Biodiversity of marine nematodes in Australian sandy beaches from tropical and temperate regions

The universal occurrence and abundance of nematodes provides opportunities to investigate ecological factors that may influence biodiversity. Clarke and Warwick (2001) have proposed diversity indices average taxonomic distance(AvTD), variation in taxonomic distinctness (VarTD) for computing marine nematode biodiversity based on classification trees. Faith [Biological Conservation 61 (1992) 1] had previously proposed a diversity index based on phylogenetic trees, though not applied to nematodes. Clarke and Warwick (2001) also considered an index AvPD analogous to AvTD. These indices have been applied to five very large collections of free-living nematodes from three exposed sandy beaches in Australia. Two were from a beach close to Darwin in northern Australia, two from the temperate southeast coast of Australia and one from the south of the Australian mainland. The collections extend over a considerable range of latitude, from 12°26S to 38°33S and the controversial hypothesis that latitudinal gradients per se influence the biodiversity of marine nematode assemblages is examined. AvTD did not vary among collections and its value for any collection was indistinguishable from that of random samples of the same size drawn from the total species pool. VarTD showed no variation for three of the collections, but was slightly higher than expected for the mid-latitude beach, attributed to unevenness in the classification trees. AvTD and VarTD were not greatly affected by differences in sampling intensity. PD varied directly with the number of species found but observed PD did not differ from the PD of random samples of the same number of species taken from the total species pool. Thus, the observed variation in PD is wholly accounted for by variations in species richness. The number of species found increased with decreasing latitude. It appears that species richness by itself is an adequate index of biodiversity for the free-living nematodes of these sandy beaches, and more complex indices such as AvTD, VarTD and PD are unnecessary.     

Environmental and historical imprints on beta diversity: insights from variation in rates of species turnover along gradients

A common approach for analysing geographical variation in biodiversity involves using linear models to determine the rate at which species similarity declines with geographical or environmental distance and comparing this rate among regions, taxa or communities. Implicit in this approach are weakly justified assumptions that the rate of species turnover remains constant along gradients and that this rate can therefore serve as a means to compare ecological systems. We use generalized dissimilarity modelling, a novel method that accommodates variation in rates of species turnover along gradients and between different gradients, to compare environmental and spatial controls on the floras of two regions with contrasting evolutionary and climatic histories: southwest Australia and northern Europe. We find stronger signals of climate history in the northern European flora and demonstrate that variation in rates of species turnover is persistent across regions, taxa and different gradients. Such variation may represent an important but often overlooked component of biodiversity that complicates comparisons of distance–decay relationships and underscores the importance of using methods that accommodate the curvilinear relationships expected when modelling beta diversity. Determining how rates of species turnover vary along and between gradients is relevant to understanding the sensitivity of ecological systems to environmental change.     

Geographic variation in the relationship between large-scale environmental determinants and bat species richness

Several studies have already shown the close relationship between geographic gradients of biodiversity and distinct environmental determinants such as energy, environmental heterogeneity and seasonality. Nevertheless, whether and how such relationships vary around the globe remains poorly understood. Here we used spatial models to answer whether the bat species richness-environment relationship on a global scale are constant across geographic space. We also partitioned the contribution of the different environmental determinants on bat species richness at different regions of the globe. We found that the relationship between bat species richness and environment is not constant across geographic space and that the shared contributions of environmental determinants are more important than their unique contributions. We conclude that understanding geographic gradients of biodiversity and its environmental determinants, particularly for bats, is more complex than previously thought because the relationship between species richness and environment varies considerably across geographic space.     

Genome size variation and species diversity in salamanders

Salamanders (Urodela) have among the largest vertebrate genomes, ranging in size from 10 to 120 pg. Although changes in genome size often occur randomly and in the absence of selection pressure, nonrandom patterns of genome size variation are evident among specific vertebrate lineages. Several reports suggest a relationship between species richness and genome size, but the exact nature of that relationship remains unclear both within and across different taxonomic groups. Here, we report (a) a negative relationship between haploid genome size (C‐value) and species richness at the family taxonomic level in salamander clades; (b) a correlation of C‐value and species richness with clade crown age but not with diversification rates; (c) strong associations between C‐value and both geographic area and climatic‐niche rate. Finally, we report a relationship between C‐value diversity and species diversity at both the family‐ and genus‐level clades in urodeles.     

Geographical variation in the 'bottom-up' control of diversity: fleas and their small mammalian hosts

Aim We searched for signs of the ‘bottom‐up’ diversity effect in the association between fleas (Siphonaptera) and their small mammalian hosts (Rodentia, Insectivora and Lagomorpha). We asked (1) whether a strong dependence of flea species richness on host species richness is characteristic for both Palaeoarctic and Nearctic realms; (2) if yes, whether the ratio of host species per flea species along the host diversity gradient is similar between the Palaeoarctic and Nearctic; and (3) whether factors other than host species richness (i.e. geographical position, climate and landscape) might better explain variation in flea species richness than host species richness. Location The study used previously published data on species richness of fleas and their small mammalian hosts from 26 Palaeoarctic and 19 Nearctic regions. Methods We regressed the number of flea species on the number of small mammal species across regions, separately for Palaeoarctic and Nearctic realms, using both non‐transformed data as well as data corrected for the confounding effects of host sampling effort and sampling area. To test whether flea species richness is determined by external factors unrelated to the host, we used stepwise multiple regressions of flea species richness against host species richness and parameters describing the geographical position, climate and relief of a region. Results When non‐transformed data were analysed, flea species richness was positively correlated with host species richness in both the Palaeoarctic and Nearctic, although the slopes of the two regressions differed significantly. After removal of the confounding effects of host sampling effort and sampling area, Palaeoarctic flea species richness remained strongly positively correlated with host species richness, whereas in the Nearctic, flea species richness appeared to be completely independent of host species richness. Results of the multiple regressions using corrected data demonstrated that in the Palaeoarctic, flea species richness was correlated with both the number of host species and the mean altitude of the region, whereas in the Nearctic, flea species richness only tended to be weakly correlated with latitude (however, this correlation turned out to be non‐significant after Bonferroni correction). Main conclusions We found evidence of bottom‐up control of flea diversity in the Palaeoarctic regions only, and not in the Nearctic. We explore several potential explanations for the different patterns observed in the two biogeographical realms, including differences in (1) levels of host specialization, (2) history of host–parasite associations and (3) landscape effects on flea diversification. We conclude that these factors combine to create different macroecological patterns in different biogeographical realms, and that diversity is not governed by the same forces everywhere.     

物种与物种多样性

本文首先讨论生物物种的科学概念和生物学本质，分析物种客观存在的自然属性和物种概念的局限性，认为物种的生物学属性和物种多样性的科学属性之间有着本质联系。物种多样性研究的实质是研究生物物种的生物学多样性。度量物种多样性程度有多种方法，但物种数目是物种多样性程度最直接、也是最基本的表达，估计物种多样性数目是当前国际上物种多样性研究的核心与热点内容。物种多样性产生的根源是物种形成，物种绝灭速率是维持物种多样性的关键因素。本文简要总结了物种形成与绝灭的基本模式和机制，通过分析生物地理区系与物种多样性研究的密切关系，说明物种的区系成份分析是物种多样性大尺度格局研究的重要内容。     

Latitudinal species diversity gradient of marine zooplankton for the last three million years

High tropical and low polar biodiversity is one of the most fundamental patterns characterising marine ecosystems, and the influence of temperature on such marine latitudinal diversity gradients is increasingly well documented. However, the temporal stability of quantitative relationships among diversity, latitude and temperature is largely unknown. Herein we document marine zooplankton species diversity patterns at four time slices [modern, Last Glacial Maximum (18 000 years ago), last interglacial (120 000 years ago), and Pliocene (~3.3–3.0 million years ago)] and show that, although the diversity‐latitude relationship has been dynamic, diversity‐temperature relationships are remarkably constant over the past three million years. These results suggest that species diversity is rapidly reorganised as species' ranges respond to temperature change on ecological time scales, and that the ecological impact of future human‐induced temperature change may be partly predictable from fossil and paleoclimatological records.     

Global patterns and drivers of genetic diversity among marine habitat-forming species

Aim

Intraspecific genetic diversity is one of the pillars of biodiversity, supporting the resilience and evolutionary potential of populations. Yet, our knowledge regarding the patterns of genetic diversity at macroecological scales, so-called macrogenetic patterns, remains scarce, particularly in marine species. Marine habitat-forming (MHF) species are key species in some of the most diverse but also most impacted marine ecosystems, such as coral reefs and marine forests. We characterize the patterns and drivers of genetic diversity in MHF species and provide a macrogenetic baseline, which can be used for conservation planning and for future genetic monitoring programmes.

Location

Global.

Time period

Contemporary.

Major taxa studied

Bryozoans, hexacorals, hydrozoans, octocorals, seagrasses, seaweeds, sponges.

Methods

We analysed a database including genetic diversity estimates based on microsatellites in more than 9,000 georeferenced populations from 140 species, which belong to seven animal and plant taxa. Focusing on expected heterozygosity, we used generalized additive models to test the effect of latitude, taxon, and conservation status. We tested the correlation between the species richness and the genetic diversity.

Results

We reveal a significant but complex biogeographic pattern characterized by a bimodal latitudinal trend influenced by taxonomy. We also report a positive species genetic diversity correlation at the scale of the ecoregions. The difference in genetic diversity between protected and unprotected areas was not significant.

Main conclusions

The contrasting results between MHF animals and plants suggest that the latitudinal genetic diversity patterns observed in MHF species are idiosyncratic, as reported in terrestrial species. Our results support the existence of shared drivers between genetic and species diversities, which remain to be formally identified. Concerning, these macrogenetic patterns are not aligned from the existing network of marine protected areas. Providing the first macrogenetic baseline in MHF species, this study echoes the call regarding the need to consider genetic diversity in biodiversity assessments and management.     

Multiregional comparison of the ecological and phylogenetic structure of butterfly species richness gradients

Aim To examine butterfly species richness gradients in seven regions/countries and to quantify geographic mean root distance (MRD) patterns. My primary goal is to determine the extent to which an explanation for butterfly richness patterns based on tropical niche conservatism and the evolution of cold tolerance, proposed for the fauna of Canada and the USA, applies to other parts of the world. Location USA/Canada, Mexico, Europe/NW Africa, Transbaikal Siberia, Chile, South Africa and Australia. Methods Digitized range maps for butterfly species in each region were used to map richness patterns in summer (for all areas) and winter (for USA/Canada, Europe/NW Africa and Australia). A phylogeny resolved to subfamily was used to map the geographic MRD patterns. Regression trees and general linear models examined climatic and vegetation correlates of species richness and MRD within and among regions. Results Various combinations of climate and vegetation were strong predictors of species richness gradients within regions, but unresolved ‘regional’ factors contributed to the multiregional pattern. Regionally based differences in phylogenetic structure also exist, but MRD is negatively correlated with temperature both within and across areas. MRD patterns consistent with tropical niche conservatism occur in most areas. With a possible partial exception of Mexico, faunas in cold climates and in mountains are more derived than faunas in lowlands and tropical/subtropical climates. In USA/Canada, Europe and Australia, winter faunas are more derived than summer faunas. Main conclusions The phylogenetic pattern previously found in the USA and Canada is widespread in both the Northern and Southern Hemispheres, and niche conservatism and the evolution of cold tolerance is the likely explanation for the development of the global butterfly species richness gradient over evolutionary time. Contemporary climate also influences species richness patterns but is unlikely to be a complete explanation globally. The importance of climate is also manifested in the seasonal loss of more basal butterfly elements outside the tropics in winter.     

The distribution and abundance of boring species of polychaetes and sipunculans in coral substrates in French Polynesia

The distribution and abundance of the dominant initial macroborers of dead coral substrate, sipunculans and polychaetes were investigated over time at seven sites within French Polynesia. Sites were located in the lagoon of high islands and atolls, and varied from highly eutrophic to oligotrophic. Significant differences occurred between sites and patterns of recruitment varied over time and between sites. With increasing exposure, the densities of polychaetes increased but not the number of species present, whereas both the densities and number of species of sipunculans increased. The atoll sites tended to be dominated by suspension feeding polychaetes and the high island sites by deposit feeding polychaetes. Sipunculans tended to dominate the high island sites in comparison to the atoll sites and they all fed by scraping algae and detritus from the substrate. We suggest that this distribution of feeding types is related to water quality and to land run off. In the atolls, the lagoonal waters are oligotrophic and little land run off occurs, whereas at the high island sites, high rates of land run off occur during the wet season with high levels of suspended material in the water column.These variations in densities of boring species, affect rates of bioerosion and have the potential to alter the equilibrium between reef growth and reef destruction. We suggest that it is critical for reef managers to try to maintain water quality and limit land-based terrestrial run off and associated nutrients into coastal waters. This is especially important if the reefs have been affected by bleaching events or Crown of Thorns plagues, resulting in extensive death of coral colonies and with it, the potential for a massive increase in the rate of bioerosion. The long-term maintenance of the reef structure is critical if coral recruitment and recovery of the reef are to occur.     

Plant species diversity in cape fynbos: Gamma and delta diversity

Summary This paper reports the number of plant species on circumscribed fynbos areas (gamma diversity), ranging in size from 0.27 km² (a site with 364 species) to 471 km² (2351 species). The composition of the floras of four of these sites was analysed to measure delta diversity, the change in flora from one site to the next. Maximum gamma diversity values fitted a species-area curve log S=2.69+0.25 log A. Gamma diversity is apparently higher than in any of the world's biogeographic zones except perhaps the tropical rain forest, and in other South African sites of areas around 1.0 km², which have about as many species. High delta diversities are reflected in differences between fynbos floras of 50 to 70 %, in spite of relative proximity; this degree of diversity is apparently unmatched anywhere. The results support the conventional view that fynbos plant diversity is partly a consequence of the peculiar geography of the zone, and of palaeo-climatic change, which have favoured geographic speciation.This paper would not have been possible without the conscientious work of staff at Jonkershoek, especially that of R.A. Haynes and E.F. Kruger. The information on the floras of each area studied here has been built up through decades of field work by various collectors. Identifications of the many difficult taxa are due to taxonomists at the National Herbarium, at the Compton Herbarium, Kirstenbosch and at the Bolus Herbarium, University of Cape Town. M. F. Thompson and E. E. Esterhuysen contributed materially in this respect.Paper presented at the Annual Congress of the South African Association of Botanists, Stellenbosch, January 1979.This work is based partly on the results of the conservation research programme of the South African Department of Forestry and the Botanical Research Institute's programme on fynbos phytosociology, and is published with permission of our respective heads of Departments.     

Patterns and controlling factors of species diversity in the Arctic Ocean

Aim The Arctic Ocean is one of the last near‐pristine regions on Earth, and, although human activities are expected to impact on Arctic ecosystems, we know very little about baseline patterns of Arctic Ocean biodiversity. This paper aims to describe Arctic Ocean‐wide patterns of benthic biodiversity and to explore factors related to the large‐scale species diversity patterns. Location Arctic Ocean. Methods We used large ostracode and foraminiferal datasets to describe the biodiversity patterns and applied comprehensive ecological modelling to test the degree to which these patterns are potentially governed by environmental factors, such as temperature, productivity, seasonality, ice cover and others. To test environmental control of the observed diversity patterns, subsets of samples for which all environmental parameters were available were analysed with multiple regression and model averaging. Results Well‐known negative latitudinal species diversity gradients (LSDGs) were found in metazoan Ostracoda, but the LSDGs were unimodal with an intermediate maximum with respect to latitude in protozoan foraminifera. Depth species diversity gradients were unimodal, with peaks in diversity shallower than those in other oceans. Our modelling results showed that several factors are significant predictors of diversity, but the significant predictors were different among shallow marine ostracodes, deep‐sea ostracodes and deep‐sea foraminifera. Main conclusions On the basis of these Arctic Ocean‐wide comprehensive datasets, we document large‐scale diversity patterns with respect to latitude and depth. Our modelling results suggest that the underlying mechanisms causing these species diversity patterns are unexpectedly complex. The environmental parameters of temperature, surface productivity, seasonality of productivity, salinity and ice cover can all play a role in shaping large‐scale diversity patterns, but their relative importance may depend on the ecological preferences of taxa and the oceanographic context of regions. These results suggest that a multiplicity of variables appear to be related to community structure in this system.     

Invasion by alligator weed,Alternanthera philoxeroides,is associated with decreased species diversity across the latitudinal gradient in China

Aims Invasive species occurrence and their effects on biodiversity may vary along latitudes. We examined the occurrence (species cover) and relative dominance (importance value) of invasive alligator weed, Alternanthera philoxeroides, in its terrestrial habitat in China through a large-scale latitudinal field investigation.Methods We established 59 plots along the latitudinal transect from 21°N to 37°N. We recorded species name, abundance, height and individual species coverage of plants in every quadrat. We then measured α-species diversity variations associated with the A. philoxeroides community across the latitudinal range. We also analyzed the effect of latitude on plant species' distributions in this community by using canonical correspondence analysis (CCA).Important findings We found that species cover and importance value of A. philoxeroides increased in areas <35°N, but decreased at higher latitudes. Lower latitudes supported greater species diversity than higher latitudes. Small-scale invasion of A. philoxeroides was associated with higher species diversity, but community diversity was lower when A. philoxeroides species cover exceeded 36%. Community plant species changed from mesophyte to hygrophyte gradually from low to high latitude. Our research suggests that latitude had significant influences on community diversity which interacted with the biotic resistance of a community and impact of invasion. Consequently, A. philoxeroides may become more invasive and have greater negative impacts on community species diversity in higher latitudes as global climate changes.     

丛枝菌根真菌物种多样性研究进展

丛枝菌根(arbuscular mycorrhiza, AM)真菌是生态系统中生物多样性的重要组分之一,具有十分丰富的物种多样性、遗传多样性和功能多样性.该真菌分类地位不断提高已上升至门,下设1个纲、4个目、13个科,19个属,现已报道214种.丛枝菌根对保持生态平衡、稳定和提高生态系统可持续生产力具有重要作用.本文分析了世界范围内丛枝菌根真菌物种多样性研究现状、不同生态系统中影响丛枝菌根真菌物种多样性的关键因子及其调控途径;认为分子生物学技术是今后丛枝菌根真菌物种多样性研究的主要方法.