Species richness and endemism in the Usambara mountain forests,Tanzania

The East Usambara Mountain forests constitute what is probably one of the richest biological communities in Africa in terms of plant and animal species numbers and endemic taxa. This review presents brief accounts of the flora and of three invertebrate and four vertebrate groups and shows the percentage endemic taxa to vary from 2% (mammals) to 95% (millipedes) as a proportion of the true forest species. Notes are given on the geology, soils, climate and present land use of the Usambaras. Biological richness is considered to be due to long periods of isolation and geological stability coupled with periods of species immigration during times of re-establishment of a continuous forest cover. The nature of the endemic elements is briefly discussed. Evidence is given to show that the forests are subject to increasing pressure from legal and illegal encroachment due to agriculture (tea, cardamon, subsistence) and forestry timber operations. Air photograph analysis shows a forest decrease of some 50% in the vicinity of Amani from 1954 to 1976. The low conservation status of most forest reserves and the lack of detailed knowledge on the distribution, status and biology of the endemic species means present conservation efforts are poor and haphazard. This review calls for greatly increased research inputs and a complete halt to all exploitation of natural forest areas until a long term conservation land use plan can be implemented.     

沿海岛屿与内陆藓类植物遗传多样性和分化的比较研究——以真藓(Bryum argenteum Hedw.)为例

基于11个内陆居群和32个岛屿居群的252份标本,采用ISSR分子标记技术对真藓（Bryum argenteum Hedw.）的遗传多样性进行了研究。结果显示：岛屿与内陆居群间的遗传多样性差异显著,岛屿居群间的分化程度（G_st=0.453）大于内陆居群（G_st=0.387）,岛屿居群的遗传分化与地理来源间存在极显著相关性（r=0.478,n=175,P<0.001）。地理隔离效应是导致岛屿居群间遗传分化的重要因素。岛内居群间的遗传分化水平较低,仅有29.4%~29.7%的遗传多样性存在于居群间。聚类分析表明,43个居群可划分为10大类群,真藓遗传关系受地理因素和生境异质性的影响,水域隔离影响了真藓繁殖体在岛屿间的传播。     

Spatial distribution of species diversity indices and their correlation with plot size

In a physiognomically uniform Leucobryo-Pineteum phytocoenose the spatial pattern of point diversity was determined and the effect of quadrat size on the assessment of alpha diversity (in Whittaker's, 1977, sense) was analysed. In both cases the Shannon index of total species diversity and the evenness index were used to measure diversity. A contagious spatial pattern of point diversity and a high variation of point diversity values, as well as a strong non-linear dependence of H and J values on quadrat size, and also a decrease in H and J variation with an increase in quadrat size were found.Nomenclature follows Ehrendorfer (1973). Liste der Gefässpflanzen Mitteleuropas.     

Chilling injury in coleus as influenced by photosynthetically active radiation, temperature and abscisic acid pretreatment. I. Morphological and physiological responses

Abstract. Coleus blumei Benth. (PI No. 354190), a green-leafed cultivar, was exposed to 5°C for 48 or 72 h after pretreatment for 48 h at two levels of photosynthetically active radiation (PAR) (8 and 320 μmol s⁻¹ m⁻²), two temperatures (13 and 20°C), and two abscisic acid (ABA) levels (0 and 200 g m⁻³ of the racemic mixture). Plants given low PAR for only 48 h prior to chilling treatment (48 or 72 h at 5°C) showed increased protection against chilling injury while those given high PAR were severely injured. The former plants were darker green, contained greater concentrations of chlorophyll- a , chlorophyll- b , total chlorophyll and anthocyanin and generally had a lower abscission rate than the latter plants. There were no differences, however, in chlorophyll- a/b ratio among plants grown at the two PAR levels, two temperatures or two ABA concentrations. Temperature and ABA pretreatment and number of hours at 5°C had no significant effect on chilling injury as measured by leaf chlorosis, but generally had a significant effect on leaf abcission, especially at 3 and 7 d after returning the plants to the greenhouse. Enclosing intact plants or excised shoots in plastic bags to maintain 100% relative humidity during 72 h chilling treatment failed to provide protection against chilling injury. These findings indicate that the protective effects of low PAR applied prior to chilling treatment may be as important or more important than that applied during chilling. They also indicate the importance of making careful measurements of PAR levels when conducting studies on chilling injury.     

Selection of diverse genotypes for heterosis in yield and response in toria (Brassica campestris L.)

Summary Thirty-one genotypes of toria (Brassica campestris L.) were grown in twelve environments and subsequently analysed in order to select potential parents which expressed diversity for both 12 different characters (estimated by Mahalanobis' D² technique) and response to the environments (estimated on the basis of negative correlation between deviations in seed yield of a pair of genotypes from their respective environmental means). Coefficients of determination (r²) were also used to measure the reliability of correlation, which is the basis of diversity of response. Stability parameters (b and S²d) and mean seed yield were also considered in selecting potential parents. On the basis of these criteria, three pairs of genotypes (ITSA and TCSU-1, TCSU-7 and TH-8 and Ludhiana Composite-1 and TH-4) are recommended to be used as parents for hybridization programmes so that heterosis both in seed yield and response may be exploited.     

Influence of the surface microlayer on nutrients,chlorophyll and algal diversity of a small eutrophic bog pond

Nutrients, chlorophyll, phaeophytin and algal abundances were investigated in the surface microlayer and at subsurface depths in a small eutrophic bog pond. Nutrient levels were consistently higher in the microlayer while algal abundance was sometimes higher but sometimes lower in the microlayer than at near subsurface depths. Algal diversity values were strongly influenced by the depth of flagellate blooms, and in contrast to previous studies, diversity in the microlayer was higher than at near subsurface depths. These results are discussed in terms of weather parameters, affinity of algal species for the surface and differences between microlayer ecology in shallow and deep water systems.     

Biomass: Is it a useful tool in paleocommunity reconstruction?

In general, more of the biomass of the community is preserved than is its numerical abundance. Thus, the paleontologist, on the average, works with more of the community when biomass is used. Community characteristics such as taxon dominance and habitat proportions are at least as accurately derived from biomass as numerical abundance. The use of biomass is clearly more appropriate in describing energy flow and trophic proportions. Whenever possible, biomass should be used as a complement to numerical abundance in future paleoecologic reconstructions.     

An experimental evaluation of diversity indices as environmental discriminators

Seven diversity indices were calculated for each of fifty-eight microcosm communities. All fifty-eight communities were initiated from equal density inoculations of fourteen algal species. Each microcosm developed in one of six controlled experimental environments; the environments differing only in their temporal patterns of disturbance. Five linear discriminating techniques were used to evaluate the diversity index most useful for discriminating between these environments. The Shannon-Wiener index was best according to two of the discriminating methodologies and second best using the other techniques. Evenness was best when the Shannon-Wiener index was second best and vice versa.     

Patterns of variation in tail ornament size in birds

In recent years several different kinds of sexual selection models have been developed, and tail ornaments in birds have frequently been used as an example of a sexually selected character where the models might apply. However, very little is known about intra- and interpopulation variation in ornament size. We have studied the elongated tail ornaments in four species of whydahs Vidua , the forktailed flycatcher Tyrannus savana and the Asian paradise flycatcher Terpsiphone paradisi. Ornaments were relatively longer in males with the longest tarsi ('heterogony' with positive allometry). Also, tail lengths were remarkably variable within each geographical area, the coefficient of variation (average = 11%) being three times as high as for body size characters. Models, with female preference of ornaments bearing no relation to male viability, usually generate lines of neutral equilibria. Thus, they predict extraordinary variation in ornaments between populations. However, elongated tail ornaments did not show higher geographical variation than the body size characters, suggesting that there is no line of equilibria for these ornaments.