Identifying climatic niche shifts using coarse‐grained occurrence data: a test with non‐native freshwater fish

Aim We tested whether coarse‐grained occurrence data can be used to detect climatic niche shifts between native and non‐native ranges for a set of widely introduced freshwater fishes. Location World‐wide. Methods We used a global database of freshwater fish occurrences at the river basin scale to identify native and non‐native ranges for 18 of the most widely introduced fish species. We also examined climatic conditions within each river basin using fine‐grained climate data. We combined this information to test whether climatic niche shifts have occurred between native and non‐native ranges. We defined climatic niche shifts as instances where the ranges of a climatic variable within native and non‐native basins exhibit zero overlap. Results We detected at least one climatic niche shift for each of the 18 studied species. However, we did not detect common patterns in the thermal preference or biogeographic origin of the non‐native fish, hence suggesting a species‐specific response. Main conclusions Coarse‐grained occurrence data can be used to detect climatic niche shifts. They also enable the identification of the species experiencing niche shifts, although the mechanisms responsible for these shifts (e.g. local adaptation, dispersal limitation or physiological constraints) have yet to be determined. Furthermore, the coarse‐grained approach, which highlights regions where climatic niche shifts have occurred, can be used to select specific river basins for more detailed, fine‐grained studies.     

淡水湿地种子库的小尺度空间格局

以长江中下游淡水湿地湖里沼泽为对象,研究了种子库在小尺度空间范围的水平分布格局。在沼泽中选择地表植被分布比较均一的16m×4m大小的方形区域,按1m间隔获取64个内径7·8cm、深5cm的圆柱状土样,通过幼苗萌发法鉴定每个土样的种子库组成。采用2个格局指数(离散系数和Lloyd平均拥挤指数)以及Moran空间自相关系数分析了种子库中优势种的空间分布格局。结果显示种子库由17个物种组成,多年生的锐棱荸荠(Eleocharisacutangula)和龙师草(E·tetraqueter)是种子库中密度最大的物种。两个格局指数显示7个分布频率大于10%的物种的种子全部为聚集分布。MoransI统计分析显示其中只有3个物种为显著的正的空间自相关,表明这3个物种的种子斑块大小超过了目前的两个取样单位之间的距离(1m),而其它4个物种的种子斑块则小于这个尺度。     

Floristic studies on freshwater algae of Lake Gondwana,Northern Victoria Land (Antarctica)

Benthic algal mats and phytoplankton of Lake Gondwana (Northern Victoria Land, Antarctica) were investigated. Biomass, chlorophyll content and floristic analyses were carried out on algal mats. The mats are composed of two layers different in colour, floristic composition and chlorophyll content. The algal flora of the mats amount to 34 taxa (19 Cyanophyta, 7 Bacillariophyta, 8 Chlorophyta). The phytoplankton community is species-poor (only 5 taxa). Crytophyta account for about 98% of total algal density.     

Trophic transfer and trophic modification of fatty acids in high Arctic lakes

1. A comparative study of fatty acid (FA) profiles in particulate matter (seston) and the key grazer Daphnia was performed in six high Arctic ponds (79°N, Svalbard). The ponds were all small and shallow, but followed a strong gradient with respect to nutrient content and optical properties. 2. A distinct locality‐specific pattern was detected by principal component analysis of FA profiles, where samples from each locality clustered both with regard to seston and Daphnia. Linear discriminant analysis using nine sestonic fatty acids as discriminant functions gave on average a correct prediction of the Daphnia lake membership in 47% of cases, with very high predictability in some lakes but poor predictability in others. 3. No significant correlation was detected between FA and nutrient concentration or levels of dissolved organic carbon. The major determinant of FA profiles as judged from a redundancy analysis was the taxonomic composition of phytoplankton communities, notably the biomass of Chlorophyceae. 4. The FA profiles of Daphnia were for some FAs strongly enriched relative to the seston, while diluted for others. Among the polyunsaturated fatty acids (PUFAs), a pronounced magnification of eicosapentaenoic acid (EPA, 20 : 5 n‐3), and to some extent 18 : 3 n‐3 and 20 : 4 n‐6 was found, while docosahexaenoic acid (DHA, 22 : 6 n‐3) contributed in general less to FAs in Daphnia than in seston and was hardly detectable in Daphnia from most localities. 5. The overall content of PUFAs in Daphnia was consistently high, close to 40% of total FA in all investigated localities, despite major differences in seston PUFA content. Daphnia thus acts as a regulator with regard to overall PUFAs, reflecting its physiological constraints and relatively fixed demands for PUFAs in general. The distinct locality‐specific profiles in Daphnia strongly suggest a kind of FA‐fingerprint, but our data do not allow strict statements on the use of specific FAs as trophic markers.     

A multi‐basin approach determines variability in host fish suitability for unionids in tributaries of the Laurentian Great Lakes

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Phylogenetic ecology of widespread uncultured clades of the Kingdom Euryarchaeota

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Utilization of oligo‐ and polysaccharides at microgram‐per‐litre levels in freshwater by Flavobacterium johnsoniae

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