Diversity Turnover Research Articles

Supplemental Material for Diversity Climate, Trust, and Turnover Intentions: A Multilevel Dynamic System

Supplemental Material for Diversity Climate, Trust, and Turnover Intentions: A Multilevel Dynamic System

Precipitation declines influence the understory patterns in Nothofagus pumilio old-growth forests in northwestern Patagonia

Forest understories are essential to plant diversity and ecosystem functioning. However, studies about changes in understory patterns as affected by varying precipitation are scarce. Pure Nothofagus pumilio (common name: lenga) forests dominate the eastern side of the Andes mountains in Patagonia across an ample range of precipitation (~1500–500 mm). By studying the same forest type, in the same developmental stage (old-growth), we aimed to isolate the effects of precipitation upon these N. pumilio ecosystems, particularly for the understory. Three sites were selected with annual average precipitations of ~1000 mm (humid), ~800 mm (mesic), and 600 mm (dry), with a distance of 30 km between the humid and the dry sites, and only 18 km between the mesic and the dry sites. In each site, we established three 40 × 40 m plots in 4 blocks, and 30 1 m2 regeneration subplots within each plot. In each subplot we measured vascular plant cover, richness and diversity (alpha and beta), litter cover and coarse woody debris, plus several abiotic variables. We analyzed the data with mixed analysis of variance, differences of understory plant communities through blocked distance-based multivariate analysis of variance, and visualized the groups (sites) with non-metric multidimensional scaling. Indicator species at each site were identified through blocked species indicator analysis. The dry site differed significantly compared to the humid and mesic sites, with the lowest understory cover (4 vs. 82–78%), plant richness (15 vs. 25–26 species), and Simpson diversity index (0.05 vs. 0.66–0.64) . Beta turnover diversity was higher between the dry site with either the humid and the mesic sites (βt = 0.613 and 0.561, respectively), which in turn had more species in common (βt = 0.115). An increase in exposed mineral soil, soil water content, and leaf area index occurred from dry to humid sites, and vice versa for transmitted radiation and litter cover. All sites had different indicator species, but with indicator values increasing from dry to humid sites. The dramatic impoverishment of the plant community once precipitation drops within the range of 800 and 600 mm per year in Northern Patagonia sets a warning to the potential effects of climate change upon N. pumilio-dominated forest ecosystems and their plant diversity. Some forest management and potential adaptation strategies are proposed.

Chemical contamination can promote turnover diversity of benthic prokaryotic assemblages: The case study of the Bagnoli-Coroglio bay (southern Tyrrhenian Sea)

Chemical contamination of marine ecosystems represents a major concern for the detrimental consequences at different levels of biological organization. However, the impact of chronic contamination on the diversity and assemblage composition of benthic prokaryotes is still largely unknown, and this limits our understanding of the potential implications on ecosystem functioning. The Bagnoli-Coroglio bay (Gulf of Naples, Tyrrhenian Sea) is a typical example of coastal area heavily contaminated by metals and hydrocarbons, released for decades by industrial activities, which ceased at the beginning of nineties. In the present study we analyzed the abundance, diversity and assemblage composition of benthic prokaryotic assemblages at increasing distance from the historical source of contamination in relation to the heavy hydrocarbons (C > 12), polycyclic aromatic hydrocarbons (PAHs) and heavy metal concentrations in the sediments. Prokaryotic abundance in the sediments differed among sites, and was mostly driven by environmental factors rather than by contamination levels. Conversely, the richness of prokaryotic taxa was relatively high in all samples, was driven by contamination levels and decreased significantly with increasing contamination (15–38%). Moreover, our results indicate large variations in the composition of the benthic prokaryotic assemblages among sites, mostly explained by the different levels and types of chemical contaminants found in the sediments. Overall, our findings suggest that chemical contaminants, even after decades from the end of their release, can profoundly influence the richness and turnover diversity of the benthic prokaryotic assemblages, in turn promoting a high diversification of the benthic bacterial and archaeal assemblages by selecting those lineages more adapted to specific mixtures of different contaminants. Our results open new perspectives for understanding of the long-term effects of chemical contamination on the benthic prokaryotic assemblages and the ecological processes they mediate.

Consistent metacommunity structure despite inconsistent drivers of assembly at the continental scale.

A fundamental goal of community ecology is to understand the drivers of community assembly and diversity. Local factors acting on community assembly are typically related to environmental conditions while regional factors are typically related to dispersal. Previous research has not consistently demonstrated the importance of local or regional factors, but this is likely because these factors act in concert and not in isolation. Studies that simultaneously integrate local and regional factors into analyses of community assembly can be a useful avenue to further our understanding of this core concept in community ecology. Here, we aimed to identify metacommunity structure and diversity and the local and regional drivers of community assembly at the continental scale. We evaluated metacommunity structure and drivers of assembly of macroinvertebrate communities in 941 rivers and streams nested within nine ecoregions distributed across the conterminous United States. Pattern-based metacommunity analyses and boosted regression tree techniques were used to (a) assign metacommunity structures and (b) identify the environmental, landscape and network drivers of assembly. We also evaluated how biodiversity scaled across hierarchical levels and varied among ecoregions. Metacommunity structures were consistent for the conterminous United States and each of the nine ecoregion subsets, with each ecoregional metacommunity displaying a Clementsian structure. Environmental variables were the predominant drivers of assembly, suggesting the importance of species sorting and environmental filtering on community structure; however, the identity of the most influential environmental variables differed among ecoregions and suggested hierarchical filtering on assembly. Partitioned diversity was found to be lower at the local and ecoregional levels, but turnover in diversity among ecoregions was higher than expected. Our results demonstrate contingencies in community assembly, notwithstanding consistency in metacommunity structure and support the importance of environmental control over community assembly and biodiversity. Moreover, biodiversity at the continental scale is likely maintained through this inherent variation in the drivers of assembly and concomitant changes in community composition among ecoregions. We suggest that further work should evaluate the assembly of other facets of community structure and the underlying mechanisms of the contingency in assembly drivers.

Abstract B59: Co-evolution between tumor cells and immune system in the setting of T-cell immunotherapy

Abstract It is now well established that the host’s adaptive immune system plays an important role in identifying and eliminating cancer cells in much the same way that intracellular pathogens are cleared during an adaptive immune response to infection. From a therapeutic standpoint, the adaptive immune system is unique in that it can co-evolve alongside a developing tumor. However, tumor acquisition of immune evasive phenotypes, such as class-I MHC downregulation, remains a major limitation of successful T-cell immunotherapy. We propose a stochastic model that couples tumor and CD8+ T-cell adaptive immune compartments. This framework accurately models relevant empirical findings, including the growth-threshold conjecture of immune activation, and predicts experimental observations including “sneak-through,” wherein intermediate-growth threats are penalized relative to their slower- and faster-growing counterparts. We demonstrate that predicted optimal growth strategies depend on whether or not the threat may acquire an immune-evasive phenotype as well as the mode of immune detection. The model is able to accurately characterize age-dependent cancer incidence data as a function of decreasing T-cell turnover and repertoire diversity. Lastly, we quantify therapeutic efficacy of immunotherapy in the setting of an immune-evasive threat. Our model serves as a first attempt at modeling stochastic cancer evolution sculpted by an adaptive immune compartment. Citation Format: Jason T. George, Haven R. Garber, Jeffrey J. Molldrem, Herbert Levine. Co-evolution between tumor cells and immune system in the setting of T-cell immunotherapy [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2018 Nov 27-30; Miami Beach, FL. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(4 Suppl):Abstract nr B59.

Spatio-temporal discrepancies in lizard species and functional diversity

Conducting multi-faceted biodiversity assessments can provide a comprehensive vision of the organization of ecological communities over space and time. In this study, the spatio-temporal species diversity and α and β functional diversity of lizard assemblages were evaluated in four vegetation types over a two-season annual cycle. Additionally, site structural elements including vegetation, soil and environmental variables were characterized and related to the composition of lizard species. Both species diversity and functional diversity varied through space and time but followed different trends. Species diversity was higher in lowland vegetation types, characterized by greater tree canopy coverage (%) as well as higher temperature and humidity conditions, while species richness, evenness and functional divergence showed distinct trends. Similarly, seasonal differences were observed in species and functional diversity: the rainy season had greater species diversity, while functional diversity was higher during the dry season. Also, species β-diversity between vegetation types was characterized by turnover; while nestedness was the main component of functional β-diversity. Seasonally, there was no turnover in species or functional diversity. We conclude that vegetation type is the primary determinant of lizard diversity. However, the functional redundancy observed in lizard communities explains the opposite tendencies found between species and functional diversity at α and β levels.

Cenomanian/Turonian oceanic anoxic event 2 in October oil field, central Gulf of Suez, Egypt

Gulf of Suez is one of the world most prolific Cretaceous and Miocene oil provinces in Egypt. In this basin the Late Cenomanian/Early Turonian organic rich limestone and shale sediments are referred to oceanic anoxic event 2 (OAE2). Two oil-cored wells (GS 197-2 and OCT-A8) have encountered the Late Cenomanian/Early Turonian Abu Qada Formation in October Field, central part of Gulf of Suez. The aim of this work is to pick the global Cenomanian/Turonian anoxic boundary in the subsurface sediments within the Gulf of Suez basin. Consequently, the core samples of the studied wells have been investigated in order to recognize the lithofacies, biostratigraphy, geochemistry and isotope content of upper Raha, Abu Qada and lower Wata formations. The microfacies association of anoxic middle to outer shelf marine were recognized. In addition, remarkable turnover and significant change in biostratigraphy and ichnological diversity and abundance were confirmed the abrupt change in oxidation and nutrition the Cenomanian-Turonian boundary. The recorded positive δ13C excursion (1.8‰) matched with maximum TOC value encountered to mark OAE2 as well as source rock maturity and potentiality of Abu Qada Formation. The neighboring exposed section of Abu Qada Formation in Gabal Nezzazat show similar isotopic and biostratigraphic characteristics that recorded in the studied wells. This work define the Cenomanian-Turonian OAE2 as material based chronostratigraphic surface boundary in Nezzazat Group from surface to subsurface integrated data to improve sequence stratigraphic interpretation of the heterogeneous Upper Cretaceous shallow marine reservoirs in Gulf of Suez.

CEO Diversity, Political Influences, and CEO Turnover in Unstable Environments: The Romanian Case

This work expands the literature on a less studied topic, the Chief Executive Officer (CEO) turnover in post-communist economies, analyzed during an unstable and ambiguous economic and financial environment. For the period 2005–2010, the results indicate the political inference in CEO turnover decision for the Romanian listed companies. In this period, with great turmoil in the economy determined by the financial crisis of 2008, we also find that CEO gender helps to explain the probability of changing the CEO. Moreover, this paper empirically tests if the financial and corporate governance determinants that are validated in the existing literature work for the Romanian listed companies. We reinforce that CEO turnover decision is negatively related to accounting-based performance. We find evidence of the “voting with their feet” behavior of institutional investors, and of the lack of Board of Directors monitoring. The CEO–Chairman duality and the controlling power of the largest shareholder act as entrenchment mechanisms.

Patterns of change in α and β taxonomic and phylogenetic diversity in the secondary succession of semi-natural grasslands in the Northern Apennines.

We studied the secondary succession in semi-natural grasslands (dry grasslands and hay meadows) located in the eastern side of the Tuscan Apennines (Tuscany, Central Italy). We compared these habitats, investigating: (i) the changes in species richness, composition and phylogenetic diversity during the succession; (ii) whether the trends in species loss and species turnover in taxonomic diversity matched those in phylogenetic diversity. We performed a stratified random sampling, in a full factorial design between habitat type and succession stage (60 sampled plots, 10 × 2 types of habitat × 3 stages of succession). We constructed a phylogenetic tree of the plant communities and compared the differences in taxonomic/phylogenetic α- and β-diversity between these two habitats and during their succession. We identified indicator species for each succession stage and habitat. Looking at α-diversity, both habitats displayed a decrease in species richness, with a random process of species selection in the earlier succession stages from the species regional pool. Nevertheless, in the latter stage of dry grasslands we recorded a shift towards phylogenetic overdispersion at the higher-level groups in the phylogenetic tree. In both habitats, while the richness decreased with succession stage, most species were replaced during the succession. However, the hay meadows were characterized by a higher rate of new species’ ingression whereas the dry grasslands became dominated with Juniperus communis. Accordingly, the two habitats showed similar features in phylogenetic β-diversity. The main component was true phylogenetic turnover, due to replacement of unique lineages along the succession. Nevertheless, in dry grasslands this trend is slightly higher than expected considering the major importance of difference in species richness of dry grasslands sites and this is due to the presence of a phylogenetically very distant species (J. communis).

Impact of historical contamination on meiofaunal assemblages: The case study of the Bagnoli-Coroglio Bay (southern Tyrrhenian Sea)

The effects of contaminants on marine organisms have been documented since decades, but the long-term responses and recovery rates of benthic communities to mixtures of contaminants, several years after the cessation of industrial activities, need to be further investigated. Bagnoli-Coroglio Bay (Gulf of Naples, Tyrrhenian Sea) is a typical example of historically contaminated coastal area due to industrial activities stopped at the beginning of nineties. In the present study we carried out a fine spatial scale analysis of the distribution of meiofaunal (and nematodes) assemblages along five bathymetric transects located at increasing distance from the historical source of contamination in relation with the polycyclic aromatic hydrocarbon and heavy metal concentrations present in the sediment. Meiofaunal abundance and biomass changed widely along transects but independent from the distance from the source of contamination. Even when the contamination levels were expected to induce significant detrimental biological consequences, meiofaunal abundance and biomass were similar to those reported in unpolluted benthic coastal areas worldwide. Conversely, biodiversity in terms of meiofaunal taxa richness was generally low (range: 5–8 taxa in 12 of the overall 15 stations investigated). This was explained by the lack of sensitive groups such as ostracods, gastrotrichs and tardigrades commonly encountered in benthic coastal ecosystems, thus reflecting an overall poor/moderate environmental quality of the investigated area. Nematode (structural and functional) diversity was also low, particularly at stations characterized by higher contamination levels. At the same time, nematode species composition did not change significantly among stations suggesting a widespread effect of contaminants able to reduce the variability (i.e., turnover diversity) within the assemblages of the whole study area. Overall, our results indicate that even decades after the cessation of contaminant emissions, benthic biodiversity was affected in terms of both meiofaunal taxa and nematode species. These findings strongly reinforce the call for reducing sources of chronic pollution in marine ecosystems and provide new insights for a better understanding of the ecological recovery of historically contaminated marine environments.

Functional diversity turnover in the western Mediterranean saltmarshes: Effects of edaphic features and biotic processes on the plant functional structure

Salinity and soil moisture are considered main drivers of the plant zonation in Mediterranean saltmarshes. Therefore, both factors could have a remarkable effect on the plant functional structure of these habitats. The aim of this study was to identify the effects of abiotic and biotic factors on the plant functional structure of western Mediterranean saltmarshes. A total of 20 saltmarshes were assessed, and seven plant traits were considered. Community weighted mean and Rao index were used to measure the functional structure of the plant communities. Redundancy analysis was used to estimate the effects of soil variables on the community-weighted mean trait and functional diversity, and standardised effect size was used to assess the effect of biotic interactions. The functional traits showed a clear zonation along the salinity gradient in Mediterranean saltmarshes, mainly related to the electrical conductivity, and mainly gathered in trait syndromes. The succulent nanophanerophytes grew at the highest salinity zones. Salt excretors, both chamaephytes and mesophanerophytes, appeared in the intermediate and lowest salinity zones, respectively. Finally, geophytes with both selective cation root uptake and rhizome were mostly located in the lowest salinity zones. The abiotic factors strongly modulated the biotic interactions, and some convergence patterns were observed. The highest functional diversity was observed in the lowest salinity zones, a marked turnover. These findings indicate that multiple assembly processes determine the plant structure of Mediterranean saltmarshes, yet abiotic environmental filters strongly shape the local species assemblages and functional diversity turnover. Our results support that the whole salinity gradient should be protected to conserve the widest range of functional traits.

Long‐term monitoring reveals forest tree community change driven by atmospheric sulphate pollution and contemporary climate change

AbstractAimMontane environments are sentinels of global change, providing unique opportunities to assess impacts on species diversity. Multiple anthropogenic stressors such as climate change and atmospheric pollution may act concurrently or synergistically in restructuring communities. Thus, a major challenge for conservation is untangling the relative importance of different stressors. Here, we combine long‐term monitoring with multivariate community modelling to estimate the anthropogenic drivers shaping forest tree diversity along an elevational gradient.LocationCamels Hump Mountain, Vermont, USA.MethodsWe used Generalized Dissimilarity Modelling (GDM) to model spatial and temporal turnover in beta diversity along an elevational gradient over a 50‐year period and tested for spatiotemporal shifts in density and elevational distribution of individual species. GDMs were used to predict community turnover as nonlinear functions of changes in elevation, climate and atmospheric pollution.ResultsWe observed significant shifts in elevational range and density of individual species, which contributed to an overall reduction in the elevational gradient in beta diversity through time. GDMs showed the combined effects of sulphate deposition and temperature as drivers of this temporal reduction in beta diversity. Spatiotemporal changes differed among species, with shifts observed both up‐ and downslope. For example, in a reversal of a previous upslope range contraction, red spruce (Picea rubens Sarg.) increased in density and shifted downslope since the 1990s, occupying warmer, drier climates.Main conclusionOur results demonstrate that global change is impacting the stratification of forest tree diversity along elevational gradients, but the responses of individual species are complex and variable in direction. We suggest abiotic drivers may directly impact individual species while also indirectly altering species interactions along elevational gradients. Our approach modelling the drivers of compositional turnover quantifies the rate and amount of change in beta diversity along environmental gradients and serves as a powerful complement to studying species‐specific responses.

Drivers of Bacterial α- and β-Diversity Patterns and Functioning in Subsurface Hadal Sediments.

Oceanic trenches at hadal (>6,000 m) depths are hot spots of organic matter deposition and mineralization and can host abundant and active bacterial assemblages. However, the factors able to shape their biodiversity and functioning remain largely unexplored, especially in subsurface sediments. Here, we investigated the patterns and drivers of benthic bacterial α- and β-diversity (i.e., OTU richness and turnover diversity) along the vertical profile down to 1.5 m sediment depth in the Izu-Bonin Trench (at ~10,000 m water depth). The protease and glucosidase enzymatic activity rates were also determined, as a proxy of organic matter degradation potential in the different sediment layers. Molecular fingerprinting based on automated ribosomal intergenic spacer analysis (ARISA) indicated that the α-diversity of bacterial assemblages remained high throughout the vertical profile and that the turnover (β-) diversity among sediment horizons reached values up to 90% of dissimilarity. Multivariate distance-based linear modeling (DISTLM) pointed out that the diversity and functioning of the hadal bacterial assemblages were influenced by the variability of environmental conditions (including the availability of organic resources and electron donors/acceptors) and of viral production rates along the sediment vertical profile. Based on our results, we can argue that the heterogeneity of physical-chemical features of the hadal sediments of the Izu-Bonin Trench contribute to increase the niches availability for different bacterial taxa, while viruses contribute to maintain high levels of bacterial turnover diversity and to enhance organic matter cycling in these extremely remote and isolated ecosystems.

Temporal turnover of the flora of lake islands: The island of Lake Pamvotis (Epirus, Greece).

Lake Pamvotis is one of the Balkan "ancient" lakes, a Quaternary refugium of great environmental importance and ecological value, that is under various anthropogenic pressures. It belongs to a Natura 2000 Special Area for Conservation and Special Protection Area. Almost in the middle of the lake, there is an inhabited island - one of the two lake islands in Greece – that also attracts touristic interest. Τhe main objectives of the present study are to provide a floristic inventory of the protected island, combining data of two different sampling periods, within a 25 year interval, in order to estimate temporal beta diversity and species turnover of the island’s plant diversity. The value of the absolute and relative turnover rates of the floristic diversity of the island studied are 4.24 and 1.72, respectively and are amongst the higher rates reported for plants. The absolute difference between extinct (E) and immigrant (l) taxa is to a great extent accounted, concerning life forms, by therophytes (1.86), hemicryptophytes (1.56) and geophytes (1.04) and, for habitats, by taxa preferring agricultural and ruderal forms (2.52).

Desertification and nitrogen addition cause species homogenization in a desert steppe ecosystem

Although the influences of desertification and nitrogen (N) addition in shaping species composition and community structure have long been explored, our understanding of the underlying processes is not yet strong. Analyses of trends in the turnover and nestedness components of beta diversity can be informative of the processes response to N addition and desertification in desert steppe ecosystems. Our investigation of the changes in beta diversity under desertification and N addition in a desert steppe ecosystem in northern China showed desertification to significantly decrease beta diversity among communities, which leads to species homogenization. Further, decreases to the turnover component of beta diversity was likely an important factor causing homogenization under desertification. Although nitrogen addition did not fundamentally influence beta diversity, dissimilarity caused by nestedness significantly increased with nitrogen addition. The contrasting effects of desertification and N addition on the turnover and nestedness components of beta diversity suggest that the ordered loss of plant species with desertification improvement. Overall, our findings provide strong evidence that the effects of desertification and N addition on beta diversity change with ecological processes. We recommend that conservation strategies that focus management practices on prevention of desertification will be most effective in maintaining species diversity.

Community signals of the effect of Didymosphenia geminata (Lyngbye) M. Schmidt on benthic diatom communities in Chilean rivers

BackgroundDidymosphenia geminata (Lyngbye) M. Schmidt is a freshwater invasive benthic diatom native to oligotrophic systems of the Northern Hemisphere. Since 2010, freshwater systems of south-austral Chile, have experienced a progressive invasion of this species between 37° 18′ S and 54° 30′ S. This invaded area is characterized by biogeographic heterogeneity, anthropic pressure and lack of knowledge. The objective of this study was to analyze the effect of D. geminata on the community structure of benthic diatoms and the variability of this effect in Chilean rivers.MethodsThe data were collected between 2010 and 2017 and pre-treated using fourth-root transformation to construct a Bray-Curtis similarity matrix and a Principal Coordinate Analysis to identify groups of sites. The α diversity and β diversity were estimated and compared using univariate indexes and the Mann-Whitney test, respectively. We used Permutational multivariate analyses of variance (PERMANOVA) and PERMDISP to estimate the spatial variation of communities, and an Analysis of Percentage Similarity (SIMPER) was performed to identify the species which contributed to the similarity between the groups of sites.ResultsThe results suggest significant differences between invaded and noninvaded rivers (54% of the total variation); the univariate indexes showed greater richness (S), greater diversity (H′), and less species turnover in invaded rivers. The PERMANOVA indicated significant interaction between D. geminata and the basins; there was also a significant effect on the internal dispersion in the basins. The SIMPER analysis showed that the groups composed exclusively of invaded sites had high mean similarity in all basins and small pedunculated benthic diatoms showed a significant response to the presence of D. geminata.ConclusionWe found high variability in the community structures, that determine a strong segregation between non-invaded and invaded sites by D. geminata, and that the main effect of D. geminata on diatoms benthic was the homogenization of the communities. This is reflected in the increase in density of small stalked diatoms and the reduction of species turnover among rivers in the same basin, leading to the loss of community heterogeneity that overcomes the spatial heterogeneity in the area invaded in Chile.

Local and regional drivers of turnover and nestedness components of species and functional beta diversity in lake macrophyte communities in China

Beta diversity describes the variation in species composition between sites and is often influenced by both local and regional processes. Partitioning beta diversity into turnover (species replacement between sites) and nestedness (richness difference between sites) components may enhance our understanding of the mechanisms behind the local and regional drivers determining species composition across spatial scales. We sampled macrophyte communities in 24 lakes in two regions (Yangtze River basin and Yunnan-Guizhou plateau) of China covering broad climate and nutrient gradients. Based on both species and functional approaches, we calculated multiple-site beta diversity using the Sørensen dissimilarity index and partitioned it into turnover and nestedness coefficients crossed with two nested spatial scales: among depths within transects (transect scale) and among transects within lakes (lake scale). The overall species beta diversity and functional beta diversity (i.e. Sørensen coefficient) were significantly lower and thus more homogeneous at lake scale. Across spatial scales, species beta diversity was mainly explained by turnover patterns (56–61%) and functional beta diversity primarily by nestedness patterns (58–65%). Both local and regional drivers contributed to structuring species and functional beta diversity patterns, largely through changes in species turnover and functional nestedness, respectively. Overall, we observed a significant increase in species beta diversity and its turnover component while a decreasing trend in functional beta diversity and its nestedness component at high altitude. Our results further emphasized that the species beta diversity and its turnover component decreased at high total phosphorus concentration (TP) across the two spatial scales, while the functional beta diversity and its nestedness component decreased at high TP at the transect scale. We conclude that understanding of the relative role of local and regional drivers in determining macrophyte diversity patterns may help managers to select the most appropriate conservation strategies for preservation of biodiversity varying with the scale in focus.

Stochastic cancer-immune coevolution: Implications for cancer incidence and immunotherapeutic efficacy.

e14023 Background: Despite recent progress, robust treatment strategies that lead to durable remission are still lacking for many cancer types. This disease is difficult to treat owing in part to the complexity introduced by a heterogeneous population of cancer cells capable of evolving mechanisms of resistance to traditional therapy. Nonetheless, the discovery and continued optimization of T-cell immunotherapy has revolutionized the treatment of many cancers. This treatment strategy stands out from other approaches in its unique ability to co-evolve alongside an evading tumor. While promising, such therapies are also complex. For example, allogeneic stem cell transplantation leverages a donor-derived T-cell repertoire to treat patients with refractory hematologic malignancies and relies upon a delicate balance between desirable anti-tumor effects and potentially life-threatening graft-versus-host-disease. Currently, the decision to utilize this therapy and others like it is largely influenced by prior empirical evidence. Thus, there is great need for quantitative models of the cancer-immune interaction to generate testable predictions of treatment outcome, which could then be validated prior to T-cell immunotherapy administration. Methods: We develop a foundational mathematical model to investigate the properties of stochastic tumor-immune co-evolution using applied stochastic process theory and probabilistic analysis. We use this model to predict the effects of reduced immunity, T-cell diversity, and thymic turnover rates on cancer incidence, and compare model simulations to cancer evolutionary data. Results: We predict that changes in T-cell diversity, and to a lesser degree thymic turnover, increase the chance of tumor progression. When applied to experimental data, we demonstrate that the observations are consistent with co-evolution between an indolent cancer population and the adaptive immune system prior to clinical disease. Conclusions: Our results provide a fundamental framework for analyzing the interaction dynamics of an evolving threat like cancer and the adaptive immune system in order to better understand and predict immunotherapeutic efficacy.

Decoupling species richness variation and spatial turnover in beta diversity across a fragmented landscape

BackgroundHow habitat fragmentation affects the relationship between local richness and the variation in community composition across space is important to both ecology and conservation biology, but this effect remains poorly understood.MethodsHere, we present an empirical study to address this topic in a fragmented landscape, the Thousand Island Lake (TIL), an artificial land-bridge island system with more than 1,000 islands, which provides an “experimental” fragmented landscape with a homogeneous matrix and similar successional history. We measured species composition and plant functional type (PFT) on 29 islands, and tested the effects of island area and isolation on the relationship between α- and β-diversity. General Linear Models were applied to test the impact of habitat fragmentation. In addition, variation partitioning was used to decouple α-diversity dependent and α-diversity independent spatial turnover in β-diversity of the plant community and across different PFTs.ResultsWe found habitat fragmentation influences β-diversity of plants primarily by modifying local α-diversity, not spatial turnover in the TIL system. We also found area-dependent environmental filtering and differential plant responses across functional types were the most likely underlying driving mechanisms.DiscussionThese results highlight the importance of hierarchical linkages between components of biodiversity across scales in fragmented landscapes, and have practical conservation implications.

Lake and catchment‐scale determinants of aquatic vegetation across almost 1,000 lakes and the contrasts between lake types

AbstractAimThe factors controlling macrophyte (aquatic plant) composition are complex, recent research having shown that the well‐studied effects of lake environmental factors (the so‐called “environmental filter”) can be constrained by hydrological and landscape factors. We investigated the factors determining macrophyte composition in lakes over water body and catchment scales and the transferability of this pattern across lake types.LocationAlmost 1,000 lakes distributed across Britain.TaxonLake macrophytes.MethodsLakes were partitioned into five types based on subdivision of alkalinity and elevation gradients. Data from botanical surveys were used to compare the spatial turnover and nestedness components of beta diversity between lake types. The relative importance of lake environment (based on local physicochemical data), hydrology (e.g. lake and stream density), landscape (e.g. fragmentation indices, land cover) and spatial autocorrelation in explaining variation in macrophyte composition were derived from variance partitioning.ResultsSpecies composition showed strong spatial structuring, suggestive of overland dispersal, enhanced by spatially correlated abiotic factors such as alkalinity and elevation. Catchment‐scale factors (e.g. land use, connectivity) promoted the establishment of different communities (more or less diverse, or differing in composition) but were of secondary importance. Turnover in composition between upland lakes was lower than in other lake types, reflecting a more specialist flora and increased potential for propagule exchange due to spatial aggregation and higher hydrological connectivity.Main conclusionsVegetation composition in lakes is more spatially structured than previously appreciated, consistent with the importance of dispersal limitation, but this does not apply evenly to all lakes, being most acute in lowland high alkalinity lakes. Thus, spatially structured abiotic factors, such as alkalinity, influence macrophyte composition most (suggestive of niche filtering) in high alkalinity lakes where human impacts tend to be greatest, although nestedness was also lowest in such lakes. By contrast, hydrological connectivity has a proportionally stronger structuring role in upland lakes.