بررسی تنوع زیستی محصولات زراعی و باغی استان اصفهان

(introduction to Special Issue: The roles of habitat heterogeneity in generating and maintaining biodiversity on continental margins A Contribution to the Census of Marine Life)

Researchers frequently discuss spatial distribution patterns of species diversity and biomass together with their correlations along geographical gradients. Typical subalpine meadows occur widely on the east of the Loess Plateau, China; here, we selected nine mountains belonging to four mountain systems from north to south on the east of the plateau. We analyzed five latitudinal and longitudinal gradients together with six elevational gradients to study the spatial distribution patterns of species diversity (including α, β, and γ diversity) and biomass plus with their relationships at various scales. Results showed that (1) for diversity, α-Diversity manifested unimodal variation patterns in horizontal spaces, peaking at high latitude and low longitude. However, α-diversity was not sensitive to elevation in vertical spaces and tended to decrease with increasing elevation. With increased latitude, longitude, and elevation, β-Diversity diminished; meanwhile, the rate of species turnover decreased and the similarity of community composition enlarged. γ-Diversity demonstrated quadratic function changes that were initially incremental and then decreased with increasing longitude, elevation, and latitude from 37.5° to 40°. In general, β-diversity had positive correlation with γ-diversity and negative correlation with α-diversity, which conformed to the function of β = γ/α. (2) For biomass, changes of aboveground biomass (AB) were more obvious along latitudinal gradients, whereas variations of belowground biomass (BB) had smaller differences along longitudinal and latitudinal gradients. More biomass was allocated to BB toward the north and east, whereas root-to-shoot ratio (R/S) was more evident at greater latitude than greater longitude. With increased elevation, more biomass was also allocated to BB, and the relationship of biomass to elevation was closer in AB. In short, the relation of biomass allocation tended to belowground plant parts with different geographical scales. (3) Species diversity had the strongest positive influence on AB. The Patrick and Shannon indices had correlations of power functions with AB and R/S, respectively, indicating that an allometric model could be used to model relationships between species diversity and biomass. In conclusion, the unique geomorphological structures with a series of basins between mountain systems on the east of the Loess Plateau, meant that subalpine meadows were mostly distributed along latitudinal directions, so the spatial distribution of species diversity and biomass was more evident along latitudinal gradients, and thus the response of aboveground biomass was more sensitive to variations of spatial gradients and species diversity.

Background. Researchers frequently discuss spatial distribution patterns of species diversity and biomass together with their correlations along geographical gradients. Typical subalpine meadows occur widely on the east of the Loess Plateau, China. In recent years, with a rapid development of tourism and pasture husbandry, subalpine meadows have experienced extensive and severe degradation caused by humans in the mountain systems of the Plateau, where their environments are sensitive and fragile, meadows degradation had been increasing, and biodiversity has been threatened seriously. Methods. In our study, we selected nine mountains belonging to four mountain systems from north to south on the east of the plateau. We analyzed five latitudinal and longitudinal gradients together with six elevational gradients to study the spatial distribution patterns of species diversity (including α, β, and γ diversity) and biomass plus with their relationships at various scales. Results. For diversity, α-Diversity manifested unimodal variation patterns in horizontal spaces, peaking at high latitude and low longitude. However, α-diversity was not sensitive to elevation in vertical spaces and tended to decrease with increasing elevation. With increased latitude, longitude, and elevation, β-Diversity diminished; meanwhile, the rate of species turnover decreased and the similarity of community composition enlarged. γ-Diversity demonstrated quadratic function changes that were initially incremental and then decreased with increasing longitude, elevation, and latitude from 37.5° to 40°. For biomass, changes of aboveground biomass (AB) were more obvious along latitudinal gradients, whereas variations of belowground biomass (BB) had smaller differences along longitudinal and latitudinal gradients. More biomass was allocated to BB toward the north and east, whereas total biomass (TB) allocation was more evident at greater latitude than greater longitude. With increased elevation, more TB was also allocated to BB, and the relationship of biomass to elevation was closer in AB. In addition, species diversity had the strongest positive influence on AB. The Patrick and Shannon indices had correlations of power functions with AB and root-to-shoot ratio, respectively, indicating that an allometric model could be used to model relationships between species diversity and biomass. Discussion. The unique geomorphological structures with a series of basins between mountain systems on the east of the Loess Plateau, meant that subalpine meadows were mostly distributed along latitudinal directions, so the spatial distribution of species diversity and biomass was more evident along latitudinal gradients, and thus the response of aboveground biomass was more sensitive to variations of spatial gradients and species diversity.

Tropical animals and plants are known to have high alpha diversity within forests, but low beta diversity between forests. By contrast, it is unknown whether microbes inhabiting the same ecosystems exhibit similar biogeographic patterns. To evaluate the biogeographies of tropical protists, we used metabarcoding data of species sampled in the soils of three lowland Neotropical rainforests. Taxa-area and distance-decay relationships for three of the dominant protist taxa and their subtaxa were estimated at both the OTU and phylogenetic levels, with presence-absence and abundance-based measures. These estimates were compared to null models. High local alpha and low regional beta diversity patterns were consistently found for both the parasitic Apicomplexa and the largely free-living Cercozoa and Ciliophora. Similar to animals and plants, the protists showed spatial structures between forests at the OTU and phylogenetic levels, and only at the phylogenetic level within forests. These results suggest that the biogeographies of macro- and micro-organismal eukaryotes in lowland Neotropical rainforests are partially structured by the same general processes. However, and unlike the animals and plants, the protist OTUs did not exhibit spatial structures within forests, which hinders our ability to estimate the local and regional diversity of protists in tropical forests.

Understanding species diversity and disturbance relationships is important for biodiversity conservation in disturbance-driven boreal forests. Species richness and evenness may respond differently with stand development following fire. Furthermore, few studies have simultaneously accounted for the influences of climate and local site conditions on species diversity. Using forest inventory data, we examined the relationships between species richness, Shannon's index, evenness, and time since last stand-replacing fire (TSF) in a large landscape of disturbance-driven boreal forest. TSF has negative effect on species richness and Shannon's index, and a positive effect on species evenness. Path analysis revealed that the environmental variables affect richness and Shannon's index only through their effects on TSF while affecting evenness directly as well as through their effects on TSF. Synthesis and applications. Our results demonstrate that species richness and Shannon's index decrease while species evenness increases with TSF in a boreal forest landscape. Furthermore, we show that disturbance frequency, local site conditions, and climate simultaneously influence tree species diversity through complex direct and indirect effects in the studied boreal forest.

The coastal deltas are ecologically diverse and complex ecosystems that can contain different habitat types. The effect of environmental heterogeneity on diatom beta diversity is a poorly understood research topic. Freshwater (floodplain forest, river) and brackish (three lagoons) water bodies in the study area construct distinct environmental heterogeneity at a small spatial scale. The connection of the lagoons with an inland sea caused a high salinity gradient. All water bodies in the wetland were determined as hypereutrophic. CCA, Cluster, ANOSIM, and SIMPER analysis clearly explained the distribution of diatom assemblages according to salinity gradient and environmental heterogeneity. The environmental heterogeneity resulted in the presence of freshwater, brackish, and marine diatom species in the studied wetland. Diatom assemblages generally consist of freshwater species with euryhaline character adapted to wide salinity gradients. We determined the rapid replacement and richness difference in diatom assemblages due to environmental heterogeneity and salinity gradient causes high overall alpha, beta, and gamma diversity. Unlike many other studies, the high beta diversity mainly consists of the richness difference rather than species replacement. The high overall beta diversity showed low similarity between the habitats, while high overall alpha diversity exposed high species diversity at the local scale in the study area.

<p>Taphonomic effects complicate the assessment of variations in biodiversity over time. Most pre-Cenozoic fossil assemblages have been altered through taphonomic effects, such as lithification and aragonite dissolution. Several studies have found alpha (local) and gamma (global) diversity in marine ecosystems to be low in the early Mesozoic and then increase throughout the Mesozoic, reaching a maximum in the Cenozoic.</p><p>The Middle to Late Triassic Cassian Formation, exposed in the Dolomites, Southern Alps, northern Italy, comprises tropical reef basin and transported platform assemblages characterized by high diversity and commonly excellent preservation of fossils. The Cassian Formation yields high alpha (mean species richness per locality: 96), beta (mean Jaccard dissimilarity: 0.95), and gamma (1421 invertebrate species) diversity. The high primary diversity is probably due to the tropical reef-associated setting, and its reduced taphonomic alteration caused 4.5 times higher biodiversity to be preserved than in comparable pre-Cenozoic settings. High beta diversity can be explained by the presence of various habitat types and may also have been driven by priority effects. The Cassian fauna, like most comparable modern ecosystems, features a large number of gastropods (39% of all invertebrates, 58% of mollusks are gastropods). Especially small species in the millimeter size range contribute to the large number of gastropod species in the Cassian Formation. Our results support the assumption that the Modern Evolutionary Fauna was already established early in the Mesozoic and that the scarcity of small gastropods in many fossil assemblages is a taphonomic phenomenon. This contradicts the view that the major radiation of gastropods and the generally very strong increase in biodiversity largely took place in the Cenozoic. We suggest that highly complex, gastropod-dominant marine benthic ecosystems are as old as Middle/Late Triassic, pointing to an earlier establishment of the Modern Evolutionary Fauna than previously assumed. An improved eco-space utilization by infaunalization and increased biotic interactions such as a predator/prey escalation may have contributed to the high biodiversity and may reflect early aspects of the Marine Mesozoic Revolution.</p>

Taxonomic diversity considers all species being equally different from each other and thus disregards species' different ecological functions. Exploring taxonomic and functional aspects of biodiversity simultaneously can better understand the processes of community assembly. We analysed taxonomic and functional alpha and beta diversities of breeding bird assemblages on land-bridge islands in the Thousand Island Lake, China. Given the high dispersal ability of most birds at this spatial scale (several kilometres), we predicted (i) selective extinction driving alpha and beta diversities after the creation of land-bridge islands of varying area and (ii) low taxonomic and functional beta diversities that were not correlated to spatial distance. Breeding birds were surveyed on 37 islands annually from 2007 to 2014. We decomposed beta diversity of breeding birds into spatial turnover and nestedness-resultant components, and related taxonomic and functional diversities to island area and isolation using power regression models (for alpha diversity) and multiple regression models on distance matrices (for beta diversity). We then ran simulations to assess the strength of the correlations between taxonomic and functional diversities. Results revealed that both taxonomic and functional alpha diversities increased with island area. The taxonomic nestedness-resultant and turnover components increased and decreased with difference in area, respectively, but functional counterparts did not. Isolation played a minor role in explaining alpha- and beta-diversity patterns. By partitioning beta diversity, we found low levels of overall taxonomic and functional beta diversities. The functional nestedness-resultant component dominated overall functional beta diversity, whereas taxonomic turnover was the dominant component for taxonomic beta diversity. The simulation showed that functional alpha and beta diversities were significantly correlated with taxonomic diversities, and the observed values of correlations were significantly different from null expectations of random extinction. Our assessment of island bird assemblages validated the predictions of no distance effects and low beta diversity due to pervasive dispersal events among islands and also suggested that selective extinction drives taxonomic and functional alpha and beta diversities. The contrasting turnover and nestedness-resultant components of taxonomic and functional beta diversities demonstrate the importance of considering the multifaceted nature of biodiversity when examining community assembly.

Effect of habitat type on algal species diversity and distribution at high altitudes

Species diversity and other integral parameters of zooplankton community in the Japan, Okhotsk, Bering, Chukchi seas and adjacent Pacific waters (total area close to 7.0 . 10 6 km 2 ) are compared on the data obtained in the large-scale surveys conducted by Pacific Fish. Res. Center (TINRO) in 1984-2013. Standard Juday net with mesh size 0.186 mm and mouth area 0.1 m 2 was used for sampling. Among four seas, the Chukchi Sea takes the 1 st place by abundance (ind./m 3 ) and biomass (mg/m 3 ) of zooplankton, 2 nd by species evenness, 3 rd by mean size of organisms, and the last by species richness and diversity. The Bering Sea is the 1 st by mean size of animals, 2 nd by species richness, diversity and biomass, 3 rd by abundance, and the last by species evenness. The Okhotsk Sea takes the 2 nd place by mean size of zooplankton, the last by its abundance, and the 3 rd by other parameters. The Japan Sea is the 1 st by species richness, evenness and diversity, 2 nd by abundance, and the last by mean size of zooplankton and therefore by its biomass. Zooplankton in the Pacific waters has the lowest abundance, but its biomass is higher there in comparison with the Japan Sea. Species richness is the highest in the Pacific, but species diversity is higher there than in the Chukchi Sea and species evenness is the lowest. Mean size of zooplankton organisms in the Pacific is rather large but smaller than in the Bering Sea. In general, zooplankton abundance increases northward in accordance with nutrients supply, as well as the mean size of animals (with exclusion of the Chukchi Sea), but uniformity of the species abundance has opposite tendency (except the Chukchi Sea again). The rank in biodiversity coincides with the rank in species richness. The latter decreases from south to north (with exclusion of the Okhotsk Sea), but depends strongly on size of the surveyed area and surveyed volume of water. Some unexpected statistically significant relationships are found between the integral parameters of zooplankton and these parameters for pelagic and bottom macrofauna which have not yet any rational interpretation.

Macroecology is concerned with changes in biodiversity as well as the causes of these changes on large scales.Biodiversity can show changes over time and over space.Species diversity,as the determinant of biodiversity,shows spatial heterogeneity. China has high biodiversity.An increasing number of scientists are interested in the large-scale spatial variation in biodiversity within China.The natural environments in China have clear boundaries,which have influence the distributions of animals and ecosystems.According to climate type,China can be divided into three natural regions: the eastern monsoon region,the northwest arid region and the Qinghai-Tibetan Plateau region.Study of the spatial pattern of the biodiversity found in China may contribute to the understanding of large-scale patterns in biodiversity. The fauna information database(FID),founded by the Wildlife and Behavioral Ecology Research Group,Institute of Zoology,Chinese Academy of Sciences,contains information on the distribution of amphibians,reptiles,birds and mammals in China.The FID was compiled with data on species checklists of amphibians,reptiles,birds and mammals from 205 nature reserves across mainland China.They covered most parts of the country except Jiangsu Province,Taiwan,Hong Kong and Macau. In this study,we explored the spatial variation in the G-F indices of birds and mammals with geostatistical techniques.As a measure of species diversity,we computed the G-F index using data on birds and mammals in the FID.The G-F index,based on the Shannon-Wiener index,provides a standardized measure of the diversity of species of common origin and similar environmental requirements.We treated the G-F index as a regional variable and obtained semivariance models and parameters of birds and mammals individually for each of the three natural regions.Semivariograms were produced using semivariance analysis methods of GS-plus software.Using the semivariograms and model parameters,we analyzed the characteristics of the spatial variation in bird and mammal diversity in each natural region. The semivariance of the G-F index of birds was fitted with a linear model in the eastern monsoon region and the northwest arid region of China.The parameters demonstrated that species diversity of birds had a weak spatial dependence in the eastern monsoon region and the northwest arid region of China.There was no spatial correlation with pure nugget effects on the Qinghai-Tibetan Plateau,indicating that the spatial variation in bird species diversity was caused by random factors.This may be due to the high dispersal abilities of birds. The semivariance of the G-F index of mammals showed no relationship in the eastern monsoon region and had pure nugget effects in the northwest arid region.However,data of the Qinghai-Tibetan Plateau was best explained by a spherical model.The parameters revealed that spatial pattern of mammalian species diversity was random in the eastern monsoon region and in the northwest arid region but had a strong spatial dependence with a correlation spatial range of 71492—1020000 m on the Qinghai-Tibetan Plateau.This spatial pattern of avian and mammalian species diversity is likely attributable to the interaction between the particular physical environment and life history of birds and mammals.The macroscale spatial pattern of species diversity should be taken into account in the formation of conservation action plans.

Sharks are one of the most threatened groups of marine animals, as high exploitation rates combined with low resilience to fishing pressure have led to population declines worldwidely. Designing conservation strategies for sharks depends on basic knowledge of the geographic distribution and diversity of known species. So far, this information has been fragmented and incomplete. In this study, observer data from 1 874 sets of Chinese tuna longline fisheries in the Eastern and Central Pacific were used to estimate the biodiversity of sharks by applying alpha diversity measures, such as species richness, Chao2 index, Shannon index, species evenness, species density and rank-abundance curves, and the relationships of species richness and Shannon index with spatiotemporal and environmental factors, such as year, season, latitude, longitude, sea surface temperature, chlorophyll-a, and sea level anomaly were analyzed using the generalized additive models. Results showed that a total number of 20 sharks were observed, mainly consisting of <italic>Prionace glauca</italic> and <italic>Carcharhinus falciformis</italic> in the Eastern and Central Pacific. We found that there was a similar species composition in the Eastern and Central Tropical Pacific (Chao2=23.98) and Southeastern Pacific (Chao2=22.50), but the species evenness in the Tropical Pacific was higher than that in the Southeastern Pacific. The shark community in the Eastern and Central Tropical Pacific was dominated by <italic>Prionace glauca</italic> (28.97%) and <italic>Carcharhinus falciformis</italic> (23.85%), while in the Southeastern Pacific it was overwhelmingly dominated by <italic>Prionace glauca</italic> (76.64%). In the Eastern and Central Pacific, the biodiversity of sharks, such as species richness (<italic>S</italic>), Shannon Index (<italic>H</italic>’), and species density in the tropical area was higher than that in the temperate area. The species richness and diversity of sharks showed large spatiotemporal differences and were significantly influenced by habitat environmental characteristics. In terms of inter-annual variation, shark community diversity showed an increasing trend from 2012 to 2017 and a slight decrease from 2017 to 2019. The season with the highest diversity was the third season and the lowest diversity was found in the first season. Sharks preferred to inhabit the areas characterized by warm waters (sea surface temperature≈25℃), intermediate productivity concentrations (chlorophyll-a>0.10 mg·m^-3) and abnormally low sea level (sea level anomaly < 0 m). The alpha diversity performed well in identifying hotspots of biodiversity. The study helps to understand the shark biodiversity in pelagic ecosystems and identify, for conservation purposes, the critical habitats of the shark’s community in tuna longline fisheries in the Eastern and Central Pacific Ocean, and contributes to the future implementation of the protected marine areas, fishing moratorium or restricted fishing zone to manage the pelagic ecosystem in a holistic and more integrated way.

Metacommunity theory generally predicts that regional dispersal of organisms among local habitat patches should influence spatial patterns of species diversity. In particular, increased dispersal rates are generally expected to increase local (alpha) diversity, yet homogenize local communities across the region (decreasing beta-diversity), resulting in no change in regional (gamma) diversity. Although the effect of dispersal on alpha-diversity has garnered much experimental attention, the influence of dispersal rates on diversity at larger spatial scales (beta and gamma) is poorly understood. Furthermore, these theoretical predictions are not well tested in the field, where other environmental factors (e.g., habitat size, resource density) likely also influence species diversity. Here, we used a system of freshwater rock pools on Appledore Island, Maine, USA, to test the effects of dispersal rate on species diversity in metacommunities. The pools exist in clusters (metacommunities) that experience different levels of dispersal imposed by gulls (Larus spp.), which we show to be frequent passive dispersers of rock-pool invertebrates. Although previous research has suggested that waterbirds may disperse aquatic invertebrates, our study is the first to quantify the rate at which such dispersal occurs and determine its effects on species diversity. In accordance with theory, we found that metacommunities experiencing higher dispersal rates had significantly more homogeneous local communities (reduced beta-diversity) and that gamma-diversity was not influenced by dispersal rate. Contrary to theoretical predictions, however, alpha-diversity in the rock pools was not significantly influenced by dispersal. Rather, local diversity was significantly positively related to local habitat size, and both alpha- and gamma-diversity were influenced by the physicochemical environment of the pools. These results provide an important field test of metacommunity theory, highlighting how local and regional factors interact to drive patterns of species diversity in metacommunities, and demonstrate that waterbirds are indeed important dispersal vectors for aquatic invertebrates.

The diversity of species on a landscape is a function of the relative contribution of diversity at local sites and species turnover between sites. Diversity partitioning refers to the relative contributions of alpha (local) and beta (species turnover) diversity to gamma (regional/landscape) diversity and can be influenced by the relationship between dispersal capability as well as spatial and local environmental variables. Ecological theory predicts that variation in the distribution of organisms that are strong dispersers will be less influenced by spatial properties such as topography and connectivity of a region and more associated with the local environment. In contrast, the distribution of organisms with limited dispersal capabilities is often dictated by their limited dispersal capabilities. Small and ephemeral wetlands are centers of biodiversity in forested ecosystems. We sampled 41 small and ephemeral wetlands in forested ecosystems six times over a two-year period to determine if three different taxonomic groups differ in patterns of biodiversity on the landscape and/or demonstrate contrasting relationships with local environmental and spatial variables. We focused on aquatic macroinvertebrates (aerial active dispersers consisting predominantly of the class Insecta), amphibians (terrestrial active dispersers), and zooplankton (passive dispersers). We hypothesized that increasing active dispersal capabilities would lead to decreased beta diversity and more influence of local environmental variables on community structure with less influence of spatial variables. Our results revealed that amphibians had very high beta diversity and low alpha diversity when compared to the other two groups. Additionally, aquatic macroinvertebrate community variation was best explained by local environmental variables, whereas amphibian community variation was best explained by spatial variables. Zooplankton did not display any significant relationships to the spatial or local environmental variables that we measured. Our results suggest that amphibians may be particularly vulnerable to losses of wetland habitat in forested ecosystems as they have high beta diversity. Consequently, the loss of individual small wetlands potentially results in local extirpations of amphibian species in forested ecosystems.

Although the relationships between species diversity and aboveground biomass (AGB) are highly debated in grassland ecosystems, it is not well understood how climatic factors influence AGB directly and indirectly via plant coverage and species diversity in large-scale grasslands along a topographic gradient. In doing so, we hypothesized that climatic factors would regulate plant coverage, species diversity and AGB due to maintaining plant metabolic and ecological processes, but the relationship of plant coverage with AGB would be stronger than species diversity due to covering physical niche space. To test the proposed hypothesis, we collected data for calculations of species richness, evenness, plant coverage and AGB across 123 grassland sites (i.e., the mean of 3 plots in each site) dominated by Leymus chinensis in northern China. We used a structural equation model for linking the direct and indirect effects of topographic slope, mean annual precipitation and temperature on AGB via plant coverage, species richness, and evenness through multiple complex pathways. We found that plant coverage increased AGB, but species evenness declined AGB better than species richness. Topographic slope influenced AGB directly but not indirectly via plant coverage and species diversity, whereas temperature and precipitation increased with increasing topographic slope. Regarding opposing mechanisms, on the one hand, precipitation increased AGB directly and indirectly via plant coverage as compared to species richness and evenness. On the other hand, temperature declined AGB indirectly via plant coverage but increased via species evenness as compared to species richness, whereas the direct effect was negligible. Our results show that niche complementarity and selection effects are jointly regulating AGB, but these processes are dependent on climatic factors. Plant coverage promoted the coexistence of species but depended greatly on precipitation and temperature. Our results highlight that precipitation and temperature are two key climatic drivers of species richness, evenness, plant coverage and AGB through complex direct and indirect pathways. Our study suggests that grasslands are sensitive to climate change, i.e., a decline in water availability and an increase in atmospheric heat. We argue that temperature and precipitation should be considered in grassland management for higher productivity in the context of both plant coverage and species diversity which underpin animals and human well-being.