Patterns of fish species richness in China's lakes

Aim To document the patterns of fish species richness and their possible causes in China's lakes at regional and national scales. Location Lakes across China. Methods We compiled data of fish species richness, limnological characteristics and climatic variables for 109 lakes across five regions of China: East region, Northeast region, Southwest region, North‐Northwest region, and the Tibetan Plateau. Correlation analyses, regression models and a general linear model were used to explore the patterns of fish species richness. Results At the national scale, lake altitude, energy availability (potential evapotranspiration, PET) and lake area explained 79.6% of the total variation of the lake fish species richness. The determinants of the fish richness pattern varied among physiographic regions. Lake area was the strongest predictor of fish species richness in the East and Southwest lakes, accounting for 22.2% and 82.9% of the variation, respectively. Annual PET explained 68.7% of the variation of fish richness in the Northeast lakes. Maximum depth, mineralization degree, and lake area explained 45.5% of the fish variation in the lakes of the North‐Northwest region. On the Tibetan Plateau, lake altitude was the first predictor variable, interpreting 32.2% of the variation. Main conclusions Lake altitude was the most important factor explaining the variation of fish species richness across China's lakes, and accounted for 74.5% of the variation. This may stem in part from the fact that the lakes investigated in our study span the largest altitudinal range anywhere in the world. The effects of the lake altitude on fish species richness can be separated into direct and indirect aspects due to its collinearity with PET. We also found that the fish diversity and its determinants were scale‐dependent. Fish species richness was probably energy‐determined in the cold region, while it was best predicted by the lake area in the relatively geologically old region. The independent variables we used only explained a small fraction of the variations in the lake fish species richness in East China and the Tibetan Plateau, which may be due to the effects of human activity and historical events, respectively.     

Correlations between type‐indicator fish species and lake productivity in German lowland lakes

Morphotypes for 67 lakes in the German lowlands were derived, based on maximum depth and mixis type. A threshold of 11 m maximum depth was identified to be the best level to discriminate shallow from deep lake morphotypes. The fish communities in these two morphotypes were significantly different. Indicator species analyses based on fish biomasses found vendace Coregonus albula in deep lakes and ruffe Gymnocephalus cernuus , bream Abramis brama , white bream Abramis bjoerkna , roach Rutilus rutilus , pikeperch Sander lucioperca and small perch Perca fluviatilis in shallow lakes to be the most representative species of their communities. Lake productivity was closely related to biomass and in part abundance of the type‐indicator species, with vendace declining with increasing chlorophyll a concentration in the deep lakes, whereas biomass of pikeperch, bream, white bream and ruffe increased and biomass of small perch decreased with increasing chlorophyll a . These results indicate that assessment of ecological integrity of lakes by their fish fauna is generally possible, if lakes are initially separated according to a depth‐related morphotype before the assessment, and if eutrophication is considered to be the main anthropogenic degradation.     

Surface water connectivity drives richness and composition of Arctic lake fish assemblages

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Global mismatch between species richness and vulnerability of reef fish assemblages

The impact of anthropogenic activity on ecosystems has highlighted the need to move beyond the biogeographical delineation of species richness patterns to understanding the vulnerability of species assemblages, including the functional components that are linked to the processes they support. We developed a decision theory framework to quantitatively assess the global taxonomic and functional vulnerability of fish assemblages on tropical reefs using a combination of sensitivity to species loss, exposure to threats and extent of protection. Fish assemblages with high taxonomic and functional sensitivity are often exposed to threats but are largely missed by the global network of marine protected areas. We found that areas of high species richness spatially mismatch areas of high taxonomic and functional vulnerability. Nevertheless, there is strong spatial match between taxonomic and functional vulnerabilities suggesting a potential win–win conservation‐ecosystem service strategy if more protection is set in these locations.     

Lake connectivity and fish species richness in southern Brazilian coastal lakes

Connectivity is a key factor in metacommunity ecology, because it influences dispersal and colonization rates. However, it has received less attention in aquatic than in terrestrial ecology research. We investigated whether connectivity is a good predictor of species richness in functional fish communities (freshwater, FS; estuarine, ES and estuarine-freshwater, EFS) from 31 coastal lakes in southern Brazil. We used a model selection approach, including lake area and distance from the ocean as additional predictors of species richness and two connectivity metrics: primary connectivity (C _P) and estuarine connectivity (C _E), which measure connectivity to neighboring lakes and system-wide connectivity, respectively. Both metrics estimate functional connectivity and were calculated on habitat-based cost distances. Connectivity was more important for predicting richness of functional communities than for total richness, particularly C _E, which was distinctively related to each functional fish community richness (directly related to ES and EFS, and inversely related to FS; C _P was related only to ES). Remarkably, connectivity was more important than area for predicting ES and EFS richness. These results add support to dispersal limitation as an important mechanism influencing fish communities. We suggest that incorporating environmental filters (habitat type) to quantify connectivity is useful for accessing the patterns of species richness.     

Native and introduced fish species richness in French lakes: local and regional influences

Aim To analyse the importance of local and regional influences on the patterns of species richness in natural and man‐made lakes and to infer the impacts of human‐mediated introductions on these patterns. Location France. Methods Species occurrence data were gathered for 25 natural and 51 man‐made lakes. Analysis is based on regression models of local richness against their related regional richness and lake environmental variables. Results Local native richness was mostly controlled by the regional richness. Conversely, local total richness was mainly explained by local variables. These statements apply to both natural and man‐made lakes. Lacustrine systems displayed weak resistance to invaders. Main conclusions Species introductions have apparently contributed to saturate fish communities in these systems even if no clear negative effect on the survival of native species (i.e. species extinction) is detectable so far.     

Size diversity and species diversity relationships in fish assemblages of Western Palearctic lakes

Body size, coupled with abundance and taxonomy, may help to understand the mechanisms shaping community structure. Since the body size of fish is closely related to their trophic niche, size diversity (based on individual body size) of fish communities may capture intraspecific variations in fish trophic niches that are not detected by species diversity. Thus, the relationship between size diversity and species diversity may help to integrate variation at both intraspecific and interspecific levels. We studied the relationship between species diversity and size diversity as a measure of the degree of overlap in size among species and thereby the potential overlap in niches in a community. We hypothesized that the relationship between size diversity and species would be different across the European continent due to different levels of size overlap in fish communities. The data were derived from samplings of fish communities using standardised benthic gill nets in 363 lakes. At the continental scale, size diversity increased with species diversity; at the ecoregion scale, the slope of the relation changed across the continent, with the greatest mismatch occurring in northern Europe where communities comprised only one or a few species, but each of which exhibited a great range in size. There was an increase in slope towards the south with significant relations for four out of six ecoregions. The steeper size diversity‐species diversity slope at lower latitudes is attributable to a lower overlap in fish size and thus likely to finer niche separation. Our results also suggest that size diversity is not a strong surrogate for species diversity in European lake fish communities. Thus, particularly in fish communities composed of few species, measuring size diversity may help to detect potential functional variation which may be neglected by measuring species diversity alone.     

Nitrate availability and hydrophyte species richness in shallow lakes

1. Submerged plant richness is a key element in determining the ecological quality of freshwater systems; it has often been reduced or completely lost. 2. The submerged and floating‐leaved macrophyte communities of 60 shallow lakes in Poland and the U.K. have been surveyed and species richness related to environmental factors by general linearised models. 3. Nitrogen, and more specifically winter nitrate, concentrations were most important in explaining species richness with which they were inversely correlated. Phosphorus was subsidiary. Such an inverse relationship is consistent with findings in terrestrial communities. Polish lakes, with less intensively farmed catchments, had greater richness than the U.K. lakes. 4. The richest U.K. communities were associated with winter nitrate‐N concentrations of up to about 1–2 mg L^?1 and may correspond with ‘good’ ecological quality under the terms of the European Water Framework Directive. Current concentrations in European lowlands are often much higher.     

Combining projected changes in species richness and composition reveals climate change impacts on coastal Mediterranean fish assemblages

Species Temporal Turnover (STT) is one of the most familiar metrics to assess changes in assemblage composition as a consequence of climate change. However, STT mixes two components in one metric, changes in assemblage composition caused by a process of species loss or gain (i.e. the nestedness component) and changes in assemblage composition caused by a process of species replacement (i.e. the species replacement component). Drawing on previous studies investigating spatial patterns of beta diversity, we propose measures of STT that allow analysing each component (species replacement vs. nestedness), separately. We also present a mapping strategy to simultaneously visualize changes in species richness and assemblage composition. To illustrate our approach, we used the Mediterranean coastal fish fauna as a case study. Using Bioclimatic Envelope Models (BEMs) we first projected the potential future climatic niches of 288 coastal Mediterranean fish species based on a global warming scenario. We then aggregated geographically the species‐level projections to analyse the projected changes in species richness and composition. Our results show that projected changes in assemblage composition are caused by different processes (species replacement vs. nestedness) in several areas of the Mediterranean Sea. In addition, our mapping strategy highlights that the coastal fish fauna in several regions of the Mediterranean Sea could experience a ‘cul‐de‐sac’ effect if exposed to climate warming. Overall, the joint exploration of changes in species richness and composition coupled with the distinction between species replacement and nestedness bears important information for understanding the nature of climate change impacts on biodiversity. These methodological advances should help decision‐makers in prioritizing action in the areas facing the greatest vulnerability to climate.     

Regulation and stability in fish assemblages of neotropical floodplain lakes

Neotropical floodplain lakes provide an excellent opportunity to examine the regulation and stability of fish assemblages. At low water, when lakes are separated, fish are concentrated in the lakes and are presumably subject to strong interspecific interactions that can shape assemblage structure. At high water, when the lakes and river channels become broadly interconnected, ample potential exists for alteration of assemblage structure because eggs, larvae, and older fish may undergo spatial reshuffling among waterbodies. Twenty lakes of the Orinoco River floodplain in Venezuela were surveyed in the early and late dry seasons of two consecutive years. Marked differences in assemblage structure among lakes were established in the early dry season. Changes in assemblage structure during the dry season were large and detectable even at the ordinal level; they reflected a strong reduction of visually oriented fish relative to fish with adaptations to low light. Changes were similar in the two years and were apparently due to species-specific differences in mortality, which was high over the dry season. The annual flood is a strong natural fluctuation that greatly modifies assemblage properties during the wet season. Nevertheless, the potential for alteration of assemblage structure by reshuffling was not realized: assemblage properties early and late in the dry season were similar in the two years, indicating a regular and predictable annual cycle of change in assemblage structure. This regularity can be explained by mechanisms of regulation which appear to be linked to piscivory and the optical environment. In contrast with the prevailing views on neotropical fish assemblages, there seems to be a strong deterministic component to assemblage structure and dynamics in Orinoco floodplain lakes.     

Cross-Cordillera exchange mediated by the Panama Canal increased the species richness of local freshwater fish assemblages

Completion of the Panama Canal in 1914 breached the continental divide and set into motion a natural experiment of unprecedented magnitude by bringing previously isolated freshwater fish communities into contact. The construction of a freshwater corridor connecting evolutionarily isolated communities in Pacific and Caribbean watersheds dramatically increased the rate of dispersal, without directly affecting species interactions. Here, we report that a large fraction of species have been able to establish themselves on the other side of the continental divide, whereas no species have become extinct, leading to a local increase in species richness. Our results suggest that communities are not saturated and that competitive exclusion does not occur over the time-scale previously envisioned. Moreover, the results of this unintentional experiment demonstrate that community composition and species richness were regulated by the regional process of dispersal, rather than by local processes such as competition and predation.     

Fish assemblages in deep Italian subalpine lakes: history and present status with an emphasis on non-native species

We provide a comprehensive overview of the status of fish assemblages in eight Italian subalpine lakes using multiple data sources: historical records, standardised sampling and fishery catch statistics. Thirty-four fish species were recorded, twenty of which are native, seven introduced historically and another seven introduced recently. The number of fish species in individual lakes has increased by between 25 and 65% from 1855 to the present, with the increase being higher in the larger lakes. Non-native species contributed between 4.0 and 71.5% to standardised catches by numbers and between 4.8 and 65.1% by biomass. Roach Rutilus rutilus and pumpkinseed Lepomis gibbosus dominated electrofishing and benthic catches by number, while open-water catches were dominated by the coregonids European whitefish Coregonus lavaretus and gangfish Coregonus macrophthalmus. In terms of biomass, electrofishing catches were dominated by crucian carp Carassius carassius, largemouth bass Micropterus salmoides and wels catfish Silurus glanis, benthic catches were dominated by roach, European whitefish and crucian carp, and open-water catches by coregonids. Commercial fisheries are important ecosystem services provided by subalpine lakes, with their harvests now dominated by non-native species. To deliver effective biodiversity conservation and ecosystem services provision, the prioritisation of targets and interventions of management of non-native species is needed.     

Assessing anthropogenic impact on boreal lakes with historical fish species distribution data and hydrogeochemical modeling

Quantifying the effects of human activity on the natural environment is dependent on credible estimates of reference conditions to define the state of the environment before the onset of adverse human impacts. In Europe, emission controls that aimed at restoring ecological status were based on hindcasts from process‐based models or paleolimnological reconstructions. For instance, 1860 is used in Europe as the target for restoration from acidification concerning biological and chemical parameters. A more practical problem is that the historical states of ecosystems and their function cannot be observed directly. Therefore, we (i) compare estimates of acidification based on long‐term observations of roach (Rutilus rutilus) populations with hindcast pH from the hydrogeochemical model MAGIC; (ii) discuss policy implications and possible scope for use of long‐term archival data for assessing human impacts on the natural environment and (iii) present a novel conceptual model for interpreting the importance of physico‐chemical and ecological deviations from reference conditions. Of the 85 lakes studied, 78 were coherently classified by both methods. In 1980, 28 lakes were classified as acidified with the MAGIC model, however, roach was present in 14 of these. In 2010, MAGIC predicted chemical recovery in 50% of the lakes, however roach only recolonized in five lakes after 1990, showing a lag between chemical and biological recovery. Our study is the first study of its kind to use long‐term archival biological data in concert with hydrogeochemical modeling for regional assessments of anthropogenic acidification. Based on our results, we show how the conceptual model can be used to understand and prioritize management of physico‐chemical and ecological effects of anthropogenic stressors on surface water quality.     

How does the taxonomic status of allopatric populations influence species richness within African cichlid fish assemblages?

Aim Current estimates of species richness within rapidly evolving species flocks are often highly dependent on the species status of allopatric populations that differ in phenotypic traits. These traits may be unreliable indicators of biological species status and systematists may have inconsistently assigned species among lineages or locations on the basis of these traits, thus hampering comparative studies of regional species richness and speciation rates. Our aim was to develop a method of generating standardized estimates of regional species richness suitable for comparative analysis, and to use these estimates to examine the extent and consistency of species assignment of allopatric populations within rapidly evolving cichlid fish flocks present in three east African lakes. Location Lakes Malawi, Victoria and Tanganyika. Methods Using published taxon co-occurrence data, a novel approach was employed to calculate standardized ‘minimum’ estimates of regional species richness for hard substrate associated complexes of cichlids within each of the lakes. Minimum estimates were based on an explicit assumption that if taxa present on equivalent habitats have disjunct distributions, then they are allopatric forms of the same species. These estimates were compared with current observed ‘high-end’ regional species richness estimates for those complexes to determine the consistency of species assignment of allopatric populations between lineages within a lake. A ‘sympatry’ index was developed to enable comparisons of levels of species assignment of allopatric populations between-lakes to be made. Results Within each lake, the minimum and high-end estimates for species richness were significantly correlated across complexes, indicating that the complexes that contain more recognized species contain the most genuine biological species. However, comparisons of complexes among lakes revealed considerable differences. For equivalent geographical areas, substantially higher proportions of recognized species were totally allopatric within the studied Lake Malawi and Lake Victoria complexes, than those of Lake Tanganyika. Main Conclusions Among African lakes, levels of assignment to species status of allopatric populations were found to be distinctly different. It is unclear whether the discrepancies are a consequence of differences between the lake faunas in degrees of phenotypic divergence among allopatric populations, or are simply the result of inconsistent taxonomic practices. In either case, these results have considerable wider relevance for they emphasize that quantitative measures of regional and beta diversity are critically dependent on the species status of allopatric populations, an issue usually neglected in comparative studies of species richness. The technique introduced here can be used to standardize measures of regional diversity of lineages for comparative analyses, potentially enabling more accurate identification of processes influencing rates of speciation.     

Regional species richness,hydrological characteristics and the local species richness of assemblages of North American stream fishes

1. Local assemblage structure, from a deterministic perspective, is presumably dictated by the regional species pool as well as regulated by local factors. We examined the relationships of the regional species pool and local hydrological characteristics to local species richness of North American freshwater fishes using data sets collected during the National Water Quality Assessment program conducted by the United States Geological Survey. 2. We predicted that local species richness is ultimately constrained by the composition of the regional species pool and further associated with local hydrological factors. Moreover, we predicted that variation in local species richness within major families can be explained by different combinations of hydrological characteristics that represent lineage‐specific responses to the environment. 3. Daily discharge and regional and local species richness data were assembled from 41 stream localities across the United States. Multiple stepwise regressions were conducted to predict local species richness, based on regional species richness, mean discharge and hydrological characteristics quantified by nine variables characterising flow variability. Species richness at each site was calculated for the entire assemblage as well as within the four most species‐rich families in the data set (Catostomidae, Centrarchidae, Cyprinidae and Percidae). 4. Local species richness was best predicted by a combination of regional species richness and discharge magnitude when all species were considered. Regional species richness was a significant explanatory variable of local species richness for three of four families (Catostomidae, Centrarchidae, Cyprinidae), but not for Percidae. Local richness in Centrarchidae and Cyprinidae was positively correlated with temporal flow variability as well as high and low flow duration, respectively, while richness in Catostomidae and Percidae tended to be associated with discharge volume. In addition, local species richness for three of the four major families was positively correlated with species richness of the other families in the assemblage, potentially suggesting the influence of local habitat quality and heterogeneity. 5. Results suggest the importance of the combined influences of the regional species pool and local hydrological characteristics on local richness in freshwater fishes, with variation in richness within each family predicted by different characteristics of flow regimes.     

Bird abundance and species richness on Florida lakes: influence of trophic status,lake morphology,and aquatic macrophytes

Data from 46 Florida lakes were used to examine relationships between bird abundance (numbers and biomass) and species richness, and lake trophic status, lake morphology and aquatic macrophyte abundance. Average annual bird numbers ranged from 7 to 800 birds km^–2 and bird biomass ranged from 1 to 465 kg km^–2. Total species richness ranged from 1 to 30 species per lake. Annual average bird numbers and biomass were positively correlated to lake trophic status as assessed by total phosphorus (r = 0.61), total nitrogen (r = 0.60) and chlorophyll a (r = 0.56) concentrations. Species richness was positively correlated to lake area (r = 0.86) and trophic status (r = 0.64 for total phosphorus concentrations). The percentage of the total annual phosphorus load contributed to 14 Florida lakes by bird populations was low averaging 2.4%. Bird populations using Florida lakes, therefore, do not significantly impact the trophic status of the lakes under natural situations, but lake trophic status is a major factor influencing bird abundance and species richness on lakes. Bird abundance and species richness were not significantly correlated to other lake morphology or aquatic macrophyte parameters after the effects of lake area and trophic status were accounted for using stepwise multiple regression. The lack of significant relations between annual average bird abundance and species richness and macrophyte abundance seems to be related to changes in bird species composition. Bird abundance and species richness remain relatively stable as macrophyte abundance increases, but birds that use open-water habitats (e.g., double-crested cormorant, Phalacrocorax auritus) are replaced by species that use macrophyte communities (e.g., ring-necked duck, Aythya collaris).     

Abundance and species richness as a function of food resources and vegetation structure: juvenile fish assemblages in rivers

Availability of food and habitat complexity are two factors generally invoked to explain the high density of fish in vegetated habitats. The role of food resources (zooplankton) and habitat complexity (expressed by a vegetation structural index) in determining juvenile fish abundance and fish species richness in three morphologically contrasted macrophyte types (Sagittaria, Ceratophyllum and Nuphar) was studied for a large, lowland river.
Our results showed that fish abundance increased with food availability, and was maximal for intermediate values of vegetation complexity. Food resources and vegetation complexity did not, however, explain the higher juvenile fish abundance observed in Sagittaria beds. We suggested that plant growth form, acting on fish foraging success and risk of predation, might influence patterns of juvenile fish distribution.
Species‐abundance relationships were similar among the three macrophyte types, but relationships between number of fish species (fish richness) and number of samples differed. Fish richness in terms of total number of fish species found at each sampling point showed the same pattern as for fish abundance: it increased with food availability and was highest at intermediate vegetation complexities. However, since both fish abundance and fish richness responded in the same manner to food availability and vegetation complexity, we were not able to distinguish statistically any effect for the specific fish richness formulated by the number of fish species per unit fish abundance. The current paradigm that structural complexity of vegetation provides a wider range of niches, increasing species diversity, was thus not verified. This finding indicates a simple species‐abundance relationship (the passive sampling hypothesis), and suggests that no special mechanism acts directly on fish species richness.