Variation In Number Of Species Research Articles

广西扶绥黑叶猴食物利用方式的初步研究

PDF HTML阅读 XML下载 导出引用 引用提醒 广西扶绥破碎化生境中黑叶猴的食物种类多样性和季节性重叠 DOI: 10.5846/stxb201307011809 作者: 作者单位: 广西师范大学生命科学学院,广西师范大学生命科学学院,广西师范大学生命科学学院 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金资助研究(31060059); 珍稀濒危动植物生态与环境保护省部共建教育部重点实验室研究基金资助(桂科能1001Z016) Dietary diversity and monthly overlap of François' langur in a fragmented habitat in Fusui, Guangxi, China Author: Affiliation: College of Life Science,Guangxi Normal University,Guilin Guangxi;Key Laboratory of Ecology of Rare and Endangered Species and Environmental Protection (Guangxi Normal University), Ministry of Education,,College of Life Science,Guangxi Normal University,Guilin Guangxi Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:动物使用生境中食物种类的方式对其适应性有重要的影响。为了研究黑叶猴在破碎化栖息地中利用食物的方式,2006年1-12月,采用焦点动物取样法和连续记录技术于每月初连续观察8 d,记录破碎化栖息地中黑叶猴取食的种类和时间,分析其食物多样性和月份间种类的重叠度。结果表明,黑叶猴年均食物多样性指数为3.03(范围1.93-2.62),且多样性指数在各月间没有显著的差异(One-sample K-S Test, P=0.99),说明黑叶猴在各月份中取食的食物种数相似,不同季节利用食物种数的变异程度不大。在所有的食物种类中,仅两种食物青檀Pteroceltis tatarinowii和潺槁树Litsea glutinosa 在12个月份都被取食,其他种类则表现了月份间明显的季节性替代。各月份间食物种类的相似性在0.42(3-4月)和0.75(9-10月)之间变化。黑叶猴对破碎化生境中食物种类的利用方式是:首先利用常年均有的食物种类以保证食物来源稳定,同时选择性地利用新出现的种类,使食物种类多样化,满足不同的营养需求。 Abstract:The manner in which animals use potential food in their environment, the diversity of species they consume, and the seasonal variation they display in their preferences for food, forms the basis of adaptive foraging strategies that maximized fitness. Although food specialists are more sensitive to environmental change than are food generalists, all species must meet their nutritional requirements while avoiding the potential harm that can result from the ingestion of noxious materials. François' langur is a rare and threatened primate that is endemic to the limestone habitat of southwest China and northern Vietnam. In recent decades, the langur population has declined rapidly, and remnant populations are severely threatened by habitat fragmentation. Elucidating the spatial and temporal foraging habits of langurs will provide an understanding of the mechanisms by which langurs respond to habitat fragmentation and allow us to speculate on the adaptive significance of these strategies. In this study, we investigated the dietary diversity and seasonal variation (i.e. the monthly overlap in species consumed) of François' langurs in a fragmented forest habitat in Fusui County, Guangxi, China. Field observations were obtained via focal animal sampling. These were conducted for eight days at the start of each month throughout 2006. On each day of sampling we randomly selected a focal adult and observed that individual from 06:30 until 19:30. This observation period was divided into 15-min sessions, with foraging behaviors (i.e. the species of food consumed and the time spent feeding) recorded only during the first 5 min of each 15-min session. Analyses were conducted to determine the monthly dietary diversity and the degree of temporal (monthly) overlap in dietary species. We found that the annual dietary diversity of langurs at this site was 3.03, with the lowest diversity recorded in January (1.93) and highest diversity recorded in December (2.62). There was no significant monthly variation in the dietary diversity index (One-sample K-S Test, Z = 0.44, n = 12, P = 0.99), which suggests that langurs exhibit little variation in the number and types of species they consume throughout the year. Nevertheless, some species (for example, Pteroceltis tatarinowii and Litsea glutinosa) were consumed in all months, whilst others were consumed more selectively, in some months but not others, despite being available in all months. The degree of monthly overlap in species consumed ranged from 0.75 (September and October) to 0.42 (March and April). Our results suggest that the foraging strategy of langurs in fragmented habitats could be characterized as being generalist as a diverse number of species were consumed throughout the year. This strategy is likely to be adaptive in this fragmented habitat, because langurs must balance the need to consume food efficiently, so as to meet their nutritional requirement, with the need to selective in their preferences, so as to avoid consuming plant species that contain noxious secondary compounds. Our work has shown that langurs maximize their foraging efficiency by foraging predominately on common species that are readily available in the environment, and subsequently, supplementing their diet with rare plant species that are of high nutritional quality. We contend that this foraging strategy maximizes the langurs' survival probability and reproductive success in fragmented habitat. 参考文献 相似文献 引证文献

Stem Barks and Roots Extravitism in Ekiti State Nigeria: Need for Conservation as a Sustainable Innovation in Healthcare Management in Rural Areas

A combination of field surveys and direct observation was used to identify botanicals whose stems and/or roots were extracted for healthcare purposes in the rural communities of Ekiti State, Nigeria. Diverse number of species was identified as being used for health care by respondents in the study area. The respondents’ consensus factor which specifies the agreement degree of the respondents revealed that their preference for healthcare maintenance was skewed towards the use of botanicals rather than the orthodox drugs. Respondents’ fidelity level was determined and the results obtained revealed that the botanicals were perceived as safe, cheap, readily available with little or no side effects. Considerable proportions of these botanicals were not cultivated and their collection pattern was mostly annihilative and unsustainable. Thus they were mostly rare on the abundance scale used in this study. Most of the uncultivated species were indigenous tree species that has forest as their primary source. With increasing and unprecedented deforestation rate in the study area, there is the need for conservation of these species.

한국 태안군 진산리 저서미세조류의 계절별 종조성 및 생물량 변화

Seasonal species composition and biomass of microphytobenthos were examined at the intertidal flats of Jinsanri, Taean, Korea, from April to December 2011. In total, 121 species were identified, including 109 diatoms, 5 blue-green algae, and 5 dinoflagellates. Seasonal variation in species number ranged from 49 to 56 species (minimum in October and maximal in April), while vertical variation across three different shore levels ranged from 64 to 77 species with maximum at high and minimum at low shore. Species diversity ranged from 3.22 to 3.42 seasonally and from 3.50 to 3.17 across vertical shore levels. Seasonal average values of the normalized difference vegetation index and the vegetation index were 0.06 and 1.14, respectively. Chlorophyll a concentrations were <TEX>$66.00-120.73mg/m^2$</TEX>, with a seasonal minimum and maximum in July and October, respectively, and a vertical shore maximum of <TEX>$137.35mg/m^2$</TEX> at mid shore. Phaeopigment concentrations peaked in October (<TEX>$50.78mg/m^2$</TEX>) and at high shore (<TEX>$61.58mg/m^2$</TEX>) and were lowest in December (<TEX>$22.53mg/m^2$</TEX>) and at low shore (<TEX>$15.28mg/m^2$</TEX>). The number of microphytobenthos ranged from 78,556 to 287,898 cells/<TEX>$cm^2$</TEX>, reaching a maximum in April and a minimum in July. The diatoms Paralia sulcata, Navicula sp., and Delphines surirella were dominant at all tidal levels over the study period. Dinoflagellates were dominant in July at low shore, and blue-green algae were abundant between July and October at mid shore. In conclusion, species composition and primary production of microphytobenthos exhibited clear seasonal and vertical patterns.

Towards effective culvert design: monitoring seasonal use and behavior by Mediterranean mesocarnivores

Drainage culverts are known to be used by a diverse number of species. To date, most studies looking at culvert usage have been restricted to the dry season. This seasonal bias has limited our understanding of how different species respond to culverts and, consequently, our ability to find effective ways to promote the use of culverts as aids to species movement. The main goal of this study was to examine the role of highway culverts for mesocarnivores throughout the year. We addressed (1) the seasonality of culvert use, (2) the relative importance of culvert structure, highway features, and surrounding landscape on culvert use, (3) the influence of the water depth and cover on culvert use, and (4) the effect of culvert structure on individual behavior. Fifteen culverts were monitored along 2 highways in southern Portugal using video-surveillance cameras and marble dust for 10 consecutive days per season. We used generalized linear mixed models to determine which factors most affected the culvert use and behavior by mesocarnivores. Our results highlight the effect of seasonality and water on culvert use. Culvert use was positively related with species activity throughout the year. All species (except otters (Lutra lutra)) were less likely to use culverts that contained water more than 3cm deep or covering more than 70% of the culvert base. Based on our results, future surveys and culvert retrofit design should address (1) the importance of seasonality in the interpretation of results and (2) the complementarity of culvert-specific features (water, ledges, and naturalization).

Plant species loss from European semi‐natural grasslands following nutrient enrichment – is it nitrogen or is it phosphorus?

ABSTRACTAim Although many studies support the prevailing paradigm of nitrogen (N)‐driven biodiversity loss, some have argued that phosphorus (P) may be the main culprit. This questions the generality of the global threat through N enrichment. The major objective here was to quantify the relative importance of soil N and P in explaining patterns of plant species richness, under different levels of N and P limitation.Location North‐western Europe.Methods We collected soil, productivity and plant species data from 132 semi‐natural grasslands located along a gradient of nutrient availability and atmospheric N deposition. We used linear mixed models to investigate the relation between soil nutrients, acidity, limitation and productivity on one side, and indices for plant species richness on the other.Results Mixed models explained between 38 and 50% of the total variation in species numbers, forbs and endangered species. Soil P was significantly negatively related to total species number, forbs and endangered species. Soil N was only significantly negatively related to number of forbs and endangered species. Compared with soil P, the explained variation attributed to soil N was between five‐ and twenty‐fold lower. P‐limited grasslands exhibited higher species richness, numbers of forbs and endangered species. Species richness and number of forbs decreased with lower soil acidity. N deposition was negatively related to the number of forbs and endangered species, as well as to soil acidity. Productivity was weakly positively related to soil P and negatively to species and forb numbers. We found no interaction factors between the explanatory variables.Main conclusions P enrichment can present a greater threat to biodiversity than N enrichment in at least some terrestrial ecosystems. However, as N‐ and P‐driven species loss appeared independent, our results suggest that simultaneously reducing N and P inputs is a prerequisite for maintaining maximum plant diversity.

Dinâmica temporal do estrato herbáceo-arbustivo de uma área de campo limpo úmido em Alto Paraíso de Goiás, Brasil

Este trabalho avaliou a dinâmica estrutural e florística de uma comunidade de espécies herbáceo-arbustivas de uma área de campo limpo úmido em Alto Paraíso de Goiás, o primeiro inventário realizado em 2000 (T0) e o segundo em 2007 (T1). A diversidade de Shannon entre os períodos foi comparada pelo teste-t de Hutcheson e a similaridade florística, pelo índice de similaridade de Chao-Sørensen. As relações florísticas e a cobertura, entre os períodos e as linhas, foram avaliadas por meio de análises de correspondência retificada (DCA). Foram amostradas 98 espécies, 88 no T0 e 67 no T1, sendo 31 exclusivas do T0 e 10 do T1. A diversidade florística na comunidade foi elevada nos dois períodos, porém diferente entre esses (t = 7,12; p &lt; 0,001), devido a variação no número e cobertura das espécies. A similaridade entre os dois inventários foi alta (Chao-Sørensen ± IC = 0,841 ± 0,074). A ordenação por DCA indicou relações entre a composição florística e a cobertura com o gradiente de umidade e de matéria orgânica no solo identificados em T0. Houve modificações nas linhas em zonas sazonais, as quais se tornaram mais semelhantes às linhas constantemente saturadas por água. Em um intervalo de sete anos o campo limpo úmido apresentou mudanças na composição florística e, principalmente na estrutura devido o aumento da cobertura de espécies perenes, cespitosas e entouceiradas, que foram favorecidas pela maior umidade no solo em resposta à elevação da pluviosidade da região.

Checklist of the Pacific marine macroalgae of Central America

Our present knowledge of marine macroalgal diversity for the Central American Pacific coast is limited by the short history of investigations (ca. 100 years) and few algal specialists through a large geographical area. While recent checklists have emerged for other regions of the eastern Pacific, there have been virtually no attempts to inventory macroalgal diversity for the Pacific of Central America. This checklist of the marine macroalgae was developed based on published scientific literature and unpublished records in student theses. A total of 379 species records are regarded as current valid names of marine macroalgae. The red algae (Rhodophyta) had the highest species number (252 species), followed by green algae (Chlorophyta: 81 species) and brown algae (Phaeophyceae: 46 species). The country with the greatest diversity of marine macroalgae is Costa Rica with 216 species, followed by Panama with 174, El Salvador with 146, Nicaragua with 24, and Guatemala with 16. At present, there are no published records for the Pacific coast of Honduras. Variation in number of species throughout the Pacific coast of Central America is likely due to differences in geomorphology, habitat heterogeneity among national coastal-marine zones, and unbalanced research efforts.

Patterns and traits of the endemic plants of Greece

Greece is characterized by high plant diversity (5800 species) and endemism (15.6%). This study attempts a first overall assessment of the taxonomy, distribution, traits and conservation status of the Greek endemic plants. The endemic species belong to 56 families and 242 genera. Most of the endemic plants have a narrow geographical and altitudinal distribution range. The southern floristic regions are richer in endemic species. The species area relationships for endemics (EARs) for island and continental floristic regions explain over 50% of the variation in number of species and are characterized by steep curves. Analysis of the distributional pattern of the endemics by similarity coefficients offers useful insights into the palaeogeography and biogeography of Greece. The endemic species occur at all altitudes, but the altitudinal distribution shows a predominance of local endemics at 0–600 m in the island regions and in higher zones in the continental regions. The life form spectra show a predominance of hemicryptophytes and chamaephytes. This trait seems indicative of their habitat and adaptive strategy and may be related to speciation processes. The overview of the conservation status of the Greek endemics indicates that over 40% of the taxa are threatened or near threatened. © 2010 The Linnean Society of London, Botanical Journal of the Linnean Society, 2010, 162, 130–422.

Changes in species richness and composition in European acidic grasslands over the past 70 years: the contribution of cumulative atmospheric nitrogen deposition

AbstractOur study investigates the negative impact of nitrogen (N) deposition on species richness in acidic grasslands, based on a temporal comparison of vegetation data spanning a period of almost 70 years. We compiled a large data base of plots assigned to the Violion caninae grassland type, composed of managed, but unfertilized semi‐natural grasslands on nutrient‐poor, acidic soils. In total 1114 plots, mainly from Great Britain, the Netherlands and Germany, were compiled, dating back to 1939. Environmental site information included geographical and soil (mean Ellenberg values) variables as well as estimates of cumulative N and sulphur (S) deposition since 1939. Statistical analyses were carried out separately for the data subsets from the three regions. In all regions, the vegetation differentiation was mainly related to soil acidity and nutrient availability, as well as to the year of sampling and the cumulative amounts of N and S deposition. Plot‐species richness of vascular plants and bryophytes (analysed for Great Britain only) decreased with time and analyses suggest these are affected by various factors, notably soil pH, but also latitude and cumulative N deposition. The latter explained more of the variation in species number than the year of sampling and cumulative S deposition, which supports the interpretation that the decline in species richness is mainly caused by increasing N availability and less by altered management and soil acidification. For Great Britain and Germany, cumulative N deposition showed a strong negative relationship with several biodiversity measures, especially the proportion of dicots, whereas it was positively related to the proportion of grass species. In general, our results give temporal evidence for the negative effect of N deposition on species richness in semi‐natural vegetation.

The use of teak (Tectona grandis) plantations by large mammals in the Kilombero Valley, southern Tanzania

AbstractThe establishment of plantations is impacting the large mammal populations of the Kilombero Valley, Tanzania. Animal spoors were used as a proxy for activity to determine the influence of teak stand age on mammals. Habitat variables were compared between different aged stands to investigate the relationship between mammal activity and vegetation characteristics. Vegetation surveys found plantation composition to differ with age; with young stands characterized by slender teak trees, limited leaf litter, abundant grass layer and substantial bare ground. Older plantations contained a high leaf litter layer and dead wood, low grass abundance and minimal bare ground. Spoor transects revealed that mammal species number decreased as the teak matured. Of those vegetation variables tested, grass and bare ground abundance explained significantly the variation in species number and in individual species’ habitat use between differently aged stands; therefore this habitat use was influenced by the foraging value of the plantation. This study showed that several species (some of which warrant conservation attention, such as elephant) use plantations &lt;6 years old to a greater extent than plantations &gt;6 years. Thus, there is a need for conservation measures, such as wildlife corridors and staggered teak planting to be continued, allowing large mammal movements in the valley.

Traditional coastal invertebrate fisheries in south-western Madagascar

The identification of key resource users and patterns of depletion alongside ecological data are presented for a small-scale traditional invertebrate fishery in south-western Madagascar. Men, women and children undertake the fishery in the Anakao region at different phases of the tide and for different purposes. Invertebrate harvest data from June to September 2000 estimated that more than 34 taxa were caught and were dominated by holothurians destined for export and molluscs for local consumption. Crustacea formed a small component of the fishery despite a high diversity and abundance of many potentially edible species. Although there was slight spatial variation in number of species caught and their relative importance to the fishery,Chicoreus ramosus, Fasciolaria trapeziumandOctopus vulgariswere generally most heavily targeted and were amongst the most abundant in the catch. There were several indications of over-exploitation of invertebrate stocks, including the absence of many large bodied species, low abundance of high yield species, greater catch effort needed for high yield taxa, and higher diversity of targeted species (including many low yield taxa) at sites of higher human habitation.

Indicator taxa revisited: useful for conservation planning?

ABSTRACTAim Indicators for biodiversity are needed to facilitate the identification of complementary reserve networks for biodiversity conservation. One widely adopted approach is to use indicator taxa, i.e. a single taxon such as birds or butterflies, despite the ongoing debate regarding their usefulness as indicators of broader biodiversity. Here we assess several aspects, such as influence of species number, of indicator taxa for three extensive data sets to improve our insight into the effectiveness of indicator taxa.Location Denmark, sub‐Saharan Africa and Uganda.Methods First, we investigate to what extent variation in species number between indicator taxa (e.g. 488 mammal spp. vs. 210 snake spp.) is causing the differences in effectiveness between indicator taxa. Second, we investigate whether indicator taxa are capable of outperforming indicator groups composed of random sets of species chosen among all taxa. Finally, we assess the correlation of specific properties such as mean range size of the indicator taxa to their effectiveness. We investigate these aspects of the effectiveness of indicator taxa through the separate analysis of three distinct distributional species data sets: sub‐Saharan Africa (4,039 spp.), Denmark (847 spp.) and Uganda (2,822 spp.).Results We overall found that indicator taxa comprising a greater number of species tend to perform better than indicator taxa with fewer species (e.g. 488 mammal spp. outperform 210 snake spp.), although there are some exceptions. Second, we found most indicator taxa to perform worse than indicator groups consisting of a comparable number of species selected among all taxa. Finally, the effectiveness of indicator taxa was seen to correlate poorly with selected distributional properties such as mean range size of the indicator taxa, suggesting that it is difficult to predict which taxa are efficient biodiversity indicators.Main conclusions Overall, these findings might suggest that focus should simply be on increasing the number of species among all taxa as basis for priority setting, rather than striving to obtain the ‘perfect’ indicator taxa.

Sex reversal of the amphibian, Xenopus tropicalis, following larval exposure to an aromatase inhibitor

Aromatase is a steroidogenic enzyme that catalyzes the conversion of androgens to estrogens in vertebrates. Modulation of this enzyme's activity by xenobiotic exposure has been shown to adversely affect gonad differentiation in a number of diverse species. We hypothesized that exposure to the aromatase inhibitor, fadrozole, during the larval development of the tropical clawed frog, Xenopus tropicalis, would result in masculinization of the developing female gonad. Tadpoles were exposed to fadrozole at nominal concentrations from 1 to 64 μg/L in a flow-through system from <24 h post-fertilization (Nieuwkoop Faber (NF) stage 15–20) to metamorphosis (NF stage 66). At metamorphosis, morphologically examined gonads indicated complete masculinization of all tadpoles at concentrations of 16 μg/L and above and a significant bias in sex ratio towards males at concentrations of 1 μg/L and above. No effects on time to metamorphosis, body mass, or body length were observed. A random subsample of frogs was raised to reproductive maturity (39 weeks post-fertilization) in control water. All frogs exposed as tadpoles to 16 μg/L fadrozole or greater possessed testes at sexual maturity. Intersexed gonads characterized by the presence of both testicular and ovarian tissue were observed in 12% of frogs in the 4 μg/L treatment. No differences in estradiol, testosterone, or vitellogenin plasma concentrations were observed in exposed males or females compared to controls. Females in the 4 μg/L treatment possessed a significantly greater percentage of pre-vitellogenic oocytes than controls and were significantly smaller in body mass. No differences in sperm counts were observed in exposed males compared to controls. Results from this study demonstrate that larval exposure to an aromatase inhibitor can result in the complete masculinization of female gonads. These masculinized females are phenotypically indistinguishable from normal males at adulthood. Lower levels of aromatase inhibition resulted in intersexed gonads and possible female reproductive impairment at adulthood. These results indicate that exposure of amphibians to xenobiotics capable of inhibiting aromatase would result in adverse reproductive consequences.

Effects of seasonality on the species–area relationship: a case study with birds in urban parks

ABSTRACTAim To examine how parameters of the species–area curve and factors determining bird species richness are affected by seasonality.Location One hundred and thirty urban parks of the city of Valencia (Spain) ranging between 0.03 and 18.6 ha.Methods Bird censuses were conducted monthly during 1998 and 2004. For each park, 27 variables were recorded as measures of size, structure and isolation. Linear regression was used to test for patterns in species richness relative to independent variables. The results of each season were compared.Results Curves corresponding to the breeding period (spring–summer) had significantly higher intercepts, but slopes did not change across seasons. Turnover rates of resident species were dependent on patch size and isolation considering spring, but not autumn, from different years. Additionally, turnover rates in spring were lower in parks in close proximity to others than in isolated ones. In all seasons, the number of bird species showed a strong relationship with park area, which explained c. 60% of the variation in species numbers. Habitat variables and park isolation explained a small amount of the variation in species numbers. The data did not give support to the random placement hypothesis.Main conclusions The overall conclusions of this study give little support to the possible influence of seasonality on species–area relationship or on the three main hypotheses explaining it. This lack of influence of seasonality could be explained by the seasonal stability of the bird populations of the parks within the study area as a consequence of different factors, mainly the characteristics of the species pool, similarity in the features of the parks irrespective of their size, and stability of resources and conditions across seasons. The question of whether this lack of influence of seasonality on the species–area relationship occurs in those ecological systems that have a larger seasonal variation than the urban parks of the study area remains unresolved. Closer examination of the seasonal patterns reported in this study is likely to be useful in increasing our understanding of the species–area relationship.

Does the width of isolated ravine forests influence moss and liverwort diversity and composition?—A study of temperate forests in South Africa

The evidence of microclimatic edge effects through forest/open area ecotones is firm. How this affects the species composition near edges is less well understood and documented. In south-western South Africa shrub-dominated regularly burnt vegetation (i.e. fynbos) is the most common vegetation with indigenous temperate forests naturally occurring mostly in ravines on mountain slopes. The size and width of these forest patches varies considerably. In order to understand how the width of forest patches affects species composition of mosses and liverworts we investigated 20 forest patches of different width. In each forest patch we compiled a total species list, and collected data on selected environmental variables, for a plot of 10×20 m. No significant relationship was found between patch width and the number of either moss or liverwort species. However, the species composition of mosses (but not liverworts) changed along the gradient of patch width. The variation in number of species was large (8–29 mosses and 11–33 liverworts) among the plots and we propose that factors other than distance to the forest edge may be more important in structuring the bryophyte community of these ravine forests. One such factor that is likely to be important is the climatic difference among the plots. There is variation in features, such as precipitation, summer temperature, cloudiness, and the amount of fog, for which we do not have data but that could overrule the microclimatic differences due to edge effects.

PLANT SPECIES RICHNESS AT DIFFERENT SCALES IN NATIVE AND EXOTIC GRASSLANDS IN SOUTHEASTERN ARIZONA

Species richness in Madrean mixed-grass prairies dominated by native or exotic species in southeastern Arizona was characterized at the community and point scales using ten 1-m2 quadrats nested within each of eight 1000-m2 plots. In the 1000-m2 plots average richness was significantly higher in oak savanna (OS, 121.0 species) than in exotic grassland on mesa tops (EMT, 52.0 species), whereas native grassland on mesa slopes (NMS, 92.5 species) and native grassland on mesa tops (NMT, 77.0 species) did not differ significantly in richness from OS or EMT. When richness was partitioned by life form, EMT was notably poorer than other community types in species of perennial grasses, perennial herbs, and summer annuals. In the 1-m2 quadrats, OS (21.2 species), NMS (20.9 species), and NMT (20.7 species) were significantly richer than EMT (5.9 species). Cover in 1-m2 plots was significantly higher in EMT than in NMT, NMS, or OS. Species richness at the point scale showed a unimodal relation to canopy cover, with cover accounting for 30% of the variation in number of species in 1-m2 quadrats. Competitive exclusion and allelopathy have perhaps limited species richness at the point scale in exotic grassland. There was no evidence of a species-pool effect between point and community scales, but such an effect between community and landscape scales was supported. Madrean mixed-grass prairies are landscapes with high species richness in comparison to other grassland types in North America, providing a large pool of potential colonizing species at the community scale. Beta-diversity (between communities) within the landscape of the Appleton-Whittell Research Ranch was consequently high despite a relative lack of habitat diversity.

ALIEN PLANTS IN TEMPERATE WEED COMMUNITIES: PREHISTORIC AND RECENT INVADERS OCCUPY DIFFERENT HABITATS

Variables determining the number of native and alien plants on arable land in Central Europe are identified. Species richness of 698 samples of weed floras recorded in the Czech Republic in plots of a standard size of 100 m2 in 1955–2000 was studied in relation to altitudinally based floristic region, soil type, type of cultivated crop, climatic variables, altitude, year of the record, crop cover and height, and human population density in the region. Vascular plant species were classified into native and alien, the latter divided in archaeophytes, introduced before AD 1500, and neophytes, introduced after this date. The use of minimal adequate models in the analysis of covariance allowed determination of the net effects of mutually correlated environmental variables. Models for particular species groups explained 33–48% of variation in species numbers and 27–51% in proportions; however, explanatory variables affected native species, archaeophytes, and neophytes differently. The number and proportion of neophytes increased in 1955–2000, whereas the number of native species and archaeophytes declined (in archaeophytes more slowly in the warm than in the moderate to cool altitudinal floristic region). In warm and dry regions and on dry soils, where most archaeophytes find optimum conditions, fewer native species are able to persist in weed communities than in colder and wetter regions. Archaeophytes respond like neophytes to some variables (climate, seasonal development of crop) and alternatively like native species to other variables (increasing agricultural intensification through time, human population density). Archaeophytes are common in old crops introduced with the beginning of agriculture (cereals), but are poorly represented in relatively recently introduced crops (rape, maize), where neophytes are most numerous. These patterns reflect the history of plant invasions in Central Europe. Neolithic agriculture, introduced from the Near East in the sixth millenium BC, brought archaeophytes with crops and, by creating intense and continuous propagule pressure and imposing new agricultural management, facilitated their invasion. By contrast, the crops introduced during the past five centuries and their specific agrotechnical management have supported spreading of other weed species, mainly invaders from overseas.

SPECIATION IN HAWAIIAN ANGIOSPERM LINEAGES: CAUSE, CONSEQUENCE, AND MODE

The biota of Hawaiian Islands is derived entirely from long distance dispersal, often followed by in situ speciation. Species descended from each colonist constitute monophyletic lineages that have diverged to varying degrees under similar spatial and temporal constraints. We partitioned the Hawaiian angiosperm flora into lineages and assessed morphological, ecological, and biogeographic characteristics to examine their relationships to variation in species number (S). Lineages with external bird dispersal (through adhesion) were significantly more species-rich than those with abiotic dispersal, but only weakly more species-rich than lineages with internal bird dispersal (involving fleshy fruits). Pollination mode and growth form (woody vs. herbaceous) had no significant effect on S, in contrast to studies of angiosperm families. S relates positively to the geographic and ecological range size of whole lineages, but negatively to local abundance and mean range sizes of constituent species. Species-rich lineages represent a large proportion of major adaptive shifts, although this appears to be an artifact of having more species. Examination of 52 sister species pairs in numerous lineages provides evidence for allopatric (including peripheral isolates) and parapatric (ecological) modes, with 15 cases of each. Although postspeciational dispersal may obscure these modes in many of the remaining cases, instances of sympatric and hybrid speciation are also discussed. Because speciation is both a consequence and a cause of ecological and biogeographic traits, speciation mode may be integral to relationships between traits. We discuss the role of speciation in shaping the regional species pool.

Comparison of floristic changes on vegetation affected by different levels of soil erosion in Miocene clays and Eocene marls from Northeast Spain

Increased soil erosion on Eocene marls from N Aragon (NE Spain) tends to reduce vegetation cover and plant species number, but little is known about its effect in the neighbouring Miocene clays. In this study, the vegetation of strongly eroded areas on Miocene clays was analysed in terms of erosion intensity and compared with Eocene marls. Releves were carried out on uniform patches of vegetation affected by different levels of erosion. The degeneration of vegetation cover explained 34% of the variation in species number as opposed to 48% in marls, and a clear pattern of species replacement through the destruction of the vegetation cover was not observed. Approximately 25% of the species decreased significantly and 4% increased, as opposed to 47% and 0% in marls, respectively. Erosion on marls may be more severe (more disturbance) and less stressing for vegetation (more water availability) than on clays. The few species that colonized intermediate degeneration stages and highly eroded sites were more common in non-eroded areas in drier bioclimatic belts. Thus, the degeneration of vegetation by soil erosion favoured the establishment of xeric species. The ecological range of erosion-resistant species was not wider than non-resistant species. Overall, increased soil erosion selected for different plant species in marls than in clays.

Coral and fish distribution patterns in Mafia Island Marine Park, Tanzania: fish–habitat interactions

We examined coral reef communities at 11 sites within Mafia Island Marine Park using a point count method for substrate and visually censused belt transects for fish populations. Multivariate ordinations showed that the benthic habitat differed among reefs. The patterns were mainly attributed to variations in depth, hydrodynamics and benthic composition. In total, the substratum was dominated by dead coral (49%) and algae (25%), with a live coral cover of only 14%. Three hundred and ninety-four fish species belonging to 56 families were recorded. According to MDS-ordinations and RELATE procedures, fish assemblage composition varied among sites in concordance with the habitats provided. Sites with highest proportion of dead coral exhibited highest degree of dispersion in the multivariate ordinations of fish assemblages. Stepwise multiple regression was used to determine the proportion of variance among sites which could be explained by depth, exposure, rugosity, substrate diversity, branching substrate, live coral cover, dead coral cover and different types of algae. The results showed that habitat variables explained up to 92% of the variation in species numbers and in total, and taxon-specific, abundance. Live coral cover was the foremost predictor of both numerical and species abundance, as well as of corallivores, invertivores, planktivores and of the families Pomacentridae, Chaetodontidae and Pomacanthidae. Our results suggest that habitat characteristics play a dominant role in determining fish assemblage composition on coral reefs.