Species Richness Productivity Research Articles

Capacity and establishment rules govern the number of nonnative species in communities of ground-dwelling invertebrates.

Nonnative species are a key agent of global change. However, nonnative invertebrates remain understudied at the community scales where they are most likely to drive local extirpations. We use the North American NEON pitfall trapping network to document the number of nonnative species from 51 invertebrate communities, testing four classes of drivers. We sequenced samples using the eDNA from the sample's storage ethanol. We used AICc informed regression to evaluate how native species richness, productivity, habitat, temperature, and human population density and vehicular traffic account for continent-wide variation in the number of nonnative species in a local community. The percentage of nonnatives varied 3-fold among habitat types and over 10-fold (0%-14%) overall. We found evidence for two types of constraints on nonnative diversity. Consistent with Capacity rules (i.e., how the number of niches and individuals reflect the number of species an ecosystem can support) nonnatives increased with existing native species richness and ecosystem productivity. Consistent with Establishment Rules (i.e., how the dispersal rate of nonnative propagules and the number of open sites limits nonnative species richness) nonnatives increased with automobile traffic-a measure of human-generated propagule pressure-and were twice as common in pastures than native grasslands. After accounting for drivers associated with a community's ability to support native species (native species richness and productivity), nonnatives are more common in communities that are regularly seasonally disturbed (pastures and, potentially deciduous forests) and those experiencing more vehicular traffic. These baseline values across the US North America will allow NEON's monitoring mission to document how anthropogenic change-from disturbance to propagule transport, from temperature to trends in local extinction-further shape biotic homogenization.

Woody Species Richness and Precipitation as drivers of Primary Productivity in Dry Forests of Northeastern Brazil

Although it is common sense in the scientific community that there is a correlation between species richness and primary productivity, empirically this is poorly addressed for semiarid ecosystems. In the present study (1) we correlate woody species richnesswith a vegetation index from satellite data (as a proxy for primary productivity); we also determined (2) the effect of rainfall on productivity, and (3) rainfall and productivity anomaly indices for 49 sites in Dry Forests of Northeastern semiarid region of Brazil. We show that both species richness and rainfall are positively correlated with productivity (r² = 0,33 and p < 0,05;r² = 0,11, n = 49 and p < 0,05, n = 49; respectively). Productivity has a significant one month lag in response to rainfall (r2 = 0.39 ± 0.16; p < 0.001; n = 49). We also found that rainfall shows an anomaly 3 times more intense than the productivity anomaly (p < 0.001, r2 = 0.5). We conclude that at the regional level, woody species richness has a stronger effect than rainfall on productivity of Dry Forests of semiarid Brazil. In addition, the anomaly results showed the vegetation´s resistance to the semiarid harsh climate, an important result for conservation and policy under a climate change scenario.

Human modification of land cover alters net primary productivity, species richness and their relationship

AbstractAimHumans have altered ecosystem productivity and biodiversity worldwide by changing land‐cover types and management. High local species richness is commonly found in geographic areas and ecosystems with high net primary productivity (NPP), but the long‐term effects of modification on productivity and biodiversity change, and particularly on the relationship between the two, are poorly understood. Here we evaluate whether human modification tends to increase biodiversity in low‐productivity ecosystems (where human management is likely to increase productivity) and decrease biodiversity in ecosystems that were originally high‐productive.LocationGlobal.Time Period2001–2013.Major Taxa StudiedPlants, mammals, birds, hexapods, arachnids, other terrestrial invertebrates, amphibians, reptiles and fungi.MethodsWe assembled a large worldwide dataset of NPP and associated species richness from MODIS land cover and NPP products and the PREDICTS biodiversity database, involving 11,849 sites. This enabled comparisons of species richness and NPP differences between samples of relatively natural and human‐modified vegetation within the same geographic regions, considering 102 types of land‐cover transitions.Results(1) Modification from non‐forest vegetation to forests on average increased NPP by 7.76%, and vice versa. (2) Human modification of less productive areas tended to increase NPP and vice versa, with stronger effects of major modification. (3) However, site‐level species richness decreases were associated with nearly all land‐cover transitions from relatively natural to modified vegetation. (4) Despite expectations, we found no significant relationship between species richness differences (between relatively natural and modified vegetation) and productivity differences, when considering conversions across land‐cover types and excluding human‐appropriated productivity in croplands.Main ConclusionsHuman modification tends to increase NPP in low‐productivity ecosystems, but species richness declines are associated with most major human‐induced land‐cover changes. Therefore, increasing or decreasing NPP did not generate corresponding increases or decreases in species richness, contrary to expectations of the general species richness‐productivity relationship.

A case for the importance of following antibiotic resistant bacteria throughout the soil food web.

It is necessary to complement next-generation sequencing data on the soil resistome with theoretical knowledge provided by ecological studies regarding the spread of antibiotic resistant bacteria (ARB) in the abiotic and, especially, biotic fraction of the soil ecosystem. Particularly, when ARB enter agricultural soils as a consequence of the application of animal manure as fertilizer, from a microbial ecology perspective, it is important to know their fate along the soil food web, that is, throughout that complex network of feeding interactions among members of the soil biota that has crucial effects on species richness and ecosystem productivity and stability. It is critical to study how the ARB that enter the soil through the application of manure can reach other taxonomical groups (e.g., fungi, protists, nematodes, arthropods, earthworms), paying special attention to their presence in the gut microbiomes of mesofauna-macrofauna and to the possibilities for horizontal gene transfer of antibiotic resistant genes.

Water depth modulates the species richness–biomass relationship in submerged macrophytes

The effect of biodiversity on ecosystem productivity has been a controversial issue in ecological research. The species richness–productivity relationship is highly variable in natural ecosystems, with a positive relationship being one of the most commonly observed relationships. Previous regional studies from terrestrial ecosystems have demonstrated that environmental gradients can regulate the species richness–productivity relationship. However, how this relationship varies in freshwater ecosystems across spatial environment gradients remains unclear. In this study, we propose that the species richness–productivity relationship can be modulated by the water depth. Here, we surveyed the submerged macrophyte community structure by establishing 24 transects and 642 quadrats in Erhai Lake, Yunnan Plateau, China. Our findings highlight that the species richness–productivity relationship gradually changed from slightly positive to strongly positive as the environment became more light-limited with the increasing water depth, supporting the stress-gradient hypothesis. The results from this study provide new insights into the biodiversity–ecosystem functioning relationships and in managing lake macrophyte communities and productivity.

Environment and time drive the links between the species richness and ecosystem multifunctionality from multitrophic freshwater mesocosms

Understanding the link between biodiversity and ecosystem functioning is imperative for ecosystem-based management. The role of multitrophic diversity in sustaining multifunctionality remains unclear, especially in highly diverse aquatic ecosystems. We performed a species-addition experiment consisting of one, two, three, and five species in simulated multitrophic ecosystems to evaluate biodiversity and ecosystem functioning relationships within and across trophic levels. Our results showed that there are positive species richness–productivity relationships within and across trophic levels. We found significant negative correlations between species richness and the cumulative variation of total phosphorus, and between species richness and ecosystem multifunctionality across trophic levels. Also, we found that the relationships between ecosystem multifunctionality and species richness within and across the trophic levels are mediated by a combination of environmental factors, including water temperature, dissolved oxygen, pH, irradiance, and time, rather than by species richness. Our results imply that species richness–ecosystem functioning relationships vary for different ecological functions; the individual ecosystem functions selected and the way multifunctionality calculated are critical when examining links between biodiversity and ecosystem multifunctionality. Our study highlights that multitrophic richness, such as for consumers, is crucial for driving ecosystem multifunctionality. Furthermore, our study implies that management practices for restoring the diversity of aquatic macrophytes in wetlands should consider not only macrophyte richness but also different functional groups and life-forms.

Tree diversity effects on productivity depend on mycorrhizae and life strategies in a temperate forest experiment.

Tree species are known to predominantly interact either with arbuscular mycorrhizal (AM) or ectomycorrhizal (EM) fungi. However, there is a knowledge gap regarding whether these mycorrhizae differently influence biodiversity-ecosystem functioning (BEF) relationships and whether a combination of both can increase community productivity. In 2015, we established a tree-diversity experiment by growing tree communities with varying species richness levels (one, two, or four species) and either with AM or EM tree species or a combination of both. We investigated basal area and annual basal area increment from 2015 to 2020 as proxies for community productivity. We found significant positive relationships between tree species richness and community productivity, which strengthened over time. Further, AM and EM tree species differently influenced productivity; however, there was no overyielding when AM and EM trees grew together. EM tree communities were characterized by low productivity in the beginning but an increase of increment over time and showed overall strong biodiversity effects. For AM tree communities the opposite was true. Although young trees did not benefit from the presence of the other mycorrhizal type, dissimilar mechanisms underlying BEF relationships in AM and EM trees indicate that maximizing tree and mycorrhizal diversity may increase ecosystem functioning in the long run.

Determining the role of richness and evenness in alpine grassland productivity across climatic and edaphic gradients.

Spatial heterogeneity of climatic and edaphic gradients can substantially affect the grassland productivity function. However, few studies have tested the importance of species richness and evenness on regulating grassland productivity across spatial-scale climatic and edaphic changes. This study examines the complex mechanisms by which species richness and evenness regulate productivity in alpine meadow and steppe. We used field survey data to explore above-ground productivity formation and sensitivity to spatial-scale climatic and edaphic response of alpine grassland based on species richness and evenness. Results showed that the growing season solar radiation was the main driving factor of above-ground biomass and was strongly negatively correlated with above-ground biomass. Furthermore, compared with alpine steppe, above-ground biomass in alpine meadow was more responsive to climatic variables, but less responsive to soil variables. Unexpectedly, we found that the regulation patterns of species richness and evenness on above-ground biomass were different in both habitats by a structural equation model analysis. Our study demonstrated that species evenness and richness were both important in co-regulating above-ground biomass in alpine meadow, whereas species richness mattered more than species evenness in regulating above-ground biomass in alpine steppe. Our results offer further support for species richness and evenness co-regulating grassland productivity across spatial-scale climatic and edaphic gradients, which helps maintain the benefits of plant diversity and alpine grassland ecosystems.

Species Richness Promotes Productivity through Tree Crown Spatial Complementarity in a Species-Rich Natural Forest

Ecological theory suggests that species with complementary architectural and physiological traits can optimize crown packing to improve resource efficiency and promote ecosystem productivity in forest communities. However, empirical evidence of this prediction is rare in species-rich natural forests, as little is known about how crown spatial complementarity regulates community species richness-productivity relationship (SRPR). In this study, we measured tree architectural traits (stem diameter, height, crown depth and width) for 11,337 trees, and quantified species richness, functional diversity, crown spatial complementarity, soil fertility and forest productivity for 44 quadrats (20 m × 20 m per quadrat) in the Badagongshan 25 ha forest plot, central China. We tested bivariate correlations between species richness, crown complementarity, functional diversity and forest productivity. We employed linear mixed effects models to predict crown complementarity and examined its relationship with functional diversity. Finally, we applied structural equation modeling to quantify the mediation effects of crown complementarity on SRPRs. Species richness promoted crown complementarity and forest productivity. Crown complementarity varied across quadrats, with increases driven primarily by changes in tree height. Crown complementarity was positively related to functional diversity and forest productivity. Species richness increased with soil total phosphorus, while functional diversity decreased with soil bulk density. Forest productivity increased with soil organic carbon and total nitrogen, but decreased with bulk density. Crown complementarity partially mediated the positive effect of species richness on forest productivity, and the mediation effect was mainly through functional diversity. Our results suggest that the crown complementarity index accurately reflects the niche complementarity through light utilization and carbon reallocation. Our study emphasizes that species richness can promote crown complementarity, leading to greater forest productivity, which provides greater insight into the mechanical understanding of the SRPRs.

Effects of enemy exclusion on biodiversity-productivity relationships in a subtropical forest experiment.

Interspecific niche complementarity is a key mechanism posited to explain positive species richness–productivity relationships in plant communities. However, the exact nature of the niche dimensions that plant species partition remains poorly known.Species may partition abiotic resources that limit their growth, but species may also be specialized with respect to their set of biotic interactions with other trophic levels, in particular with enemies including pathogens and consumers. The lower host densities present in more species‐diverse plant communities may therefore result in smaller populations of specialized enemies, and in a smaller associated negative feedback these enemies exert on plant productivity.To test whether such host density‐dependent effects of enemies drive diversity–productivity relationships in young forest stands, we experimentally manipulated leaf fungal pathogens and insect herbivores in a large subtropical forest biodiversity–ecosystem functioning experiment in China (BEF‐China).We found that fungicide spraying of tree canopies removed the positive tree‐species richness–productivity relationship present in untreated control plots. The tree species that contributed the most to this effect were the ones with the highest fungicide‐induced growth increase in monoculture. Insecticide application did not cause comparable effects. Synthesis. Our findings suggest that tree species diversity may not only promote productivity by interspecific resource‐niche partitioning but also by trophic niche partitioning. Most likely, partitioning occurred with respect to enemies such as pathogenic fungi. Alternatively, similar effects on tree growth would have occurred if fungicide had eliminated positive effects of a higher diversity of beneficial fungi (e.g. mycorrhizal symbionts) that may have occurred in mixed tree species communities.

Nitrogen enrichment alters climate sensitivity of biodiversity and productivity differentially and reverses the relationship between them in an alpine meadow

Biodiversity and productivity that highly determine ecosystem services are varying largely under global change. However, the climate sensitivity of them and their relationship are not well understood, especially in the context of increasing nitrogen (N) deposition. Here, based on a six-year N manipulation experiment in an alpine meadow, we quantified interannual climate sensitivity of species richness (SR) and above-ground net primary productivity (ANPP) as well as SR-ANPP relationship as affected by six N addition rate (Nrate) gradients. We found that interannual variations in ANPP and SR were mainly driven by temperature instead of precipitation. In the plots without N addition, higher temperature substantially increased ANPP but reduced SR across years, thus resulting in a negative SR-ANPP relationship. However, the negative and positive responses of SR and ANPP to temperature increased and declined significantly with increasing Nrate, respectively, leading to a shift of the negative relationship between SR and ANPP into a positive one under high Nrate. Moreover, the adverse influence of drought on SR and ANPP would be aggravated by N fertilization, as indicated by the increased positive effect of precipitation on them under N enrichment. Our findings indicate that climate sensitivity of productivity and biodiversity may be misestimated if the impact of N deposition is not considered, and the importance of biodiversity to maintain productivity would enhance as N deposition increases. This study provides a new insight to explain variation of biodiversity-productivity relationship along with environmental changes.

Geographic context is a key driver of spatial variation of bird species richness during migration

AbstractAimDetermine whether primary productivity or location (distance to the coast) is more important to migrating bird habitat selection.LocationYucatan Peninsula, Mexico.Time periodAugust–December and February–May 2009–2016.TaxaMigratory birds.MethodsUsing eBird data, we modelled spatial variation in species richness as a function of primary productivity and distance to the coast and how the relationships vary with time during spring and autumn migration. We compared the standardized regression coefficients of linear models with a Poisson error distribution.ResultsWe found that three primary productivity indices [normalized difference vegetation index (NDVI), enhanced vegetation index (EVI), heterogeneity] performed similarly in predicting species richness. However, species richness was more strongly associated with distance to the coast. In autumn, richness was higher closer to the coast through most of the season and then shifted inland late in autumn. Richness was also higher in more productive habitats. In spring, richness was higher inland early in the season but then increased closer to the coast. Species richness was relatively similar across the primary productivity gradient, even declining slightly with increasing NDVI.Main conclusionsWe did not find convincing evidence for a strong relationship between species richness and primary productivity. Instead, migration constrains birds such that they concentrate in coastal environments. In autumn, migrants may favour habitats that are both coastal and productive, such as those that occur along the Caribbean coast. In spring, migrants may also use the less productive Gulf of Mexico coast, possibly due to high arthropod production occurring during an otherwise dry time of year.

The effect of trait‐based diversity on productivity results mainly from intraspecific trait variability in the macrophyte community

Abstract Trait‐based methods are key to understanding the biodiversity–productivity relationship (BPR) of macrophyte communities. Community‐weighted mean traits (i.e., community trait structure) have been proven to have more influence on macrophyte community productivity than species richness. However, the underlying mechanism by which community trait structure variation affects macrophyte community productivity along an environmental gradient is still not well understood. A mesocosm experiment was used to investigate how community trait structure shapes macrophyte community productivity along the water depth gradient. Three submerged macrophyte species (Myriophyllum spicatum, Vallisneria natans and Potamogeton malaianus) were assembled into all possible combinations (one, two and three species per community) at three different water depths (1, 2.5 and 4 m). We fitted the relationships between community‐weighted mean traits and community productivity, and between species richness and community productivity as a comparison. We compared functional traits under different water depths and species composition at the species and community levels and disentangled the community trait structure into species turnover and intraspecific trait variability effects. The results showed that community trait structure had various influences on macrophyte community productivity, which was based on traits per se. However, species richness had a non‐significant impact on macrophyte community productivity. Water depth had a significant impact on most traits of the three species at the species level, whereas both water depth and species composition had significant impacts on community trait structure which was mainly affected by intraspecific trait variability along the water depth gradient. Our findings highlight the importance of considering intraspecific trait variability and species turnover under water depth gradients to understand the relationship between trait‐based biodiversity and productivity.

Studying biodiversity-ecosystem function relationships in experimental microcosms among islands.

Ecological studies on islands have provided fundamental insights into the mechanisms underlying biodiversity of larger organisms, but we know little about the factors affecting island microbial biodiversity and ecosystem function. We conducted a field experiment on five Baltic Sea islands where we placed aquatic microcosms with different levels of salinity mimicking environmental stress and allowed diatoms to colonize the microcosms via the air. Using structural equation models (SEM), we investigated the interconnections among environmental and dispersal‐related factors, diatom biodiversity, and ecosystem productivity (represented by chlorophyll a concentration). We also tested whether the body size structure of the community influences productivity together with biodiversity. In SEMs, we found no relationship between species richness or evenness and productivity. However, productivity increased with increasing mean body size of species in the communities. The effects of environmental stress on both biodiversity and ecosystem productivity were highlighted as species richness and evenness declined, whereas productivity increased at the highest salinity levels. In addition to salinity, wind exposure affected both biodiversity metrics and productivity. This study provides new insights into microbial community assembly in a field experimental setting and the relationship between biodiversity and ecosystem function. Our results indicate that salinity presents a strong abiotic filter, leading to communities that may be species poor, yet comprise salinity‐tolerant and relatively productive species at high salinity. Our findings also emphasize the importance of mean community body size in mediating the effects of environmental conditions on productivity and suggest that this trait should be considered more broadly in biodiversity–ecosystem function studies.

Nitrogen Deposition Shifts Grassland Communities Through Directly Increasing Dominance of Graminoids: A 3-Year Case Study From the Qinghai-Tibetan Plateau.

Nitrogen (N) deposition has been increasing for decades and has profoundly influenced the structure and function of grassland ecosystems in many regions of the world. However, the impact of N deposition on alpine grasslands is less well documented. We conducted a 3-year field experiment to determine the effects of N deposition on plant species richness, composition, and community productivity in an alpine meadow of the Qinghai-Tibetan Plateau of China. We found that 3 years of N deposition had a profound effect on these plant community parameters. Increasing N rates increased the dominance of graminoids and reduced the presence of non-graminoids. Species richness was inversely associated with aboveground biomass. The shift in plant species and functional group composition was largely responsible for the increase in productivity associated with N deposition. Climatic factors also interacted with N addition to influence productivity. Our findings suggest that short-term N deposition could increase the productivity of alpine meadows through shifts in composition toward a graminoid-dominated community. Longer-term studies are needed to determine if shifts in composition and increased productivity will be maintained. Future work must also evaluate whether decreasing plant diversity will impair the long-term stability and function of sensitive alpine grasslands.

The species richness–productivity relationship varies among regions and productivity estimates, but not with spatial resolution

The relationship between species richness and productivity (SRPR) has been a long‐studied and hotly debated topic in ecology. Different studies have reported different results with variable shapes (i.e. unimodal, linear) and directions (i.e. positive, negative) of SRPRs depending on spatial grain (i.e. size of sampling unit for species richness), productivity estimates and study extent. In this study, we quantified the effect of multiple estimates of productivity (aboveground, belowground and total biomass, and various measures of soil fertility) on species richness across three spatial grains (0.04, 1 and 25 m2) across temperate grasslands from two regions in central Europe. We analyzed SRPR in each of the two regional datasets separately, as well as the two datasets pooled together. Our results have revealed that differences caused by spatial grain were unexpectedly small, and the direction of the SRPR was consistent within each productivity estimate, but differed between regions. Productivity estimates (across all spatial scales) had different, sometimes contrasting effects on SRPR (together with predictive power) within a region, and this pattern was more pronounced when compared between regions. The combination of different datasets led to very different results than when these were analyzed separately. We did not find any evidence for a unimodal response. This study points to the necessity of careful assessing when combining datasets from different regions, even if the plant communities belong to the same vegetation type. The dataset combination may blur the role of different drivers, which likely determine the shape and strength of SRPR. We suggest that data and study comparability may be enhanced by consistently using the same productivity estimates, which would allow for more robust interpretation of possible ecological drivers underlying the SRPR.

Win some, lose some: Mesocosm communities maintain community productivity despite lower phosphorus availability because of increased species diversity

AbstractAimsThe restoration of degraded ecosystems typically focuses on establishing assemblages of target species, but successful recovery should also be evaluated by the ecosystem's functioning to guarantee long‐term persistence. We investigated how the processes underlying community assembly (i.e. species loss, species gain and changes in abundance of resident species) influenced ecosystem functioning in experimental grassland communities in different states of restoration.LocationA greenhouse experiment in northern Flanders, Belgium.MethodsWe set up a mesocosm experiment with communities of 19 planted species, ranging from slow‐growing species from poorly productive Nardus grasslands to fast‐growing species from highly productive Lolium perenne grasslands. We categorised the mesocosms into different grassland restoration states based on known abiotic and biotic restoration barriers for semi‐natural grassland restoration: soil phosphorus levels and soil biota communities. After two growing seasons, we used the CAFE approach, an ecological application of the Price equation, to partition the effects of plant community assembly on ecosystem functioning (here community productivity) for the different restoration states.ResultsAdding soil biota communities sampled from reference Nardus grasslands vs more intensively managed grasslands did not have a significant effect on either plant species richness or biomass productivity. Lower soil phosphorus concentrations (i.e. abiotic restoration) resulted in a higher plant species richness. However, the net effect on productivity was close to zero. The increase in productivity caused by species gains was compensated through decreases in productivity caused by species loss and by decreases in the abundance or functioning of species that are present in both abiotically degraded and abiotically restored states.ConclusionsNot only species richness but also species identity resulted in changes in ecosystem functioning (i.e. productivity), even though the net functional effects were close to zero. More specifically, we found that species richness‐driven increases in productivity were counterbalanced by resource‐driven and species identity‐driven reductions in productivity.

Invasion, Impact and Control Techniques for Invasive Ipomoea hildebrandtii on Maasai Steppe Rangelands

The ecosystem integrity of the Simanjiro Maasai steppe rangeland in Tanzania is threatened by the invasive plant Ipomoea hildebrandtii Vatke. However, its invasion status, impact and control techniques are unclear in the country. We conducted a study in Terrat and Sukuro villages in Simanjro District, Tanzania, to assess its invasion status and impact across grassland–woodland habitats using point sampling techniques. Key informant interviews and questionnaires were used to assess techniques used by the Maasai pastoralists to control I. hildebrandtii. A total of 10 plots (70 m2 each) with 9 quadrats (1 m2 each) in the invaded and non–invaded sites were established to study I. hildebrandtii invasions. The impact of I. hildebrandtii on rangelands was investigated by comparing herbage (herbaceous vegetation) species composition, richness, basal cover and biomass productivity between invaded and non–invaded plots. Results revealed that I. hildebrandtii invasion was higher in grass woodland habitats (90%) than in non-invaded plots. Non–invaded plots exhibited higher biomass productivity (0.289 ± 0.03 t DM/ha) than invaded plots (0.202 ± 0.02 t DM/ha). Furthermore, non–invaded plots had a higher basal cover (grasses: 54.71 ± 1.95%, forbs: 45.29 ± 1.95%) compared with invaded plots. We also recorded high native plants abundance in quadrats with low I. Hildebrandtii density (22.00 ± 1.36). Additionally, 81% of Maasai pastoralists reported to manually (uproot) control I. hildebrandtii. Based on the results of our study, we recommend further research and novel control techniques coupled with education to be implemented in the Simanjiro.

Temperature Fluctuation Attenuates the Effects of Warming in Estuarine Microbial Plankton Communities

Sea surface warming has the potential to alter the diversity, trophic organization and productivity of marine communities. However, it is unknown if temperature fluctuations that ecosystems naturally experience can alter the predicted impacts of warming. We address this uncertainty by exposing a natural marine plankton community to warming conditions (+3°C) under a constant vs. fluctuating (±3°C) temperature regime using an experimental mesocosm approach. We evaluated changes in stoichiometry, biomass, nutrient uptake, taxonomic composition, species richness and diversity, photosynthetic performance, and community metabolic balance. Overall, warming had a stronger impact than fluctuating temperature on all biological organization levels considered. As the ecological succession progressed toward post-bloom, the effects of warming on phytoplankton biomass, species richness, and net community productivity intensified, likely due to a stimulated microzooplankton grazing, and the community metabolic balance shifted toward a CO2 source. However, fluctuating temperatures reduced the negative effects of warming on photosynthetic performance and net community productivity by 40%. Our results demonstrate that temperature fluctuations may temper the negative effect of warming on marine net productivity. These findings highlight the need to consider short-term thermal fluctuations in experimental and modeling approaches because the use of constant warming conditions could lead to an overestimation of the real magnitude of climate change impacts on marine ecosystems.

Island Colonization and Environmental Sustainability in the Postglacial Mediterranean

Island environments present challenges to human colonization, but we have a poor understanding of how environmental difference drives heterogeneous patterns of insular settlement. In this paper, we assess which environmental and geographic variables positively or negatively affect the long-term sustainability of human settlement on islands. Using the postglacial Mediterranean basin as a case study, we assess the impact of area, isolation index, species richness, and net primary productivity (NPP) on patterns of island occupation for both hunter-gatherer and agropastoral populations. We find that models involving area most effectively accounts for sustainability in hunter-gatherer island settlement. The agropastoral data are noisier, perhaps due to culturally specific factors responsible for the distribution of the data; nonetheless, we show that area and NPP exert profound influence over sustainability of agropastoral island settlement. We conclude by suggesting that this relates to the capacity of these variables to impact demographic robusticity directly.