Description: Driven by climate change, marine biodiversity is undergoing a phase of rapid change that has proven to be even faster than changes observed in terrestrial ecosystems. Understanding how these changes in species composition will affect future marine life is crucial for conservation management, especially due to increasing demands for marine natural resources. Here, we analyse predictions of a multiparameter habitat suitability model covering the global projected ranges of 〉33,500 marine species from climate model projections under three CO2 emission scenarios (RCP2.6, RCP4.5, RCP8.5) up to the year 2100. Our results show that the core habitat area will decline for many species, resulting in a net loss of 50% of the core habitat area for almost half of all marine species in 2100 under the high-emission scenario RCP8.5. As an additional consequence of the continuing distributional reorganization of marine life, gaps around the equator will appear for 8% (RCP2.6), 24% (RCP4.5), and 88% (RCP8.5) of marine species with cross-equatorial ranges. For many more species, continuous distributional ranges will be disrupted, thus reducing effective population size. In addition, high invasion rates in higher latitudes and polar regions will lead to substantial changes in the ecosystem and food web structure, particularly regarding the introduction of new predators. Overall, our study highlights that the degree of spatial and structural reorganization of marine life with ensued consequences for ecosystem functionality and conservation efforts will critically depend on the realized greenhouse gas emission pathway.

Description: Der Biodiversitätsverlust schreitet in bedrohlichem Ausmaß voran. Mit dem Global Biodiversity Framework und voraussichtlich dem Nature Restoration Law bestehen nun auf internationaler und europäischer Ebene vielversprechende Ansätze, ihm Herr zu werden. Jetzt ist der Bundesgesetzgeber – nicht zuletzt aus verfassungsrechtlichen Erwägungen – aufgerufen, daran anzuknüpfen. Dazu bietet sich die Regelungsform eines Rahmen- und Politikplanungsgesetzes an, wie sie schon aus dem Klimaschutzgesetz und dem Klimaanpassungsgesetz bekannt ist. Der Aufsatz beleuchtet den internationalen, europa- und verfassungsrechtlichen Hintergrund eines solchen ‘Biodiversitätsschutzgesetzes’ und diskutiert – unter Zusammenarbeit sowohl rechts- als auch naturwissenschaftlicher Autor:innen – formale und materielle Ausgestaltungsmöglichkeiten.

Description: The sea-surface microlayer (SML) at the boundary between atmosphere and hydrosphere represents a demanding habitat for bacteria. Wind speed is a crucial but poorly studied factor for its physical integrity. Increasing atmospheric burden of CO2, as suggested for future climate scenarios, may particularly act on this habitat at the air-sea interface. We investigated the effect of increasing wind speeds and different pCO2 levels on SML microbial communities in a wind-wave tunnel, which offered the advantage of low spatial and temporal variability. We found that enrichment of bacteria in the SML occurred solely at a U10 wind speed of 〈=5.6 m/s in the tunnel and 〈=4.1 m/s in the Baltic Sea. High pCO2 levels further intensified the bacterial enrichment in the SML during low wind speed. In addition, low wind speed and pCO2 induced the formation of a distinctive bacterial community as revealed by 16S rRNA gene fingerprints and influenced the presence or absence of individual taxonomic units within the SML. We conclude that physical stability of the SML below a system-specific wind speed threshold induces specific bacterial communities in the SML entailing strong implications for ecosystem functioning by wind-driven impacts on habitat properties, gas-exchange and matter cycling processes.

Description: To understand ecosystem responses to anthropogenic global change, a prevailing framework is the definition of threshold levels of pressure, above which response magnitudes and their variances increase disproportionately. However, we lack systematic quantitative evidence as to whether empirical data allow definition of such thresholds. Here, we summarize 36 meta-analyses measuring more than 4,600 global change impacts on natural communities. We find that threshold transgressions were rarely detectable, either within or across meta-analyses. Instead, ecological responses were characterized mostly by progressively increasing magnitude and variance when pressure increased. Sensitivity analyses with modelled data revealed that minor variances in the response are sufficient to preclude the detection of thresholds from data, even if they are present. The simulations reinforced our contention that global change biology needs to abandon the general expectation that system properties allow defining thresholds as a way to manage nature under global change. Rather, highly variable responses, even under weak pressures, suggest that ‘safe-operating spaces’ are unlikely to be quantifiable.

Description: Estimates of biodiversity change are essential for the management and conservation of ecosystems. Accurate estimates rely on selecting representative sites, but monitoring often focuses on sites of special interest. How such site‐selection biases influence estimates of biodiversity change is largely unknown. Site‐selection bias potentially occurs across four major sources of biodiversity data, decreasing in likelihood from citizen science, museums, national park monitoring, and academic research. We defined site‐selection bias as a preference for sites that are either densely populated (i.e., abundance bias) or species rich (i.e., richness bias). We simulated biodiversity change in a virtual landscape and tracked the observed biodiversity at a sampled site. The site was selected either randomly or with a site‐selection bias. We used a simple spatially resolved, individual‐based model to predict the movement or dispersal of individuals in and out of the chosen sampling site. Site‐selection bias exaggerated estimates of biodiversity loss in sites selected with a bias by on average 300–400% compared with randomly selected sites. Based on our simulations, site‐selection bias resulted in positive trends being estimated as negative trends: richness increase was estimated as 0.1 in randomly selected sites, whereas sites selected with a bias showed a richness change of −0.1 to −0.2 on average. Thus, site‐selection bias may falsely indicate decreases in biodiversity. We varied sampling design and characteristics of the species and found that site‐selection biases were strongest in short time series, for small grains, organisms with low dispersal ability, large regional species pools, and strong spatial aggregation. Based on these findings, to minimize site‐selection bias, we recommend use of systematic site‐selection schemes; maximizing sampling area; calculating biodiversity measures cumulatively across plots; and use of biodiversity measures that are less sensitive to rare species, such as the effective number of species. Awareness of the potential impact of site‐selection bias is needed for biodiversity monitoring, the design of new studies on biodiversity change, and the interpretation of existing data.

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.

Description: Environmental change can result in substantial shifts in community composition. The associated immigration and extinction events are likely constrained by the spatial distribution of species. Still, studies on environmental change typically quantify biotic responses at single spatial (time series within a single plot) or temporal (spatial beta diversity at single time points) scales, ignoring their potential interdependence. Here, we use data from a global network of grassland experiments to determine how turnover responses to two major forms of environmental change – fertilisation and herbivore loss – are affected by species pool size and spatial compositional heterogeneity. Fertilisation led to higher rates of local extinction, whereas turnover in herbivore exclusion plots was driven by species replacement. Overall, sites with more spatially heterogeneous composition showed significantly higher rates of annual turnover, independent of species pool size and treatment. Taking into account spatial biodiversity aspects will therefore improve our understanding of consequences of global and anthropogenic change on community dynamics.

Description: Resource use efficiency (RUE) is an ecological concept that measures the proportion of supplied resources, which is converted into new biomass, i.e., it relates realized to potential productivity. It is also commonly perceived as one of the main mechanisms linking biodiversity to ecosystem functioning based on the assumption that higher species numbers lead to more complementary and consequently more efficient use of the available resources. While there exists a large body of literature lending theoretical and experimental support to this hypothesis, there are a number of inconsistencies regarding its application: First, empirical tests use highly divergent approaches to calculate RUE. Second, the quantification of RUE is commonly based on measures of standing stock instead of productivity rates and total pools of nutrients instead of their bioavailable fractions, which both vary across systems and therefore can introduce considerable bias. Third, conceptual studies suggest that the relationship between biodiversity, productivity and RUE involves many more mechanisms than complementary resource use, resulting in variable magnitude and direction of biodiversity effects on productivity. Moreover, RUE has mainly been applied to single elements, ignoring stoichiometric, or metabolic constraints that lead to co-limitation by multiple resources. In this review we illustrate and discuss the use of RUE within and across systems and highlight how the various drivers of RUE affect the diversity-productivity relationship with increasing temporal and spatial scales as well as under anthropogenic global change. We illustrate how resource supply, resource uptake and RUE interactively determine ecosystem productivity. In addition, we illustrate how in the context of biodiversity and ecosystem functioning, the addition of a species will only result in more efficient resource use, and consequently, higher community productivity if the species' traits related to resource uptake and RUE are positively correlated.

Description: Harmful algal blooms (HABs) are globally increasing in number and spatial extent. However, their propagation dynamics along environmental gradients and the associated interplay of abiotic factors and biotic interactions are still poorly understood. In this study, a nutrient gradient was established in a linear meta‐ecosystem setup of five interconnected flasks containing an artificially assembled phytoplankton community. The harmful dinoflagellate Alexandrium catenella was introduced into different positions along the nutrient gradient to investigate dispersal and spatial community dynamics. Overall, total algal biovolume increased, while community evenness decreased with increasing nutrient concentrations along the gradient. Alexandrium was able to disperse through all flasks. On the regional scale, diatoms dominated the community, whereas on the local scale the dinoflagellate showed higher contributions at low nutrient concentrations and dominated the community at the lowest nutrient concentration, but only when initiated into this flask. A control treatment without dispersal revealed an even stronger dominance of Alexandrium at the lowest nutrient concentration, indicating that dispersal and the associated nutrient exchange may weaken dinoflagellate dominance under low nutrient conditions. This study presents a first approach to experimentally investigate spatial dynamics and ecological interactions of a harmful dinoflagellate along an environmental gradient in a meta‐ecosystem setup, which has the potential to substantially enhance our understanding of the relevance of dispersal for HAB formation and propagation in combination with local environmental factors.

Description: Volkswagen Foundation http://dx.doi.org/10.13039/501100001663