Current and future threats to plant biodiversity on the Cape Peninsula, South Africa

The biodiversity of the Cape Peninsula (49127 ha in extent) has been considerably affected by various factors since European settlement in 1652. Urbanization and agriculture have transformed 37% of the original area of natural vegetation. Lowland vegetation types have been worst affected, with almost half of the transformation occurring in one of the 15 recognized vegetation types. Vegetation at high altitudes has been little affected by urbanization and agriculture, but alien trees and shrubs are now threatening biodiversity in these areas. Of the area not affected by urbanization and agriculture 10.7% is currently under dense stands (>25% canopy cover) of alien plants and another 32.9% is lightly invaded. Dense stands of Acacia cyclops, the most widespread invader, cover 2510 ha, 76% of the total area under dense alien stands. This paper assesses the impacts of these factors on aspects of the plant biodiversity of the area, namely, the distribution of major vegetation types and of endemic, rare and threatened plant taxa and of taxa in the Proteaceae (a prominent element in almost all communities, taken as an indicator of overall plant biodiversity).Possible future impacts on biodiversity are assessed by considering the effects of several scenarios involving increased urbanization and changes to alien plant control strategies and further spread over the next 50–100 years. The worst-case scenario for urbanization sees the area under natural vegelation reduced to 12163 ha (39.3% of its extent in 1994, or 24.8% of its original extent). Under this scenario almost a quater of the 161 endemic, rare and threatened (special) taxa are confined totally to urban areas; 57.4% of the known localities of these taxa, and 40.1% of the remaining localities of Proteaceae taxa are transformed. Dense alien stands currently affect 29.8% of the localities of special taxa known from herbarium records and 8.4% of these taxa currently occur only in areas at present affected by aliens. Clearing all dense stands would result in 62.9% of special taxa having less than half of their known localities affected (49.1% at present). Under this scenario, 92% of Proteaceae taxa have more than 75% of their localities unaffected by aliens. If clearing is confined to specific areas (the Cape Peninsula Protected Natural Environment or all publicly-owned land) and the aliens spread further outside these areas, the area of natural vegetation remaining shrinks (to 82.4% of the current extent if control is confined to public land). The further losses in biodiversity associated with these scenarios are described. If control programmes collapse and all potentially invadable land is occupied by dense alien stands, only 407 ha of natural vegetation would remain (1.5% of the current extent).The probability of the various scenarios materializing is discussed. To minimize further losses in biodiversity it is essential that: (1) a major initiative is launched immediately to clear (firstly) the 10184 ha of lightly invaded vegetation and then the 3313 ha of densely invaded vegetation; (2) no urban development be permitted within the boundaries of the Cape Peninsula Protected Natural Environment; (3) a systematic programme of prescribed burning (linked to the alien control programme) is initiated; and (4) contingency measures are implemented to improve the status of seriously threatened taxa, habitats and vegetation types.     

The use of epiphytic algae to indicate environmental changes

The distribution of an epiphytic alga, shown in earlier studies to be an indicator species, has changed after modification of environmental conditions.     

Association between Opuntia species invasion and changes in land-cover in the Mediterranean region

In Mediterranean regions, biological invasions pose a major threat to the conservation of native species and the integrity of ecosystems. In addition, changes in land‐cover are a widespread phenomenon in Mediterranean regions, where an increase in urban areas and major changes from agricultural abandonment to shrub encroachment and afforestation are occurring. However, the link between biological invasions and changes in land‐cover has scarcely been analyzed. We conducted a regional survey of the distribution of the two alien prickly‐pear cacti Opuntia maxima and O. stricta in Cap de Creus (Catalonia, Spain) and related patterns of invasion to spatially explicit data on land‐cover/change from 1973 to 1993 to test the hypotheses that the two Opuntia species invade areas that have experienced large land‐cover transformations. We found that Opuntia invasion is particularly high in shrublands and woodlands located near urban areas. O. maxima are over‐represented in the shrublands and O. stricta in the woodlands that were former crops. Crop coverage has dropped by 71% in this 20‐year period. This study highlights the role of past land‐cover in understanding the present distribution of plant invasions.     

温带次生林的岛屿化对鸟类物种多样性及密度的影响

由于自然事件的影响和人类活动的干扰,越来越多的大片森林破碎成彼此孤立、面积不一的森林岛屿,这种变化无疑会对某些动物的分布模式及行为特征产生影响。于2000和2001年的春夏季,在吉林省左家自然保护区及土门岭地区,采用点样法对18块森林岛屿(面积范围:4.3–76.9hm2)中的鸟类物种多样性及密度进行了调查。主要目的是检测森林岛屿的面积效应是否对鸟类物种多样性及密度产生影响,同时分析经典的岛屿生物地理理论是否可以解释破碎化后的森林岛屿面积与物种的关系。结果表明,鸟类物种多样性在年间没有显著变化,但鸟类的密度在不同年间变化较大。不同面积森林岛屿中的鸟类物种多样性有所差异,所包含的鸟类物种数从12种到43种不等。尽管有些面积较大的斑块所包含的物种数较少,但鸟类物种数的总体趋势是随着斑块面积的增大而增多。不同鸟类对森林岛屿面积的反应并不相同,灰椋鸟(Sturnuscineraceus)、红尾伯劳(Laniuscristatus)、灰头鹀(Embrizaspodocephala)等在面积较小的斑块中密度较大,而山鹡鸰(Dendronanthusindicus)、树鹨(Anthushodg-soni)、灰背鸫(Turdushortulorum)等几乎不分布于小面积斑块之中。森林岛屿中鸟类物种随着面积变化的变异方式符合经典的岛屿生物地理理论的基本模式,但Z值和C值差异较大     

城市化对植物多样性影响的研究进展

本文综述了城市化对植物多样性影响的研究进展。随着全球特别是发展中国家城市化水平的提高, 城市化对生物多样性的影响逐渐引起了人们的重视。城市化造成了本土植物物种的丢失和外来物种的增加。在空间分布上, 城市化还常使城区本土植物多样性沿着远郊农区－城郊－城区梯度性下降; 但是由于引进大量外来物种, 总体植物多样性反而升高, 沿着远郊农区－城郊－城区梯度性升高。城市化对植物种类组成也有很大影响,优势种在远郊农区、城郊和城区呈现不同。城市化对植物多样性影响的机制主要有人为引入外来物种、小生境改变以及景观格局的变化三个方面。以下四个研究方向将越来越重要: (1) 不同区域、不同方法、不同学科的系统整合研究;(2) 城市化扩张与植物多样性变化过程的定位监测研究; (3) 本土植物多样性丢失以及性状改变的内在机制研究, 特别是外来物种与本地物种的相互作用过程和机制的研究; (4) 城市植物多样性保护研究。     

Measuring the synanthropy of species and communities to monitor the effects of urbanization on biodiversity

Urbanization is considered as one of the most important land-use and land-cover (LULC) changes with multiple pervasive effects on biodiversity. However, the quantitative assessment of biodiversity responses to urbanization remains challenging because some species can be directly and negatively affected by the spread of human settlements, while others can benefit from this LULC change. Moreover, although species sensitivity to urban settlements (their “synanthropy”) can either correspond to the spatial segregation of individuals within urban habitats or to their positive temporal trends in these habitats, these two facets are hardly distinguished explicitly. Here, we confronted the fine-scale spatial distribution of all the buildings in France with the spatial distribution and population trends of the 119 most common French breeding birds monitored in 2124 plots from 2001 to 2012. We developed and tested two indicators of “synanthropy”. The first indicator (S1) differentiates species along a continuous gradient from urban “avoiders” (low S1) to urban “dwellers” (high S1). The second indicator measures the beneficial or detrimental effect of building densities on the temporal trends of the populations. It allows the segregation among urban “losers” having lower temporal trends with increasing buildings (low S2) from urban “winners” (high S2) having more positive trends in more urbanized areas. We then tested the relationships between S1 and S2 with a set of species and life history traits. Finally, we transposed these species indicators to communities using community weighted means to test the link between the synanthropy of communities with bird species richness, and the spatial, temporal and spatio-temporal trends of the synanthropy of bird communities. We found that 43% of the species were “urban dwellers”, and 18% “urban winners”. Both urban dwellers and winners were species widely distributed and locally abundant. Urban dwellers were mainly ground feeders but did not nest on the ground. At the community level, high species richness was associated with medium-values of community synanthropy, following the intermediate-disturbance hypothesis. We found that the average value of community synanthropy and their trend were not randomly distributed in space. These two indicators of synanthropy can be used in different taxonomic groups and areas to assess the proportion of synanthropic species within communities, to monitor their temporal trends and their spatial distribution and represent a straightforward complement to the synthetic indicators of human footprint on biodiversity.     

The iterative process of plant species inventorying for obtaining reliable biodiversity patterns

We require representative data of species occurrence to explain plant diversity patterns, but most of the available information is incomplete and biased. To improve our knowledge, we suggest that species inventorying should be an iterative process encompassing the following: (1) the detection of taxonomic and geographical gaps; (2) the planning of a survey design to reduce such gaps; and (3) the evaluation of field sampling results. Here, we focus on the latter phase for the bryophytes of Terceira Island (Azores) for which we have previously estimated < 1% of the area as well surveyed based on historical collections. To examine the performance of our stratified survey based on two factors (land use and environmental regions), we used rarefaction curves, ANOVA tests and bootstrap sampling. We recorded 40% of all the species known for the island and presented eight new citations. The species assemblages remained similar between historical and current inventories. Most localities had completeness values > 85%, but we always exceeded the optimal sampling effort. Land uses and environmental regions affected species diversity, but, unexpectedly, to a different degree. Our study illustrates the difficulties of planning field surveys to obtain reliable biodiversity patterns, even when prior information and standardized sampling protocols are explicitly considered. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 177 , 491–503.     

Partitioning the biodiversity effects on productivity into density and size components

Plant density and size — two factors that represent plant survival and growth — are key determinants of yield but have rarely been analysed explicitly in the context of biodiversity–productivity relationships. Here, we derive equations to partition the net, complementarity and selection effects of biodiversity into additive components that reflect diversity-induced changes in plant density and size. Applications of the new method to empirical datasets reveal contrasting ways in which plant density and size regulate yield in species mixtures. In an annual plant diversity experiment, overyielding is largely explained by selection effects associated with increased size of highly productive plant species. In a tree diversity experiment, the cause of overyielding shifts from enhanced growth in tree size to reduced mortality by complementary use of canopy space during stand development. These results highlight the capability of the new method to resolve crucial, yet understudied, demographic links between biodiversity and productivity.     

On the use of sample indices to reflect changes in benthic fauna biodiversity

This paper focuses on the difference between the value of some commonly used diversity indices (Simpson, Shannon, abundance, richness) calculated from benthic grab samples and their value in the population or region from which the samples are taken. The ability of the sample indices, as well as a recently derived relative Shannon index, to reflect change in biodiversity is examined in a short simulation study based on changing one of the diversity parameters (abundance, richness and evenness) in the population, whilst keeping the other two components constant. Our results suggest that, whilst their population equivalents do not always reflect biodiversity changes, the sample Simpson, Shannon and Richness indices perform well. We note that this will be true for any surveys where the sampling programme fails to detect many species in a population, and hence will be applicable for most benthic surveys. The use of sample indices to detect changes in biodiversity from long-running time series in the Thames and Tyne estuaries is illustrated.     

The Cape Peninsula, South Africa: physiographical, biological and historical background to an extraordinary hot-spot of biodiversity

The Cape Peninsula, a 470 km² area of rugged scenery and varied climate, is located at the southwestern tip of the Cape Floristic Region, South Africa. The Peninsula is home to 2285 plant species and is a globally important hot-spot of biodiversity for higher plants and invertebrates. This paper provides a broad overview of the physiography, biological attributes and history of human occupation of the Peninsula. The Peninsula is characterized physiographically by extremely high topographical heterogeneity, very long and steep gradients in annual rainfall, and a great diversity of nutrient-poor soils. Thus, the Peninsula supports a high number of habitats and ecological communities. The predominant vegetation is fynbos, a fire-prone shrubland, and 12 broadly characterized fynbos types have been described on the Peninsula. Animal community structure, especially with regard to invertebrates, is poorly known. Vertebrate community structure is probably strongly influenced by nutrient poverty and recurrent fire. Generally, most vertebrates are small and typically occur in low numbers. Some invertebrates play keystone roles in facilitating ecological processes. Human occupation of the Peninsula was limited, until relatively recently, by nutrient poverty. After Dutch colonization in 1652, direct and indirect impacts on the natural ecosystems of the Peninsula escalated dramatically, and by 1994, some 65% of original natural habitat was either transformed by urbanization and agriculture, or invaded by alien plants. Nonetheless, there is still excellent potential to conserve the Cape Peninsula's remaining biodiversity.     

The environmental control of plant species density on a Himalayan elevation gradient

Aim In eastern Nepal, forests occupy an elevation gradient of 4000 m with bioclimatic zones from near tropical to alpine. Understorey plants and trees were censused to measure species density and identify patterns of ecological change. By sampling in a manner robust against spurious mid‐domain effects, I aim to identify biologically valid controls on species density. Location The study area consists of land below 4250 m elevation between 27.1 and 27.8° N latitude, 86.5 and 88.0° E longitude on the southern slopes of the Himalaya Range in eastern Nepal. Sampling sites are limited to intact, natural forest with relatively little human impact. Methods Team members counted species of understorey plants and trees ≥ 10 cm d.b.h. in 0.04 ha plots throughout the study area. In addition, basal area, leafing phenology and species composition were determined for the trees in each plot. Estimates of regional species density were compiled for successive 250 m elevation bands from 250 to 4250 m elevation. Species density trends were identified and compared with the expectations of O'Brien's [Journal of Biogeography 25 (1998) 379–398] climate‐based water–energy dynamics model. Results Stand basal area, tree leafing phenology and taxonomic composition (angiosperm vs. gymnosperm) show non‐random change with elevation. Understorey plant and tree species density both have a humped, unimodal trend with more species near the bottom of the gradient and fewest at the top. These trends are consistent with expected effects of the climatically active water and energy variables. After curve‐fitting, significant spatial structure in the residuals suggests that tree communities within the 1750–2250 m elevation range do not realize their climatic potential species richness. Main conclusions Neither mid‐domain effects nor biologically valid boundary effects like dispersal limitation explain the plant species density trends observed. Trends do fit a model in which species density is controlled by the same ‘active’ climatic variables that predict species richness on continental scales. Patterns of leafing phenology on the elevation gradient provide further support for the hypothesis of environmental control of species density. The productivity–diversity linkage that exists on continental scales may also apply on the smaller scale of a Himalayan elevation gradient. Human activity and possible competitive exclusion by Castanopsis tribuloides are the two best explanations for the observed decline in tree species density at 1750–2250 m elevation. Burning, lopping for fodder and livestock grazing might account for the decline, but this study does not assess the relative importance of these activities. The elevation richest for understorey plant and tree species (500–1500 m) also has the most severe reduction in forest cover. Local farmers deserve credit for sustaining plant biodiversity in forest enclaves, but further loss of forest at these elevations should be discouraged.     

The effects of host plant species and larval density on immune function in the polyphagous moth Spodoptera littoralis

Immune functions are costly, and immune investment is usually dependent on the individual''s condition and resource availability. For phytophagous insects, host plant quality has large effects on performance, for example growth and survival, and may also affect their immune function. Polyphagous insects often experience a large variation in quality among different host plant species, and their immune investment may thus vary depending on which host plant species they develop on. Larvae of the polyphagous moth Spodoptera littoralis have previously been found to exhibit density‐dependent prophylaxis as they invest more in certain immune responses in high population densities. In addition, the immune response of S. littoralis has been shown to depend on nutrient quality in experiments with artificial diet. Here, I studied the effects of natural host plant diet and larval density on a number of immune responses to understand how host plant species affects immune investment in generalist insects, and whether the density‐dependent prophylaxis could be mediated by host plant species. While host plant species in general did not mediate the density‐dependent immune expression, particular host plant species was found to increase larval investment in certain functions of the immune system. Interestingly, these results indicate that different host plants may provide a polyphagous species with protection against different kinds of antagonisms. This insight may contribute to our understanding of the relationship between preference and performance in generalists, as well as having applied consequences for sustainable pest management.     

The effects of intraspecific density dependence on species richness and species abundance distributions

Species richness and patterns of abundance result from the interplay between niche differences, realized as intraspecific density dependence (IDD), and so-called neutral processes that arise when species fitnesses are similar. This paper presents an extension of neutral models that incorporates delays in IDD that could result from resource-mediated competition or through a pathogen pool. These delays reduce standing species richness and qualitatively change the shape of species abundance distributions and render them consistent with the hollow curve shape even in the presence of strong IDD.     

Resource availability, species composition and sown density effects on productivity of experimental plant communities

Productivity of artificial grassland communities was investigated in a 6-year field experiment on the Qinghai-Tibetan Plateau. In the experiment, assemblages varying in seven species compositions and four density gradients were grown in fertilized and non-fertilized subplots. We measured biomass of sown species as an indicator of community productivity. In general, 6-years of experiments indicated that: (i) species composition had a significant influence on community productivity. During the initial phase of the experiment, sown density significantly affected community productivity, but the effects disappear with the increase of grown years. This productivity increased with biodiversity increase and fertilization, while the biodiversity effects disappeared when the influence of composition was removed. (ii) The increase of community productivity with biodiversity was resulted from joint effects of selection and complementarity. (iii) With an increase of growth time, the selection effects become weaker while complementarities become enhanced. Influence of density on both effects was significantly different in early stages, but ultimately this all became insignificant. Fertilization dramatically increased the complementarity effects in all experiment processes, but had different influences on selection effects during different experimental period.     

A simple method to analyze the similarity of biological sequences based on the fuzzy theory

In this paper, we propose a simple method to analyze the similarity of biological sequences. By taking the average contents of biological sequences and their information entropies as the variables, the fuzzy method is used to cluster them. From the results of application, it finds that the method is relatively easy and rapid. Unlike other methods such as the graphical representation methods, which is usually very complex to compute some invariants of matric derived from graphical representation, our method pays more attention to the information of biological sequences themselves. Especially with the help of the software (SPSS), it seems to be very convenient. Therefore, it may be used to study the new biological sequences such as their evolution relationship and structures.     

Scale-dependent effects of land use on plant species richness of mountain grassland in the European Alps

Traditionally managed mountain grasslands in the Alps are species‐rich ecosystems that developed during centuries of livestock grazing. However, changes in land use including fertilisation of well accessible pastures and gradual abandonment of remote sites are increasingly threatening this diversity. In five regions of the Swiss and French Alps we assessed the relationship between land use, soil resource availability, cover of the unpalatable species Veratrum album, species richness and vegetation composition of mountain grasslands across four spatial scales ranging from 1 to 1000 m². Mean species richness and the increase in the number of species with increasing area were lower in intensively grazed, fertilised pastures than in traditional pastures or in abandoned pastures. Species composition of abandoned pastures differed from that of the other management types. Plant species richness was influenced by different factors at different spatial scales. At the 1 m² scale, plant species richness was negatively related to soil nitrate and influenced by the cover of V. album, depending on land use: species richness and cover of V. album were negatively correlated in abandoned pastures, but positively correlated in fertilised grasslands. At the 1000 m² scale, a negative effect of fertilization on richness was evident. These results indicate that at small scales species richness in mountain grasslands is determined by competition for light, which should be more important if nutrient availability is high, and by positive and negative interactions with unpalatable plants. In contrast, species richness at the large scale appears to be mainly influenced by land use. This result emphasizes the importance of studying such inter‐relationships at multiple scales. Our study further suggests that the maintenance of the traditional land use scheme is crucial for the conservation of plant species richness of mountain pastures as both intensification and abandonment changed species composition and reduced plant species diversity.     

The effects of acetosyringone and pH on Agrobacterium-mediated transformation vary according to plant species

Summary Expiants of five plant species (Allium cepa, Antirrhinum majus, Brassica campestris. Glycine max, and Nicotiana tabacum) were co-cultivated with three Agrobacterium tumefaciens strains under different conditions to assess the effects of acetosyringone and medium pH on strain virulence. Tumours were incited on all dicotyledonous species by strains N2/73 and A281. The presence of acetosyringone during co-cultivation generally enhanced the virulence of these strains, most markedly N2/73 on A. majus and G. max, and A281 on G. max. Strain Ach5 was virulent only on N. tabacum in the absence of acetosyringone, which, when present, extended the host range to include A. majus. There was evidence to suggest that acetosyringone may suppress virulence in some strain/plant species interactions. Virulence was affected in some cases by medium pH, but there was no general effect across plant species.Abbreviations T-DNA DNA transferred to plant cells by Agrobacterium - BAP benzyl aminopurine - MS medium Murashige and Skoog (1962) medium     

黄土丘陵半干旱区柠条林密度对土壤水分和柠条生长的影响

研究密度对土壤水分和植物生长的影响对森林植被恢复和生态建设具有重要的意义。以黄土丘陵半干旱区人工柠条为研究对象,对相同立地条件下不同密度柠条林生长与林地土壤水分进行了长期定位观测和分析。研究表明,1—5年生柠条不同密度林地土壤水资源量差异显著,从第3年开始,土壤水资源量随着密度增加而增加;10—12年生柠条密度越低土壤水资源量越高(Treatment4除外,T4),不同密度之间水资源量差异不显著。1—3年生柠条密度越高会促进其株高生长;从第四年开始,柠条密度过高会抑制其株高生长;1—5年生柠条密度越高基径生长越快,不同密度生长差异不显著;10—12年生密度过高(Treatment1,T1)或过低(T4)均会抑制柠条株高与基径生长。在柠条播种后第5年,高密度试验小区(T1和Treatment2,T2)柠条林地最大入渗深度土壤水资源量降到水资源利用限度,此时需要依据土壤水分植被承载力通过平茬来降低林分密度,以达到减少土壤水分消耗和可持续利用土壤水资源之目的。