Within-lake patterns in depth penetration of emergent vegetation

SUMMARY. 1. Within-lake relations of wave exposure (WE), and substratum softness (cone penetration depth; CPD) and organic content (loss on ignition; LOI), to water depth penetration of the emergent vegetation (DPE) was investigated in seven eutrophic lakes in southern Sweden, ranging in area from 1 to 46km².
2. There was a positive relationship between WE and DPE within lakes. This relationship, however, only occurred for sites with relatively soft substrata, for which CPD and LOI were negatively related to both WE and DPE.
3. Analysis of aerial photographs revealed that expansion of the emergent vegetation towards open water, or recession from open water, was not related to wave exposure or water depth, except in one lake where expansion mainly occurred at high exposures.
4. For relatively static vegetation on soft substrata, regressions with CPD°.⁵ explained 62–88% of the within-lake variation of DPE. These regressions did not differ among lakes. Expanding and recessing vegetation were significantly dislocated towards shallower and deeper water, respectively, than predicted from the regression models for static vegetation.
5. Phragmites australis dominated at the lakeward edge of the emergent vegetation, followed in frequency by Typha angustifolia . More broad-leaved species were generally restricted to shallow water and very soft substrata.
6. The results suggest that changes in the distribution of emergent vegetation in moderately wave exposed eutrophic lakes can be predicted largely from substratum character and water depth.     

Fish communities in the eastern,seasonal-floodplain of the Sudd,Southern Sudan

Annual flooding of the permanent Sudd swamps innundates large areas of Oryza longistaminata grasslands. Fish migration into a southeast section of the seasonal floodplain was led by Clarias gariepinus, Polypterus senegalus and several small species which were intent on spawning. Channa obscura and juveniles of Oreochromis niloticus were prominent among later entrants. From a total of 23 species caught in seasonal habitats, 7 contributed over 97% of total estimated numerical and biomass densities. The latter ranged from 435–580 kg ha^–1. In the 1982–83 flood-season entry to the floodplain was essentially restricted to species tolerant of oxygen-deficient waters and thereby able to penetrate the papyrus and Typha swamps of the permanent wetland. Migrants became stranded in temporary pools and subject to heavy cropping by birds.     

Lakes of south-western Uganda

The vegetation of Lake Bunyonyi, a high altitude lake in Kigezi, S.W. Uganda, is described. The lake had two distinct plant communities. In the shallow sheltered bays and inflows extensive floating swamps of Cyperus papyrus L. and Cladium janiaicen. se Cranz. existed. On the steep, exposed shores there was only a narrow band of vegetation, dominated by firmly rooted Phragmites australis (Cav.) Steud., usually with papyrus behind. Floating-leaved Potamogeton and Nymphaea sometimes occurred outside the emergent species, and submerged species, including Ceratophyllum demersum L. grew down to 8 m. The pattern of vegetation, and the contribution of floating islands to the distribution of plants in the lake is discussed. Susceptibility to fragmentation, and distribution by wind are thought to be major factors governing the pattern. Oxygen proflies measured at the fringe of swamps indicated that the swamps did not cause appreciable deoxygenation of the water.     

The vegetation of Nyumba ya Mungu reservoir, Tanzania

A study was made of the aquatic macrophyte ecology of Nyumba ya Mungu; a nine year old man-made lake in northern Tanzania. The vegetation is described with the aid of percentage cover histograms and standing crop estimates. Concurrent physical, chemical and biological studies helped in ecological interpretations. Distinct vegetation communities were found in the deltaic swamps of the two major inflow rivers and it is concluded that this was due to water chemical differences. The water of the more alkaline River Kikuletwa appeared to influence the greater part of the perimeter swamps as the species composition largely coincided with that reported for higher pH, higher conductivity African lakes. Typha domingensis swamp was predominant and extensive, whilst Cyperus alopecuroides and Paspalidium geminatum were also common emergent species. Floating and submerged plants were relatively unimportant in the lake with respect to cover. The major zonations of species appeared to be a function of water depth, while chemistry seemed the main factor controlling vegetation pattern. In conclusion the significance of interrelationships between the macrophytes and other aquatic organisms is discussed.     

Fish species and trophic diversity of haplochromine cichlids in the Kyoga satellite lakes (Uganda)

Prior to the 1980s, lakes Kyoga and Victoria previously supported an exceptionally diverse haplochromine fish fauna comprising at least 11 trophic groups. The species and trophic diversity in these lakes decreased when the introduced Nile perch depleted haplochromine stocks. From December 1996 to October 1998, we studied species and trophic diversity of haplochromine fishes in six satellite lakes without Nile perch in the Kyoga basin and compared them with the Kyoga main lake against historical data from Lake Victoria where Nile perch were introduced. Forty‐one species were found in the study area, of which, the Kyoga satellite lakes contributed 37 species in comparison to only 14 from the Kyoga main lake. Analysis of trophic diversity based on 24 species that contained food material revealed seven haplochromine trophic groups (insectivores, peadophages, piscivores, algal eaters, higher plant eaters, molluscivores and detritivores) in the Kyoga satellite lakes in comparison to two trophic groups (insectivores and molluscivores) in the Kyoga main lake. Many of the species and trophic groups of haplochromines depleted by the introduced Nile perch in lakes Kyoga and Victoria still survive in the Kyoga satellite lakes. This is attributed to the absence of Nile perch in those lakes. Nile perch has been prevented from spreading into the satellite lakes by swamp vegetation that separate them from the main lakes. If these swamps prevent Nile perch from spreading into the lakes, it is possible to conserve fish species, especially haplochromines, which are threatened by introduction of Nile perch in the main lakes.     

Permanent swamp vegetation of the Upper Nile

This paper describes vegetation in the nothern Sudd area of the Sudan. A visit by boat was made in April 1978 along the White Nile from Malakal to Lake No; to the inflow regions of the Bahr el Jebel, the Bahr el Zeraf and to the Bahr el Ghazal. Only the vegetation along the fringe of the rivers was observed as plants were tall and dense and it was not possible to penetrate into the inner swamps.The outer edge of the vegetation was fringed by extensive mats of free-floating Eichhornia crassipes which was easily dislodged and formed floating islands to be carried downstream. The main rivers, excluding the Bahr el Ghazal, were too deep and turbid to support beds of submerged species but plants such as Ceratophyllum demersum could be found amongst floating plants. Vossia cuspidata usually produced a broad zone to the landward of Eichhornia. It dominated the shallow water with a floating raft of stems growing out from the shore over the water surface. Massive stands of Cyperus papyrus and/or Phragmites karka, over 5 metres tall, dominated the vegetation behind and sometimes excluded the Vossia zone. The papyrus could form dense, floating rafts of rhizomes at the water's edge, but Phragmites always remained firmly rooted to the bottom. Floating papyrus and Vossia would become detached from the main beds and drifted downstream with Eichhornia.Creepers were common amongst papyrus but less common amongst Phragmites where the vegetation was generally more dense. Large stands of Typa domingensis were observed behind the fringe vegetation.The vegetation of the Bahr el Ghazal, in marked contrast to the rest, was stunted, and reasons for this are suggested. Species diversity was greater and the less turbid waters allowed considerable development of floating-leaved and submerged species.Estimates of fresh weights and heights of dominant vegetation types were attained but methods were very laborious and alternative ways have been suggested. The fresh weight of Eichhornia from a one metre square quadrat in the White Nile was around 70 kg. The shoots of Phragmites weighed 18.5 kg and Cyperus papyrus, 11.0 kg m^–2.     

Phylogeography and speciation in the <Emphasis Type="Italic">Pseudocrenilabrus philander</Emphasis> species complex in Zambian Rivers

Haplochromine cichlids form the most species-rich lineage of cichlid fishes that both colonized almost all river systems in Africa and radiated to species flocks in several East African lakes. The enormous diversity of lakes is contrasted by a relatively poor albeit biogeographically clearly structured species diversity in rivers. The present study analyzed the genetic structure and phylogeographic history of species and populations of the genus Pseudocrenilabrus in Zambian rivers that span two major African drainage systems, the Congo- and the Zambezi-system. The mtDNA phylogeny identifies four major lineages, three of which occur in the Congo-system and one in the Zambezi system. Two of the Congo-clades (Lake Mweru and Lunzua River) comprise distinct albeit yet undescribed species, while the fish of the third Congo-drainage clade (Chambeshi River and Bangweulu swamps), together with the fish of the Zambezi clade (Zambezi and Kafue River) are assigned to Pseudocrenilabrus philander. Concerning the intraspecific genetic diversity observed in the sampled rivers, most populations are highly uniform in comparison to lacustrine haplochromines, suggesting severe founder effects and/or bottlenecking during their history. Two bursts of diversification are reflected in the structure of the linearized tree. The first locates at about 3.9% mean sequence divergence and points to an almost simultaneous colonization of the sampled river systems. Subsequent regional diversification (with about 1% mean sequence divergence) occurred contemporaneously within the Kafue River and the Zambezi River. The clear-cut genetic biogeographic structure points to the dominance of geographic speciation in this lineage of riverine cichlid fishes, contrasting the importance of in situ diversification observed in lake cichlids.     

Coastal vegetation on the Western, Southern, and Eastern coasts of South Korea

We used the Braun-Blanquet method to study the vegetation of coastal wetlands in South Korea. Three habitat types were found, i.e., salt marshes, salt swamps, and sand dunes. These plant communities were classified as: 1) two groups (five associations each) in the salt marshes that comprised either annual herbaceous halophytes (ClassThero-Salicornietea), or biennial/perennial herbaceous species (ClassAsteretea tripolii); 2) one group in the salt swamps consisting of five hydrophilous halo-tolerant associations (ClassPhragmitetea); and 3) three groups in the sand dunes, including one association of annual herbaceous halophytes (ClassSalsoletea komarovii), seven associations of herbaceous perennial halophytes (ClassGlehnietea littoralis), and one association of shrub perennial halophytes (ClassVrticetea rotundifoliae). These three habitat types accounted for the majority of the six main classifications of coastal vegetation distributed in South Korea.     

Some observations on the geomorphological impact of hippopotamus (Hippopotamus amphibius L.) in the Okavango Delta, Botswana

The Okavango Delta is a large wetland system situated in northern Botswana. The hippopotamus forms an integral part of this dynamic ecosystem, as it exerts a catalytic effect on geomorphological change. In the distal reaches of the wetland, regular movement of hippos to feeding grounds results in the development of incised channels, which are kept clear of vegetation and act as nodes for swamp expansion. Hippos maintain pathways in backswamp areas, which lead to the development of new channel systems during channel avulsion. They create breaches in the vegetation levees which flank channels in the permanent swamps, causing diversion of water and sediment to backswamp areas. Their paths often lead to lakes in the permanent swamps. During channel avulsion, diversion of a channel into lakes may occur via these paths, which can result in lake closure.     

Papyrus swamps and the respiratory ecology of Barbus neumayeri

Synopsis In seasonally flooding fresh waters, dissolved oxygen and fluctating water levels combine to create strong seasonal changes in habitat availability and dispersal pathways for fishes. In this study we demonstrate how respiratory mode can affect the use of and dispersal through hypoxic papyrus swamps for a small cyprinid fish, Barbus neumayeri, a species which uses aquatic surface respiration (ASR) in response to severe hypoxia. Monthly records of the distribution and relative abundance of B. neumayeri across 28 stations in a papyrus swamp in Uganda were used to examine seasonal patterns of habitat use and movement. The distribution of B. neumayeri was very restricted during the drier months. Most fish were captured in open pools and channels with large areas of open water surface and higher oxygen. Movement of B. neumayeri was limited to short periods during the wet season when peak water levels produced high levels of oxygen and pathways for movement. Three lines of evidence suggest that these patterns relate to its respiratory mode. These include: the positive :relationship between dissolved oxygen and the number of stations used per month, the positive relationship between fish density at dry season stations and dissolved oxygen, and the absence of fish from stations with. little open water surface area during the dry season. Significant differences in the gill morphology between B. neumayeri from the papyrus swamp and those from the main river suggest that papyrus swamps may contribute to the diversification of B. neumayeri by limiting movement and demanding specialization for extremely hypoxic waters.     

The food and feeding habits of five freshwater and brackish-water fish species in Nigeria

The food and feeding habits of five economically important fresh-and brackish-water fishes, Channa obscura, Chrysichthys nigrodigitatus, Heterotis niloticus, Synodontis nigrita and Trachinotus maxillosus, were investigated. A number of techniques were used to carry out gut content analysis, including the Hynes 'point' system based on volume estimations expressed as relative percentages. Juveniles of C. nigrodigitatus were omnivorous, consuming 32% gastropods, 30% nematodes, 14% diatoms and 8% crustaceans, while adults were planktotrophic, consuming 23% diatoms, 33% Chlorophyceae and 22% crustaceans. Synodontis nigrita juveniles fed almost exclusively (91%) on nematodes, while adults were predominantly planktotrophic, their diet comprising 50% diatoms and 50% crustaceans. Trachinotus maxillosus was exclusively benthotrophic, consuming 99.5% gastropods and 0.46% nematodes. Heterotis niloticus was planktotrophic at the adult stage and consumed 72% crustaceans, 12% gastropods, 3% fish and about 90% planktotrophic at the juvenile phase. Chrysichthys obscura was purely benthotrophic at the juvenile stage, feeding 100% on nematodes, but fed mainly (89%) on fish at the adult stage.     

PHENOTYPIC PLASTICITY AND HETEROCHRONY IN CICHLASOMA MANAGUENSE (PISCES,CICHLIDAE) AND THEIR IMPLICATIONS FOR SPECIATION IN CICHLID FISHES

Cichlid fishes in African rift lakes have undergone rapid speciation, resulting in “species flocks” with more than 300 endemic species in some of the lakes. Most researchers assume that there is little phenotypic variation in cichlid fishes. I report here extensive phenotypic plasticity in a Neotropical cichlid species. I examined the influence of diet on trophic morphology during ontogeny in Cichlasoma managuense. Two groups of full siblings were fed two different diets for eight months after the onset of feeding; thereafter both groups were fed a common diet. Phenotypes that differed significantly at 8.5 months converged almost completely at 16.5 months. If feeding on two different diets is continued after 8.5 months, the phenotypes remain distinct. Differences in diet and possibly in feeding mode are believed to have caused these phenotypic changes. Phenotypic plasticity is described in terms of a qualitative model of heterochrony in which phenotypic change in morphology is explained as retardation of the normal developmental rate. If phenotypic expression of morphology is equally plastic in African cichlid species as it may be in the American cichlids, as exemplified by C. managuense, then taxonomic, ecological, and evolutionary analyses of “species flocks” may be in need of revision. However, Old World cichlids may be less phenotypically plastic than New World cichlids, and this may contribute to the observed differences in speciation rate and degree of endemism.     

Anthropogenic ecological change and impacts on mosquito breeding and control strategies in salt-marshes, Northern Territory, Australia

Darwin, in the tropical north of Australia, is subject to high numbers of mosquitoes and several mosquito-borne diseases. Many of Darwin's residential areas were built in close proximity to tidally influenced swamps, where long-term storm-water run-off from nearby residences into these swamps has led to anthropogenic induced ecological change. When natural wet-dry cycles were disrupted, bare mud-flats and mangroves were transformed into perennial fresh to brackish-water reed swamps. Reed swamps provided year-round breeding habitat for many mosquito species, such that mosquito abundance was less predictable and seasonally dependent, but constant and often occurring in plague proportions. Drainage channels were constructed throughout the wetlands to reduce pooled water during dry-season months. This study assesses the impact of drainage interventions on vegetation and mosquito ecology in three salt-marshes in the Darwin area. Findings revealed a universal decline in dry-season mosquito abundance in each wetland system. However, some mosquito species increased in abundance during wet-season months. Due to the high expense and potentially detrimental environmental impacts of ecosystem and non-target species disturbance, large-scale modifications such as these are sparingly undertaken. However, our results indicate that some large scale environmental modification can assist the process of wetland restoration, as appears to be the case for these salt marsh systems. Drainage in all three systems has been restored to closer to their original salt-marsh ecosystems, while reducing mosquito abundances, thereby potentially lowering the risk of vector-borne disease transmission and mosquito pest biting problems.     

Aquaculture, non-native salmonid invasions and associated declines of native fishes in Northern Patagonian lakes

1. Even though intensive aquaculture production of salmonids in lakes occurs in many locations around the world published studies on the survival and reproductive success of escaped cultured salmonids in freshwater ecosystems are not common. A recent expansion of aquaculture in Chile has led it to become the world's second largest producer of cultured salmonids.
2. We document the recent history of escaped and self-sustaining salmonid populations over a wide spatial scale and a long temporal scale in Chilean Patagonian lakes. Our hypotheses are that salmonid density in lakes will be higher where there is intensive aquaculture, due to greater numbers of potential escapees. Secondly, if non-native salmonids have adverse impacts on native fishes, increases in the abundance of non-native species should be associated with decreases in relative abundance of native species. Finally, if the first two hypotheses are correct we anticipate that diets of salmonids may show evidence of predation on native fishes, diet overlap with native species, and evidence of the influence of feed from aquaculture operations in the diets of salmonids and native fishes.
3. We sampled six lakes with gill nets from 1992 to 2001. Our results show that the relative abundance of free-living salmonids is closely related to the level of fish farming production. Salmonids are the top predators and in lakes with fish farming the main prey item is native fishes. The relative abundance of native fishes has decreased, most likely due to predation by salmonids.
4. Our study contributes to the understanding of the effects of non-native salmonids in oligotrophic lakes, and it provides a starting point to judge the establishment of new fish farming sites in lakes around the world.     

The impact of the introduction of Nile perch, Lates niloticus (L.) on the fisheries of Lake Victoria

The piscivorous Nile perch was introduced into Lake Victoria some 30 years ago, since when it has completely transformed the fishing industry and the species composition of the fish fauna of the lake. The original multispecies fishery, based mostly on cichlids (haplochromines, tilapias), cyprinids ( Barbus, Labeo, Rastrineobola ) and siluroids ( Bagrus, Clarias, Synodontis, Schilbe ), has changed dramatically to one based on three species: the introduced Nile perch, the cyprinids, Rastrineobola argenrea (Pellegrin), and the introduced Nile tilapia, Oreochromis niloticus (Linnaeus).
Within 25 years of its introduction the Nile perch became ubiquitous and now occurs in virtually every habitat with the exception of swamps and affluent rivers. It has preyed on all other species with profound effects, especially on the stocks of haplochromines. These originally comprised 80% of the total fish biomass in Lake Victoria, but have now decreased to less than 1% offish catches from the Kenyan waters of the lake. The fishermen of Lake Victoria have adjusted to this ecological crisis by using large-meshed nets to catch Nile perch, which has become the most important commercial species. For the first time in the history of Lake Victoria, fish fillets are now being exported to several overseas countries: the fillets are all from Nile perch.     

Development of macrophytic vegetation in the Agmon Wetland of Israel by spontaneous colonization and reintroduction

The draining of the Lake Hula and swamps, northern Israel, during the late 1950s resulted in the loss of a very diverse and rare ecosystem. Oxidation of the peat soil resulted in ground surface subsidence, while heavy autumn winds have eroded the dry peat. Moreover, agriculture on the peat soils is restricted, because of a nitrate surplus. Predictions that the sinking would continue and that more areas would go out of agricultural production led authorities to re-flood a portion of the Hula Valley in 1994. The aim of the present study was to monitor the spontaneous establishment of vegetation in the re-flooded area, the Agmon wetlands, and to reestablish some of the major plant species lost from the valley when Lake Hula was drained. Within the first two years, 74 plant species colonized the wetland spontaneously. Five out of 11 species designated for reintroduction were successfully established. Cyperus papyrus and Cynodon dactylon demonstrated sustainable potential for lake-shore stabilization. Cyperus papyrus was reintroduced from seedlings and rapidly became the dominant riparian species, while Cynodon dactylon established spontaneously. Re-introduced Nymphaea alba clones were established only in enclosures protected from grazing by the semi-aquatic mammal Myocastor coypu. Nuphar lutea and Iris pseudacorus showed better resistance to grazing. These results demonstrate a high potential for successful re-establishment of much of the original Hula swamp macrophytic vegetation by either spontaneous colonization by extant species from the surrounding areas or by introduction of locally extinct species. As such, there is a good chance that the associated faunal components of the former Lake Hula and swamps that have returned to the region since the Hula rehabilitation project commenced will continue to flourish.     

Recent papyrus swamp habitat loss and conservation implications in western Kenya

Papyrus Cyperus papyrus swamps are characteristic of many wetlands of tropical Africa. Like most wetland habitats worldwide, they are under human pressure due to harvesting and reclamation for agriculture. Changes in papyrus cover were assessed using aerial photographs at three Important Bird Areas (IBAs) in the Kenyan sector of Lake Victoria. Papyrus area losses of 50% (Dunga), 47% (Koguta) and 34% (Kusa) occurred between 1969 and 2000. The habitat loss and degradation at the sites appeared purposeful, driven by demand for agricultural land and other papyrus products. Cleared papyrus and cultivated areas around all sites increased over the same period. If papyrus habitat loss continues at current rates, papyrus swamps at Dunga and Koguta will disappear by 2020, and Kusa will be reduced to only 19% of its 1969 area. Human population growth around the sites, with concomitant increase in land use activities and papyrus harvesting are the major factors that account for papyrus area reductions. Loss of total habitat is accompanied by deterioration in habitat quality within remaining areas. Papyrus physical structure (height and density) inversely correlate to human disturbances that include footpaths, cutting, burning, grazing and farming. The continued papyrus habitat loss and degradation represents a significant threat to biodiversity conservation particularly for papyrus-specialist birds and other papyrus-reliant species in western Kenya. The observed pattern of papyrus extents and land use changes at all sites provide the site-scale information necessary for papyrus conservation planning. In particular, conservation action is needed most urgently at Dunga and Koguta as they face severe land use pressures.     

Habitat associations of papyrus specialist birds at three papyrus swamps in western Kenya

Birds of papyrus swamps have not been adequately studied in Kenya, and little is known about their ecology and habitat associations. Using fixed‐radius point counts and playbacks, we counted papyrus specialist birds and evaluated papyrus physical characteristics and levels of disturbance at a series of sample stations at three papyrus swamps of Dunga, Koguta and Kusa in the Kenyan sector of Lake Victoria. Papyrus height and density were significantly correlated across all sites but negatively correlated with levels of disturbance. Standardized point counts of swamp birds showed the papyrus gonolek Laniarius mufumbiri and Carruthers's cisticola Cisticola carruthersi to be the most abundant papyrus specialists across sites. Only Carruthers's cisticola numbers differed between sites. Overall, papyrus cover was the best predictor of the presence and abundance of all papyrus specialist birds, and significantly predicted the numbers of papyrus gonolek and white‐winged warbler Bradypterus carpalis.     

Convective gas flow development and the maximum depths achieved by helophyte vegetation in lakes

Background and Aims

Convective gas flow in helophytes (emergent aquatic plants) is thought to be an important adaptation for the ability to colonize deep water. In this study, the maximum depths achieved by seven helophytes were compared in 17 lakes differing in nutrient enrichment, light attenuation, shoreline exposure and sediment characteristics to establish the importance of convective flow for their ability to form the deepest helophyte vegetation in different environments.

Methods

Convective gas flow development was compared amongst the seven species, and species were allocated to ‘flow absent’, ‘low flow’ and ‘high flow’ categories. Regression tree analysis and quantile regression analysis were used to determine the roles of flow category, lake water quality, light attenuation and shoreline exposure on maximum helophyte depths.

Key Results

Two ‘flow absent’ species were restricted to very shallow water in all lakes and their depths were not affected by any environmental parameters. Three ‘low flow’ and two ‘high flow’ species had wide depth ranges, but ‘high flow’ species formed the deepest vegetation far more frequently than ‘low flow’ species. The ‘low flow’ species formed the deepest vegetation most commonly in oligotrophic lakes where oxygen demands in sediments were low, especially on exposed shorelines. The ‘high flow’ species were almost always those forming the deepest vegetation in eutrophic lakes, with Eleocharis sphacelata predominant when light attenuation was low, and Typha orientalis when light attenuation was high. Depths achieved by all five species with convective flow were limited by shoreline exposure, but T. orientalis was the least exposure-sensitive species.

Conclusions

Development of convective flow appears to be essential for dominance of helophyte species in >0·5 m depth, especially under eutrophic conditions. Exposure, sediment characteristics and light attenuation frequently constrain them to a shallower depth than their flow capacity permits.Key words: Aeration, convective flow, exposure, helophytes, lakes, lakeshore vegetation, light attenuation, redox, regression tree, sediment motion, trophic state, waves     

Fish community comparisons along environmental gradients in lakes of France and north-east USA

Aim  To assess whether eight traits of fish communities (species richness, three reproductive traits and four trophic traits) respond similarly to environmental gradients, and consequently display convergence between the lakes of France and north-east USA (NEUSA).
Location  75 French and 168 north-east USA lakes.
Methods  The data encompass fish surveys, the assignment of species into reproductive and trophic guilds, and environmental variables characterizing the lakes and their catchments. The analytical procedure was adapted from the recommendations of Schluter (1986 ) [ Ecology , 67 , 1073–1085].
Results  The comparison of the regional pools of lacustrine fishes indicated that NEUSA was about twice as speciose as France, mostly due to higher species turnover across lakes, although NEUSA lakes were consistently about 20% more speciose than French lakes for a given surface area. Warmer environments were consistently inhabited by a higher proportion of phytophilous and guarder species than were colder lakes. Hence there was convergence in community reproductive traits. Conversely, there was no evidence of convergence in the trophic structure of lacustrine fish communities between regions.
Main conclusions  The influence of temperature on the availability and quality of spawning substrates appears to be a major constraint on present-day lacustrine fish communities. In parallel, phylogenetic constraints, past events such as the diversification of the North American fish fauna, and selective extinctions during Pleistocene glaciations and subsequent recolonizations contribute to explaining the dissimilarities between the communities of the two regions and differences in their relationship to the environment.