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  • 1
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    Diel light cycle as a key factor for modelling phytoplankton biogeography and diversity (2018)
    Elsevier
    In:  Ecological Modelling, 384 . pp. 241-248.
    Details
    Publication Date: 2021-02-08
    Description: Understanding the mechanisms driving species biogeography and biodiversity remains a major challenge in phytoplankton ecology. Using a model of two phytoplankton species with a gleaner-opportunist trade-off and competing for light and a limiting nutrient, we show that the diel light cycle may be an essential factor to explain large-scale ecological patterns. When only the seasonal light cycle is considered (control scenario) the model predicts that, independently of the nutrient supply, gleaners should dominate across all latitudes and oppor- tunists can obtain a temporal niche only at high latitudes. However, the diel light cycle makes the competition outcome also a function of nutrient supply by affecting the amplitude of diel nutrient oscillations, with gleaners dominating when nutrient supply is low, opportunists when nutrient supply is high, and both species coexisting at intermediate levels of nutrient supply. The combined effects of seasonal and diel light cycles (diel scenario) shape a latitudinal diversity gradient with decreasing diversity towards higher latitudes and a unimodal de- pendence of diversity on nutrient supply and, therefore, on ecosystem productivity. The proposed mechanism can help interpret the biogeography of major phytoplankton functional groups in the global ocean and link them with large-scale biodiversity patterns.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/j.ecolmodel.2018.06.022
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    Shape matters: cell geometry determines phytoplankton diversity (2020)
    In:  EPIC3bioRxiv
    Details
    Publication Date: 2020-11-26
    Description: Organisms’ size and shape have a profound influence on ecophysiological performance and evolutionary fitness, suggesting a link between morphology and diversity. While unimodal relationships between size and species richness were found for many taxa(1–4), much less is known on how richness is related to shape, in particular in the microbial realm. Here we analyse a novel globally extensive data set of marine unicellular phytoplankton, the major group of photosynthetic microbes, which exhibit an astounding diversity of cell sizes and shapes(5). We quantify the variation in size and shape and explore their effects on taxonomic diversity(6, 7). We find that cells of intermediate volume exhibit the greatest shape variation, with shapes ranging from oblate to extremely elongated forms, while very small and large cells are mostly compact (e.g., spherical or cubic). We show that cell shape has a strong effect on phytoplankton diversity, comparable in magnitude to the effect of cell volume, with both traits explaining up to 92% of the variance in phytoplankton diversity. Species richness decays exponentially with cell elongation and displays a log-normal dependence on cell volume, peaking for compact cells of intermediate volume. Our findings highlight different selective pressures and constraints on phytoplankton of different geometry and improve our understanding of the evolutionary rules of life.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , notRev
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  • 3
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    Shape matters: the relationship between cell geometry and diversity in phytoplankton (2020)
    Cold Spring Harbor Laboratory
    In:  EPIC3bioRxiv, Cold Spring Harbor Laboratory, ISSN: 0362-4331
    Details
    Publication Date: 2020-10-07
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 4
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    Resource competition and species coexistence in a two-patch metaecosystem model (2019)
    SPRINGER HEIDELBERG
    In:  EPIC3Theoretical Ecology, SPRINGER HEIDELBERG, ISSN: 1874-1738
    Details
    Publication Date: 2019-11-06
    Description: The metaecosystem framework has been proposed to conceptualize the interactive effects of dispersal and resource flows on the structure and functioning of communities in a heterogeneous environment. Here, we model a two-patch metaecosystem where two species with a trade-off in resource requirements compete for two limiting resources—generalizing the so-called gradostat experimental setup. We study the competition outcome in dependence of resource heterogeneity and between-patch diffusion for different combinations of resource supply ratios. Our numerical simulations show that community composition and local and regional diversity are determined by the interplay of resource heterogeneity, resource supply stoichiometry, and diffusion rate. High resource heterogeneity increases regional diversity, with species coexisting due to spatial segregation, whereas low resource heterogeneity favors local diversity, as species coexist mainly by local resource partitioning. Regional diversity averaged across a gradient of resource ratios decreases monotonically with diffusion rate, while local diversity follows a unimodal dependency. However, these dependencies become bimodal for high resource heterogeneity because various bistable states occur at intermediate diffusion rates. We identify three kinds of bistable states with species priority effect: (i) bistability between the dominance of one or the other competitor, (ii) bistability between one species dominance or species coexistence, and (iii) two alternative coexistence regimes differing in species-relative abundances. Most bistable states appear at high resource levels when biomass fluxes strongly interact with resource fluxes. Our analysis provides new insights for the potential effects of metaecosystem dynamics on biodiversity patterns.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 5
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    Competition-induced starvation drives large-scale population cycles in Antarctic krill (2017)
    Springer Nature
    In:  EPIC3Nature Ecology & Evolution, Springer Nature, 1(0177)
    Details
    Publication Date: 2017-11-29
    Description: Antarctic krill (Euphausia superba)—one of the most abundant animal species on Earth—exhibits a five to six year population cycle, with oscillations in biomass exceeding one order of magnitude. Previous studies have postulated that the krill cycle is induced by periodic climatological factors, but these postulated drivers neither show consistent agreement, nor are they supported by quantitative models. Here, using data analysis complemented with modelling of krill ontogeny and population dynamics, we identify intraspecific competition for food as the main driver of the krill cycle, while external climatological factors possibly modulate its phase and synchronization over large scales. Our model indicates that the cycle amplitude increases with reduction of krill loss rates. Thus, a decline of apex predators is likely to increase the oscillation amplitude, potentially destabilizing the marine food web, with drastic consequences for the entire Antarctic ecosystem.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 6
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    Biodiversity change is uncoupled from species richness trends: consequences for conservation and monitoring (2017)
    WILEY-BLACKWELL PUBLISHING
    In:  EPIC3Journal of Applied Ecology, WILEY-BLACKWELL PUBLISHING, pp. 1-16, ISSN: 0021-8901
    Details
    Publication Date: 2017-11-08
    Description: Global concern about human impact on biological diversity has triggered an intense research agenda on drivers and consequences of biodiversity change in parallel with international policy seeking to conserve biodiversity and associated ecosystem functions. Quantifying the trends in biodiversity is far from trivial, however, as recently documented by meta-analyses, which report little if any net change in local species richness through time. Here, we summarise several limitations of species richness as a metric of biodiversity change and show that the expectation of directional species richness trends under changing conditions is invalid. Instead, we illustrate how a set of species turnover indices provide more information content regarding temporal trends in biodiversity, as they reflect how dominance and identity shift in communities over time. We apply these metrics to three monitoring datasets representing different ecosystem types. In all datasets, nearly complete species turnover occurred, but this was disconnected from any species richness trends. Instead, turnover was strongly influenced by changes in species presence (identities) and dominance (abundances). We further show that these metrics can detect phases of strong compositional shifts in monitoring data and thus identify a different aspect of biodiversity change decoupled from species richness. Synthesis and applications: Temporal trends in species richness are insufficient to capture key changes in biodiversity in changing environments. In fact, reductions in environmental quality can lead to transient increases in species richness if immigration or extinction has different temporal dynamics. Thus, biodiversity monitoring programmes need to go beyond analyses of trends in richness in favour of more meaningful assessments of biodiversity change.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 7
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    Length-volume relationship of lake phytoplankton (2019)
    AMER SOC LIMNOLOGY OCEANOGRAPHY
    In:  EPIC3Limnology and Oceanography-Methods, AMER SOC LIMNOLOGY OCEANOGRAPHY, 17(1), pp. 58-68, ISSN: 1541-5856
    Details
    Publication Date: 2019-02-13
    Description: The shapes of phytoplankton units (unicellular organisms and colonies) are extremely diverse, and no unique relationship exists between their volume, V, and longest linear dimension, L. However, an approximate scaling between these parameters can be found because the shape variations within each size class are constrained by cell physiology, grazing pressure, and optimality of resource acquisition. To determine this scaling and to test for its seasonal and interannual variation under changing environmental conditions, we performed weighted regression analysis of time-dependent length-volume relations of the phytoplankton community in large deep Lake Constance from 1979 to 1999. We show that despite a large variability in species composition, the V(L) relationship can be approximated as a power law, V similar to L-alpha, with a scaling exponent alpha = 3 for small cells (L 〈 25 mu m) and alpha = 1.7 if the fitting is performed over the entire length range, including individual cells and colonies. The best description is provided by a transitional power function describing a regime change from a scaling exponent of 3 for small cells to an exponent of 0.4 in the range of large phytoplankton. Testing different weighted fitting approaches we show that remarkably the best prediction of the total community biovolume from measurements of L and cell density is obtained when the regression is weighted with the squares of species abundances. Our approach should also be applicable to other systems and allows converting phytoplankton length distributions (e.g., obtained with automatic monitoring such as flow cytometry) into distributions of biovolume and biovolume-related phytoplankton traits.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 8
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    Temporal declines in Wadden Sea phytoplankton cell volumes observed within and across species (2021)
    John Wiley & Sons, Inc. | Hoboken, USA
    Details
    Publication Date: 2022-03-30
    Description: Cell size is a master trait in the functional ecology of phytoplankton correlating with numerous morphological, physiological, and life‐cycle characteristics of species that constrain their nutrient use, growth, and edibility. In contrast to well‐known spatial patterns in cell size at macroecological scales or temporal changes in experimental contexts, few data sets allow testing temporal changes in cell sizes within ecosystems. To analyze the temporal changes of intraspecific and community‐wide cell size, we use the phytoplankton data derived from the Lower Saxony Wadden Sea monitoring program, which comprises sample‐ and species‐specific measurements of cell volume from 1710 samples collected over 14 yr. We find significant reductions in both the cell volume of most species and the weighted mean cell size of communities. Mainly diatoms showed this decline, whereas the size of dinoflagellates seemed to be less responsive. The magnitude of the trend indicates that cell volumes are about 30% smaller now than a decade ago. This interannual trend is overlayed by seasonal cycles with smaller cells typically observed in summer. In the subset of samples including environmental conditions, small community cell size was strongly related to high temperatures and low total phosphorus concentration. We conclude that cell size captures ongoing changes in phytoplankton communities beyond the changes in species composition. In addition, based on the changes in species biovolumes revealed by our analysis, we warn that using standard cell size values in phytoplankton assessment will not only miss temporal changes in size, but also lead to systematic errors in biomass estimates over time.
    Description: Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: Interreg V A program Deutschland‐Nederland of the European Union
    Description: Niedersächsisches Ministerium für Wissenschaft und Kultur http://dx.doi.org/10.13039/501100010570
    Description: https://doi.org/10.5281/zenodo.5799263
    Keywords: ddc:579.8 ; ddc:577.2
    Language: English
    Type: doc-type:article
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    CITATION GEO-LEO
  • 9
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    Shape matters: the relationship between cell geometry and diversity in phytoplankton (2021)
    In:  EPIC3Ecology Letters, 24(4), pp. 847-861, ISSN: 1461-023X
    Details
    Publication Date: 2021-09-14
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 10
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    Modeling drivers of biodiversity change emphasizes the need for multivariate assessments and rescaled targeting for management (2022)
    Wiley
    In:  EPIC3Conservation Science and Practice, Wiley, 4(10), ISSN: 2578-4854
    Details
    Publication Date: 2023-10-04
    Description: The current policy and goals aimed to conserve biodiversity and manage biodiversity change are often formulated at the global scale. At smaller scales however, biodiversity change is more nuanced leading to a plethora of trends in different metrics of alpha diversity and temporal turnover. Therefore, large-scale policy targets do not translate easily into local to regional management decisions for biodiversity. Using long-term monitoring data from the Wadden Sea (Southern North Sea), joining structural equation models and general dissimilarity models enabled a better overview of the drivers of biodiversity change. Few commonalities emerged as birds, fish, macroinvertebrates, and phytoplankton differed in their response to certain drivers of change. These differences were additionally dependent upon the biodiversity aspect in question and which environmental data were recorded in each monitoring program. No single biodiversity metric or model sufficed to capture all ongoing change, which requires an explicitly multivariate approaches to biodiversity assessment in local ecosystem management.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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