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  • 1
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    Manipulation of Non-random Species Loss in Natural Phytoplankton: Qualitative and Quantitative Evaluation of Different Approaches (2017)
    Frontiers
    In:  Frontiers in Marine Science, 4 .
    Details
    Publication Date: 2020-02-06
    Description: Ecological research in recent decades revealed that species loss has a predominantly negative effect on ecosystem functioning and stability. Most of these studies were based on random species loss scenarios, but extinctions in nature are not random. Recent experimental studies using macroscopic communities largely advanced knowledge about the effects of non-random species loss. However, in microscopic communities like the phytoplankton, implementing realistic species loss scenarios is challenging and experimental data are scarce. Creating more realistic experiments to study the role of phytoplankton diversity for ecosystem functioning is particularly important, as they provide up to 50% of global primary productivity, form the basis of all pelagic food webs, and are important for biogeochemical cycling. In this study, we experimentally tested and evaluated three methods for non-random species loss in a natural marine phytoplankton community. Dilution, filtration, and heat stress removed the targeted rare, large, and sensitive species, respectively. All these species groups are extremely vulnerable to extinction in future climate scenarios and play important roles in the communities. Dilution and filtration with a fine mesh additionally decreased initial biomass, which increased the variability of species left in the respective replicates. The methods tested in this study can be used to non-randomly manipulate phytoplankton species diversity in communities used for experiments. However, in studies where species identities are more important than species richness, the dilution and filtration methods should be modified to eliminate the effect of decreasing initial biomass.
    Type: Article , PeerReviewed
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    DOI: 10.3389/fmars.2017.00317
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    Extinction Debt in Source-Sink Metacommunities (2011)
    Public Library of Science
    In:  PLoS ONE, 6 (3). e17567.
    Details
    Publication Date: 2019-09-23
    Description: In an increasingly modified world, understanding and predicting the consequences of landscape alteration on biodiversity is a challenge for ecologists. To this end, metacommunity theory has developed to better understand the complexity of local and regional interactions that occur across larger landscapes. While metacommunity ecology has now provided several alternative models of species coexistence at different spatial scales, predictions regarding the consequences of landscape alteration have been done exclusively for the competition-colonization trade off model (CC). In this paper we investigate the effects of landscape perturbation on source-sink metacommunities. We show that habitat destruction perturbs the equilibria among species competitive effects within the metacommunity, driving both direct extinctions and an indirect extinction debt. As in CC models, we found a time lag for extinction following habitat destruction that varied in length depending upon the relative importance of direct and indirect effects. However, in contrast to CC models, we found that the less competitive species are more affected by habitat destruction. The best competitors can sometimes even be positively affected by habitat destruction, which corresponds well with the results of field studies. Our results are complementary to those results found in CC models of metacommunity dynamics. From a conservation perspective, our results illustrate that landscape alteration jeopardizes species coexistence in patchy landscapes through complex indirect effects and delayed extinctions patterns.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1371/journal.pone.0017567
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Nutrient enrichment alters phytoplankton biomass and composition via silicon limitation (2024)
    Frontiers
    Details
    Publication Date: 2024-06-05
    Description: Despite management efforts, anthropogenic nutrient enrichments continue to enhance phytoplankton blooms worldwide. Release of nitrogen and phosphorus compounds not only provides surplus of nutrients but also disbalances their stoichiometry. Declines in the relative availability of dissolved silicon might induce limitation in diatoms, major primary producers with silicified shells. We studied experimentally how nutrient enrichment and resulting decline in dissolved silicon to nitrogen ratios (Si:N) affect the structure and functioning of natural plankton communities. Nitrate was added to create a range of Si:N ratios and phosphate was supplied in Redfield ratio to nitrogen. We also manipulated copepod abundance to understand the top-down effects on communities experiencing nutrient enrichment. Nitrogen and phosphorus additions resulted in a steep phytoplankton biomass increase, followed by a post-bloom decline. Phytoplankton bloom biomass was higher in high nitrogen treatments but during the post-bloom period this trend switched. Biomass was sustained longer in high Si:N treatments, indicating that silicon limitation terminates the bloom. Many diatom species did not benefit from nitrogen and phosphorus enrichment and diatom dominance ceased below Si:N of 0.4:1. Under high grazing pressure, silicate was taken up faster suggesting that silicification is important in diatom defense. Copepods shaped plankton communities via feeding on dinoflagellates, chlorophytes and the diatom Skeletonema costatum but there was no significant effect of nitrogen and phosphorus enrichment on copepod abundance. Our results, combined with previous studies, show that while nutrient concentrations define the total phytoplankton bloom biomass, resource ratios are important in sustaining biomass and determining community structure and composition.
    Type: Article , PeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    Eco-Evolutionary Interaction in Competing Phytoplankton: Nutrient Driven Genotype Sorting Likely Explains Dominance Shift and Species Responses to CO2 (2020)
    Frontiers
    Details
    Publication Date: 2023-02-08
    Description: How ecological and evolutionary processes interact and together determine species and community responses to climate change is poorly understood. We studied long-term dynamics (over approximately 200 asexual generations) in two phytoplankton species, a coccolithophore (Emiliania huxleyi), and a diatom (Chaetoceros affinis), to increased CO2 growing alone, or competing with one another in co-occurrence. To allow for rapid evolutionary responses, the experiment started with a standing genetic variation of nine genotypes in each of the species. Under co-occurrence of both species, we observed a dominance shift from C. affinis to E. huxleyi after about 120 generations in both CO2 treatments, but more pronounced under high CO2. Associated with this shift, we only found weak adaptation to high CO2 in the diatom and none in the coccolithophore in terms of species’ growth rates. In addition, no adaptation to interspecific competition could be observed by comparing the single to the two-species treatments in reciprocal assays, regardless of the CO2 treatment. Nevertheless, highly reproducible genotype sorting left only one genotype remaining for each of the species among all treatments. This strong evolutionary selection coincided with the dominance shift from C. affinis to E. huxleyi. Since all other conditions were kept constant over time, the most parsimonious explanation for the dominance shift is that the strong evolutionary selection was driven by the experimental nutrient conditions, and in turn potentially altered competitive ability of the two species. Thus, observed changes in the simplest possible two-species phytoplankton “community” demonstrated that eco-evolutionary interactions can be critical for predicting community responses to climate change in rapidly dividing organisms such as phytoplankton.
    Type: Article , PeerReviewed
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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