical population of the unicellular marine cyanobacterium Synechococcus

The extent and ecological significance of intraspecific diversity within marine microbial populations is still poorly understood, and it remains unclear if such strain-level microdiversity will affect fitness and persistence in a rapidly changing ocean environment. In this study, we cultured 11 sympatric strains of the ubiquitous marine picocyanobacterium Synechococcus isolated from a Narragansett Bay (Rhode Island, USA) phytoplankton community thermal selection experiment. Despite all 11 isolates being highly similar (with average nucleotide identities of >99.9%, with 98.6-100% of the genome aligning), thermal performance curves revealed selection at warm and cool temperatures had subdivided the initial population into thermotypes with pronounced differences in maximum growth temperatures. Within the fine-scale genetic diversity that did exist within this population, the two divergent thermal ecotypes differed at a locus containing genes for the phycobilisome antenna complex. Our study demonstrates that present-day marine microbial populations can contain microdiversity in the form of cryptic but environmentally-relevant thermotypes that may increase their resilience to future rising temperatures. SignificanceNumerous studies exist comparing the responses of distinct taxonomic groups of marine microbes to a warming ocean (interspecific thermal diversity). For example, Synechococcus, a nearly globally distributed unicellular marine picocyanobacterium that makes significant contributions to oceanic primary productivity, contains numerous taxonomically distinct lineages with well documented temperature relationships. Little is known though about the diversity of functional responses to temperature within a given population where genetic similarity is high (intraspecific thermal diversity). This study suggests that understanding the extent of this functional intraspecific microdiversity is an essential prerequisite to predicting the resilience of biogeochemically essential microbial groups such as marine Synechococcus to a changing climate.

microbiology↗

bioRxiv2020

Modeling How Community Assembly Alters the Functioning of Ecosystems

Although the effects of species richness on ecosystem functioning have been extensively studied, there is increased interest in understanding how community assembly in general might alter the functioning of ecosystems. We focus on two complementary approaches for evaluating how community assembly influences ecosystem function (here, productivity). The first quantifies the relative importance of complementarity and selection by contrasting monocultures with polycultures. The second identifies the effects of species losses and/or gains relative to the baseline polyculture, as well as the indirect effects on other species productivity. We evaluate and contrast these two approaches, using simulated communities structured by different, known competition mechanisms, where species compete for different resources and experience varying levels of environmental heterogeneity. We find that the metrics provided by these approaches can jointly discriminate the mechanisms of competition driving productivity. We then apply our methods to data from a long-term biodiversity-ecosystem experiment (the Jena Experiment) and find that the data do not correspond to any of the competition scenarios we modeled. We address two additional possible complications: facilitation by nitrogen fixing plants, and non-equilibrium behavior during community assembly, and find that a combination of resource competition and facilitation by nitrogen fixing plants is the more likely explanation for the results obtained at Jena.

ecology↗