Size and shape profoundly influence an organism’s ecophysiological performance and evolutionary fitness, suggesting a link between morphology and diversity. However, not much is known about how body ...shape is related to taxonomic richness, especially in microbes. Here we analyse global datasets of unicellular marine phytoplankton, a major group of primary producers with an exceptional diversity of cell sizes and shapes and, additionally, heterotrophic protists. Using two measures of cell shape elongation, we quantify taxonomic diversity as a function of cell size and shape. We find that cells of intermediate volume have the greatest shape variation, from oblate to extremely elongated forms, while small and large cells are mostly compact (e.g. spherical or cubic). Taxonomic diversity is strongly related to cell elongation and cell volume, together explaining up to 92% of total variance. Taxonomic diversity decays exponentially with cell elongation and displays a log‐normal dependence on cell volume, peaking for intermediate‐volume cells with compact shapes. These previously unreported broad patterns in phytoplankton diversity reveal selective pressures and ecophysiological constraints on the geometry of phytoplankton cells which may improve our understanding of marine ecology and the evolutionary rules of life.
Cell shape and size are the result of natural selection, but little is known about how shape depends on size and how they affect biodiversity. Using data on dimensions of unicellular marine algae, we show that shape and volume are interrelated: shapes of intermediate‐volume cells range from flattened to extremely elongated, while shapes of small and large cells are always compact. Taxonomic diversity peaks for intermediate‐volume cells with compact shapes, displays a log‐normal dependence on cell volume and decrease exponentially with cell surface extension for elongated or flattened cells.
Understanding the mechanisms of phytoplankton community assembly is a fundamental issue of aquatic ecology. Here, we use field data from transitional (e.g. coastal lagoons) and coastal water ...environments to decode patterns of phytoplankton size distribution into organization and adaptive mechanisms. Transitional waters are characterized by higher resource availability and shallower well-mixed water column than coastal marine environments. Differences in physico-chemical regime between the two environments have been hypothesized to exert contrasting selective pressures on phytoplankton cell morphology (size and shape). We tested the hypothesis focusing on resource availability (nutrients and light) and mixed layer depth as ecological axes that define ecological niches of phytoplankton. We report fundamental differences in size distributions of marine and freshwater diatoms, with transitional water phytoplankton significantly smaller and with higher surface to volume ratio than marine species. Here, we hypothesize that mixing condition affecting size-dependent sinking may drive phytoplankton size and shape distributions. The interplay between shallow mixed layer depth and frequent and complete mixing of transitional waters may likely increase the competitive advantage of small phytoplankton limiting large cell fitness. The nutrient regime appears to explain the size distribution within both marine and transitional water environments, while it seem does not explain the pattern observed across the two environments. In addition, difference in light availability across the two environments appear do not explain the occurrence of asymmetric size distribution at each hierarchical level. We hypothesize that such competitive equilibria and adaptive strategies in resource exploitation may drive by organism's behavior which exploring patch resources in transitional and marine phytoplankton communities.
Behaviour related to patch resource exploitation is a major determinant of individual fitness. Assuming the size-dependency of patch departure behaviour, model-based approaches have shown ...size-mediated coexistence in systems of competing species. However, experimental evidence for the influence of body size on patch use behaviour is scarce. In this study, we explore whether allometric principles provide an underlying framework for interspecific patterns of resource use. To this end, we propose a meso-cosm approach using three species of gastropods differing in size as a model system and 32P radio-isotopic techniques as a measure of resource use. Foragers of different size were placed in an artificial patch, provided with a limited amount of labelled resource and let them free to move as resources decrease and scarcity is sensed. We investigated the extent to which individual body size affects the exploitation of resources by examining Giving Up Density (GUD), Giving Up Time (GUT), resource absorption rate and exploitation efficiency as components of individual exploitation behaviour. To compare positive, constant and negative individual size scaling of population energy requirements, experimental trials with an equal numbers and equal biomass of differently sized foragers were carried out, and an experimental trial with equal metabolic requirements was simulated. We observed clear size dependency in the patch departure behaviour of the experimental organisms. Even under conditions of equivalent overall population energy requirements, larger foragers decided to leave the resource patch earlier and at a higher density of resources than smaller ones. Smaller foragers were able to prolong their presence and make more use of the resources, resulting in an inverse body-size scaling of resource exploitation efficiency.
Functional trait-based approaches have undergone an extraordinary expansion in phytoplankton ecology. Morpho-functional traits have been shown to vary both within and between populations and species, ...potentially affecting individual fitness and the network of inter-individual relationships. Here we integrate six fully harmonized phytoplankton morpho-functional trait datasets, characterized by a fine data grain, reporting individual-level data over a large biogeographical area. Datasets refer to transitional water ecosystems, from five biogeographical areas: Northern Atlantic Ocean (Scotland), South-Western Atlantic Ocean (Brazil), South-Western Pacific Ocean (Australia), Indo Pacific Ocean (Maldives) and Mediterranean Sea (Greece and Turkey). The integrated dataset includes 127311 individual phytoplankton records with sampling locations, taxonomic and morphometric information according to Darwin Core standards and semantic annotations. The six FAIR datasets are openly available in the LifeWatch Italy data portal. The datasets have already been used for morpho-functional analyses and hypothesis testing on phytoplankton guilds at different levels of data aggregation and scale, from local to global.
Elucidating the underlying mechanisms behind variations of animal space and resource use is crucial to pinpoint relevant ecological phenomena. Organism's traits related to its energy requirements ...might be central in explaining behavioral variation, as the ultimate goal of a forager is to fulfill its energy requirements. However, it has remained poorly understood how energy requirements and behavioral patterns are functionally connected. Here we aimed to assess how body mass and standard metabolic rate (SMR) influence behavioral patterns in terms of cumulative space use and time spent in an experimental patchy environment, both within species and among individuals irrespective of species identity. We measured the behavioral patterns and SMR of two invertebrate species, that is, amphipod Gammarus insensibilis, and isopod Lekanesphaera monodi, individually across a range of body masses. We found that species of G. insensibilis have higher SMR level, in addition to cumulatively exploring a larger space than L. monodi. Cumulative space use scaled allometrically with body mass, and it scaled isometrically with SMR in both species. While time spent similarly in both species was characterized by negative body mass and SMR dependence, it was observed that L. monodi individuals tended to stay longer in resource patches compared to G. insensibilis individuals. Our results further showed that within species, body mass and metabolic rate explained a similar amount of variation in behavior modes. However, among individuals, regardless of species identity, SMR had stronger predictive power for behavioral modes compared to body mass. This suggests that SMR might offer a more generalized and holistic description of behavioral patterns that extend beyond species identity. Our study on the metabolic and body mass scaling of space and resource use behavior sheds light on higher‐order ecological processes such as species' competitive coexistence along the spatial and trophic dimensions.
Our study explores how metabolic rate and body size are related to space use behavior, using invertebrate as model species. It shows that metabolic rate, encompassing variations related to species‐specific characteristics, is associated with behavior beyond mere size.
Phytoplankton guilds are commonly characterised by dominance effects, while the main contribution to biological diversity is given by rare species. Here, we analysed the influence of rare species on ...taxonomic and functional diversity, which is described by taxa richness and composition, cell size, and size–abundance relationships in phytoplankton guilds. We explore these relationships at global and regional scales by analysing phytoplankton guilds from five biogeographical regions: the Northern Atlantic Ocean (Scotland), the South-Western Atlantic Ocean (Brazil), the South-Western Pacific Ocean (Australia), the Indo-Pacific Ocean (Maldives), and the Mediterranean Sea (Greece and Turkey). We have comparatively analysed the phytoplankton taxonomic diversity of the whole dataset and with the datasets obtained by progressively subtracting taxa occurring in the last 1%, 5%, 10%, and 25% of both numerical abundance and overall biomass. Globally, 306 taxa were identified across five ecoregions with only 27 taxa accounting for 75% of overall numerical abundance and biomass; almost 50% of taxa were lost on every step. The removal of 1% of most rare taxa significantly affected the phytoplankton size–abundance relationships and body-size structure, strongly impacting on small taxa. The progressive removal of additional rare taxa did not further affect phytoplankton size–abundance relationships and size structure.
•Phytoplankton data sets of more than 4000 samples and 849 taxa were analysed.•Diversity indices were evaluated for the environmental assessment of pelagic habitat.•Some indices can distinguish two ...levels of anthropogenic impact.•Phytoplankton communities at SE sites are more diverse than at NW sites.
According to the methodological standards established by Marine Strategy Framework Directive, the assessment for the pelagic habitat under the Biodiversity Descriptor should be carried out at the regional or sub-regional level. In the case of Mediterranean Sea, the sub-regional assessment seems optimal to take into account biogeographic differences in species composition and functional characteristics. Previous research has shown that phytoplankton diversity indicators are efficient for reliable environmental assessments, although more effort has been recommended to test these indicators on a wide spatial scale to cover wider gradients of natural and anthropogenic pressures. In this work, a set of eight diversity indices was tested against the pressure levels within a common data set of the structure and abundance of phytoplankton communities from the Adriatic, Ionian and Aegean Seas. Expert knowledge was used to define four categories of impacts that take into account partial pressures, such as point and non-point pollution, industry, ports and fisheries. At the level of the common data set, most of the diversity, evenness and dominance indices could only distinguish between the highest level of impact and the rest of impact categories. These indices maintained the distinction between two levels of subsequently dichotomised impacts (no to low impact vs. high impact) across latitudinal and longitudinal gradients. On average, the indices were less sensitive to impacts in the northernmost and westernmost areas than in the southernmost and easternmost areas, although they still showed a significant response. The results also suggest that phytoplankton communities become more uniform and less dominated by a single taxon as sampling depth increases at sites with low impact, while evenness and dominance at impacted sites remain similar at all depths. In order to establish meaningful definitions of good environmental status and targets for pelagic habitats in the Mediterranean Sea, it is necessary to establish spatially specific thresholds by additional examination of indices of good performance.
Individual space and resource use are central issues in ecology and conservation. Recent technological advances such as automated tracking techniques are boosting ecological research in this field. ...However, the development of a robust method to track space and resource use is still challenging for at least one important ecosystem component: motile aquatic macroinvertebrates. The challenges are mostly related to the small body size and rapid movement of many macroinvertebrate species and to light scattering and wave signal interference in aquatic habitats.
We developed a video tracking method designed to reliably assess space use behavior among individual aquatic macroinvertebrates under laboratory (microcosm) conditions. The approach involves the use of experimental apparatus integrating a near infrared backlight source, a Plexiglas multi‐patch maze, multiple infrared cameras, and automated video analysis. It allows detection of the position of fast‐moving (~ 3 cm/s) and translucent individuals of small size (~ 5 mm in length, ~1 mg in dry weight) on simulated resource patches distributed over an experimental microcosm (0.08 m2).
To illustrate the adequacy of the proposed method, we present a case study regarding the size dependency of space use behavior in the model organism Gammarus insensibilis, focusing on individual patch selection, giving‐up times, and cumulative space used.
In the case study, primary data were collected on individual body size and individual locomotory behavior, for example, mean speed, acceleration, and step length. Individual entrance and departure times were recorded for each simulated resource patch in the experimental maze. Individual giving‐up times were found to be characterized by negative size dependency, with patch departure occurring sooner in larger individuals than smaller ones, and individual cumulative space used (treated as the overall surface area of resource patches that individuals visited) was found to scale positively with body size.
This approach to studying space use behavior can deepen our understanding of species coexistence, yielding insights into mechanistic models on larger spatial scales, for example, home range, with implications for ecological and evolutionary processes, as well as for the management and conservation of populations and ecosystems. Despite being specifically developed for aquatic macroinvertebrates, this method can also be applied to other small aquatic organisms such as juvenile fish and amphibians.
We developed a video tracking method designed to reliably assess space use behavior among individual aquatic macroinvertebrates.To illustrate the utility of the proposed method, we present a case study regarding the size dependency of space and resource use behavior in Gammarus insensibilis, focusing on individual's patch selection, giving‐up time, and cumulative space used .We observed the negative size dependency of individual giving‐up time, showing that patch departure occurred sooner in larger individuals than smaller ones and that individual cumulative space used scaled positively with body size.
Biological trait analysis (BTA) is a method that describes ecological functioning of species assemblages incorporating information on species' distributions and their biological characteristics. In ...the present study, soft bottom communities of three Mediterranean coastal lagoons with different degree of salinity range were analyzed for seven biological traits (mobility, habitat, feeding type, habitat modification, body form, body size and feeding apparatus) in order to investigate the differences in communities' structure and functional diversity across a scale of natural stress. In more variable environments semi-mobile and epibenthic organisms prevailed, while predators were found under more stable conditions. Multivariate analyses using biological traits gave similar results with those obtained by the traditional analyses using species abundances; however, the distinction among lagoons was less evident, indicating that in transitional waters species can be different but their biological traits similar. This supports the idea of species redundancy in transitional water ecosystems.
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