Species succession and the development of a lacustrine fish community in an ephemeral lake

Here, we present a gillnet survey of Lake Liambezi a 370 km² shallow ephemeral floodplain lake situated in north-eastern Namibia, which is fed irregularly by the upper Zambezi and Kwando Rivers during years of high flooding. The lake dried up in 1985 and, with the exception of sporadic minor annual inundation events, remained dry until 2007. We describe the temporal succession of fish species over an 8 year period from initial inundation 2007 to maturation in 2014. The succession of the fish community did not follow the typical pattern of opportunistic strategists during colonisation, to periodic strategists that are eventually succeeded by equilibrium strategists. Instead, the evolution of the fish community was characterised by three distinct phases. The first phase involved the inundation and colonisation of the lake in 2007, followed by its decline until the floods that filled the lake in 2009. During this phase the lake was colonised by fishes from the adjacent upper Zambezi and Chobe River floodplains. Fish communities predominantly comprised floodplain specialists including the barbs Enteromius paludinosus and Enteromius poechii, the mormyrid Marcusenius altisambesi and catfishes Schilbe intermedius and Clarias gariepinus. The filling of the lake in the March 2009 floods marked the beginning of the second, successional phase. The barbs declined in abundance and the alestid Rhabdalestes maunensis underwent explosive population growth between 2009 and 2010, but populations crashed equally rapidly and were replaced by Brycinus lateralis which, together with S. intermedius went on to dominate the fish community 2011–2014. Larger, slower growing tilapiine cichlids increased steadily in abundance and became the dominant components in a 2700 t y^–1 artisanal fishery that developed on the lake. The fish community in the ephemeral Lake Liambezi is clearly influenced by numerous factors including connectivity, lake level fluctuations, competition and the effects of fishing, which may disrupt typical succession processes in floodplain ecosystems.     

荒漠植物功能性状及其多样性对土壤水盐变化的响应

植物功能性状及其多样性对环境变化的响应研究有助于揭示极端环境下植物适应策略和群落构建机制。通过实地调查和实验分析,研究艾比湖荒漠植物形态、生理和化学等8个功能性状的特征,并从多维性状和一维性状角度揭示功能多样性对土壤水分和盐分变化的响应规律。结果表明:高水盐环境下(SW1),(1)群落加权株高、叶绿素含量(SPAD)及叶片碳(C)和钙(Ca)含量显著高于低水盐环境,叶片氮(N)、磷(P)、硫(S)含量在不同水盐环境间无显著差异。(2)SW1环境下,沿乔木-小乔木-灌木-草本层次,上层生活型植物性状值普遍高于下层植物,其中灌木叶片仅N、钾(K)含量显著高于草本;沿该生活型层次植物性状呈趋同变化。(3)低水盐环境下(SW2),乔木叶片性状差异特征与SW1相似;小乔木叶片C、N含量分别显著高于和低于灌木及草本;相比于草本,灌木SPAD、S含量显著高,K含量显著低,株高、C、N、P含量差异不显著;SW2环境下各生活型植物性状呈趋同变化。(4)SW1环境下多维功能丰富度、功能离散度显著高于SW2环境,但均匀度无显著差异。(5)一维功能均匀度在不同水盐环境间均无显著差异,但化学性状的均匀度总体高于植物株高;高水盐环境下叶片N、S和Ca的功能分异指数显著高于低水盐环境。研究为掌握胁迫环境下的植物适应策略和荒漠植被恢复提供参考。     

Distribution and genetic structure of the Japanese wood pigeon (Columba janthina) endemic to the islands of East Asia

The Japanese wood pigeon (Columba janthina) is endemic to the islands of East Asia and it is included in the Japanese and Asian Red Lists because of its narrow habitat range that is restricted to mature forests on small islands and because of the destruction of these habitats. We examined the genetic structure of Columba janthina by studying 463 base pairs of the mitochondrial control region sequences. We analyzed 154 samples from eight populations and identified 27 haplotypes. Three population groups were identified based on the pairwise Φ_ST values. A substantial gene flow, as reflected by the low and non-significant Φ_ST values, is maintained among the northern group that includes six populations found on the Okinawa, Tokara, Goto, Setouchi, Oki, and Izu islands. In contrast, the southeastern group found on the Ogasawara Islands had large Φ_ST values with every population from other regions (0.910 < Φ_ST < 0.962). The southwestern group found on the Sakishima Islands also had significant but small Φ_ST values with every population from the northern group (0.081 < Φ_ST < 0.205). The Mantel test showed a highly significant correlation between the Φ_ST values and the route length of the habitat network, as well as the linear distance with correction of the habitat gap effect, indicating the importance of the closely connected structure of the habitats. The three groups mentioned above could be considered as independent management units, and the southeastern group has the highest conservation priority due to its narrow distribution range and small population size. Electronic Supplementary Material The online version of this article (doi: ) contains supplementary material, which is available to authorized users.     

Studies on Temporal and Spatial Variations of Phytoplankton in Lake Chaohu

Temporal and spatial variations of the phytoplankton assemblage in Lake Chaohu, a large shallow eutrophic lake in China, were studied from September 2002 to August 2003. A total of 191 phytoplankton species was identified, among which Chlorophytes （101） ranked the first, followed by Cyanophytes （46） and Bacillariophytes （28）. On aver- age over the entire lake, the maximum total algal biomass appeared in June （19.70 mg/L） with a minimum （5.05 mg/ L） in November. In terms of annual mean biomass, cyanobacteria contributed 45.43% to total algal biomass, followed by Chlorophytes （27.14%）, and Bacillariophytes （20.6%）. When nitrate （NOs-N） and ammonium （NH4-N） concentrations dropped in spring, fixing-nitrogen cyanobacterium （Anabaena） developed quickly and ranked the first in terms of biomass in summer. It is likely that dominance of zooplanktivorous fish and small crustacean zooplankton favored the development of the inedible filamentous or colony forming cyanobacteria. The persistent dominance of cyanobacteria throughout all seasons may indicate a new tendency of the response of phytoplankton to eutrophication in Lake Chaohu.     

Relationship between bacterioplankton and phytoplankton community dynamics during late spring and early summer in Lake Taihu, China

The relationship between bacterioplankton and phytoplankton community compositions was investigated from April to June, 2005 with samples taken at five different stations in Lake Taihu, China. Bacterioplankton and phytoplankton community compositions as determined by denaturing gradient gel electrophoresis of polymerase chain reaction amplified bacterial 16S rRNA gene fragments (PCR-DGGE) and microscopic examination, respectively, revealed a high degree of diversity. In total, 43 unique bands were identified amongst the DGGE profiles, and 29 dominant phytoplankton populations were observed. The DGGE profiles were clustered into two distinct groups. These two clusters were closely associated with two dominant phytoplanktons, Ulothrix sp. and Microcystis spp., as observed on April 19, May 27 and June 27, 2005, respectively. The relationship between bacterioplankton and phytoplankton community compositions was investigated using Canonical Correspondence Analysis (CCA) with the Shannon-Wiener diversity index of phytoplankton community (Hp), the total cell abundance of phytoplankton (N) and the relative abundance of Microcystis spp. (M) as the variables. The CCA results indicated a 30.9 % correlation coefficient, suggesting a high degree of correlation between bacterioplankton and phytoplankton community compositions.     

Land use/cover change and its drivers: a case in the watershed of Lake Kasumigaura, Japan

Land use/land cover (LULC) changes in the watershed (2,157 km²) of Lake Kasumigaura during 1979–1996 (Period-1: 1979–1990, Period-2: 1990–1996) were analyzed, and their socio-economic and biophysical drivers were compared using time-series, high-quality GIS datasets in order to examine the characteristics of a model forecasting the future LULC. The changes occurred over an area of more than 90 km² during the overall period at changing rates of 0.22% year⁻¹ in Period-1 and 0.25% year⁻¹ in Period-2. Forestland decreased most in both periods at changing rates of 0.45% year⁻¹ in Period-1 and 0.61% year⁻¹ in Period-2. However, predominant changing patterns differed, i.e., from forest to golf course in Period-1 and from forest to artificial field in Period-2. Particularly in Period-2, a significant LULC change was observed in an area of high population increase on the edge of an already high-population area. Relationships examined among LULC change, population, and rate of population change suggested that the urbanized area was highly resistant to LULC change, and that such change was less frequent in areas of population decline. Statistical analyses indicated that the most influential drivers for total LULC changes were population in Period-1 and distance from the Tokyo Station in Period-2. Since the change potentials differed between the periods, we could not assume a stationary process for the corresponding drivers. Somewhat low S values (indices for demonstrability) show that LULC changes in the watershed of Lake Kasumigaura occurred rather randomly, probably resulting in fragmentation of the landscape.     

Role of host identity in effects of phytogenic mounds on plant assemblages and species richness on coastal arid dunes

Question: Phytogenic mounds (nebkhas) ‐ the natural accumulation of wind‐blown sediments within or around the canopies of plants ‐ have been proposed as important structures for locally maintaining high species richness in coastal and arid ecosystems. Nebkhas are assumed to increase habitat heterogeneity, but what is the importance of the nebkha host species relative to other nebkha characteristics in determining the associated plant assemblages? Are some host species more effective in creating diversity hotspots, or does a single species‐area relationship apply to all nebkhas, regardless of host species? Can the influence of the host be ascribed to its indirect effects on abiotic attributes of the nebkha complex? Methods and location: We investigated plant species richness and composition on nebkhas around six psammophytic species on Mediterranean coastal dunes of the Sinai Peninsula. Results: Plant species richness was significantly related to nebkha size by the single power function according to the general prediction of island biogeography theory, but this relationship was modified ‐ though to a limited degree ‐ by nebkha host species identity. Canonical Correspondence Analysis revealed that nebkha host species identity and nebkha environmental and non‐environmental factors significantly explained species composition on the nebkhas, but host species identity did so to a greater extent. The latter might reflect differences in seed trapping ability or free space for colonization between host species. Conclusion: Differences in community composition and richness among nebkhas formed by different host species represent a key factor in the maintenance of plant diversity on arid coastal dunes.     

Stress responses and metal tolerance of <Emphasis Type="Italic">Chlamydomonas acidophila</Emphasis> in metal-enriched lake water and artificial medium

Chlamydomonas acidophila faces high heavy-metal concentrations in acidic mining lakes, where it is a dominant phytoplankton species. To investigate the importance of metals to C. acidophila in these lakes, we examined the response of growth, photosynthesis, cell structure, heat-shock protein (Hsp) accumulation, and metal adsorption after incubation in metal-rich lake water and artificial growth medium enriched with metals (Fe, Zn). Incubation in both metal-rich lake water and medium caused large decreases in photosystem II function (though no differences among lakes), but no decrease in growth rate (except for medium + Fe). Concentrations of small Hsps were higher in algae incubated in metal-rich lake-water than in metal-enriched medium, whereas Hsp60 and Hsp70A were either less or equally expressed. Cellular Zn and Fe contents were lower, and metals adsorbed to the cell surface were higher, in lake-water-incubated algae than in medium-grown cells. The results indicate that high Zn or Fe levels are likely not the main or only contributor to the low primary production in mining lakes, and multiple adaptations of C. acidophila (e.g., high Hsp levels, decreased metal accumulation) increase its tolerance to metals and permit survival under such adverse environmental conditions. Supposedly, the main stress factor present in the lake water is an interaction between low P and high Fe concentrations.     

Geochemistry of Lake Biwa sediments revisited

Extensive chemical data for the Lake Biwa sediments were examined with statistical factor analysis to find any correlation patterns among elements and among samples. Based on those patterns, a series of x-y correlation plots of the concentrations of selected elements was constructed to see in detail how the concentrations of elements vary among different sample groups and explain the observed variation patterns.     

Linking major nutrients (C,H, N,and P) to trace metals (Fe,Mn, and Cu) in lake seston in southern Brazil

We investigated the relationships between major nutrients (C, H, N, and P) and trace metals (Cu, Fe, and Mn) in seston samples from ten lake/lagoon systems in southern Brazil. The systems were characterized by a diverse set of limnological features, including surface areas from 10⁻¹ to 10² km², water color, a _CDOM(440), from 1.4 to 12.9 m⁻¹, and electrical conductivity from 50 to 100 000 μS cm⁻¹. Seston concentrations also varied a great deal, 32-fold. The elemental (C: N, C: P, and N: P) and C: Chl-a ratios in the seston samples indicated, however, common features; i.e., most of the lakes were N-and/or P-limited, and the seston organic fraction was composed of nonvascular plants (e.g., phytoplankton). Our intersystem comparison revealed that the relative content of organic matter in seston and seston concentrations in lake water tended to correlate positively and negatively, respectively, with trace metal concentrations across the seston samples. Possible influences of elemental and C: Chl-a ratios on the association of metals with seston matrices, although theoretically important, were only partially evidenced here; positive correlations were found between C: N and also Org-H: N ratios with trace metal concentrations. We speculate that such results could be circumstantial, as the nature of the seston matrices appeared to be very similar among them. This hypothesis should thus be the theme of further research. In short, our findings suggest that C: N and Org-H: N ratios as well as the relative content of major nutrients in seston and seston concentrations can be importantly related to trace metal concentrations in seston samples. In discussing the results, however, we consider that metal-seston relationships depend on a variety of physical, chemical, and biological factors and/or variables other than those measured in this study, which could also contribute for defining and explaining variations in metal-seston concentrations in lake ecosystems.