Large-Scale Spatial Distribution Patterns of Gastropod Assemblages in Rocky Shores

Gastropod assemblages from nearshore rocky habitats were studied over large spatial scales to (1) describe broad-scale patterns in assemblage composition, including patterns by feeding modes, (2) identify latitudinal pattern of biodiversity, i.e., richness and abundance of gastropods and/or regional hotspots, and (3) identify potential environmental and anthropogenic drivers of these assemblages. Gastropods were sampled from 45 sites distributed within 12 Large Marine Ecosystem regions (LME) following the NaGISA (Natural Geography in Shore Areas) standard protocol (www.nagisa.coml.org). A total of 393 gastropod taxa from 87 families were collected. Eight of these families (9.2%) appeared in four or more different LMEs. Among these, the Littorinidae was the most widely distributed (8 LMEs) followed by the Trochidae and the Columbellidae (6 LMEs). In all regions, assemblages were dominated by few species, the most diverse and abundant of which were herbivores. No latitudinal gradients were evident in relation to species richness or densities among sampling sites. Highest diversity was found in the Mediterranean and in the Gulf of Alaska, while highest densities were found at different latitudes and represented by few species within one genus (e.g. Afrolittorina in the Agulhas Current, Littorina in the Scotian Shelf, and Lacuna in the Gulf of Alaska). No significant correlation was found between species composition and environmental variables (r≤0.355, p>0.05). Contributing variables to this low correlation included invasive species, inorganic pollution, SST anomalies, and chlorophyll-a anomalies. Despite data limitations in this study which restrict conclusions in a global context, this work represents the first effort to sample gastropod biodiversity on rocky shores using a standardized protocol across a wide scale. Our results will generate more work to build global databases allowing for large-scale diversity comparisons of rocky intertidal assemblages.     

Aspects of benthic decapod diversity and distribution from rocky nearshore habitat at geographically widely dispersed sites

Relationships of diversity, distribution and abundance of benthic decapods in intertidal and shallow subtidal waters to 10 m depth are explored based on data obtained using a standardized protocol of globally-distributed samples. Results indicate that decapod species richness overall is low within the nearshore, typically ranging from one to six taxa per site (mean = 4.5). Regionally the Gulf of Alaska decapod crustacean community structure was distinguishable by depth, multivariate analysis indicating increasing change with depth, where assemblages of the high and mid tide, low tide and 1 m, and 5 and 10 m strata formed three distinct groups. Univariate analysis showed species richness increasing from the high intertidal zone to 1 m subtidally, with distinct depth preferences among the 23 species. A similar depth trend but with peak richness at 5 m was observed when all global data were combined. Analysis of latitudinal trends, confined by data limitations, was equivocal on a global scale. While significant latitudinal differences existed in community structure among ecoregions, a semi-linear trend in changing community structure from the Arctic to lower latitudes did not hold when including tropical results. Among boreal regions the Canadian Atlantic was relatively species poor compared to the Gulf of Alaska, whereas the Caribbean and Sea of Japan appeared to be species hot spots. While species poor, samples from the Canadian Atlantic were the most diverse at the higher infraordinal level. Linking 11 environmental variables available for all sites to the best fit family-based biotic pattern showed a significant relationship, with the single best explanatory variable being the level of organic pollution and the best combination overall being organic pollution and primary productivity. While data limitations restrict conclusions in a global context, results are seen as a first-cut contribution useful in generating discussion and more in-depth work in the still poorly understood field of biodiversity distribution.     

Patterns of spatial variation of assemblages associated with intertidal rocky shores: a global perspective

Assemblages associated with intertidal rocky shores were examined for large scale distribution patterns with specific emphasis on identifying latitudinal trends of species richness and taxonomic distinctiveness. Seventy-two sites distributed around the globe were evaluated following the standardized sampling protocol of the Census of Marine Life NaGISA project (www.nagisa.coml.org). There were no clear patterns of standardized estimators of species richness along latitudinal gradients or among Large Marine Ecosystems (LMEs); however, a strong latitudinal gradient in taxonomic composition (i.e., proportion of different taxonomic groups in a given sample) was observed. Environmental variables related to natural influences were strongly related to the distribution patterns of the assemblages on the LME scale, particularly photoperiod, sea surface temperature (SST) and rainfall. In contrast, no environmental variables directly associated with human influences (with the exception of the inorganic pollution index) were related to assemblage patterns among LMEs. Correlations of the natural assemblages with either latitudinal gradients or environmental variables were equally strong suggesting that neither neutral models nor models based solely on environmental variables sufficiently explain spatial variation of these assemblages at a global scale. Despite the data shortcomings in this study (e.g., unbalanced sample distribution), we show the importance of generating biological global databases for the use in large-scale diversity comparisons of rocky intertidal assemblages to stimulate continued sampling and analyses.     

Latitudinal gradient of species diversity: multi-scale variability in rocky intertidal sessile assemblages along the Northwestern Pacific coast

This study examined the latitudinal gradient of species diversity of rocky intertidal sessile assemblages on the slopes of rocks along the Northwestern Pacific coast of Japan, located between 31°N and 43°N, by explicitly incorporating an hierarchical spatial scale into the monitoring design. The specific questions were to examine: (1) whether there is a latitudinal gradient of regional diversity, (2) how spatial components of the regional diversity (local diversity and turnover diversity) vary with latitude depending on spatial scale, and (3) whether the latitudinal gradient differs between different measures of species diversity, i.e. species richness and Simpsons diversity index. We measured coverage and the presence or absence of all sessile organisms in a total of 150 census plots established at five shores in each of six regions. The results showed that there were clear latitudinal gradients in regional species richness and in species turnover among shores. However, these patterns were not reflected in smaller-scale local species richness. For Simpsons diversity index, there was no evidence of latitudinal clines either in regional diversity or in spatial components. These results suggest that relative abundance of common species does not vary along latitude, while the number of rare species increases with decreasing latitude.

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An erratum to this article can be found at     

长江口潮间带底栖生物生态及变化趋势

基于长江口3个区域潮间带(崇明东滩、南汇边滩和嵊山岛)监测数据,对长江口区域潮间带底栖生物生态现状及变化趋势进行评价。结果表明,2019年长江口海域泥相和岩相潮间带共鉴定大型底栖生物9门57种,软体动物、甲壳类和多毛类构成主要类群。崇明东滩、南汇边滩两个泥相潮间带底栖生物平均栖息密度分别为96.4个/m~2和160.4个/m~2,平均生物量分别为68.42 g/m~2和45.71 g/m~2;嵊山岛岩相潮间带平均栖息密度和生物量分别为488.9个/m~2和763.72 g/m~2。各断面多样性、丰富度和均匀度指数分别位于1.36—3.24、0.75—2.88和0.48—0.77,泥相潮间带低潮区生物多样性优于中潮区和高潮区,岩相潮间带中潮区生物多样性最好。聚类分析可见长江口海域潮间带底栖生物分为泥相和岩相2个大组群,物种分布存在明显的分潮区现象,高潮区站位成群或与个别中潮区站位成群,低潮区站位成群或与个别中潮区站位成群,表明底质类型和潮汐是影响潮间带大型底栖生物群落结构的主要因子。近30年来,崇明东滩和南汇边滩底栖生物种类数存在一定波动,嵊山后陀湾断面生物种类数明显下降;3个区域潮间带...     

An environmental stress model correctly predicts unimodal trends in overall species richness and diversity along intertidal elevation gradients

Environmental stress is a major factor structuring communities. An environmental stress model (ESM) predicts that overall species richness and diversity should follow a unimodal trend along the full stress gradient along which assemblages from a regional biota can occur (not to be confused with the intermediate disturbance hypothesis, which makes predictions only for basal species along an intermediate-to-high stress range). Past studies could only provide partial support for ESM predictions because of the limited stress range surveyed or a low sampling resolution. In this study, we measured overall species richness and diversity (considering all seaweeds and invertebrates) along the intertidal elevation gradient on two wave-sheltered rocky shores from Helgoland Island, on the NE Atlantic coast. In intertidal habitats, tides cause a pronounced gradient of increasing stress from low to high elevations. We surveyed up to nine contiguous elevation zones between the lowest intertidal elevation (low stress) and the high intertidal boundary (high stress). Nonlinear regression analyses revealed that overall species richness and diversity followed unimodal trends across elevations on the two studied shores. Therefore, our study suggests that the ESM might constitute a useful tool to predict local richness and diversity as a function of environmental stress. Performing tests on other systems (marine as well as terrestrial) should help to refine the model.     

Context‐dependent functional dispersion across similar ranges of trait space covered by intertidal rocky shore communities

Functional diversity is intimately linked with community assembly processes, but its large‐scale patterns of variation are often not well understood. Here, we investigated the spatiotemporal changes in multiple trait dimensions (“trait space”) along vertical intertidal environmental stress gradients and across a landscape scale. We predicted that the range of the trait space covered by local assemblages (i.e., functional richness) and the dispersion in trait abundances (i.e., functional dispersion) should increase from high‐ to low‐intertidal elevations, due to the decreasing influence of environmental filtering. The abundance of macrobenthic algae and invertebrates was estimated at four rocky shores spanning ca. 200 km of the coast over a 36‐month period. Functional richness and dispersion were contrasted against matrix‐swap models to remove any confounding effect of species richness on functional diversity. Random‐slope models showed that functional richness and dispersion significantly increased from high‐ to low‐intertidal heights, demonstrating that under harsh environmental conditions, the assemblages comprised similar abundances of functionally similar species (i.e., trait convergence), while that under milder conditions, the assemblages encompassed differing abundances of functionally dissimilar species (i.e., trait divergence). According to the Akaike information criteria, the relationship between local environmental stress and functional richness was persistent across sites and sampling times, while functional dispersion varied significantly. Environmental filtering therefore has persistent effects on the range of trait space covered by these assemblages, but context‐dependent effects on the abundances of trait combinations within such range. Our results further suggest that natural and/or anthropogenic factors might have significant effects on the relative abundance of functional traits, despite that no trait addition or extinction is detected.     

Testing latitudinal patterns of tidepool fish assemblages: local substrate characteristics affect regional-scale trends

We tested the regional-scale latitudinal patterns of occurrence and community structure of rocky tidepool fishes in relation to local environmental factors, particularly substrate characteristics. Data were derived from intensive field observations conducted on 36 shore sites spread across ca. 1,000 km north–south (24°03′N–32°45′N) in the south-western Japan. While numbers of families, genera, species and individuals per unit area decreased with latitude, these were dependent on substrate types: sites with non-limestone rock substrates tended to harbour larger numbers than limestone sites at the same latitude. Relative abundances of two dominant families (Blenniidae and Gobiidae) varied among sites with weak latitudinal gradients. Species-specific trends of latitudinal distribution were observed in most of the common intertidal fishes, with over half of the species demonstrating substrate-dependent variation. Species composition was clearly different between the Kyushu Island and the Ryukyus and also between limestone and non-limestone sites. Thus, our results clearly demonstrated that the regional-scale latitudinal trends of tidepool fish assemblages were partially dependent on local environmental characteristics (substrate types). Consideration was given to the influences of the Kuroshio Current and other factors including species interactions that might have helped modify observed latitudinal patterns.     

局域与区域生态过程对太白山牛皮桦林林隙内草本植物物种丰富度的影响

以太白山牛皮桦林林隙内草本植物总数为区域物种丰富度,分别采用0.25m2和1m2样方重复抽样的丰富度平均值为局域物种丰富度,来探讨区域物种多样性变异对局域多样性的影响。结果显示:(1)0.25m2和1m2局域物种丰富度与区域物种丰富度显著相关(r=0.791和r=0.861),且随区域物种丰富度的增加而增加;同时,林隙面积也能显著增加局域和区域物种丰富度。(2)控制林隙面积变量的多元回归分析显示,0.25m2和1m2局域物种丰富度与区域物种丰富度存在显著线性回归关系(R2=0.642和R2=0.743);方差分离分析显示,林隙面积仅能解释0.25m2和1m2局域物种丰富度变异的4.0%和4.4%,而区域物种丰富度能解释25.8%和35.3%。研究表明,区域物种丰富度变异在一定程度上决定着局域物种丰富度的组成。     

Ecoregional Vulnerability Assessment for the Functional Richness of South American Carnivorans (Mammalia: Carnivora)

Mapping geographic trends in biodiversity is a key step in conservation planning, which has been mainly focused on taxonomic criteria or species of particular concern. More recently, higher consideration of ecosystem functioning has been advocated, allocating more attention to traits and functional diversity of species assemblages. Carnivorans (Mammalia: Carnivora) are charismatic, albeit threatened, species that variously affect ecosystem functioning through consumptive processes, and whose functional diversity depends on traits associated with their trophic habits and energetic requirements. Yet, analyses of spatial trends in the diversity and vulnerability of carnivoran assemblages have mostly focused on taxonomic and phylogenetic criteria. Then, the present study assessed the vulnerability of the functional richness of South American carnivoran assemblages, both at continental and regional levels. As a first diagnostic of vulnerability, the form of the association between functional richness and species richness (FRS) was assessed through simulations. The resulting nearly linear association indicated low functional redundancy and high sensitivity to global extinctions. A more realistic FRS accounting for actual extinction threats exacerbated losses of functional richness. Further, a positive correlation between effect and response traits suggests non-compensatory responses to environmental stressors by functionally redundant species and, thus, sensitivity of carnivoran functional richness to ongoing trends in land conversion and habitat degradation. Regionally, functional richness paralleled latitudinal gradients in species richness, but vulnerability did not entirely match these variables in space, nor did it risk estimates that accounted for regions’ conservation status. This suggests regional differentiation in conservation priorities, complementing existing taxonomically oriented prioritization schemes.     

Temporal stability of European rocky shore assemblages: variation across a latitudinal gradient and the role of habitat‐formers

Compensatory dynamics, overyielding and statistical averaging are mechanisms promoting the temporal stability of natural communities. Using the model of European intertidal rocky shore assemblages and collating 17 datasets, we investigated how the strength of these stability‐enhancing mechanisms varies with latitude and how it can be altered by the loss of habitat‐formers (e.g. canopy‐forming macroalgae). Community stability decreased with increasing latitude, mostly as a consequence of a greater synchronization of species fluctuations. Statistical averaging and overyielding (i.e. richness effect) promoted stability, but their strength did not vary with latitude. An experimental removal of macroalgal canopies caused a strengthening of the statistical averaging effect that was consistent across the latitudinal gradient investigated. Nonetheless, the loss of canopies depressed stability by enhancing the synchronization of species fluctuations on southernmost shores, while it had weak effects on shores at higher latitudes. Variation in life‐history traits among canopy‐forming species and/or in prevailing environmental conditions across a gradient of latitude could underlie variable effects of habitat‐formers on species fluctuations. Our study shows 1) that the stability of intertidal assemblages and strength of compensatory dynamics varies with latitude, 2) that canopy‐forming macroalgae, exerting a strong control on understorey species, can influence the strength of compensatory dynamics and 3) that biological forcing (i.e. facilitation) can be as important as environmental forcing in enhancing the synchronization of species fluctuations.     

Spatial analyses of intertidal assemblages on sheltered rocky shores

Abstract Understanding processes in complex assemblages depends on good understanding of spatial and temporal patterns of structure at various spatial scales. There has been little quantitative information about spatial patterns and natural temporal changes in intertidal assemblages on sheltered rocky shores in temperate Australia. Natural changes and responses to anthropogenic disturbances in these habitats cannot be accurately measured and assessed without quantitative data on patterns of natural variability in space and through time. This paper describes some suitable quantitative methods for examining spatial and temporal patterns of diversity and abundances of highshore, midshore and lowshore intertidal assemblages and the important component species for a number of shores in a bay that has not been severely altered by human disturbance. Despite a diverse flora and fauna on these shores, the midshore and lowshore assemblages on sheltered shores were characterized by a few species which were also the most important in discriminating among assemblages on a shore and, for each assemblage, among different shores. The same set of species was also important for measuring small-scale patchiness within each assemblage (i.e. between replicate sites on a shore). Therefore, these data provide a rationale for selecting species that are useful for measuring differences and changes in abundance among places and times at different scales and, hence, can be used in the more complex sampling designs necessary to detect environmental impacts. There was considerable spatial variability in all assemblages and all species (or taxa) examined at scales of metres, tens of metres and kilometres. There were no clear seasonal trends for most measures, with as much or more variability at intervals of 3 months as from year to year. Most interactions between spatial and temporal measures were at the smallest scale, with different sites on the same shore generally showing different changes from time to time. The cause(s) of this apparently idiosyncratic variability1 were not examined, but some potential causes are discussed. These data are appropriate for testing hypotheses about the applicability of these findings to other relatively undisturbed sheltered shores, about effects of different anthropogenic disturbances on sheltered intertidal assemblages and to test hypotheses about differences in intertidal assemblages on sheltered versus wave-exposed shores.     

Spatial patterns of richness and abundance of benthic decapod crustaceans and fishes in the North-west Atlantic as measured by cobble-filled bio-collectors

Examination of spatial patterns of organisms in the rocky subtidal zone is logistically challenging, particularly over large geographic distances. In the present study, we describe patterns of richness and abundance of decapod crustaceans and small demersal fishes colonizing cobble-filled bio-collectors in 2008 and 2009 at nearshore sites across an important oceanographic and biogeographic gradient in the North-west Atlantic from Rhode Island, USA to Newfoundland, Canada. At least 17 decapod and 24 fish genera were caught, including cryptic fish taxa not readily sampled with other gear. Species richness and abundance of decapods and fishes in collectors at shallow sites (5–10 m) was similar among nearby sites and was greatest in the southernmost region, but did not follow a simple latitudinal cline. The lack of clear latitudinal patterns is likely to be a result of the complex geography of summer temperatures along this coast, with the lowest temperatures at the mouth of the Bay of Fundy, the centre of the study domain. In 2008, the abundance of crabs was positively related to temperature while that of shrimp was negatively related. There was also a significant interaction between depth and study area, with greater similarity among areas at greater depths (up to 76 m), and greater similarity among depths in areas with little temperature stratification. Our results indicate that bio-collectors are a powerful tool for sampling decapod crustaceans and small demersal fishes in nearshore rocky habitats. Given the anthropogenic impacts in coastal habitats, this information is likely to prove useful for detecting changes in rocky subtidal habitats.     

Species richness and diversity in different functional groups across environmental stress gradients: a model for marine rocky shores

We present a model predicting how the species richness and diversity within benthic functional groups should vary across the full environmental stress gradient across which a regional biota from marine rocky shores can occur. Built upon previous models, our model makes predictions for sessile species (macroalgae and filter feeders), herbivores, and carnivores. We tested some of its predictions by surveying vertical (intertidal elevation) and horizontal (wave exposure and ice scour) stress gradients in northern Nova Scotia, Canada. Because of harsh winter conditions, these coasts only depict approximately intermediate‐to‐high yearly levels of stress that the cold‐temperate, rocky intertidal biota from the northwestern Atlantic can experience. The observed trends matched predictions for sessile species in 75% of the studied gradients, and showed a moderate agreement for herbivores and carnivores only when they were combined as mobile consumers. Agreement meant that both richness and diversity increased from the most stressful to the most benign habitats that can be found in northern Nova Scotia. Also as predicted, sessile species generally showed a faster rate of increase in richness than mobile consumers. Our model also predicted a higher overall richness for sessile species than for mobile consumers, which was true by a factor of 3. Therefore, our model may constitute a useful tool to understanding community composition as a function of abiotic stress, which may in turn facilitate studies on community functioning. Model predictions for lower stress ranges could be tested on more southern shores where the same regional biota occurs.     

Modelling Stream-Fish Functional Traits in Reference Conditions: Regional and Local Environmental Correlates

Identifying the environmental gradients that control the functional structure of biological assemblages in reference conditions is fundamental to help river management and predict the consequences of anthropogenic stressors. Fish metrics (density of ecological guilds, and species richness) from 117 least disturbed stream reaches in several western Iberia river basins were modelled with generalized linear models in order to investigate the importance of regional- and local-scale abiotic gradients to variation in functional structure of fish assemblages. Functional patterns were primarily associated with regional features, such as catchment elevation and slope, rainfall, and drainage area. Spatial variations of fish guilds were thus associated with broad geographic gradients, showing (1) pronounced latitudinal patterns, affected mainly by climatic factors and topography, or (2) at the basin level, strong upstream-downstream patterns related to stream position in the longitudinal gradient. Maximum native species richness was observed in midsize streams in accordance with the river continuum concept. The findings of our study emphasized the need to use a multi-scale approach in order to fully assess the factors that govern the functional organization of biotic assemblages in ‘natural’ streams, as well as to improve biomonitoring and restoration of fluvial ecosystems.     

Temporal comparison of the composition and zonation of rocky intertidal organisms at Cocos Island National Park, Pacific, Costa Rica

Several biological and physical factors change the rocky shore communities. The desiccation time and the tolerance of the intertidal species produce the vertical zonation. In many studies around the world, a temporal change in this zonation is presented.In Costa Rica, only studies that include temporal trends were carried out in Punta Mala and Montezuma, Pacific coast in 80's. The rocky intertidal of the Cocos Island National Park, Costa Rica were surveyed photographically. The Chatham bay was sampled in three expeditions (January 2007, October 2007 and April 2008). Photos corresponding to 25x25cm quadrats were taken with the goal to determine diversity and composition differences in rocky shore organisms between sampling dates. The Wafer bay was sampled in January and October 2007. The intertidal of Chatham consists of basaltic rock, while Wafer has basaltic and ignimbrite boulders. The main difference between sites were the higher algae cover (erect-frondose forms) and number of organism bands at Chatham bay. Temporal change was not found in the total cover of sessile fauna and autotrophs. The barnacle Tetraclita stalactifera, that occurs above the algal fringe (lower intertidal), was the invertebrate with the highest coverage. The mobile fauna biodiversity presented no significant trend between sampled months. However, the identity of species, their cover and their abundance showed a moderate temporal change. In October 2007, when the sea surface temperature was 23 degrees C the infralittoral zone had an increase in green algae cover. The red algae (crust and erect-frondose forms) were dominant in January and April. The pulmonate limpet, Siphonaria gigas and a bacterial biofilm at mid littoral showed a negative association. The snails of the high littoral and the supralittoral zone showed a temporal change in their abundance, but with contrasting patterns between sites. The temporal variation in the assemblages increased from the supralittoral to the infralittoral possibly due to changes in the water temperature and climatic conditions, that could influence the intertidal zone during the high and low tide, respectively.     

Species richness and diversity across rocky intertidal elevation gradients in Helgoland: testing predictions from an environmental stress model

Environmental stress affects species richness and diversity in communities, but the precise form of the relationship is unclear. We tested an environmental stress model (ESM) that predicts a unimodal pattern for total richness and diversity in local communities across the full stress gradient where a regional biota can occur. In 2008, we measured richness and diversity (considering all macrobenthic species) across the entire intertidal range on three rocky shores on Helgoland Island, Germany. Intertidal elevation is known to be positively related to abiotic stress. Since Helgoland is between the northern and southern biogeographic boundaries for the cold-temperate NE Atlantic intertidal biota, it exhibits low stress levels for this biota at low elevations and high stress at high elevations because of long (>6 h) emersion times. Thus, we predicted a unimodal trend for richness and diversity across elevation. On all three shores, richness increased from high to middle elevations, but remained similar between middle and low elevations. Diversity followed the same trend on one shore and different trends (although also non-unimodal) on the other two. Evenness explained the trend differences between richness and diversity. Overall, our study yielded little support for the ESM. Reasons for richness and diversity not decreasing at low elevations may be related to influences of mostly subtidal species, Helgoland’s intertidal range, or sampling resolution. Our study also suggests that the ESM must be developed further to differentiate between richness and diversity. We offer recommendations to improve future ESM research using intertidal systems.     

Elevational patterns of fern species assemblages and richness in central Japan

We conducted field surveys in 807 quadrats to evaluate the elevational belts, boundary and richness patterns of ferns and lycophytes in the temperate region of central Japan. We analysed fern species assemblages at 100 m elevational steps by cluster analysis and tested the number of upper and lower boundaries for elevational intervals against a null model of random distribution of elevational limits. We compared the pattern of fern species richness along the elevational gradients in central Japan with patterns in several locations to evaluate the fern flora in central Japan in relation to the rest of the world. We recorded 261 ferns species in total, which is one-third of the Japanese ferns. We found clear elevational boundaries of fern assemblages at 900 and 1,800 m and three fern elevational zones, which corresponded well to the elevational limits of forest types in central Japan. The pattern of fern species richness in central Japan was an asymmetric hump-shaped pattern that peaked close to the sea level, with the peak of local richness at lower elevations than that of regional richness. We found that the peak of fern species richness along the elevational gradient in Japan was located at lower elevations than that of fern elevational patterns in several locations around the world.     

Arthropod community structure in pastures of an island archipelago (Azores): looking for local-regional species richness patterns at fine-scales

The arthropod species richness of pastures in three Azorean islands was used to examine the relationship between local and regional species richness over two years. Two groups of arthropods, spiders and sucking insects, representing two functionally different but common groups of pasture invertebrates were investigated. The local-regional species richness relationship was assessed over relatively fine scales: quadrats (= local scale) and within pastures (= regional scale). Mean plot species richness was used as a measure of local species richness (= alpha diversity) and regional species richness was estimated at the pasture level (= gamma diversity) with the 'first-order-Jackknife' estimator. Three related issues were addressed: (i). the role of estimated regional species richness and variables operating at the local scale (vegetation structure and diversity) in determining local species richness; (ii). quantification of the relative contributions of alpha and beta diversity to regional diversity using additive partitioning; and (iii). the occurrence of consistent patterns in different years by analysing independently between-year data. Species assemblages of spiders were saturated at the local scale (similar local species richness and increasing beta-diversity in richer regions) and were more dependent on vegetational structure than regional species richness. Sucking insect herbivores, by contrast, exhibited a linear relationship between local and regional species richness, consistent with the proportional sampling model. The patterns were consistent between years. These results imply that for spiders local processes are important, with assemblages in a particular patch being constrained by habitat structure. In contrast, for sucking insects, local processes may be insignificant in structuring communities.