Plant species richness, endemism, and genetic resources in Namibia

Namibia is a floristically diverse, arid to mesic country, with several highly distinct taxa. Including naturalized plants, there are about 4334 vascular plant species and infraspecific taxa within the country's borders, a substantial increase from the existing major reference work. Dominant families are the Poaceae (422species), Fabaceae (377), Asteraceae (385) and Mesembryanthemaceae (177). Freshwater algae and most other groups of lower plants remain poorly known. Concentrations of plant species richness are found in the Succulent Karoo biome, Kaokoveld, Otavi highland/Karstveld area, Okavango Basin, and Khomas highlands. Recent studies have led to a new estimate of 687 endemic plant species, defined as those contained wholly within Namibia's borders, amounting to about 17% of the Namibian flora. At least a further 275 species are Namib Desert endemics shared between the Kaokoveld and southern Angola (75spp.) and between the Succulent Karoo and northwestern South Africa (200spp.). Research on plant genetic resources is focused on species of potential or actual agricultural importance, such as pearl millet, Pennisetum glaucum, and cucurbits. Many wild plants have considerable genetic diversity and development potential. Primary threats to plant diversity fall in the category of poor land management and inappropriate development.     

Stability and species richness in complex communities

Using both numerical simulations and analytical methods, we investigate how the stability of ecological communities depends on the number of species they contain. To investigate complex communities, we construct communities from modular subcommunities that can have arbitrary community structure; e.g. subcommunities could consist of pairs of predator and prey species, trios of prey, specialist predator and generalist predator, or any collection of interacting species. By building entire communities from subcommunities, we can change the number of species in the community without changing community structure. We further suppose that species sharing the same ecological role in different subcommunities act additively on the per capita population growth rates of other species. Under these assumptions, the inter-actions between species from different subcommunities have no effect on community-level stability, measured by the variability in the combined densities of species sharing the same ecological role in different subcommunities. Furthermore, increasing species richness (i.e. the number of subcommunities comprising the community) increases community-level stability only when it introduces species that respond differently to environmental fluctuations. Therefore, our results support the insurance hypothesis that species richness increases community-level stability by insuring that some species in a community are tolerant of different environmental fluctuations.     

Determinants of species richness in southern African fig wasp assemblages

Summary We investigated the species richness of 24 fig wasp (Hymenoptera) assemblages associated with southern African fig trees (Ficus species, Moraceae). Assemblage sizes ranged between 3 and 30 species on different host tree species, with parasitoids slightly outnumbering gall-forming phytophages. Ten potential taxonomic, geographic and ecological determinants of assemblage richness were examined. Galler richness differed significantly between taxonomic sub-groups of Ficus and was significantly correlated with several ecological characteristics of the host trees, but there was no species-area effect. Parasitoid richness was strongly correlated with galler richness. We conclude that both ecological and historical factors have combined to determine the numbers of species that form fig wasp assemblages.     

Numbers,species richness and equitability of coastal birds at Darwin,Northern Territory

Studies of the species richness and equitability were made of coastal birds at Darwin, Northern Territory, following censusing. A general decrease in numbers and species richness of indigneous and palaearctic migrants occurred in the wet season. Equitability values were depressed at the beginning of the wet season indicating an ecologically disturbed situation Freshwater discharge and its complex mixing patterns in neritic and estuarine water may be responsible for such a disturbance through its effects on the bird's food supply.     

Lake connectivity and fish species richness in southern Brazilian coastal lakes

Connectivity is a key factor in metacommunity ecology, because it influences dispersal and colonization rates. However, it has received less attention in aquatic than in terrestrial ecology research. We investigated whether connectivity is a good predictor of species richness in functional fish communities (freshwater, FS; estuarine, ES and estuarine-freshwater, EFS) from 31 coastal lakes in southern Brazil. We used a model selection approach, including lake area and distance from the ocean as additional predictors of species richness and two connectivity metrics: primary connectivity (C _P) and estuarine connectivity (C _E), which measure connectivity to neighboring lakes and system-wide connectivity, respectively. Both metrics estimate functional connectivity and were calculated on habitat-based cost distances. Connectivity was more important for predicting richness of functional communities than for total richness, particularly C _E, which was distinctively related to each functional fish community richness (directly related to ES and EFS, and inversely related to FS; C _P was related only to ES). Remarkably, connectivity was more important than area for predicting ES and EFS richness. These results add support to dispersal limitation as an important mechanism influencing fish communities. We suggest that incorporating environmental filters (habitat type) to quantify connectivity is useful for accessing the patterns of species richness.     

Behavioural flexibility predicts species richness in birds, but not extinction risk

The number of species varies greatly among taxa. In birds, for example, the parvorder Passerida contains 3556 species while the Odontophorida contains only six species. This uneven distribution of species among bird groups is not a consequence of random branching patterns and therefore warrants an explanation. According to the behavioural drive hypothesis, behavioural innovation coupled with social transmission of the new skill to other members of the population may lead to accelerated rates of evolution, and could therefore account for differences in species richness. In this paper, we test the behavioural drive hypothesis by examining the link between behavioural flexibility and the number of species per taxon. We estimate flexibility with relative brain size and feeding innovation rate and predict that both will be positively associated with the number of species per taxon. Since the number of species at any given time results from a balance between speciation and extinction rates, we also examine the link between flexibility and the number of species threatened with extinction. We predict that the two flexibility correlates will be negatively associated with the number of species at risk. In simple regressions, both flexibility correlates were significantly associated with species number per taxon. However, only innovation rate remained in the final model. Relative brain weight dropped out of the multiple regression due to its association with innovation rate. Relative brain weight, innovation rate and species number per taxon were all significantly correlated with the number of threatened species in the simple regression, but only the latter remained significant in the final model. The same results were obtained on independent contrasts, indicating that behavioural flexibility predicts richness but not extinction risk in birds. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.      

Country-based patterns of total species richness,endemicity, and threatened species richness in African rodents and insectivores

Country-based patterns of total species richness, endemicity, and threatened species richness in African rodents and insectivores are studied in this paper. We found several patterns which were similar between insectivores and rodents. Indeed, in both groups we observed: (i) a significantly uneven distribution of species richness across countries and geographic regions with highest species richness peaks being in Middle Africa and lowest peaks in Northern Africa, (ii) species richness increasing with rainfall but being independent on a country’s surface area, (iii) in each country, the insectivore total species richness and endemic species richness increases were positively correlated with rodent total species richness and endemic species richness increases. However, number of endemics peaked in South Africa and D.R. Congo in both groups, but also in Tanzania for Insectivores and in Ethiopia for rodents. In addition, the highest numbers of threatened species occurred in D.R. Congo, Rwanda and Uganda for rodents and in South Africa, Tanzania and Cameroon for insectivores. The conservation implications of these results were discussed.     

Variation in species richness and species pool size across a pH gradient in forests of the southern Blue Ridge Mountains

Pärtel (Ecology 83: 2361–2366, 2002) andEwald (Folia Geobot. 38: 357–366, 2003) suggest that the relationship between local species density and soil pH is determined by regional species pool size, which in turn reflects the relative abundance of soil types during the evolutionary history of the flora. Ewald observed that calcareous sites in Central Europe have higher species density and larger species pools than acidic sites, and argues that this is the consequence of a Pleistocene bottleneck for acidophiles.The flora of the southern Blue Ridge Mountains USA has always been associated with primarily acidic soils. We used vegetation and soil data from 3328 100 m² southern Blue Ridge forest plots to examine the generality of the Pärtel-Ewald hypothesis. The Blue Ridge flora with less than 20% of species confined to sites above pH 4.7 contrasts dramatically with that of Europe. However, regional species pool size increases with pH. Genus- and family-level pools increase with pH, suggesting an ancient origin for this pattern. Mean species density is also strongly positively correlated with soil pH. Thus, both regional species pool size and plot species density of southern Blue Ridge forests fail to conform to predictions derived from the work of Pärtel and Ewald.The increase in species pool with increase in pH exhibited by southern Blue Ridge forests appears to reflect broad species distributions and tolerance for high pH conditions among species that grow predominantly under acid conditions. We conclude that richness on higher pH sites is a consequence of generally more favorable conditions for plant growth and/or establishment. Ewald may be correct in asserting that the abundance of high pH specialists in Central Europe is an historical artifact, but our data contradict the assertion of Pärtel and Ewald that evolution of a flora in a primarily low pH environment will necessarily translate into a negative correlation between pH and species density in local vegetation.     

Kin selection,species richness and community

Can evolutionary and ecological dynamics operating at one level of the biological hierarchy affect the dynamics and structure at other levels? In social insects, strong hostility towards unrelated individuals can evolve as a kin-selected counter-adaptation to intraspecific social parasitism. This aggression in turn might cause intraspecific competition to predominate over interspecific competition, permitting coexistence with other social insect species. In other words, kin selection—a form of intra-population dynamics—might enhance the species richness of the community, a higher-level structure. The converse effect, from higher to lower levels, might also operate, whereby strong interspecific competition may limit the evolution of selfish individual traits. If the latter effect were to prove more important, it would challenge the common view that intra-population dynamics (via individual or gene selection) is the main driver of evolution.     

Historical biogeography, ecology and species richness

Ecology and historical (phylogeny-based) biogeography have much to offer one another, but exchanges between these fields have been limited. Historical biogeography has become narrowly focused on using phylogenies to discover the history of geological connections among regions. Conversely, ecologists often ignore historical biogeography, even when its input can be crucial. Both historical biogeographers and ecologists have more-or-less abandoned attempts to understand the processes that determine the large-scale distribution of clades. Here, we describe the chasm that has developed between ecology and historical biogeography, some of the important questions that have fallen into it and how it might be bridged. To illustrate the benefits of an integrated approach, we expand on a model that can help explain the latitudinal gradient of species richness.     

Root quality and decomposition environment,but not tree species richness,drive root decomposition in tropical forests

Plant and Soil - Tropical forests contribute significantly to the global carbon cycle, yet the relative importance of tree diversity on key ecosystem processes such as root decomposition remains...     

Regional species richness,hydrological characteristics and the local species richness of assemblages of North American stream fishes

1. Local assemblage structure, from a deterministic perspective, is presumably dictated by the regional species pool as well as regulated by local factors. We examined the relationships of the regional species pool and local hydrological characteristics to local species richness of North American freshwater fishes using data sets collected during the National Water Quality Assessment program conducted by the United States Geological Survey. 2. We predicted that local species richness is ultimately constrained by the composition of the regional species pool and further associated with local hydrological factors. Moreover, we predicted that variation in local species richness within major families can be explained by different combinations of hydrological characteristics that represent lineage‐specific responses to the environment. 3. Daily discharge and regional and local species richness data were assembled from 41 stream localities across the United States. Multiple stepwise regressions were conducted to predict local species richness, based on regional species richness, mean discharge and hydrological characteristics quantified by nine variables characterising flow variability. Species richness at each site was calculated for the entire assemblage as well as within the four most species‐rich families in the data set (Catostomidae, Centrarchidae, Cyprinidae and Percidae). 4. Local species richness was best predicted by a combination of regional species richness and discharge magnitude when all species were considered. Regional species richness was a significant explanatory variable of local species richness for three of four families (Catostomidae, Centrarchidae, Cyprinidae), but not for Percidae. Local richness in Centrarchidae and Cyprinidae was positively correlated with temporal flow variability as well as high and low flow duration, respectively, while richness in Catostomidae and Percidae tended to be associated with discharge volume. In addition, local species richness for three of the four major families was positively correlated with species richness of the other families in the assemblage, potentially suggesting the influence of local habitat quality and heterogeneity. 5. Results suggest the importance of the combined influences of the regional species pool and local hydrological characteristics on local richness in freshwater fishes, with variation in richness within each family predicted by different characteristics of flow regimes.     

中国广西地区格特隐球菌菌种复合体的基因型分析

目的探讨中国广西地区格特隐球菌菌种复合体的基因型特点、种群结构特征和全球菌株的进化关系。方法收集2014—2018年间分离自临床确诊为隐球菌病患者的隐球菌临床株,利用CGB培养基初步筛选格特隐球菌菌种复合体。采用多位点序列分型方法(MLST)确定基因型。通过MEGA7软件构建系统发育树,利用R语言进行主成分分析。使用微量肉汤稀释法M27-A3方案行体外抗真菌药物敏感性检验。结果120株临床隐球菌中,分离出11株格特隐球菌菌种复合体,6株属于C.deuterogattii(AFLP6/VGII),5株属于C.gattii sensus stricto(AFLP4/VGI)。分离自广西的AFLP6/VGII呈遗传多样性,主要起源进化自南美巴西格特隐球菌菌种复合体。11株分离菌株均对常用抗真菌药物敏感。结论中国广西可能出现高致病性AFLP6/VGII,对格特隐球菌菌种复合体进行有效的全国性监测是必要的。     

Diet of the Chilean sandperch, Pinguipes chilensis (Perciformes, Pinguipedidae) in southern Chile

A study of the Pinguipes chilensis Valenciennes 1833 diet was carried out on 414 specimens captured on the Talcahuano, Chile coastline (36°41′S; 73°06′E) between October 1998 and March 2000. P. chilensis, endemic to the southeast Pacific (from Tumbes, Peru to Magallanes, Chile), is confirmed as a general predator over a wide trophic spectrum including 61 taxa. Crustaceans (mostly mysids, but also a wide variety of decapods) made up the principal dietary component, followed by fish and annelids. Prey belonging to Mollusca, Ophiuroidea, Echinoidea, Rhynchocoela, Sipunculida, Echiura and Urochordata were also present. There were no significant differences between male and female diets, although they shared only 32 prey. A significant dietary difference was found, however, between analysed size groups: specimens under 30 cm total length (TL) preyed mainly on the amphipod, Ampelisca araucana; those over 30 cm TL preyed on the mysid, Neomysis sp.; and those over 40 cm TL on fish, annelids, molluscs and echinoderms. Seasonal differences, due in large part to the dynamics of the prey species, were also found to be significant. Crustaceans were the predominant prey throughout the study with the exception of autumn, when fish were the most common prey.     

Environmental correlates of species and genetic richness in lungless salamanders (family plethodontidae)

Biological diversity is distributed across the planet in non-random, organised ways. At the species level, numerous environmental variables have been proposed to explain this non-random distribution with available energy and habitat heterogeneity receiving the most empirical support. With regard to genetic organisation, environmental stress and habitat heterogeneity have been widely supported. However, few studies have addressed if these two scales of biological organisation are structured via similar processes. Here, we tested whether or not the distributional organisation of genetic and species richness were driven by similar environmental variables for salamanders of the family Plethodontidae across North America. In general, we found that those environmental variables related to energy, particularly energy made accessible to salamanders via the actions of available moisture, were the primary determinants of both genetic and species richness. This finding is consistent with both the “more individuals hypothesis” of species richness and neutral-theory expectations for genetic richness. Additionally, greater habitat heterogeneity, as measured by increased topographic variance, was of secondary importance in positively influencing species richness, although its effects on genetic richness were far more variable. In total, our results suggest that both of these scales of biological organisation are influenced by similar environmental variables, even though increased genetic richness at the population-level does not always translate into greater species richness.     

Native species richness buffers invader impact in undisturbed but not disturbed grassland assemblages

Many systems are prone to both exotic plant invasion and frequent natural disturbances. Native species richness can buffer the effects of invasion or disturbance when imposed in isolation, but it is largely unknown whether richness provides substantial resistance against invader impact in the face of disturbance. We experimentally examined how disturbance (drought/burning) influenced the impact of three exotic invaders (Centaurea stoebe, Linaria dalmatica, or Potentilla recta) on native abundance across a gradient of species richness, using previously constructed grassland assemblages. We found that invaders had higher cover in experimentally disturbed plots than in undisturbed plots across all levels of native species richness. Although exotic species varied in cover, all three invaders had significant impacts on native cover in disturbed plots. Regardless of disturbance, however, invader cover diminished with increasing richness. Invader impacts on native cover also diminished at higher richness levels, but only in undisturbed plots. In disturbed plots, invaders strongly impacted native cover across all richness levels, as disturbance favoured invaders over native species. By examining these ecological processes concurrently, we found that disturbance exacerbated invader impacts on native abundance. Although diversity provided a buffering effect against invader impact without disturbance, the combination of invasion and disturbance markedly depressed native abundance, even in high richness assemblages.     

Strain selection and genetic variation in Gracilaria chilensis (Gracilariales, Rhodophyta)

Strain selection processes in seaweed often have assumed that sterile clones could be maintained for long periods in a diversity of environments without major genetic changes. However, clonal species such as Gracilaria chilensis exhibit intra-clonal variation in performance and ongoing studies suggest such changes may be due to rapid changes in DNA composition associated with growth, via mitotic recombinations. Therefore performance of a given ramet in this type of seaweed should be understood as the dynamic outcome of rapid reactions between the environment and the changing genotype of the selected strain. To evaluate this idea, we measured changes in genetic variability, as detected by DNA-fragment polymorphism using RAPDs-PCR, exhibited by clones of G. chilensis after two transfers to different environmental conditions (from field to controlled laboratory conditions and from the laboratory to large-scale tank culture). The transfer to laboratory conditions reduced the frequency of low similarity values and increased the frequency of intermediate similarity values in DNA banding patterns, suggesting the branchlets produced under controlled laboratory conditions have less genetic variability (evaluated as total DNA polymorphism) than plants recently collected in the field. Tank incubation reduced the total range of similarity and significantly increased the frequency of high similarity values. Results thus suggest the dynamic of genetic changes in vegetative clones of Gracilaria chilensis that is fast and strongly affected by the external environment. This revised version was published online in July 2006 with corrections to the Cover Date.