Biology subjects

Ghedini, G.

Publications and source records attributed to Ghedini, G..

9 recordsLinked to original sources

bioRxiv2026

Species demography, not metabolic rate, predicts community dominance independently of initial evenness

Understanding how species traits shape community properties is a central goal in ecology. But whether traits drive consistent patterns of dominance and assembly regardless of initial species abundances (evenness) remains unclear. We addressed this question using phytoplankton microcosm experiments to disentangle the effects of evenness and traits on community assembly and functioning, focusing on traits related to energy use (photosynthesis, size) alongside demographic parameters. Community assembly was highly deterministic, indicating that initial evenness had little influence on species dominance and final community structure. Instead, evenness drove community functioning. Demography was a stronger predictor of dominance than photosynthetic rates or individual size, suggesting that growth and competitive success depend on multiple metabolic processes that cannot be reduced to simpler proxies. These results show that community structure can emerge predictably across a range of initial conditions, and highlight the importance of demographic metrics over simpler metabolic descriptors for forecasting community outcomes.

ecology↗

bioRxiv2026

Trait-dependent species responses weaken the effects of response diversity on community stability

The diversity of species responses to environmental change (response diversity) is a key mechanism of ecological stability. However, anticipating where strong or weak stabilizing responses emerge is challenging because species responses can depend on the local community and the specific stability metric. Whether species traits can consistently inform on how species respond to disturbances - enabling less context-dependent predictions - remains an open question. To address this gap, we use microcosm experiments on marine phytoplankton to test how response diversity supports multiple aspects of community stability under pulse temperature changes, testing both an increase (heatwave) and a decrease in temperature (coldspell). We then map species traits to their responses in a community to identify which traits modulate and predict species sensitivities. Fundamental response diversity, based on the diversity of species responses to temperature measured in isolation, was a weak predictor of community stability, and relationships differed between disturbances (i.e., heatwave and coldspell). Instead, species traits were consistent predictors of species responses in communities. Small, fast-growing species were more tolerant and benefited from the disturbance, while large, slow-growing species were less tolerant and decreased in proportion - these patterns were consistent across disturbances and community compositions. These results suggest that strong trait-performance relationships might reduce the importance of response diversity for stability. But these findings also show that general species traits, such as size and growth rate, can predict which species, and how, contribute to community responses, providing an empirical basis to relate species traits to stability outcomes under climate change.

ecology↗

bioRxiv2026

Ecological predictability emerges at the population level in phytoplankton communities

Predicting the composition and dynamics of ecological communities is challenging because complexity increases rapidly with species richness. A common strategy is to adopt a reductionist framework in which community dynamics are inferred from simpler components, such as population-level parameters or organismal traits. However, it remains unclear at which level of biological organization ecological predictability emerges. Here we experimentally test this reductionist cascade in marine phytoplankton communities. We first ask whether multispecies dynamics can be quantitatively predicted from demographic parameters measured in monocultures and species pairs. We then test whether these predictive parameters can themselves be inferred from organismal traits, focusing on cell size. We find that community composition is highly reproducible and can be accurately predicted from population-level parameters measured in simpler experimental settings. In contrast, these parameters do not show systematic relationships with cell size and cannot be predicted from this commonly used trait. These results demonstrate that ecological predictability emerges at the population level, where demographic parameters capture the combined effects of underlying biological processes, but resist further reduction to simple trait-based descriptions, suggesting that ecological interactions reshape organismal performance across levels of organisation.

ecology↗

bioRxiv2025

Universal sublinear population growth density dependence unrelated to resource limitation

Growth slows as population density increases, sensitively influencing species coexistence, conservation, and resource management. This slowdown is widely attributed to declining per-capita access to energy and nutrients, and standard models of resource-limited growth predict superlinear declines of growth rate with density. However, we observed sublinear declines for 94% of 4,022 bacterial and eukaryotic growth curves. High-resolution experiments with Escherichia coli revealed a two-phase density dependence: a dominant sublinear regime that transitions to superlinear decline only very near population saturation. The sublinear pattern was invariant across initial resource concentrations, ruling out resource depletion as the cause of early slowing. Our results challenge the standard resource-limitation paradigm and identify non-resource inhibitory processes as a widespread and previously unappreciated regulator of population growth.

ecology↗

bioRxiv2025

Drivers of metabolic density-dependence: how resource availability and conspecific cues affect phytoplankton metabolism

Metabolism is density-dependent from unicellular to multicellular organisms. Understanding what drives metabolic suppression is important to explain population growth given the link between metabolism and biomass production. In the simplest scenario, metabolic suppression is caused by a reduction in resource availability with increasing population density. But both theory and experiments suggest that organisms can actively downregulate metabolism in crowded conditions. We experimentally disentangle the importance of resource competition and conspecific cues that signal crowding on the metabolism of three phytoplankton species of varying cell sizes at different growth phases. All species downregulated some aspects of their metabolism in response to cues; this response varied in strength but could not be explained by differences in species size. The addition of nutrients weakened and, in some cases, completely removed metabolic suppression, indicating that resource availability mediates responses to cues. Overall, respiration rates were more responsive to cues than photosynthesis, showing a differential regulation of processes of energy intake and expenditure depending on both resource availability and conspecific cues. These factors also led to rapid plastic changes in cell size possibly related to cell division and growth. Altogether, changes in size and metabolism indicate that cues can trigger self-regulatory adjustments that might limit growth, but these effects are modulated by nutrient availability and species traits not related to size. These results suggests that growth predictions solely based on resource availability might overestimate the rates at which organisms and populations grow, with important implications for how we describe species and community dynamics.

ecology↗

bioRxiv2025

Eco-evolutionary dynamics between multiple competitors reduce phytoplankton coexistence but have limited impacts on community productivity

Species can evolve rapidly in response to competition but how evolution within communities affects community properties is unclear. To test this, we grew three marine phytoplankton species in monoculture (alone) or polyculture (together) for 17 weeks. We then combined them in communities based on their competition history (monoculture or polyculture isolates) and tracked their composition and productivity over time. We found that species dominance was unaffected, but coexistence was reduced when species evolved together (polyculture isolates). Total biovolume was robust to changes in species relative abundances. However, polyculture isolates had greater oxygen fluxes during exponential phase and were less robust to the addition of an invader. Our results suggest that evolution within communities can strengthen competitive differences between species with uneven effects on different aspects of community functioning. Thus, we should be cautious in extrapolating the consequences of evolution on community biomass to other aspects of productivity or stability.

ecology↗

bioRxiv2024

Evolution under competition increases phytoplankton production by reducing the density-dependence of net energy fluxes and growth

Competition can drive rapid evolution but forecasting how species evolve in communities remains difficult. Life history theory predicts that evolution in crowded environments should maximise population production, with intra- and inter-specific competition producing similar outcomes if species compete for similar resources. Despite its appeal, this prediction has rarely been tested in communities. To test its generality and identify its physiological basis, we experimentally evolved four species of marine phytoplankton (spanning three orders of magnitude in cell size) alone or together in a community for 4.5 months. We then quantified changes in their metabolism, demography, and competitive ability at two timepoints ([~]60 and 120 generations) in common garden experiments. One species was outcompeted during the evolution experiment. For the other three, we found the same evolutionary outcome: species evolved greater biovolume production regardless of competition treatment but did so either by increasing max. population size or individual cell size. Biovolume production increased because of the differential evolution of photosynthesis and respiration under intense competition. These metabolic changes meant that intraspecific competition decreased and cells maintained higher rates of net energy production and growth as populations neared the stationary phase. Overall, these results show that intra- and inter-specific competition influence physiological and population parameters similarly in species that compete for essential resources. Life history theory thus provides a valuable base for predicting how species evolve in communities, and our results show how these predictions connect with the evolution of metabolism and competitive ability.

ecology↗

bioRxiv2024

Biomass competition unifies individual and community scaling patterns

Both metabolism and growth scale sublinearly with body mass for most species. Ecosystems show the same sublinear scaling between production and total biomass but ecological theory cannot reconcile the existence of these nearly identical scalings at different levels of biological organization. We solve this paradox using marine phytoplankton to connect individual and ecosystem scalings across three orders of magnitude in body size and biomass. Competitive interactions determined by biomass, rather than differences in species size, slow metabolism in a consistent fashion across species that dominates over species-specific peculiarities, resulting in a unique behavior across community compositions. The allometry of ecosystem production thus emerges from this metabolic density-dependence, independently of the equilibrium state or resource regime of the system. Our findings demonstrate the mechanistic basis of ecosystem allometries, unifying aspects of physiology and ecology to explain why growth patterns are so strikingly similar across scales.

ecology↗

bioRxiv2022

Metabolic and demographic evolution in response to interspecific competition

Competition can drive rapid evolution which, in turn, alters the trajectory of ecological communities. The role of eco-evolutionary dynamics in ecological communities is increasingly well-appreciated, but a mechanistic framework for identifying the types of traits that will evolve, and their trajectories, is required. Metabolic theory makes explicit predictions about how competition should shape the evolution of metabolism and size but these predictions have gone largely untested, particularly in eukaryotes. We use experimental evolution of a eukaryotic phototroph to examine how metabolism, size, and demography coevolve under both inter- and intra-specific competition. We find that the focal species evolves a smaller body size in response to competition, reducing density-dependence and maximizing carrying capacity. Metabolic theory successfully predicted most of these adaptations, but we also find important departures from theory. Longer-term evolution (70 generations) led to Pareto improvements in both population growth rate and carrying capacity, suggesting that classic r-K trade-offs observed among species can be evaded within species. The evasion of this trade-off appeared to arise due to the rapid evolution of enhanced metabolic plasticity: lineages exposed to competition evolved more labile metabolisms that tracked resource availability more effectively than lineages that were competition-free. We predict that rapid evolution in both size and metabolism may be a ubiquitous feature of adaptation to changing resource regimes that occur via species invasions and environmental change.

ecology↗