Biomass compensation: Behind the diversity gradients of tidepool fishes

Species richness is unevenly distributed on the Earth, with biodiversity gradients of various spatial scales supposedly being affected by abiotic as well as biotic factors including community traits such as body size spectra and relative abundance patterns. To explore large-scale spatial variation in species diversity and their processes, tidepool fish communities were investigated through an intensive field work conducted on 55 shore sites in south-western Japan. Multiple ecological measures were taken into account to assess changes in local community structures with changes in the number of species. Biomass (total fish wet weight) per unit area showed no systematic change with latitude, while taxa richness and number of individuals tended to increase toward lower latitudes. In addition, median fish body weight scaled positively with latitude, which was more conspicuous in Blenniidae than in Gobiidae. The latitudinal gradient of diversity in tidepool fish assemblages appears to be characterized by partitioning of total biomass that tends to stay constant across latitudes, suggesting the phenomenon of “biomass compensation” whereby body size and abundance/diversity change in opposite directions with latitude. Our study highlights that biomass compensation can be part of processes involved in generating gradients of species richness even without an apparent energy/resource gradient.     

A marine protected area network does not confer community structure resilience to a marine heatwave across coastal ecosystems

Marine protected areas (MPAs) have gained attention as a conservation tool for enhancing ecosystem resilience to climate change. However, empirical evidence explicitly linking MPAs to enhanced ecological resilience is limited and mixed. To better understand whether MPAs can buffer climate impacts, we tested the resistance and recovery of marine communities to the 2014–2016 Northeast Pacific heatwave in the largest scientifically designed MPA network in the world off the coast of California, United States. The network consists of 124 MPAs (48 no-take state marine reserves, and 76 partial-take or special regulation conservation areas) implemented at different times, with full implementation completed in 2012. We compared fish, benthic invertebrate, and macroalgal community structure inside and outside of 13 no-take MPAs across rocky intertidal, kelp forest, shallow reef, and deep reef nearshore habitats in California's Central Coast region from 2007 to 2020. We also explored whether MPA features, including age, size, depth, proportion rock, historic fishing pressure, habitat diversity and richness, connectivity, and fish biomass response ratios (proxy for ecological performance), conferred climate resilience for kelp forest and rocky intertidal habitats spanning 28 MPAs across the full network. Ecological communities dramatically shifted due to the marine heatwave across all four nearshore habitats, and MPAs did not facilitate habitat-wide resistance or recovery. Only in protected rocky intertidal habitats did community structure significantly resist marine heatwave impacts. Community shifts were associated with a pronounced decline in the relative proportion of cold water species and an increase in warm water species. MPA features did not explain resistance or recovery to the marine heatwave. Collectively, our findings suggest that MPAs have limited ability to mitigate the impacts of marine heatwaves on community structure. Given that mechanisms of resilience to climate perturbations are complex, there is a clear need to expand assessments of ecosystem-wide consequences resulting from acute climate-driven perturbations, and the potential role of regulatory protection in mitigating community structure changes.     

Climatic drivers of hemispheric asymmetry in global patterns of ant species richness

Although many taxa show a latitudinal gradient in richness, the relationship between latitude and species richness is often asymmetrical between the northern and southern hemispheres. Here we examine the latitudinal pattern of species richness across 1003 local ant assemblages. We find latitudinal asymmetry, with southern hemisphere sites being more diverse than northern hemisphere sites. Most of this asymmetry could be explained statistically by differences in contemporary climate. Local ant species richness was positively associated with temperature, but negatively (although weakly) associated with temperature range and precipitation. After contemporary climate was accounted for, a modest difference in diversity between hemispheres persisted, suggesting that factors other than contemporary climate contributed to the hemispherical asymmetry. The most parsimonious explanation for this remaining asymmetry is that greater climate change since the Eocene in the northern than in the southern hemisphere has led to more extinctions in the northern hemisphere with consequent effects on local ant species richness.     

Patterns in species richness,species density,and evenness in groundfish assemblages on the continental slope of the U.S. Pacific coast

For many taxa, diversity, often measured as species richness, decreases with latitude. In this report patterns of diversity (species richness, species diversity, and evenness) in groundfish assemblages were investigated in relation to depth (200–1200 m) and latitude (33–47°N) on the continental slope of the U.S. Pacific coast. The data originated from the 1999–2002 upper continental slope groundfish surveys conducted by the National Marine Fisheries Service. When the data were pooled across depths, species density and evenness were found to decline with latitude. All three diversity measures declined with depth, with the lowest overall diversity in the 600- to 900-m depth range where longspine thornyhead Sebastolobus altivelis constituted close to 70% of the catch. When latitudinal gradients were examined within four depth zones (200–300 m, 400–500 m, 600–900 m, and 1000–1200 m) more complex patterns emerged. At depth species richness and evenness were inversely correlated with latitude as longspine thornyhead dominated catches to the north. However, in shallower areas of the slope, species richness and evenness were positively correlated with latitude. Latitudinal patterns of diversity in the deeper zones and when pooled across depths were positively correlated with temperature and broadly consistent with the Ambient Energy hypothesis discussed by Willig et al. [Annu Rev Ecol System 34:273–309 (2003)].     

Ultraviolet radiation and consumer effects on a field-grown intertidal macroalgal assemblage in Antarctica

Ultraviolet radiation (UVR) research on marine macroalgae has hithero focussed on physiological effects at the organism level, while little is known on the impact of UV radiation on macroalgal assemblages and even less on interactive effects with other community drivers, e.g. consumers. Field experiments on macrobenthos are scarce, particularly in the Antarctic region. Therefore, the effects of UVR and consumers (mainly limpets were excluded) on early successional stages of a hard bottom macroalgal community on King George Island, Antarctica, were studied. In a two‐factorial design experimental units [(1) ambient radiation, 280–700 nm; (2) ambient minus UVB, 320–700 nm and (3) ambient minus UVR, 400–700 nm vs. consumer–no consumer] were installed between November 2004 and March 2005 (n= 4 plus controls). Dry mass, species richness, diversity and composition of macroalgal assemblages developing on ceramic tiles were followed. Consumers significantly suppressed green algal recruits and total algal biomass but increased macroalgal richness and diversity. Both UVA and UVB radiation negatively affected macroalgal succession. UVR decreased the density of Monostroma hariotii germlings in the first 10 weeks of the experiment, whereas the density of red algal recruits was significantly depressed by UVR at the end of the study. After 106 days macroalgal diversity was significantly higher in UV depleted than in UV‐exposed assemblages. Furthermore, species richness was significantly lower in the UV treatments and species composition differed significantly between the UV‐depleted and the UV‐exposed treatment. Marine macroalgae are very important primary producers in coastal ecosystems, serving as food for herbivores and as habitat for many organisms. Both, UVR and consumers significantly shape macroalgal succession in the Antarctic intertidal. Consumers, particularly limpets can mediate negative effects of ambient UVR on richness and diversity till a certain level. UVB radiation in general and an increase of this short wavelength due to stratospheric ozone depletion in particular may have the potential to affect the zonation, composition and diversity of Antarctic intertidal seaweeds altering trophic interactions in this system.     

Large-scale spatial distribution patterns of echinoderms in nearshore rocky habitats

This study examined echinoderm assemblages from nearshore rocky habitats for large-scale distribution patterns with specific emphasis on identifying latitudinal trends and large regional hotspots. Echinoderms were sampled from 76 globally-distributed sites within 12 ecoregions, following the standardized sampling protocol of the Census of Marine Life NaGISA project (www.nagisa.coml.org). Sample-based species richness was overall low (<1-5 species per site), with a total of 32 asteroid, 18 echinoid, 21 ophiuroid, and 15 holothuroid species. Abundance and species richness in intertidal assemblages sampled with visual methods (organisms >2 cm in 1 m(2) quadrats) was highest in the Caribbean ecoregions and echinoids dominated these assemblages with an average of 5 ind m(-2). In contrast, intertidal echinoderm assemblages collected from clearings of 0.0625 m(2) quadrats had the highest abundance and richness in the Northeast Pacific ecoregions where asteroids and holothurians dominated with an average of 14 ind 0.0625 m(-2). Distinct latitudinal trends existed for abundance and richness in intertidal assemblages with declines from peaks at high northern latitudes. No latitudinal trends were found for subtidal echinoderm assemblages with either sampling technique. Latitudinal gradients appear to be superseded by regional diversity hotspots. In these hotspots echinoderm assemblages may be driven by local and regional processes, such as overall productivity and evolutionary history. We also tested a set of 14 environmental variables (six natural and eight anthropogenic) as potential drivers of echinoderm assemblages by ecoregions. The natural variables of salinity, sea-surface temperature, chlorophyll a, and primary productivity were strongly correlated with echinoderm assemblages; the anthropogenic variables of inorganic pollution and nutrient contamination also contributed to correlations. Our results indicate that nearshore echinoderm assemblages appear to be shaped by a network of environmental and ecological processes, and by the differing responses of various echinoderm taxa, making generalizations about the patterns of nearshore rocky habitat echinoderm assemblages difficult.     

Grazing effects in macroalgal communities depend on timing of patch colonization

Rocky macroalgal assemblages are typically composed of patches differing in age and species composition and grazing is generally a very important modifier of such assemblages. We hypothesized that patch colonization time determines its algal community and that grazing effects depend on the colonization time and vary with depth. We created patches by placing empty substrates at two sublittoral depths over five consecutive months, manipulated grazer entry and determined the algal species composition in each patch in the next growing season. Distinct algal colonization periods resulted in different algal assemblages. Although algal communities in our study area consist mainly of opportunistic species, thus being highly dynamic, the resulting macroalgal assemblages differed in species richness, diversity, composition, and total biomass even a year after first colonization. Substrates close to the water-surface supported a higher species richness and diversity than those in the deeper littoral. The community characteristics, total density, total biomass and species richness were only slightly, if at all affected by grazing. However, individual algal species or taxa showed varying and even contrasting responses to grazing, often differently between depths and depending on colonization time. In the deeper littoral, but not close to the water surface, grazing increased the density of filamentous brown algae while reducing the green alga Cladophora glomerata. In these taxa, grazing effects were strongest in patches colonized during the early growing season. Grazing at the colonization stage had lasting consequences for the density of several individual species.     

Ecosystem functioning impacts of the invasive seaweed Sargassum muticum (Fucales,Phaeophyceae)

Ongoing changes in natural diversity due to anthropogenic activities can alter ecosystem functioning. Particular attention has been given to research on biodiversity loss and how those changes can affect the functioning of ecosystems, and, by extension, human welfare. Few studies, however, have addressed how increased diversity due to establishment of nonindigenous species (NIS) may affect ecosystem function in the recipient communities. Marine algae have a highly important role in sustaining nearshore marine ecosystems and are considered a significant component of marine bioinvasions. Here, we examined the patterns of respiration and light‐use efficiency across macroalgal assemblages with different levels of species richness and evenness. Additionally, we compared our results between native and invaded macroalgal assemblages, using the invasive brown macroalga Sargassum muticum (Yendo) Fensholt as a model species. Results showed that the presence of the invader increased the rates of respiration and production, most likely as a result of the high biomass of the invader. This effect disappeared when S. muticum lost most of its biomass after senescence. Moreover, predictability–diversity relationships of macroalgal assemblages varied between native and invaded assemblages. Hence, the introduction of high‐impact invasive species may trigger major changes in ecosystem functioning. The impact of S. muticum may be related to its greater biomass in the invaded assemblages, although species interactions and seasonality influenced the magnitude of the impact.     

Demersal fish assemblages and spatial diversity patterns in the Arctic-Atlantic transition zone in the Barents Sea

Direct and indirect effects of global warming are expected to be pronounced and fast in the Arctic, impacting terrestrial, freshwater and marine ecosystems. The Barents Sea is a high latitude shelf Sea and a boundary area between arctic and boreal faunas. These faunas are likely to respond differently to changes in climate. In addition, the Barents Sea is highly impacted by fisheries and other human activities. This strong human presence places great demands on scientific investigation and advisory capacity. In order to identify basic community structures against which future climate related or other human induced changes could be evaluated, we analyzed species composition and diversity of demersal fish in the Barents Sea. We found six main assemblages that were separated along depth and temperature gradients. There are indications that climate driven changes have already taken place, since boreal species were found in large parts of the Barents Sea shelf, including also the northern Arctic area. When modelling diversity as a function of depth and temperature, we found that two of the assemblages in the eastern Barents Sea showed lower diversity than expected from their depth and temperature. This is probably caused by low habitat complexity and the distance to the pool of boreal species in the western Barents Sea. In contrast coastal assemblages in south western Barents Sea and along Novaya Zemlya archipelago in the Eastern Barents Sea can be described as diversity "hotspots"; the South-western area had high density of species, abundance and biomass, and here some species have their northern distribution limit, whereas the Novaya Zemlya area has unique fauna of Arctic, coastal demersal fish. (see Information S1 for abstract in Russian).     

Complex patterns of expression of heat-shock protein 70 across the southern biogeographical ranges of the intertidal mussel Mytilus californianus and snail Nucella ostrina

Aim It is often assumed that species reach their highest densities in the centre of their ranges and decline in abundance toward the edges of the range. Implicit in this notion, which we call the abundant centre hypothesis, is the assumption that the edges of the range are more stressful to organisms and are more likely to show responses to climate change. However, an earlier review and empirical study of patterns of abundance across the range of intertidal invertebrates show little support for the abundant centre hypothesis and further demonstrated that few studies have examined patterns in either abundance or stress across species ranges. In part this gap is due to the logistical difficulties of sampling species across large geographical ranges. Here we use intertidal invertebrates, which have relatively simple linear latitudinal ranges, and heat‐shock proteins, which have been shown to be an integrative measure of organismal stress, to test the hypothesis that species are more stressed at the edges of their range. We use complementary data on population density to test the relationship between stress proteins and overall species density across the species’ range. Location Our sampling programme covered the southern half of the large geographical ranges of two intertidal invertebrates on the Pacific Coast of North America. Sites were spread between northern Baja California, Mexico and Vancouver Island, Canada, a range of c. 22 degrees of latitude. Method We sampled levels of heat‐shock protein 70 (Hsp70) in eight to 12 individuals from each of 20 sites for the intertidal mussel Mytilus californianus and 11 sites for the intertidal snail Nucella ostrina, spread throughout the southern half of their geographical ranges. The relationships between levels of Hsp70 in individuals from a site and (1) latitude of the site, (2) the site's position in the species’ range and (3) average population density were determined. Results No significant relationship was found in either species between levels of Hsp70 and latitude, position in the range or population density. Complex patterns that did emerge may be explained by nonlinear gradients in environmental conditions along the Pacific coast. Specifically, we observed peak values of Hsp70 for both species in northern Oregon, where intertidal zones are disproportionately exposed to daytime emersion (exposure to air) in the summer months of collections. A second peak for M. californianus was found south of Point Conception, California, which is marked by dramatic shifts toward warmer sea temperatures and decreased wave exposure. Main conclusions Patterns that emerged were not predicted by simple models based on the abundant centre hypothesis. However, they are consistent with more complex pictures of heat stress, organismal condition and abundance along a latitudinal gradient that have been demonstrated in recent studies. We suggest that latitudinal complexity, species‐specific differences and local effects must be considered before generalizing the relationship between environmental stress, abundance, range limits and responses of ranges to climate change.     

The good,the bad and the Ulva: the density dependent role of macroalgal subsidies in influencing diversity and trophic structure of an estuarine community

Worldwide, ecological subsidies enhance ecosystem productivity and therefore trophic support for greater biodiversity of taxa. While studies in terrestrial and aquatic ecosystems demonstrate that the magnitude of subsidies into ecosystems differs widely, the thresholds where subsidies may switch from exerting positive to negative effects are poorly understood. In estuaries, eutrophication promotes drift macroalgae that deposit on the benthos, cover intertidal flats for months and serve as pressed resource subsidies for benthic consumers. We hypothesized there would be a critical threshold of macroalgal biomass where ecosystem‐level effects would turn from positive to negative. We used manipulative field experiments varying macroalgal mat thickness (0.5, 1.5 and 4 cm) over eight weeks and quantified effects on macrofauna on a lagoon mudflat in California. We documented that plots with mat depths of 0.5 and 1.5 cm had higher diversity by supporting both surface feeding and burrowing detritivores. Non‐metric multidimensional scaling showed that the benthic community diverged with mat depth over the course of the experiment. After eight weeks, surface deposit feeders were associated mainly with 0.5 cm macroalgal subsidies, whereas subsurface deposit feeding capitellids were closely linked with 4 cm mats. Depth profiles of pore water sulfide concentration collected from 4 cm mats were 7622 ± 5294 μM, mean ± SE, (mean of means across depth profiles), whereas 0.5 cm treatments resulted in sulfide concentrations that were 0.25% of the 4 cm treatments. This suggests that the mechanism of negative effects for elevated macroalgal subsidies was development of anoxic conditions promoting sulfide accumulation. Thus, our study was the first to find a critical threshold, or ecological tipping point, beyond which the effects of anthropogenically enhanced subsidies to estuarine mudflat communities switched from positive to negative and to describe the mechanism by which elevated subsides altered the abiotic environment and likely reduced ecosystem functioning.     

Microhabitat preferences of benthic fauna in a woodland stream

Estimates of numbers, biomass, and diversity of benthic macroinvertebrates were made quarterly over a two-year period to investigate microhabitat preferences. Although biomass of most taxa was significantly different among sampling times, physical factors also appeared to be important in determining abundance of many taxa. Optimum depth, velocity, substrate type, and turbulence were determined for major taxa. Optimum conditions for diversity appeared to be 34 cm depth, 60 cm s^?1 velocity, and rubble and boulder substrate type. Habitat preference functions were derived for several taxa based on significant polynomial regressions of biomass on depth, velocity, substrate, and Froude number (turbulence). The relationship between abundance and physical habitat conditions was tested by using the product of the preference factors (range: 0–1) for depth, velocity and substrate type as a measure of habitat suitability (joint preference factor). There were significant correlations between biomass [transformed by log_e (x + 1)] of 10 benthic species and the joint preference factor. The joint preference factors accounted for from 11 to 61% of the variation of biomass of the 10 benthic species. The intercepts of the relationships between biomass of individual species and the joint preference factor were not significantly different from zero for any species. Therefore, the joint preference factors appear to be valid indicators of biomass. The preference functions have utility in habitat assessment studies, specifically with regard to minimum instream flow determinations.     

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.     

Legacy effects of canopy disturbance on ecosystem functioning in macroalgal assemblages

Macroalgal assemblages are some of the most productive systems on earth and they contribute significantly to nearshore ecosystems. Globally, macroalgal assemblages are increasingly threatened by anthropogenic activities such as sedimentation, eutrophication and climate change. Despite this, very little research has considered the potential effects of canopy loss on primary productivity, although the literature is rich with evidence showing the ecological effects of canopy disturbance. In this study we used experimental removal plots of habitat-dominating algae (Order Fucales) that had been initiated several years previously to construct a chronosequence of disturbed macroalgal communities and to test if there were legacy effects of canopy loss on primary productivity. We used in situ photo-respirometry to test the primary productivity of algal assemblages in control and removal plots at two intertidal elevations. In the mid tidal zone assemblage, the removal plots at two sites had average primary productivity values of only 40% and 60% that of control areas after 90 months. Differences in productivity were associated with lower biomass and density of the fucoid algal canopy and lower taxa richness in the removal plots after 90 months. Low-shore plots, established three years earlier, showed that the loss of the large, dominant fucoid resulted in at least 50% less primary productivity of the algal assemblage than controls, which lasted for 90 months; other smaller fucoid species had recruited but they were far less productive. The long term reduction in primary productivity following a single episode of canopy loss of a dominant species in two tidal zones suggests that these assemblages are not very resilient to large perturbations. Decreased production output may have severe and long-lasting consequences on the surrounding communities and has the potential to alter nutrient cycling in the wider nearshore environment.     

Abundance and diversity of birch‐feeding leafminers along latitudinal gradients in northern Europe

Latitudinal patterns in biotic interactions, including herbivory, have been widely debated during the past years. In particular, recent meta‐analysis questioned the hypothesis that herbivory increases from the poles towards the equator. Our study was designed to verify this hypothesis by exploring latitudinal patterns in abundance and diversity of birch‐feeding insect herbivores belonging to the leafminer guild in northern Europe, from 59° to 69°N. We collected branches from five mature trees of two birch species (Betula pendula and B. pubescens) at each study site (ten sites for each of five latitudinal gradients) twice per season (in early and late summer of 2008–2011) and attributed all mines found on leaves of these branches to a certain taxon of insects. Latitudinal patterns were quantified by calculating Spearman rank correlation coefficients between both abundance and diversity of leafmining taxa and latitudes of sampling sites. In general, both abundance and diversity of leafminers significantly decreased with latitude. However, we discovered pronounced variation in patterns of latitudinal changes among study years and leafminer taxa. Variation among study years was best explained by mean temperatures in July at the northern ends of our gradients. During cold years, abundance of leafminers significantly decreased with latitude, while during warm years the abundance was either independent of latitude or even increased towards the pole. In the northern boreal forests (66° to 69°N), herbivores demonstrated larger changes in densities in response to temperature variations than in the boreo‐nemoral forests (59° to 62°N). Our data suggest that climate warming will result in a stronger increase in herbivory at higher latitudes than at lower latitudes.     

The legacy of past climate and landscape change on species' current experienced climate and elevation ranges across latitude: a multispecies study utilizing mammals in western North America

Aim Elevation and climate ranges across latitude experienced by 21 wide‐ranging mammal species in western North America were summarized to examine two questions: (1) do populations in the northern and southern portions of a species’ range experience different climates or are environments selected to remain similar to climates at the core of ranges; and (2) how do species’ elevational ranges, experienced temperature seasonality and temperature ranges change across latitude? Given the larger effects of climate oscillations in the north vs. the south, a predicted outcome is for species to conserve climate niches across latitude and to show reduced climate and elevation ranges in the north. An alternative outcome is latitudinal niche diversification and increased climate variation in the north. Location Western North America. Methods The questions above were examined using a combination of species occurrence data bases, climate data bases, simple summaries of means and standard deviations and by testing summaries against random distributions across latitude for 21 mammal species from a variety of orders. Results The results showed that: (i) most species conserve their niche strongly or weakly given overall temperature gradients from north to south; (ii) seasonality experienced by species is relatively static until the highest latitudes despite directional trends across the region; and (iii) the elevation range and temperature variation that species experience decreases from south to north. Main conclusions Populations at range edges appear to partition environments to remain closer to temperature values similar to those at the core of the range. In addition, seasonality is not a likely explanatory factor of genetic diversity in latitudinal gradients. The data are instead more consistent with predictions that a combination of higher gene‐flow, increasing environmental instability and decreasing elevation gradients in the north compared to the south may lead to negative correlations between latitude and species’ climate variation. The results corroborate risks faced by northern mammal populations to global climate changes.     

The effects of macroalgal cover on the spatial distribution of macrobenthic invertebrates: the effect of macroalgal morphology

The growth of green macro-algae in response to nutrient inputs is a common phenomenon in marine estuaries and sheltered bays. While the ecological effects of the growth of the most commonly occurring macroalgal taxa (Enteromorpha, Chaetomorpha, Ulva, Cladophora) have been well studied, the effects of a morphologically very different species, Vaucheria subsimplex, have not been investigated. This study investigated the ecological effects of the establishment of V. subsimplex on a relatively exposed intertidal sandflat, Drum Sands, Firth of Forth, Scotland. Because of the spatially heterogeneous development of the weed, the short term (4 weeks) and long term (20 weeks) effects of the weed could be studied using a survey approach in which the weed-affected and weed-free plots were interspersed. After 4 weeks, V. subsimplex significantly increased the mean number of individuals and diversity of the macrofauna, eight of the ten most abundant species showed significant increases in abundance compared to weed-free areas. After 20 weeks, mean number of species and individuals were significantly higher under weed patches, while species diversity was reduced due to the numerical dominance of Pygospio elegans (Claparède). The weed, therefore, had an enriching effect on the macrofaunal communities on Drum Sands. The increased numbers of P. elegans, the numerical dominant infaunal species on Drum Sands, resulted mainly from enhanced larval recruitment to weed-affected areas. The effects of V. subsimplex on sediment characteristics were similar to those reported for other macroalgal taxa, i.e., increased water, organic and silt/clay contents, medium particle size and sorting coefficients, and reduced redox potentials. The results from this study are compared to those for other, morphologically different macroalgal species, with particular reference to an Enteromorpha-implanted experiment on the same sandflat. Since the general effect of such macroalgal taxa on macrofaunal communities is a detrimental one, the present study supports the contention that macroalgal morphology is an important feature in algal–faunal interactions.     

Untangling latitudinal richness gradients at higher taxonomic levels: familial perspectives on the diversity of New World bat communities

Aims (i) To describe at the level of local communities latitudinal gradients in the species richness of different families of New World bats and to explore the generality of such gradients. (ii) To characterize the relative effects of changes in the richness of each family to the richness of entire communities. (iii) To determine differences in the rate and direction of latitudinal gradients in species richness within families. (iv) To evaluate how differences among families regarding latitudinal gradients in species richness influence the latitudinal gradient in species richness of entire communities. Location Continental New World ranging from the northern continental United States (Iowa, 42° N) to eastern Paraguay (Canindeyú, 24° S). Methods Data on the species composition of communities came from 32 intensively sampled sites. Analyses focused on species richness of five of nine New World bat families. Multivariate analysis of variance and discriminant function analysis determined and described differences among temperate, subtropical, and tropical climatic zones regarding the species richness of bat families. Simple linear regression described latitudinal gradients in species richness of families. Path analysis was used to describe: (i) the direct effect of latitude on species richness of communities, (ii) the indirect effects of latitude on the species richness of communities through its effect on the species richness of each family, (iii) the relative effects of latitude on the species richness of bat families, and (iv) the relative contribution of each family to variation in the species richness of communities. Results Highly significant differences among climatic zones existed primarily because of a difference between the temperate zone and the tropical and subtropical zones combined. This difference was associated with the high number of vespertilionids in the temperate zone and the high number of phyllostomids in the tropical and subtropical zones. Latitudinal gradients in species richness were contingent on phylogeny. Although only three of the five families exhibited significant gradients, all families except for the Vespertilionidae exhibited indistinguishable increases in species richness with decreases in latitude. The Emballonuridae, Phyllostomidae and Vespertilionidae exhibited significant latitudinal gradients whereby the former two families exhibited the classical increase in species richness with decreasing latitude and the latter family exhibited the opposite pattern. Variation in species richness of all families contributed significantly to variation in the species richness of entire communities. Nonetheless, the Phyllostomidae made a significantly stronger contribution to changes in species richness of communities than did all other families. Much of the latitudinal gradient in species richness of communities could be accounted for by the effects of latitude on the species richness of constituent families. Main conclusions Ecological and evolutionary differences among higher taxonomic units, particularly those differences involving life‐history traits, predispose taxa to exhibit different patterns of diversity along environmental gradients. This may be particularly true along extensive gradients such as latitude. Nonetheless, species rich taxa, by virtue of their greater absolute rates of change, can dominate and therefore define the pattern of diversity at a higher taxonomic level and eclipse differences among less represented taxa in their response to environmental gradients. This is true not only with respect to how bats drive the latitudinal gradient in species richness for all mammals, but also for how the Phyllostomidae drives the latitudinal gradient for all bats in the New World. Better understanding of the mechanistic basis of latitudinal gradients of diversity may come from comparing and contrasting patterns across lower taxonomic levels of a higher taxon and by identifying key ecological and evolutionary traits that are associated with such differences.     

陆地植物群落物种多样性的梯度变化特征

研究陆地植物落物种多样性随环境因子及群落演替梯度的变化特征是揭示生物多样性与生态因子相互关系的重要方面,根据近期国内外的文献,综述了这方面的研究进展。随纬度的降低,通常物咱多样性随中,随不分梯度的变化,物种多样性的变化有６种趋势;随海拔高的变化,物处多样性有５种模式;随土壤养分梯度的变化,表现出不同的规律;演替过程中物种多样生的变化趋势相似。关于植物群落物种多样性梯度格局的机制有多种假说,但仍需进