Floristic composition in relation to environmental gradients across KwaZulu‐Natal,South Africa

Conservation planning in the face of global change is still in its infancy. A suggested approach is to incorporate environmental gradients into conservation planning as they reflect the ecological and evolutionary processes generating and maintaining diversity. Our study provides a framework to identify the dominant environmental gradients determining floristic composition and pattern. Nonmetric multidimensional scaling was used on 2155 sampling plots in savanna and grassland habitat located across the province of KwaZulu‐Natal, South Africa (94 697 km²), a floristically rich region having steep environmental gradients, to determine the dominant gradients. Hierarchical cluster analysis was used to group similar plots which were then used in a Classification and Regression Tree analysis to determine the environmental delimiters of the identified vegetation clusters. Temperature‐related variables were the strongest delimiters of floristic composition across the province, in particular mean annual temperature. Frost duration was the primary variable in the Classification and Regression Tree analysis with important implications for savanna/grassland dynamics. Soil properties (base, pH status) and moisture variables accounted for most of the variation for the second and third axes of floristic variation. Given that climatic and edaphic variables were well correlated with floristic composition, it is anticipated that a changing climate will have a marked influence on floristic composition. We predict warmer temperatures may facilitate the spread of frost sensitive savanna species into previously cooler, grassland areas. Species associated with specific soil types will not easily be able to move up the altitudinal gradient to cooler climes because geology is aligned in an approximately north‐south direction compared with increasing altitude from east‐west. Future conservation planning should take cognisance of these gradients which are surrogates for ecological and evolutionary processes promoting persistence.     

香溪河流域梯级水库大型底栖动物群落变化及其与环境的关系

分别于2005年10月和2011年10月对香溪河流域3个梯级水库的大型底栖动物群落进行了调查,探讨了大型底栖动物群落变化及其与环境的关系.结果表明:与2005年相比,2011年古洞口一级水库仍以寡毛类占优势,大型底栖动物总密度升高;古洞口二级水库中,摇蚊的优势度降低,前突摇蚊相对丰度由94.5％降低至35.5％,霍甫水丝蚓的相对丰度升至36.0％,总密度增加;香溪河库湾大型底栖动物群落发生很大变化,前突摇蚊取代颤蚓科种类成为绝对优势类群,相对丰度达到89.0％,而总密度降低,三峡水库水位剧烈波动对这一变化有推动作用.各水库大型底栖动物群落与环境因子的典型对应分析(CCA)结果表明,浊度较大的水体,前突摇蚊容易占优势,而颤蚓科的霍甫水丝蚓和正颤蚓则在水柱稳定性较高、底层水温较低的水体中更易占优势.     

Key factors controlling the size, biomass, and sprouting of Japanese alder swamp forest in Kushiro Mire, Hokkaido, Japan

The interrelation among size, biomass, and sprouting of alder trees was studied to extract the most important hydrochemistrical factors controlling the growth of alder forest in Kushiro Mire, northern Japan. The gradient was mostly explained by chemical variables such as pH, ash content, and P₂O₅, which showed strong positive correlation with each other, and secondarily by fluctuation of the water table (WL, i.e., water level range). These variables are more important than other hydrochemical ones, because neutral and turbid flood water replaces acidic mire water and conveys fine sediment with adsorbed phosphorus, which in turn could regulate the pH and amount of phosphorus. Also, the number of sprouts showed negative correlation mainly with tree size and redox potential (Eh), which suggested a flooded environment. Because of this, the size of alder was suppressed by hydrochemical variables; however, alder individuals producing new sprouts were maintained. We conclude that variation in size, biomass, and sprouting of alder was mainly controlled by acidity and phosphorus availability, and was significantly influenced by water fluctuation.     

Tree mortality of five major species on Hokkaido Island, northern Japan

The mortality rates of five major tree species (Abies sachalinensis, Acer mono, Magnolia obovata, Quercus crispula, Tilia japonica) on Hokkaido Island, northern Japan were modeled using logistic regressions based on the long-term observation of 8929 individuals in 65 permanent plots. Individual size, recent growth, one-sided and two-sided interactions with neighbors, climatic and topographic factors were used as independent variables in the logistic regressions, and relevant variables were selected using the stepwise method. For all species analyzed, the final models significantly explained tree mortality rates. The regression analyses indicated that individual size and/or recent growth had effects on tree mortality. A significant effect of one-sided interaction on tree mortality was detected for three species, and a significant effect of two-sided interaction was detected for two species. The interactions with neighbors were not necessarily competitive. For all species analyzed, climatic and topographic factors affected tree mortality. The mortality models obtained can be used for forest dynamics simulations. One ecological question was examined using these models. Species that can grow fast in forest stands with smaller basal areas tended to have high mortality rates in forest stands with larger basal areas. Some ecological characteristics of the analyzed species are described based on the results of the regressions.     

Breeding bird diversity in relation to environmental gradients in China

Geographic variation in species richness has been explained by different theories such as energy, productivity, energy–water balance, habitat heterogeneity, and freezing tolerance. This study determines which of these theories best account for gradients of breeding bird richness in China. In addition, we develop a best-fit model to account for the relationship between breeding bird richness and environment in China. Breeding bird species richness in 207 localities (3271 km² per locality on average) from across China was related to thirteen environmental variables after accounting for sampling area. The Akaike's information criterion (AIC) was used to evaluate model performance. We used Moran's I to determine the magnitude of spatial autocorrelation in model residuals, and used simultaneous autoregressive model to determine coefficients of determination and AIC of explanatory variables after accounting for residual spatial autocorrelation. Of all environmental variables examined, normalized difference vegetation index, a measure of plant productivity, is the best variable to explain the variance in breeding bird richness. We found that species richness of breeding birds at the scale examined is best predicted by a combination of plant productivity, elevation range, seasonal variation in potential evapotranspiration, and mean annual temperature. These variables explained 47.3% of the variance in breeding bird richness after accounting for sampling area; most of the explained variance in richness is attributable to the first two of the four variables.     

The macroinvertebrate communities of two contrasting Norwegian glacial rivers in relation to environmental variables

1. Macroinvertebrate communities in two Norwegian glacial rivers, one in the western fjords (Dalelva) and one in the eastern mountains (Leirungsåi), were investigated during three time periods in 1996 and 1997.
2. Channel stability variables (substratum heterogeneity/Pfankuch index/hydraulic stress) and water temperature accounted for 54% of the total inertia in the principal components analysis (PCA) ordination of environmental variables. The importance of these variables was confirmed by cluster analysis.
3. The two rivers were well separated in the ordinations, with Leirungsåi showing much greater heterogeneity. This is explained by differences in altitudinal range, terrestrial vegetation and the importance and nature of tributary inputs.
4. Channel stability and temperature were also important in determining faunal communities in the two glacial rivers, supporting the main determining variables in the conceptual model of glacial streams ( Milner & Petts, 1994 ). However, clear temporal differences were apparent in the data, the two rivers being more similar during the summer period of high discharge dominated by glacial meltwater. During spring and especially during autumn environmental conditions and the macroinvertebrate fauna differed both within and between rivers.
5. Diamesinae dominated in the upper reaches of both rivers, with Orthocladiinae becoming more common downstream. The dominance of Diamesinae persisted further down Dalelva because of the continued influence of glacial tributaries, whereas in Leirungsåi the influence of non-glacial tributaries led to a change towards a greater proportion of Orthocladiinae. Lakes modified macroinvertebrate communities in both river systems.     

Trichinella nativa and Trichinella T9 in the Hokkaido island, Japan

Trichinella sp. muscle larvae were isolated from the thigh muscle of two red foxes (Vulpes vulpes) captured in Sapporo and Otofuke, Hokkaido, Japan, in 2003. Multiplex PCR designed for genotyping the genus Trichinella revealed that the Sapporo isolate showed a specific pattern to T. britovi complex (T. britovi, Trichinella T8 and Trichinella T9) and the Otofuke isolate showed that to T. nativa. Nucleotide sequences of a part of the mitochondrial cytochrome oxidase subunit I (COI) gene and internal transcribed spacer 2 (ITS2) of the Sapporo isolate showed the highest similarity to those of Trichinella T9, a species detected in the mainland of Japan. This study shows that both T. nativa and Trichinella T9 are circulating in wildlife of the Hokkaido island.     

Vegetation succession on reclaimed coal wastes in Spain: the influence of soil and environmental factors

Question: How is vegetation succession on coal mine wastes under a Mediterranean climate affected by the restoration method used (topsoil addition or not)? How are plant successional processes influenced by local landscape and soil factors? Location: Reclaimed coal mines in the north of Palencia province, northern Spain (42°47′‐42°50′ N, 4°32′‐4°53′ W). Methods: In Jun–Jul 2008, vascular plant species cover was monitored in 31 coal mines. The mines, which had been restored using two restoration methods (topsoil addition or not), comprised a chronosequence of different ages from 1 to 40 yr since restoration started. Soil and environmental factors at each mine were monitored and related to species cover using a combination of ordination methods and Huisman–Olff–Fresco modeling. Results: Plant succession was affected by restoration method . Where topsoil was added, succession was influenced by age since restoration and soil pH. Where no topsoil was added, soil factors seem to arrest succession. Vegetation composition on topsoiled sites showed a gradient with age, from the youngest, with early colonizing species, to oldest, with an increase in woody species. Vegetation on non‐topsoiled sites comprised mainly early‐successional species. Response to age and pH of 37 species found on topsoiled mines is described. Conclusions: Restoration of coal mines under this Mediterranean climate can be relatively fast if topsoil is added, with a native shrub community developing after 15 yr. However, if topsoil is not used, it takes more than 40 yr. For topsoiled mines, the species found in the different successional stages were identified, and their tolerance to soil pH was derived. This information will assist future restoration projects in the area.     

生态脆弱带波动性、人口压力、脆弱度之间的关系

中国北方农牧交错带自然经济系的高波动性是生态脆弱带的显著特征之一。系统的波动性、人口压力、脆弱性三者之间在空间分布和成因上均有密切的联系。坝上后山地区粮食单产的波动性高,并自南向北递增;而以农牧业总产值为代表的土地生产力的波动性与粮食的波动性正好相反,从牧区向农牧区逐渐加大,在张北尚义一带形成高中心。在温饱型的热量营养标准下,人口的绝对和相对超载状况同土地生产力的波动性成正比,线笥相关在０．８３以     

Ordination of deep river invertebrate communities in relation to environmental variables

A deep Main river was examined to determine the effects of selected environmental variables on benthic invertebrate community structure. Thirty-three sites were sampled by divers using artificial substrates. The Bray-Curtis ordination was used to establish community types based upon combinations of current velocity, siltation, and organic detritus. While some invertebrates were tightly clustered within particular communities, most taxa tended to concentrate in one community type but were not excluded from others. The results tended to support the individualistic hypothesis of species distribution.     

Aquatic macrophyte composition in relation to environmental factors of irrigation ponds around Lake Shinji,Shimane, Japan

A comparative study of aquatic vegetation of 149 irrigation ponds in the surrounding area of Lake Shinji, Shimane Prefecture, Japan, was done to document the present status of aquatic flora and water chemistry. In addition, influence of 17 environmental factors on the between-pond variation in aquatic macrophyte composition was assessed by using detrended correspondence analysis (DCA). A total of 38 taxa were recorded, and the most frequent taxon was Trapa spp. (>50%). Number of taxa per pond ranged from 1 to 14 and mean number was 4.1. Floristic composition was primarily related to variation of the factors such as conductivity, Mg, Ca, Na, alkalinity, altitude, pH and depth. In contrast, no significant correlations were found with total P, PO₄-P, transparency, COD, ignition loss of bottom soil, Mn and Fe. Of the 33 significant species associations between 19 species with more than 5% frequency occurrence, 28 were positive and the remaining 5 were negative. All of these negative associations involved Trapa spp., and not only water chemistry but some other factors like competition and bottom soil preference were assumed to influence species associations.Abbreviations (DCA) Detrended Correspondence Analysis     

Growth characteristics of six tree species on Hokkaido Island, northern Japan

Based on growth data obtained from 13 804 individual trees in 110 permanent plots, diameter at breast height (d.b.h.) growth was modeled for six major tree species growing in Hokkaido Island, northern Japan. For each species, d.b.h. growth was regressed on independent variables, indicating the effects of initial size, competition, climate and topography. In developing the d.b.h. growth models, independent variables were selected using the stepwise method. For all species analyzed, the final models accounted for significant amounts of the variation (r² = 5.65–20.99%; P < 5%) in d.b.h. growth. Significant (P < 5%) effects of competition, climate and topography on d.b.h. growth were detected. The model obtained can be used in simulations of forest dynamics. Some ecological questions were examined using the d.b.h. growth models obtained. For hardwoods, the d.b.h. growth rate did not correlate with the published grouping of species in terms of shade-tolerance; however, the plasticity in d.b.h. growth in the presence of competition seemed to be correlated with the shade-tolerance of species. The degree of asymmetry in competition evaluated for each species was not correlated with the availability of underground resources, which was expressed by surrogate variables (mean values of climatic and topographic variables for species). The degree of asymmetry in competition was not different between conifers and hardwoods.     

Phylogenetic relationships between Lymnaeidae in relation to infection with Fasciola sp. in Hokkaido,Japan

ABSTRACT

In this paper, lymnaeid snails collected from 107 localities in Hokkaido, Japan were examined for infection by Fasciola larvae. DNA sequences from the snails were analysed phylogenetically based on their mitochondrial cytochrome c oxidase (COI) gene. Based on shell morphology, the snails were identified as Galba truncatula, Radix auricularia, and Austropeplea ollula and were divided into distinct clades in the COI tree. No Fasciola larvae were detected in any of the collected snails. The 58 haplotypes of Galba truncatula which were found in Hokkaido included five detected previously in snails infected with Fasciola larvae, and constituted a closely related haplogroup (Gt-c1), suggesting that Gt-c1 snails would be susceptible to Fasciola sp. The Gt14 haplotype snails were considered to be Lymnaea schirazensis, an intermediate host of F. hepatica. The COI haplotypes of A. ollula belonged to a single clade, and were considered conspecific, whereas those of R. auricularia constituted three genetically distinct haplogroups, each of which was possibly a distinct species. This study suggests that morphologically-identified lymnaeid snails possibly include additional species. Further study of these snails is required to clarify their susceptibility to Fasciola sp.     

A reappraisal of the mechanisms leading to ombrotrophy in British raised mires

Previous theories of raised mire initiation stress the role of autogenic processes aided by climatic forcing towards increased oceanicity. Recent evidence from stratigraphic surveys in Great Britain and Ireland, however, suggests that raised mire initiation can occur under conditions of falling or fluctuating water tables. Macrofossil assemblages from the lowermost raised peat strata can indicate repeated aeration of the newly formed peat surface. A previously unexplored mechanism for the fen-bog transition is discussed. New research is needed to assess its importance since a sound understanding of the way in which raised mires first formed is important for mire rehabilitation and conservation.     

Distribution of plants in relation to microsites on recent volcanic substrates on Mount Koma,Hokkaido, Japan

On Mount Komas volcanically devastated summit six common plant species colonized 12 microsite types differentially. Flat sites covered 65%, rills and gullies 16% and biotic sites 13% of the study area. Most species preferred sites near rocks and avoided flat and biotic microsites. Polygonum and Salix preferred gully bottoms and edges. Polygonum and Salix seedlings avoided flat areas and Polygonum seedlings strongly colonized gullies. Carex oxyandra seedlings preferred Salix patches. The distributions of seedlings and adult plants were correlated. Biotic microsites supported the largest Carex individuals, rills supported the largest Agrostis individuals and the largest Salix individuals were in gully bottoms and flats.     

Vegetation fluctuation in mediterranean dune ponds in relation to rainfall variation and water extraction

Abstract. The structure of dune ponds hygrophytic vegetation has a spatial organisation in belts around the pond basin, closely related to water level and flooding regime. Doñana National Park has an important representation of temporal dune ponds, which are subjected to rainfall fluctuations and may be suffering the impact of water extraction from the neighbouring tourist resort. Permanent transects in a vegetation complex of five dune ponds have been monitored during a eight year period (1990-1997). This period was characterised by a number of dry years (annual rainfall around 300 mm), located between two wet cycles (800-900 mm). Transects were analysed in 1990 (wet period), 1994 (dry) and 1997 (wet) by hierarchical agglomera-tive clustering. During the dry period hygrophytic species showed regression, with a high mortality of some species like Ulex minor, while the xerophytic species advanced to lower areas. Seedlings of some xerophytic species colonised the dry surface of the pond basin. The lowering of the water table varied in the different ponds, ranging from 312 to 190 cm depending on topography and the distance to the pumping area. The new period of flooding during 1995-96 and 1996-97 cycles provided the opportunity for hygrophytic spe cies to re-establish themselves in their original places. This study suggest that changes in vegetation are caused by the interaction between weather conditions and human disturbance (water extractions). In our example man-made disturbance is more marked during the dry periods while wet periods tend to obscure the effects of water extractions. From a management perspective, long-term monitoring of water table and vegetation structure is revealed as a key procedure to the management of land-water ecotones on pressured areas and threatened habitats.     

Size structure of benthic freshwater fish communities in relation to environmental gradients

The benthic fish communities of 161 Swedish lakes, sampled with multi-mesh gillnets, were examined by direct gradient analyses with ten environmental factors. A geographic gradient, correlated with climatic factors and productivity, was most important for ordination of species optima. By contrast, the distribution of biomass in different size-classes and trophic groups, was influenced more directly by local factors such as water quality (pH) and lake morphometry (area and maximum depth). The communities are not only structured at the species level, but also by size-related allocation of resources, within and between coexisting species. This national survey confirmed patterns observed in previous local field studies, as well as experiments designed for testing mechanisms acting on size-structured populations. However, it highlighted the need for more extensive studies on if and how large-scale environmental variation affects the cues for size-related ontogenetic niche shifts in facultative piscivores, because species such as perch Perca fluviatilis , brown trout Salmo trutta , and Arctic charr Salvelinus alpinus often dominate the benthic fish community.     

Changes in abundances of Alexandrium tamarense resting cysts after the tsunami caused by the Great East Japan Earthquake in Funka Bay,Hokkaido, Japan

The 2011 Great East Japan Earthquake and the subsequent huge tsunami greatly affected both human activity and the coastal marine ecosystem along the Pacific coast of Japan. The tsunami also reached Funka Bay in northern Japan and caused serious damage to the scallop cultures there, and this tsunami was believed to have affected the coastal environments in the bay. Therefore, we investigated the changes in the spatial abundance and distribution of the toxic dinoflagellates Alexandrium tamarense cysts before the tsunami (August 2010) and after the tsunami (May 2011, August 2011, May 2012 and August 2012) in the bay. Further, monthly sampling was conducted after the tsunami to identify seasonal changes of Alexandrium catenella/tamarense cysts and vegetative cells. Significant increases were observed in the populations of A. catenella/tamarense cysts, comparing the abundances before the tsunami (in August 2010; 70 ± 61 cysts g⁻¹ wet sediment) to those just after it (in May 2011; 108 ± 84 cysts g⁻¹ wet sediment), and both A. tamarense bloom (a maximum density was 1.3 × 10³ cells L⁻¹) and PSP (Paralytic Shellfish Poisoning) toxin contamination of scallops (9.4 mouse unit g⁻¹ was recorded) occurred in the bay. Seasonal sampling also revealed that the encystment of A. tamarense and the supply of the cysts to bottom sediments did not occur in the bay from September to April. These results strongly suggested that the mixing of the bottom sediments by the tsunami caused the accumulation of the toxic A. tamarense cysts in the surface of bottom sediment through the process of redeposition in Funka Bay. Moreover, this cyst deposition may have contributed to the toxic bloom formation as a seed population in the spring of 2011.