Drivers Of Species Richness Research Articles

Precipitation variation: a key factor regulating plant diversity in semi-arid livestock grazing lands.

Livestock presence impacts plant biodiversity (species richness) in grassland ecosystems, yet extent and direction of grazing impacts on biodiversity vary greatly across inter-annual periods. In this study, an 8-year (2014-2021) grazing gradient experiment with sheep was conducted in a semi-arid grassland to investigate the impact of grazing under different precipitation variability on biodiversity. The results suggest no direct impact of grazing on species richness in semi-arid Stipa grassland. However, increased grazing indirectly enhanced species richness by elevating community dominance (increasing the sheltering effect of Stipa grass). Importantly, intensified grazing also regulates excessive community biomass resulting from increased inter-annual wetness (SPEI), amplifying the positive influence of annual humidity index on species richness. Lastly, we emphasize that, in water-constrained grassland ecosystems, intra-annual precipitation variability (PCI) was the most crucial factor driving species richness. Therefore, the water-heat synchrony during the growing season may alleviate physiological constraints on plants, significantly enhancing species richness as a result of multifactorial interactions. Our study provides strong evidence for how to regulate grazing intensity to increase biodiversity under future variable climate patterns. We suggest adapting grazing intensity according to local climate variability to achieve grassland biodiversity conservation.

Functional biogeography of coastal marine invertebrates along the south‐eastern Pacific coast reveals latitudinally divergent drivers of taxonomic versus functional diversity

Characterizing the spatial structure of taxonomic and functional diversity (FD) of marine organisms across regional and latitudinal scales is essential for improving our understanding of the processes driving species richness and those that may constrain or enhance the set of species traits that define the functional structure of communities. Here, we present the functional diversity of coastal invertebrate macrofaunal species along the south‐eastern Pacific from 7°N to 56°S, describe spatial variation of species traits, and examine the relationship with environmental variables. For that, we defined the functional traits and distribution ranges of 2350 marine macroinvertebrates calculated eight metrics of FD. Random forest regression was applied to identify significant relationships between FD and six environmental variables. Finally, functional β‐turnover was estimated to detect alongshore shifts in functional structure and their coincidence with biogeographical domains. Our results show, in contrast with taxonomic richness that measures of trait differences, functional space and functional specialisation increase with latitude, while functional evenness exhibits a non‐linear shape, peaking at mid latitudes. Functional redundancy decreased significantly poleward, while indicators of vulnerability increase. In contrast to taxonomic richness, FD was tightly connected to variables indicative of stress and productivity, such as dissolved oxygen and nutrients. Sea surface temperature and coastal area best explained the increased FD redundancy and richness towards the tropics. The high spatial correlation between taxonomic and functional turnover suggests environmental filters play an important role in the functional structure of the seascape. Our findings suggest that processes favouring taxonomic richness are latitudinally divergent from those favouring functional diversity. Correlations with environmental variables suggest that increased sea surface temperature and measures of stability increase redundancy, while variations in dissolved oxygen and nutrients positively affect functional diversification. Moreover, the functional diversity patterns suggest low resilience of high latitude coastal ecosystems, which are heavily exploited and threatened by climate change, hence highlighting the urgent need for effective conservation policies.

Mechanistic partitioning of species richness in diverse tropical forest tree communities with immigration and temporal environmental stochasticity

Abstract Hyperdiverse tropical forest tree communities illustrate a fundamental problem in ecology: How can many species coexist given relatively few limiting resources? Neutral theory provides a solution by positing that species have equal fitness and hence drift to extinction slowly. However, neutral theory seriously under‐predicts temporal changes in species abundances. This can be remedied by breaking neutrality and adding temporal environmental stochasticity (TES), but the mechanisms mediating the effects of TES on species richness remain unclear. Here, we make progress by analysing a local community model with species competing for a common resource under TES, to derive formulae partitioning species richness according to different mechanisms. By applying our formulae to generic parameter sets for tropical forest tree communities, we found that when the autocorrelation time of TES was short, the dominant mechanism driving species richness was non‐linear averaging of the interspecific competition term over time, which reduced the typical strength of interspecific competition and boosted richness relative to the neutral case. However, greater immigration to the community resulted in more species and hence weaker non‐linear averaging due to the law of large numbers. In contrast, when the autocorrelation time of TES was long, the dominant mechanism driving species richness was strong selection between changes in environmental conditions, which increased the typical strength of interspecific competition and reduced richness relative to the neutral case. By applying our formulae to a specific parameter set for a tropical forest tree community in Panama, we found that TES had minor effects on species richness because (i) the immigration rate was sufficiently large for non‐linear averaging of the interspecific competition term to be weak and (ii) the autocorrelation time was sufficiently short to suppress the effects of selection. Synthesis. We provide a novel mechanistic explanation of how TES affects tree species richness in tropical forests, in particular how TES often has minor effects on richness despite having substantial effects on temporal changes in species abundances. This provides a deeper insight into why a neutral model with added TES can accurately capture static and dynamic aspects of tree community diversity in the tropics.

Species richness and endemism patterns of Sternorrhyncha (Insecta, Hemiptera) in China.

One of the main goals in biogeography and ecology is the study of patterns of species diversity and the driving factors in these patterns. However, such studies have not focused on Sternorrhyncha in China, although this region hosts massive species distribution data. Here, based on the 15,450 distribution records of Sternorrhyncha species in China, we analyzed patterns in species richness and endemism at 1° × 1° grid size and determined the effects of environmental variables on these patterns using correlations analysis and the model averaging approach. We found that species richness and endemism of Sternorrhyncha species are unevenly distributed, with high values in the eastern and southeastern coastal regions of mainland China, as well as Taiwan Island. Furthermore, the key factors driving species richness and endemism patterns are inconsistent. Species richness patterns were strongly affected by the normalized difference vegetation index, which is closely related to the feeding habits of Sternorrhyncha, whereas endemism patterns were strongly affected by the elevation range. Therefore, our results indicate that the range size of species should be considered to understand the determinants of species diversity patterns.

Divergent trait responses to nitrogen addition in tall and short species

Abstract Asymmetrical light competition and direct detrimental effect of nitrogen have been proposed as two main mechanisms driving species richness declines following nitrogen (N) addition. N addition is also known to alter functional trait composition towards increased dominance of tall and fast‐growing species. However, whether trait changes vary between species and, in particular, how the traits of tall and short species respond to N addition has rarely been studied. Understanding whether different trait changes occur for tall and short species would provide insight into mechanisms underlying N addition effects. Based on a long‐term N addition experiment, we measured the natural height of 44 plant species and the photosynthetic active radiation (PAR) at seven heights in the vegetation and identified a clear stratification of the plant community into tall species (>30 cm tall), which experienced high light conditions, and short species that grew under the canopy. We also measured four functional traits, including maximum plant height, specific leaf area, leaf dry matter content and leaf thickness, on 35 species that occurred in fertilized and unfertilized plots. Structural equation modelling revealed that nitrogen (N) addition significantly reduced species richness by enhancing light asymmetry and had no direct effects, suggesting that N detrimental effects are negligible in our system. Consistent with this, we found different responses of traits and diversity for the tall and short species. Specifically, N addition reduced the number of short species but increased the number of tall species. In addition, specific leaf area increased, and leaf dry matter content decreased, for short species only, suggesting that they shifted to a fast growth strategy to cope with lower light levels. In contrast, tall species increased their height further to capture more light at the top of the canopy. Synthesis. The divergent trait responses observed for tall and short species show that although certain traits, like height and leaf traits, show correlated responses at the whole community level, these correlations may not be consistent across all species. Together, our results highlight that light competition is the main mechanism driving species loss following N addition.

Fewer chromosomes, more co-occurring species within plant lineages: A likely effect of local survival and colonization.

Plant lineages differ markedly in species richness globally, regionally, and locally. Differences in whole-genome characteristics (WGCs) such as monoploid chromosome number, genome size, and ploidy level may explain differences in global species richness through speciation or global extinction. However, it is unknown whether WGCs drive species richness within lineages also in a recent, postglacial regional flora or in local plant communities through local extinction or colonization and regional species turnover. We tested for relationships between WGCs and richness of angiosperm families across the Netherlands/Germany/Czechia as a region, and within 193,449 local vegetation plots. Families that are species-rich across the region have lower ploidy levels and small monoploid chromosomes numbers or both (interaction terms), but the relationships disappear after accounting for continental and local richness of families. Families that are species-rich within occupied localities have small numbers of polyploidy and monoploid chromosome numbers or both, independent of their own regional richness and the local richness of all other locally co-occurring species in the plots. Relationships between WGCs and family species-richness persisted after accounting for niche characteristics and life histories. Families that have few chromosomes, either monoploid or holoploid, succeed in maintaining many species in local communities and across a continent and, as indirect consequence of both, across a region. We suggest evolutionary mechanisms to explain how small chromosome numbers and ploidy levels might decrease rates of local extinction and increase rates of colonization. The genome of a macroevolutionary lineage may ultimately control whether its species can ecologically coexist.

Diversifying modelling techniques to disentangle the complex patterns of species richness and diversity in the protected afromontane grasslands

Ecological research has focused on the importance of environmental factors on spatial biodiversity variations and organisation. This is important because of scant conservation resources. We used stepwise backward selection and random feature selection (RFE) to identify a parsimonious model that can predict species richness and diversity metrics in response to three models; biotic, abiotic, and topo-edaphic. Our results show that both metrics are good predictors of one another, mainly because species diversity is a combination of species richness and abundance, and further highlights the importance of biotic variables in predicting species distribution. The two modelling techniques selected soil texture and its interactions with topographic variables as the most important variables. However, random forest performed worse than multiple linear regression in the prediction of diversity metrics. This research highlights the importance of topographically controlled edaphic factors as drivers of species richness and diversity in mountainous grasslands where topography inherently controls the geomorphic, hydrological, and, as a result, ecological processes.

Drivers of species richness and beta diversity of fishes in an Afrotropical intermittent river system.

Tropical freshwater ecosystems are some of the most threatened systems yet remain understudied relative to temperate systems. Here, we look at the drivers of community structure of fishes in a tropical and intermittent system in central Kenya. We conducted monthly sampleswithin the upper Northern Ewaso Ng'iro to assess variation in community composition and abiotic characteristics. We analyzed species richness along the longitudinal gradient, computed beta diversity within the system, relative contributions of each site, and partitioned beta diversity metrics into nestedness and turnover components. We found that, similar to temperate intermittent systems, species richness varied along the longitudinal gradient, nestedness contributions to beta diversity exceeded those of turnover, and environmental and spatial variables determined patterns of beta diversity. Sites at the highest and lowest ends of the species richness gradient showed the highest contributions to beta diversity, suggesting sites important for preservation or restoration initiatives, respectively. With ongoing water extraction and conflict over resources throughout the region, this study highlights the need for further investigations of the effects of multiple stressors on biodiversity patterns and ecosystem functioning in tropical stream communities.

Stream diatom biodiversity in islands and continents—A global perspective on effects of area, isolation and environment

AbstractAimThe species–area relationship (SAR) is one of the most distinctive biogeographic patterns, but global comparisons of the SARs between island and mainland are lacking for microbial taxa. Here, we explore whether the form of the SAR and the drivers of species richness, including area, environmental heterogeneity, climate and physico‐chemistry, differ between islands and similarly sized areas on mainland, referred to as continental area equivalents (CAEs).LocationGlobal.TaxonStream benthic diatoms.MethodsWe generated CAEs on six continental datasets and examined the SARs of CAEs and islands (ISAR). Then, we compared CAEs and islands in terms of total richness and richness of different ecological guilds. We tested the factors contributing to richness in islands and CAEs with regressions. We used structural equation models to determine the effects of area versus environmental heterogeneity, climate and local conditions on species richness.ResultsWe found a non‐significant ISAR, but a significant positive SAR in CAEs. Richness in islands was related to productivity. Richness in CAEs was mainly dependent on area and climate, but not directly on environmental heterogeneity. Species richness within guilds exhibited inconsistent relationships with island isolation and area.Main conclusionsEcological and evolutionary processes shaping diatom island biogeography do not depend on area at the worldwide scale probably due to the presence of distinct species pool across islands. Conversely, area was an important driver of diatom richness in continents, and this effect could be attributed to dispersal. Continents had greater richness than islands, but this was a consequence of differences in environmental conditions such as specific island climatic conditions. We stress the need for more island data on benthic diatoms, particularly from archipelagos, to better understand the biogeography of this most speciose group of algae.

Functional rarity of plants in German hay meadows - Patterns on the species level and mismatches with community species richness.

Functional rarity (FR) — a feature combining a species' rarity with the distinctiveness of its traits — is a promising tool to better understand the ecological importance of rare species and consequently to protect functional diversity more efficiently. However, we lack a systematic understanding of FR on both the species level (which species are functionally rare and why) and the community level (how is FR associated with biodiversity and environmental conditions). Here, we quantify FR for 218 plant species from German hay meadows on a local, regional, and national scale by combining data from 6500 vegetation relevés and 15 ecologically relevant traits. We investigate the association between rarity and trait distinctiveness on different spatial scales via correlation measures and show which traits lead to low or high trait distinctiveness via distance‐based redundancy analysis. We test how species richness and FR are correlated, and use boosted regression trees to determine environmental conditions that are driving species richness and FR. On the local scale, only rare species showed high trait distinctiveness while on larger spatial scales rare and common species showed high trait distinctiveness. As infrequent trait attributes (e.g., legumes, low clonality) led to higher trait distinctiveness, we argue that functionally rare species are either specialists or transients. While specialists occupy a particular niche in hay meadows leading to lower rarity on larger spatial scales, transients display distinct but maladaptive traits resulting in high rarity across all spatial scales. More functionally rare species than expected by chance occurred in species‐poor communities indicating that they prefer environmental conditions differing from characteristic conditions of species‐rich hay meadows. Finally, we argue that functionally rare species are not necessarily relevant for nature conservation because many were transients from surrounding habitats. However, FR can facilitate our understanding of why species are rare in a habitat and under which conditions these species occur.

The relative influence of history, climate, topography and vegetation structure on local animal richness varies among taxa and spatial grains.

Understanding the spatial scales at which environmental factors drive species richness patterns is a major challenge in ecology. Due to the trade-off between spatial grain and extent, studies tend to focus on a single spatial scale, and the effects of multiple environmental variables operating across spatial scales on the pattern of local species richness have rarely been investigated. Here, we related variation in local species richness of ground beetles, landbirds and small mammals to variation in vegetation structure and topography, regional climate, biome diversity and glaciation history for 27 sites across the USA at two different spatial grains. We studied the relative influence of broad-scale (landscape) environmental conditions using variables estimated at the site level (climate, productivity, biome diversity and glacial era ice cover) and fine-scale (local) environmental conditions using variables estimated at the plot level (topography and vegetation structure) to explain local species richness. We also examined whether plot-level factors scale up to drive continental scale richness patterns. We used Bayesian hierarchical models and quantified the amount of variance in observed richness that was explained by environmental factors at different spatial scales. For all three animal groups, our models explained much of the variation in local species richness (85%-89%), but site-level variables explained a greater proportion of richness variance than plot-level variables. Temperature was the most important site-level predictor for explaining variance in landbirds and ground beetles richness. Some aspects of vegetation structure were the main plot-level predictors of landbird richness. Environmental predictors generally had poor explanatory power for small mammal richness, while glacial era ice cover was the most important site-level predictor. Relationships between plot-level factors and richness varied greatly among geographical regions and spatial grains, and most relationships did not hold when predictors were scaled up to the continental scale. Our results suggest that the factors that determine richness may be highly dependent on spatial grain, geography, and animal group. We demonstrate that instead of artificially manipulating the resolution to study multiscale effects, a hierarchical approach that uses fine grain data at broad extents could help solve the issue of scale selection in environment-richness studies.

Scale-dependent patterns and drivers of vascular plant, bryophyte and lichen diversity in dry grasslands of the Swiss inneralpine valleys

The inner-alpine dry valleys of the Swiss Alps are characterized by subcontinental climate, leading to many peculiarities in dry grassland species composition. Despite their well-known uniqueness, comprehensive studies on biodiversity patterns of the dry grasslands in these valleys were still missing. To close this gap, we sampled 161 10-m2 vegetation plots in the Rhône, Rhine and Inn valleys, recording vascular plants, terricolous bryophyte and lichen species, as well as environmental data. Additionally, we tested the scale-dependence of environmental drivers using 34 nested-plot series with seven grain sizes (0.0001–100 m2). We analysed the effects of environmental drivers related to productivity/stress, disturbance and within-plot heterogeneity on species richness. Mean species richness ranged from 2.3 species in 0.0001 m2 to 58.8 species in 100 m2. For all taxa combined, the most relevant drivers at the grain size of 10 m2 were southing (negative), litter (negative), mean annual precipitation (unimodal), gravel cover (negative), inclination (unimodal) and mean annual precipitation (unimodal). For vascular plants the pattern was similar, while bryophyte and lichen richness differed by the opposite relationship to mean annual precipitation as well as negative influences of mean herb layer height, grazing and mowing. The explained variance of the multiple regression model increased with grain size, with very low values for the smallest two grain sizes. While southing and litter had high importance for the fiver larger grain sizes, pH and gravel cover were particularly important at the intermediate grain sizes, and inclination and mean annual precipitation for the two largest grain sizes. The findings emphasize the importance of taxonomic group and grain size for patterns and drivers of species richness in vegetation, consistent with ecological theory. Differences in the diversity–environment relationships among the three taxonomic groups can partly be explained by asymmetric competition that leads to low bryophyte and lichen diversity where vascular plants do well and vice versa. The relatively low alpha diversity of vascular plants in dry grasslands in Swiss inner-alpine valleys compared to similar communities in other parts of the Palaearctic remains puzzling, especially because Swiss stands are often large and well-preserved.

Avifaunal feeding guilds’ response to landscape compositional heterogeneity and their drivers in forest mosaic, Uttarakhand, India

AbstractThe positive association between landscape compositional heterogeneity and avian species richness is widely accepted, however, birds of different feeding guilds are expected to respond differently because of diverse resource utilisation patterns and ecological tolerance. In the present study, we assessed the response of avian species and avifaunal feeding guilds to landscape compositional heterogeneity and factors associated with their richness. Bird richness and landscape variables, edge density, landscape diversity, and area of land cover types were evaluated at 30 sampling sites in the Terai-Arc landscape of Uttarakhand, India. Univariate regression was performed to investigate the response of birds and various feeding guilds to landscape compositional heterogeneity. Average weighted models of most parsimonious generalised linear regression models (<Δ 2AICc) were developed for various feeding guilds to identify significant predictors of species richness. The richness of overall birds and most feeding guilds, except piscivores and frugivores, responded positively to landscape compositional heterogeneity at variable spatial scales. The scale of effect was largest for carnivore (1.5 km), followed by granivore (1 km), insectivore (0.75 km), and frugi-insectivore, nectarivore, and omnivore (0.5 km). Overall bird species richness was positively associated with landscape diversity, teak plantation, and Sal-mixed forest. The average-weighted models identified edge density and dry riverine forest for frugi-insectivore, barren land and water body for the carnivore, teak plantation, Sal-mixed forest and dry-riverine forest for insectivore, edge density, human habitation/agriculture, teak plantation, barren land and scrubland for granivore, human habitation/agriculture for omnivore and waterbodies for piscivore and frugivore guilds as the significant drivers of species richness. The study concludes that the response to landscape compositional heterogeneity differs among feeding guilds and varies with the spatial scale of analysis. The results of our study are expected to serve as a reference for future studies, exploring the landscape relationship to the avian community in similar environmental conditions.

Environmental filters and biotic interactions drive species richness and composition in ecotone forests of the northern Brazilian Amazonia

The structure of tree communities in tropical forests depends on environmental filters and biotic interactions such as competition and facilitation. Many ecotone forests in Northern Amazonia are intriguingly populated by tree assemblages characterized by distinct abundances of a single species, Peltogyne gracilipes (Leguminosae). It is unclear whether this pattern solely reflects environmental filters or also antagonistic interactions among species with similar habitat requirements. The aim of this study was to determine the response of species richness and composition to environmental filters, and analyze the role of P. gracilipes in structuring tree communities in ecotone forest areas of the Northern Brazilian Amazonia. We sampled 129 permanent plots along a hydro-edaphic gradient. All arboreal individuals with stem diameter ≥10 cm were measured and identified. Multiple regressions were performed to test the effects of environmental filters, and abundance of P. gracilipes on the tree species richness and composition. Species richness and composition responded to the same filters which, in turn, affected species composition directly and indirectly, through the abundance of P. gracilipes. Our results indicate that both abiotic filters and biotic interactions shape the studied tree communities. P. gracilipes can be considered an indicator species of hydro-edaphic conditions, but also is itself a driver of tree community structure.

Long-term development of species richness in a central European beech (Fagus sylvatica) forest affected by windthrow-Support for the intermediate disturbance hypothesis?

On the basis of long‐term surveys of permanent plots and traps, we examined the communities of saproxylic beetles, fungi, herbs, and trees on an untreated 22 ha large beech forest windthrow and asked whether the results lend support to the intermediate disturbance hypothesis (IDH). We studied species richness and the similarity of community composition. Additionally, we grouped species by their frequency trend over time to successional model types to examine whether, corresponding to the IDH, the diversity of these groups explained peak richness at intermediate intervals after the disturbance. In line with the IDH, species richness showed a hump‐backed temporal course for alpha and gamma diversity. We found evidence for a linear succession directly after the disturbance. This, however, did not continue, and in all species groups, a partial recovery of the initial community was observed. In the case of fungi, herbs, and trees, but not for saproxylic beetles, alpha diversity was driven by the diversity of the successional model types. Our results underline that the mechanisms driving species richness after disturbances are more complex than the IDH suggests and that these mechanisms vary with species group. We assumed that, besides competition, legacy effects, facilitation, habitat heterogeneity, and random saturation of the species pool are important. In case of trees and herbs, we found indications for strong legacy and competition effects. For fungi and beetles, substrate heterogeneity and microclimate were assumed to be important. We concluded that disturbances contribute to increasing species richness not only by reducing the effectiveness of competitors but also by increasing the amount and diversity of resources, as well as their rate of change over time.

Environmental heterogeneity explains contrasting plant species richness between the South African Cape and southwestern Australia

AbstractAimGiven the importance of environmental heterogeneity as a driver of species richness through its effects on species diversification and coexistence, we asked whether the dramatic difference in species richness per unit area between two similar Mediterranean‐type biodiversity hotspots is explained by differences in environmental heterogeneity.LocationThe Greater Cape Floristic Region, South Africa (GCFR) and Southwest Australian Floristic Region (SWAFR).TaxonVascular plants (tracheophytes).MethodsComparable, geospatially explicit environmental and species occurrence data were obtained for both regions and used to generate environmental heterogeneity and species richness raster layers. Heterogeneity in multiple environmental variables and species richness per unit area were compared between the two regions at a range of spatial scales. At each scale, richness was also regressed against these individual axes and against a major axis of heterogeneity, derived by principal component analysis (PCA).ResultsThe GCFR is generally more environmentally heterogeneous and species‐rich than the SWAFR. Species richness per unit area is significantly related to the major axis of heterogeneity across both regions, the latter describing c. 38%–50% of overall heterogeneity, the slope of this relationship differing between the two regions only at the finest spatial scale. Multivariate regressions, and regressions against the first axes of the PCAs (PC1), revealed variations in the dependence of species richness on environmental heterogeneity between the two regions.Main conclusionsNotwithstanding some region‐specific effects, we present evidence of a common positive relationship between floristic richness and environmental heterogeneity across the GCFR and SWAFR. This is dependent on spatial scale, being strongest at the coarsest level of sampling. The generally greater richness per unit area of the GCFR compared to the SWAFR is thus explained by the former's generally greater environmental heterogeneity and is concordant with its greater levels of floristic turnover.

Mowing does not redress the negative effect of nutrient addition on alpha and beta diversity in a temperate grassland

Abstract Species loss due to an increasing the number of added nutrients has been explained by both light competition through biomass increase and by niche dimension reduction as a result of species‐specific limiting soil resources trade‐offs. Disturbances, by reducing community biomass, species dominance and increasing light availability, may counteract above‐ground nutrient effects. However, it is unknown if diversity loss at local or spatial scales generated by increasing the number of added nutrients can be redressed with canopy disturbance. We evaluated if local (alpha) and spatial scale (beta) diversity loss generated by the number of added nutrients can be reverted by disturbances in Flooding Pampa grasslands, Argentina. In a 4‐year replicated field experiment, we added soil resources combining nitrogen, phosphorus and potassium to obtain 0, 1, 2 or 3 nutrients and manipulated the regime of canopy disturbance by seasonal mowing and biomass removal. We found that the increasing the number of added nutrients strongly reduced local and spatial plant diversity, despite biomass and light changes generated by mowing. In mown plots, nutrient‐driven local diversity loss intensified along time, thus increasing species dominance. While mowing did not affect dominant species loss, increasing the number of added nutrients promoted rare species loss and reduced spatial dissimilarity. Furthermore, mowing increased local and spatial diversity regardless of light or biomass effects, suggesting alternative pathway effects for disturbance. Synthesis. Our results demonstrate that even when disturbance generated a positive effect on local and spatial diversity, it did not completely counteract the negative effect of number of added nutrients. Thus, the relative importance of above‐ and below‐ground resource competition may change when chronic disturbances alter community dominance. Under low light availability, above‐ground competition may drive species richness loss but when disturbance reduces light limitation, the increasing the number of added nutrients may reduce niche dimensionality and thus species coexistence. In sum, faced with the need to manage eutrophized grasslands, our study showed that disturbance may not completely mitigate the negative effect of multiple nutrient inputs on local and spatial grassland diversity.

Drivers of species richness, biomass, and dominance of invasive macrophytes in temperate lakes

Presence and abundance of invasive species depend on likelihood of introduction and environmental limitations to their distributions. Propagule pressure and anthropogenic disturbance are hypothesized to increase invasions, yet assessing the importance of propagule pressure and anthropogenic factors independently is challenging, and properties of invaded systems (e.g., habitat availability) likely contribute to invasions. We sampled macrophyte assemblages in 20 lakes in New York, varying in boater visitations and number of previous waterbodies visited, to test if increased propagule risk (proxy for propagule pressure measuring potential for introducing invasives from different sources) resulted in greater species richness, biomass (g/m2) and dominance (% invasive biomass) of invasive macrophytes. We then tested watershed land use, in-lake water properties, and lake morphology on presence, abundance, and dominance of invasive macrophytes. Increased propagule risk resulted in greater species richness of invasive macrophytes. In invaded lakes, increased abundance of invasive macrophytes was correlated with increased agriculture in watersheds and littoral:total area. Increased dominance of invasive macrophytes was observed in lakes with greater littoral:total areas. Results suggest propagule risk can explain spatial variability in macrophyte invasions, while area-specific biomass in invaded lakes can be correlated with watershed and in-lake water properties. In lakes with increased suitable habitat (relative proportion of littoral:total area ratio), invasive macrophytes may dominate aquatic plant assemblages. Many factors correlated with the abundance of invasive macrophytes are not easily managed (e.g., watershed agricultural land use and lake morphology). Limiting introductions of propagules is likely the best approach to prevent macrophyte invasions, especially at high risk lakes.

On the relative importance of landscape variables to plant diversity and phylogenetic community structure on uninhabited islands, South Korea

Although there have been methodological advances in the analysis of biodiversity and landscape properties, most studies in landscape ecology primarily explore whether certain landscape properties, such as island area and isolation, have universal effects on species-centric measures. We assessed how landscape variables drive species richness, phylogenetic diversity (PD), and phylogenetic community structure. Moreover, we explored the dominant processes structuring plant community assembly, including phylogenetic community structure. We used plant data from 235 uninhabited islands in the western and southern seas, South Korea. Species richness, Faith’s PD, and standardized effect size of mean pairwise phylogenetic distance (SES.MPD) were quantified for three plant groups, all, woody, and herbaceous plants for each island. Island area, distance from mainland, habitat heterogeneity, and structural connectivity were also calculated to examine the relationships between indices of plant diversity and community structure. The relative importance of landscape variables differed among indices of diversity and community structure as well as among plant groups. Island area and distance from mainland were the main drivers of species richness and PD across plant groups, whereas distance from mainland significantly affected community structure measured by SES.MPD. We found that the community structure in islands farther from mainland showed phylogenetic clustering patterns driven by niche-based deterministic processes across the three plant groups. We found that community structure analysis provides more information related to ecological processes and assembly mechanisms than diversity indices alone. Therefore, we recommend that community structure analysis with plant diversity should be implemented as an additional measure of biodiversity for landscape ecology and for conservation planning in island ecosystems.

Biodiversity and conservation of terricolous lichens and bryophytes in continental lowlands of northern Italy: the role of different dry habitat types

In dry habitats of European lowlands terricolous lichens and bryophytes are almost neglected in conservation practises, even if they may strongly contribute to biodiversity. This study aims at (a) testing the role of heathlands, acidic and calcareous dry grasslands for lichen and bryophyte diversity and conservation in lowland areas of northern Italy characterized by high human impact and habitat fragmentation; (b) detecting the effect of environmental drivers and vegetation dynamics on species richness and composition. Lichens, bryophytes, vascular plants, and environmental variables were recorded in 287 circular plots for 75 sites. Our results indicate that heathlands, acidic and calcareous dry grasslands host peculiar terricolous lichen and bryophyte communities that include several species of conservation concern. Thus, each habitat provides a complementary contribution to lichen and bryophyte diversity in continental lowland landscapes. Furthermore, in each habitat different factors drive species richness and composition with contrasting patterns between lichens and bryophytes. In terms of conservation, our results indicate that management of lowland dry habitats should act at both local and landscape scales. At local scale, vegetation dynamics should be controlled in order to avoid biodiversity loss due to vegetation dynamics and wood encroachment. At the landscape scale, patches of all the three habitats should be maintained to maximize regional diversity.