Biology subjects

Gjoni, V.

Publications and source records attributed to Gjoni, V..

7 recordsLinked to original sources

bioRxiv2026

Thermal constraints shape metabolic scaling and distribution of the tufted ghost crab (Ocypode cursor) in the Mediterranean Sea

The Mediterranean Sea is undergoing significant environmental changes due to climate change and the introduction of non-native species, impacting biodiversity and ecosystem dynamics. Ocypode cursor (tufted ghost crab) has expanded its range, likely in response to changing thermal conditions.This study investigates the metabolic scaling of O. cursor across three active months (July, August, and September) under air- and water-breathing conditions during both daytime and nighttime. The results revealed seasonal variation in metabolic scaling, with significant differences in intercept values and scaling slopes among months. During daytime air-breathing conditions, metabolic rates increased in August and September regardless of body size, while at night in August, larger crabs exhibited higher metabolic rates. Under water-breathing conditions, smaller crabs showed greater metabolic responses in August during the day, whereas nighttime activity remained stable across months. These results indicate that temperature, diel cycle, and respiratory mode shape metabolic scaling as a comparative indicator of thermal performance rather than a direct proxy for fitness. Understanding these responses provides insight into O. cursors ecological flexibility and contributes to assessing ectotherm responses to ongoing Mediterranean warming.

ecology↗

bioRxiv2025

Temperature and predation alter metabolic scaling without changing size-based structure community in freshwater macroinvertebrates

Body size is a key trait that influences ecological processes such as metabolism, abundance, and species interactions. While the metabolic theory of ecology (MTE) proposes a universal scaling of metabolic rate with body mass, recent evidence shows that this relationship is not fixed. Environmental factors like temperature and predation can alter the metabolic scaling exponent, potentially reshaping size distribution. However, most research has examined these patterns within individual species, leaving open questions about how environmental drivers affect scaling at the community level. To address this, we performed a mesocosm experiment manipulating both temperature and fish predator presence in freshwater macroinvertebrate communities. We found that metabolic scaling at the community level is highly responsive to environmental context: warming steepened the scaling exponent in predator-free tanks but flattened it when predators were present. This suggests that larger individuals reduce their baseline metabolic rates under predation risk, especially at higher temperatures. Interestingly, the slope of the community size distribution remained stable across treatments, indicating that shifts in metabolic scaling occurred independently of changes in size structure. Together, these findings highlight the environmental sensitivity of metabolic scaling and suggest that links between metabolism scaling and size distribution may be more complex than MTE predicts.

ecology↗

bioRxiv2025

Biodiversity modulates the size-abundance relationship in changing environments

Organismal abundance tends to decline with increasing body size. Metabolic theory links this size structure with energy use and productivity, postulating a size-abundance slope of -0.75 that is invariant across environments. We tested the robustness of this relationship across gradients of protist species richness (1-6 species), temperature (15-25 {degrees}C), and time. Using replicated microcosms, we provide an empirical test of how temperature and biodiversity jointly shape the cross-community scaling relationship (CCSR). While our results support the expected of slope -0.75, we also found interactive effects showing the relationship is not invariant. Warming altered abundance scaling with size depending on richness; in high-richness communities, temperature favoured small protists, steepening the CCSR slope. These context-dependent responses emerged over time, suggesting a role of size-dependent species interactions in shaping responses to environmental change. Our findings demonstrate that cross-community size scaling is not fixed but shifts dynamically with ecological context.

ecology↗

bioRxiv2024

Size spectra in freshwater streams are consistent across temperature and resource supply

The study explores the individual size distribution (ISD) pattern in ecological communities, characterized by a negative correlation between individual body size and abundance (N [~] M{lambda}). The parameter {lambda} denotes the rate of decline in relative abundance from small to large individuals. Despite known influences of temperature and resource availability on body size, their effects on {lambda} remain diverse. Leveraging data from 2.4 million individual body sizes in continental freshwater streams, the research the hypothesis that {lambda} varies as a function of temperature and resource supply. Surprisingly, despite varied environmental conditions and complete species turnover, minimal variation in {lambda} (mean = -1.2, sd = 0.04) was observed, with no discernible impact from temperature or resource supply. The unexpected {lambda} value of -1.2 suggests a higher-than-expected relative abundance of large individuals, challenging assumptions of metabolic scaling at 0.75 and implying large subsidy inputs to large predators. Simulation and mesocosm experiments support a metabolic scaling coefficient of [~]0.4 for freshwater macroinvertebrates. The findings underscore remarkable consistency of individual size distributions in freshwater streams, likely driven by shallow metabolic scaling and large subsidies to large consumers.

ecology↗

bioRxiv2023

Detecting differences in Size Spectra

O_LIThe distribution of body size in communities is remarkably consistent across habitats and taxa and can be represented by size spectra, which are described by a power law. The focus of size spectra analysis is to estimate the exponent ({lambda}) of the power law. C_LIO_LIMany methods have been proposed for estimating{lambda} most of which involve binning the data, summing abundance within bins, and then fitting a ordinary least squares (OLS) regression in log-log space. However, recent work has shown that binning procedures may return biased estimates of size spectra exponents compared to procedures that directly estimate{lambda} using maximum likelihood estimation (MLE). Despite this variability in estimates, it is unclear if the relative change across environmental gradients is consistent across methodologies. Here, we used simulation to compare the ability of two binning methods (NAS, ELBn) and MLE to 1) recapture known values of{lambda} , and 2) recapture parameters in a linear regression measuring the change in{lambda} across a hypothetical environmental gradient. We also compared the methods using two previously published body size datasets across a pollution gradient and a temperature gradient C_LIO_LIMaximum likelihood methods always performed better than common binning methods, which demonstrated consistent bias depending on the simulated values of{lambda} . This bias carried over to the regressions, which were more accurate when{lambda} was estimated using MLE compared to the binning procedures. Additionally, the variance in estimates using MLE methods is markedly reduced when compared to binning methods. C_LIO_LIThe uncertainty and variation in estimates when using binning methods is often greater than or equal to the variation previously published in experimental and observational studies, bringing into question the effect size of previously published results. However, while the methods produced different slope estimates from previously published datasets, they were in qualitative agreement on the sign of those slopes (i.e., all negative or all positive). Our results provide further support for the direct estimation of{lambda} using MLE (or similar procedures) over the more common methods of binning. C_LI

ecology↗

bioRxiv2023

Bayesian hierarchical modeling of size spectra

O_LIA fundamental pattern in ecology is that smaller organisms are more abundant than larger organisms. This pattern is known as the individual size distribution (ISD), which is the frequency of all individual body sizes in an ecosystem. C_LIO_LIThe ISD is described by a power law and a major goal of size spectra analyses is to estimate the exponent of the power law, {lambda}. However, while numerous methods have been developed to do this, they have focused almost exclusively on estimating {lambda} from single samples. C_LIO_LIHere, we develop an extension of the truncated Pareto distribution within the probabilistic modeling language Stan. We use it to estimate multiple {lambda}s simultaneously in a hierarchical modeling approach. C_LIO_LIThe most important result is the ability to examine hypotheses related to size spectra, including the assessment of fixed and random effects, within a single Bayesian generalized (non)-linear mixed model. While the example here uses size spectra, the technique can also be generalized to any data that follows a power law distribution. C_LI

ecology↗

bioRxiv2022

Temperature and resources interact to shape phytoplankton size-abundance relationships at a continental scale

Communities contain more individuals of small species and fewer individuals of large species. The observed -3/4 slope relating mean size and mean abundance across communities (the cross-community scaling relationship or CCSR) is thought to arise from a 3/4-power scaling of metabolic rate with body size. Assuming that 3/4-power metabolic scaling is universal, as claimed by the metabolic theory of ecology (MTE), size-abundance relationships should also be invariant with a scaling exponent of -3/4 or nearly so, across environmental conditions. However, we find that the CCSR slope is actually -1 overall (perhaps due to isometric metabolic scaling), and varies substantially across temperature and nutrient gradients in 1048 freshwater lake phytoplankton communities in the USA. The size-abundance relationship is most shallow at low temperatures and high nutrients, and steeper and relatively insensitive to nutrients at high temperatures. Phytoplankton communities have orders of magnitude more small or large cells depending on environmental conditions than would be predicted from the MTE. Although based on observational data, these results suggest that the environment alters either metabolic scaling or other poorly understood processes shaping community size distributions.

ecology↗