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1.
This paper and a companion article present illustrated guides to the identification of sub-fossil chironomid larvae (Insecta: Diptera: Chironomidae) preserved in the sediments of low- and mid-elevation lakes in East Africa. They are based on analysis of surface-sediment death assemblages from 61 lakes located in the humid to semi-arid environments of equatorial East Africa (Uganda, Kenya, Tanzania), supplemented with similar surface-sediment samples from 12 lakes in the Horn of Africa (Ethiopia), and sub-recent core samples from six lakes in Kenya and two in Uganda. We analyzed about 11,000 specimens and identified 98.4% of these to species, species group, genus, or tribe level depending on current -taxonomic knowledge of the various genera considered and the taxonomic resolution of preserved diagnostic features. We distinguished 90 different sub-fossil morphotypes, of which 16 are Tanypodinae, 19 are Orthocladiinae, and 55 are Chironominae. Diagnostic characters distinguishing these morphotypes from each other resemble differences at the species level in the better-known Holarctic fauna, hence we consider most of our morphotypes equivalent to morphological species or groups of closely related species. In this paper we focus on the Tanypodinae and Orthocladiinae, with special attention to the high taxon richness among the Pentaneurini. Patterns of cephalic setation were found to facilitate identification of Tanypodinae both at the genus and species level, and contributed to improved taxonomic resolution in sub-fossil East African material. High taxon richness and numerical abundance of the Orthocladiinae in our study lakes indicates that a considerable number of African Orthocladiinae is adapted to warm standing-water environments. 相似文献
2.
Analysis of subfossil remains of larval Chironomidae in 38 surface-sediment samples from between 53 and 189 m depth in Lake Tanganyika (East Africa) yielded 77 different morphotypes, including 7 Tanypodinae, 19 Orthocladiinae, and 51 Chironominae. Character-state differences between these morphotypes resemble differences at the species level in the better-known Holarctic fauna, hence we consider most of our Lake Tanganyika morphotypes equivalent to morphological species. Individual morphotypes were identified to species, genus, or tribe level depending on current alpha-taxonomic knowledge on the larvae of the group concerned, and the taxonomic resolution of preserved diagnostic features. This paper presents taxon diagnoses and an illustrated key to the Tanypodinae and Orthocladiinae in this Lake Tanganyika collection, with the aim to promote consistency of identification in studies using African Chironomidae as biological indicators of natural and anthropogenic environmental change in lacustrine ecosystems. 相似文献
3.
Analysis of subfossil remains of larval Chironomidae in 38 surface-sediment samples from between 53 and 189 meter depth in Lake Tanganyika (East Africa) yielded 77 morphotypes, among which 7 Tanypodinae, 19 Orthocladiinae, and 51 Chironominae. Character-state differences between these morphotypes resemble differences at the species level in the better-known Holarctic fauna, hence we consider most of our Lake Tanganyika morphotypes equivalent to morphological species. Individual morphotypes were identified to species, genus, or tribe level depending on current alpha-taxonomic knowledge on the larvae of the group concerned, and the taxonomic resolution of preserved diagnostic features. This paper presents taxon diagnoses and an illustrated key to the Chironominae (Chironomini and Tanytarsini) in this collection. As the living chironomid fauna of Lake Tanganyika has never been comprehensively studied, we also briefly discuss faunistic aspects, and the ecology of the recovered species and genera in relation to benthic habitat diversity in Lake Tanganyika. 相似文献
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6.
This paper and a companion article present illustrated guides to the identification of sub-fossil chironomid larvae (Insecta: Diptera: Chironomidae) preserved in the sediments of low- and mid-elevation lakes in East Africa. They are based on analysis of surface-sediment death assemblages from 61 lakes located in the humid to semi-arid environments in equatorial East Africa (Uganda, Kenya, Tanzania), supplemented with similar surface-sediment samples from 12 lakes in the Horn of Africa (Ethiopia), and sub-recent core samples from six lakes in Kenya and two in Uganda. We analyzed about 11,000 specimens and identified 98.4% of these to species, species group, genus, or tribe level, depending on current -taxonomic knowledge of the various considered genera and the taxonomic resolution of preserved diagnostic features. We distinguished 90 different sub-fossil morphotypes, of which 16 are Tanypodinae, 19 are Orthocladiinae, and 55 are Chironominae. In this paper we focus on the subfamily Chironominae (tribes Chironomini and Tanytarsini). The diagnostic characters distinguishing these morphotypes from each other resemble differences at the species level in the better-known Holarctic fauna, hence we consider most of our morphotypes equivalent to morphological species or groups of closely related species. Given that core samples yielded only seven morphotypes not also found in the surface-sediment samples, the current inventory of 90 taxa likely represents the large majority of distinct sub-fossil chironomid larval types to be found in East African lakes, excluding the few very large Rift lakes, cold-water lakes above treeline, and special standing-water environments such as fens and bogs. Consistent use of a single set of morphological characters to identify both fossil and living chironomid larvae would ensure exchangeability of information between modem and paleoenvironmental studies on aquatic invertebrate communities in African lakes, and increase the relevance of paleoenvironmental reconstructions to water-quality evaluations aimed at sustainable management of scarce, fluctuating surface-water resources in tropical East Africa. 相似文献
7.
Alexandra Schmäh 《Journal of Paleolimnology》1993,9(2):99-108
In paleolimnology, subfossil head capsules of chironomids play an important role as ecological indicators of lake history. It is important to determine, therefore, whether fossil assemblages are representative of former biocoenoses. There is evidence that headcapsules washed in from other places can make up a significant percentage of the total. As interpretations are usually drawn from the examination of a single core, it is of special interest to know whether a fossil assemblage of a single site properly reflects limnological conditions of the whole lake. This study examined the taxonomic distribution of subfossil chironomids in the surficial sediments of the Bodensee-Untersee, with the aim of assessing the variability in chironomid assemblages. Apparently, most of the head capsules of the profundal fossil assemblages in the Untersee had been washed in from the littoral zone or from the slope. Although the Bodensee-Untersee is a rather large lake, variability is surprisingly low among all samples. Therefore a correct interpretation from a single core may be possible. 相似文献
8.
Jessica D. Tomkins Dermot Antoniades Scott F. Lamoureux Warwick F. Vincent 《Journal of Paleolimnology》2008,40(1):577-582
We describe a method for preserving the upper sediments of fragile sediment cores during transport from field sites and assess
potential effects on subsequent laboratory analyses. This method addresses the need to minimize disturbance to the surfaces
of unfrozen sediment cores used for paleoenvironmental or other high-resolution sedimentological analyses during transport.
A polymer gel (sodium polyacrylate) applied above the sediment surface acts as a barrier to movement while also preserving
surface undulations. The gel seal can preserve even exceptionally fine sedimentary structures (<0.2 mm) in the upper sediments
of lacustrine and fiord sediment cores, but may react with organic material (e.g. algal mats) present on some sediment surfaces.
This reaction creates an adhesive layer at the gel’s base but it can be handled effectively during sampling. The gel seal
minimizes surface deformation and preserves surficial sediments better than traditional seals made of water-absorbent floral
foam, wax or paper towel. In addition to permitting detailed sedimentary and subfossil investigations of the sediment–water
interface, this method shows no detectable effects on measurements of total organic carbon or total nitrogen values in the
sediment. This method is inexpensive, non-hazardous and applicable to many coring systems and sediment types. 相似文献
9.
The seed-like larval cases of hydroptilid caddis flies may be mistaken for plant remains in subfossil studies. However, being correctly identified, they may be important for the interpretation of former freshwater environments. Two such subfossil caddis fly remains from Holocene lake sediments and river deposits are described morphologically and their palaeoecological significance interpreted. 相似文献
10.
Spatial variability of chironomid death assemblages in the surface sediments of a fluctuating tropical lake (Lake Naivasha,Kenya) 总被引：1，自引：0，他引：1
Studies addressing within-lake variability of fossil chironomid assemblages are very few, and all deal with hydrologically
stable temperate lakes where the question of spatial integration mostly relates to the mixing of faunal assemblages associated
with shallow, warm-water habitat and those associated with deeper, cold-water habitat. Here we study within-lake variability
of surface-sediment chironomid assemblages in the fairly large (∼100–170 km2 since 1983) and shallow (Z
max = 5–8 m) fluctuating tropical lake basin of Lake Naivasha, Kenya, and compare the patterns observed with those in two smaller
adjacent basins, one similarly shallow (Lake Oloidien, 5.1–5.7 km2, 5–8 m), the other deep and stratified (Crescent Island
Crater, 1.9 km2, 14–17 m). Chironomid assemblages were analysed in core-top samples and surface sediments along inshore to offshore transects,
and how well individual samples represented the total (basin-wide mean) subfossil assemblage was considered both in terms
of taxon richness and taxon percent composition. Within-lake variability of subfossil chironomid concentrations (with generally
higher absolute values in nearshore samples) could be explained by effects of sediment winnowing and focusing, whereas between-lake
variability reflected their relative susceptibility to wind-driven sediment disturbance or bottom anoxia. In all study lakes,
but most significantly in lakes Naivasha and Oloidien, species distribution in the subfossil chironomid assemblages showed
a strong nearshore to offshore gradient, which in these shallow lakes, reflects the dominant control of substrate and food
quality on species distribution in the living community. Particularly in the larger basins, nearshore samples better represented
the total lake assemblage than offshore samples, because the former always contained a component of mud-dwelling species whereas
the latter often lacked a component of macrophyte-dwelling species. Our results show that although sedimentation dynamics
in the shallow, wind-stressed Lake Naivasha is dominated by frequent resuspension and random sediment redistribution, the
near- to offshore gradient in chironomid habitat remains imprinted on subfossil assemblages. We conclude that also in shallow
fluctuating lakes, given sufficient size, incomplete pre-burial spatial integration of habitat-specific chironomid assemblages
can be exploited for within-lake calibration of environmental gradients. 相似文献
11.
Assemblages of subfossil Chaoboridae mandibles from 80 thermally-stratified shield lakes in southern central Canada were examined
to explore the influence of subfossil Chaoborus on subfossil Chironomidae-based paleolimnological inference models of deepwater oxygen, as volume-weighted hypolimnetic oxygen
(VWHO). Inclusion of subfossil Chaoborus in subfossil Chironomidae-based VWHO models only improved model performance modestly, however it produced substantively better
inferences of hypolimnetic oxygen in anoxic lakes, because Chaoborus had a much stronger positive relationship with low VWHO compared to chironomid taxa indicative of anoxic conditions, such
as Chironomus. A Chaoborus mandible:Chironomidae head capsule ratio (chaob:chir) may be a useful index in paleolimnological studies, as chaob:chir in
a surface sediment training set was significantly related to VWHO, and displayed little co-variation with other limnological
variables such as trophic status (e.g. TP, TN) or lake depth (e.g. Z
max). Chaob:chir values in a stratigraphic analysis tracked chironomid-inferred VWHO, however the use of chaob:chir in regional
‘top–bottom’ paleolimnological studies must be used with caution. 相似文献
12.
陕南化龙山种子植物区系地理成分研究 总被引：7，自引：0，他引：7
化龙山种子植物区系的地理成分复杂,联系广泛,温带成分为主(有428属,占60.62%),热带成分次之(有235属,占33.28%),具有明显的暖温带向亚热带过渡特征。本区集中了丰富的中国特有成分及大量原始的温带属和众多的古老孑遗植物,是我国第三纪植物区系的重要“避难所”.区系地理成分的比较分析表明,化龙山应位于华中植物区系的边缘地带,很可能是东亚植物区系东西两大植物亚区的交汇地。 相似文献
13.
Jesse C. Vermaire Marie-Hélène Greffard Émilie Saulnier-Talbot Irene Gregory-Eaves 《Journal of Paleolimnology》2013,50(4):447-456
Submerged macrophyte abundance strongly influences aquatic ecosystems. Because of a lack of monitoring data, however, the long-term dynamics of such aquatic plants are poorly understood. Increasingly, paleolimnologists use changes in subfossil algae and invertebrates to infer past submerged macrophyte dynamics and assess how human activities have altered this important primary producer component of aquatic ecosystems. We evaluated the sensitivity of subfossil diatom and chironomid assemblages to historically documented changes in macrophyte abundance in Chenango Lake, New York, USA, where macrophyte cover has been monitored since 1978. We also tested the ability of a semi-quantitative diatom-based macrophyte-abundance inference model to detect the pronounced macrophyte decline that was observed between 1993 and 2001. Diatoms responded to the recent loss of macrophytes, with a decline in the relative abundance of macrophyte-associated taxa. Estimates of macrophyte abundance fluctuated according to the diatom-based inference model. Chironomid changes were coherent with the diatom-inferred macrophyte zones. The largest shifts in subfossil assemblages occurred before the start of the monitoring record and coincided with construction of a ~4.3-m-high dam on the lake, which substantially expanded the littoral habitat. Even in heavily managed systems, large reductions in macrophyte abundance can be detected with paleolimnological approaches. 相似文献
14.
ILSE BARTSCH 《Polar research》1988,6(2):181-184
Thalassophthirius auster gen. et spec. nov., collected off Staten Island, South Atlantic Ocean, is described. The species is suspected of being parasitic in habit. This speculation is based on characteristics such as extremely long and robust recumbent dorsal setae, absence of eye pigment and bulbous idiosoma. A short survey of parasitic halacarids is given. 相似文献
15.
Spatial relations,reflecting the complex association between geographical phenomena and environments,are very important in the solution of geographical issues. Different spatial relations can be expressed by indicators which are useful for the analysis of geographical issues. Urbanization,an important geographical issue,is considered in this paper. The spatial relationship indicators concerning urbanization are expressed with a decision table. Thereafter,the spatial relationship indicator rules are extracted based on the application of rough set theory. The extraction process of spatial relationship indicator rules is illustrated with data from the urban and rural areas of Shenzhen and Hong Kong,located in the Pearl River Delta. Land use vector data of 1995 and 2000 are used. The extracted spatial relationship indicator rules of 1995 are used to identify the urban and rural areas in Zhongshan,Zhuhai and Macao. The identification accuracy is approximately 96.3%. Similar procedures are used to extract the spatial relationship indicator rules of 2000 for the urban and rural areas in Zhongshan,Zhuhai and Macao. An identification accuracy of about 83.6% is obtained. 相似文献
16.
Spatial relations, reflecting the complex association between geographical phenomena and environments, are very important in the solution of geographical issues. Different spatial relations can be expressed by indicators which are useful for the analysis of geographical issues. Urbanization, an important geographical issue, is considered in this paper. The spatial relationship indicators concerning urbanization are expressed with a decision table. Thereafter, the spatial relationship indicator rules are extracted based on the application of rough set theory. The extraction process of spatial relationship indicator rules is illustrated with data from the urban and rural areas of Shenzhen and Hong Kong, located in the Pearl River Delta. Land use vector data of 1995 and 2000 are used. The extracted spatial relationship indicator rules of 1995 are used to identify the urban and rural areas in Zhongshan, Zhuhai and Macao. The identification accuracy is approximately 96.3%. Similar procedures are used to extract the spatial relationship indicator rules of 2000 for the urban and rural areas in Zhongshan, Zhuhai and Macao. An identification accuracy of about 83.6% is obtained. 相似文献
17.
蒙古沙拐枣(Calligonum mongolicum)与其相关种的果实形态差异性分析 总被引：2，自引：1，他引：1
在野外考察和实验室工作相结合的基础上,以沙拐枣属(Calligonum L.)主要的分类学依据——果实形态为对象,研究了在分类学上具有争议的蒙古沙拐枣(C. mongolicum) 和其相关种[戈壁沙拐枣(C. gobicum)、甘肃沙拐枣(C. chinense）、小沙拐枣(C. pumilum）、阿拉善沙拐枣（C. alashanicum）、柴达木沙拐枣（C. zaidamense）、塔里木沙拐枣（C. roborowskii）]的分类学关系。其果实形状、果实长度、果实果宽、刺毛长度、两刺间距、两肋间距、瘦果形状、瘦果长度、瘦果宽度、每肋刺行数、果实大小,共11个果实性状指标都在不同居群间表现出不同程度的变异。果实性状在蒙古沙拐枣不同居群之间的差异均达到极显著,在蒙古沙拐枣及其相关种的各居群之间也达到极显著。果实性状聚类分析的结果表明,地理距离比较近的居群可聚为一支。蒙古沙拐枣和其相关种之间的果实性状平行呈现,形成复杂的多形交叉现象。基于以上的研究结果,建议将6个相关种归并于蒙古沙拐枣。 相似文献
18.
We used multivariate statistical techniques to analyse the distributions of surface sediment chironomid assemblages with respect to surface-water temperature, and an additional set of 27 environmental variables, in 30 freshwater lakes of northern Fennoscandia. Our study transect spans boreal coniferous forest to subarctic tundra and includes a steep temperature gradient. Canonical correspondence analysis (CCA) with forward selection and associated Monte Carlo permutation tests revealed that there were statistically significant (P<0.05) relationships between chironomid distributions and two environmental variables, namely lakewater temperature and maximum lake depth. A constrained CCA with temperature as the only predictor variable suggested that the relationship between lakewater temperature and chironomid composition was sufficiently robust for developing a weighted-averaging (WA) based quantitative inference model that will allow palaeotemperature reconstructions using subfossil chironomid remains preserved in lake sediments. 相似文献
19.
西藏阿里西部地区种子植物区系研究 总被引：1，自引：0，他引：1
基于路线调查和样地调查资料,鉴定记录到西藏阿里西部地区共有种子植物319种,隶属于53科159属。其中,裸子植物1科1属2种,被子植物52科158属317种,表明该地区植物种类贫乏。种子植物的区系成分复杂,划分为5个科分布区类型和9个属分布区类型,其中温带成分分布占绝对优势:温带科16科,占总科数的72.73%,温带属99属,占总属数的77.34%,说明本区系具有明显的温带性质。而热带成分仅有几个科属作为代表,表明本区系在发生发展过程中曾经历过与热带相联系的历史渊源。此外,特有性程度极低,没有中国特有科和特有属分布,证实了本区系植物的年轻性及其较短的演化发展历史。 相似文献
20.
山西种子植物区系地理研究 总被引：9，自引：0，他引：9
山西省植物种类多样性相对丰富,共有野生种子植物143科、816属和2576种,科内属种分布极不平衡,有趋向大科分布特点;山西种子植物区系以温带分布区类型占绝对优势,共有410属、1540种,分别占总种子植物总属数的50.2%,总种数59.8%;该区系具有一定数量的古老成分;地理成分混杂且具有明显的过渡性,在中国植物属的15个分布类型和31个变型中,该区系就占15个分布类型和16个变型。 相似文献