Watercourse Distance Research Articles

Species sorting drives variation of boreal lake and river macrophyte communities

Metacommunity paradigms are increasingly studied to explain how environmental control and spatial patterns determine variation in community composition. However, the relative importance of these patterns on biological assemblages among different habitats is not well known. We investigated the relative roles of local, catchment and spatial variables based on overland and watercourse distances in explaining the variation of community structure of lake and river macrophytes in two large river basins at two spatial extents (within and across river basins). Partial redundancy analysis was used to explore the share of variability in macrophyte communities attributable to local environmental conditions, catchment land cover and space (generated with Principle Coordinates of Neighbour Matrices). We found that local variables had the highest effect on both lake and river macrophyte communities, followed by catchment variables. Space had no or only marginal influence on the community structure regardless of used distance measure. Total phosphorus, conductivity and turbidity of the local variables contributed most for lake macrophytes, whereas pH and color had largest independent contribution for variation in river macrophytes. Size of catchment area and proportion of lakes and agriculture were the most important catchment variables in both habitats. The strong importance of environmental control suggests that both lake and river macrophyte communities are structured by species sorting. This finding gives support to the validity of assessment systems based on the European Water Framework Directive.

Dispersal ability determines the role of environmental, spatial and temporal drivers of metacommunity structure.

Recently, community ecologists are focusing on the relative importance of local environmental factors and proxies to dispersal limitation to explain spatial variation in community structure. Albeit less explored, temporal processes may also be important in explaining species composition variation in metacommunities occupying dynamic systems. We aimed to evaluate the relative role of environmental, spatial and temporal variables on the metacommunity structure of different organism groups in the Upper Paraná River floodplain (Brazil). We used data on macrophytes, fish, benthic macroinvertebrates, zooplankton, periphyton, and phytoplankton collected in up to 36 habitats during a total of eight sampling campaigns over two years. According to variation partitioning results, the importance of predictors varied among biological groups. Spatial predictors were particularly important for organisms with comparatively lower dispersal ability, such as aquatic macrophytes and fish. On the other hand, environmental predictors were particularly important for organisms with high dispersal ability, such as microalgae, indicating the importance of species sorting processes in shaping the community structure of these organisms. The importance of watercourse distances increased when spatial variables were the main predictors of metacommunity structure. The contribution of temporal predictors was low. Our results emphasize the strength of a trait-based analysis and of better defining spatial variables. More importantly, they supported the view that “all-or- nothing” interpretations on the mechanisms structuring metacommunities are rather the exception than the rule.

The Role of Environmental and Spatial Processes in Structuring Stream Macroinvertebrates Communities in a Large River Basin

Understanding spatial patterns of stream biological communities is important for stream ecosystem management. The questions which variables (spatial variables vs. environmental variables) are driving stream community structure, and whether stream network configuration could influence spatial patterns of the structure, are less investigated. We used stream macroinvertebrates community and environmental data collected from 142 sites in August 2010 across the Huai River basin, China, to answer these questions. Spatial variables were constructed based on symmetrical Euclidean distance and stream distance by using Moran's eigenvector maps. We evaluated the relative impacts of local environmental (physicochemical variables) and spatial (generated by overland and watercourse distances among sites) variables on the structure of macroinvertebrates using variation partitioning methods. Our results showed that both space and environment had significant effects on macroinvertebrates community composition, and the former explained more variations. Moreover, spatial variables based on the watercourse distance captured slightly more variation of macroinvertebrates community in stream networks than those derived from the overland distance.

Metacommunity structuring in stream networks: roles of dispersal mode, distance type, and regional environmental context

Within a metacommunity, both environmental and spatial processes regulate variation in local community structure. The strength of these processes may vary depending on species traits (e.g., dispersal mode) or the characteristics of the regions studied (e.g., spatial extent, environmental heterogeneity). We studied the metacommunity structuring of three groups of stream macroinvertebrates differing in their overland dispersal mode (passive dispersers with aquatic adults; passive dispersers with terrestrial adults; active dispersers with terrestrial adults). We predicted that environmental structuring should be more important for active dispersers, because of their better ability to track environmental variability, and that spatial structuring should be more important for species with aquatic adults, because of stronger dispersal limitation. We sampled a total of 70 stream riffle sites in three drainage basins. Environmental heterogeneity was unrelated to spatial extent among our study regions, allowing us to examine the effects of these two factors on metacommunity structuring. We used partial redundancy analysis and Moran's eigenvector maps based on overland and watercourse distances to study the relative importance of environmental control and spatial structuring. We found that, compared with environmental control, spatial structuring was generally negligible, and it did not vary according to our predictions. In general, active dispersers with terrestrial adults showed stronger environmental control than the two passively dispersing groups, suggesting that the species dispersing actively are better able to track environmental variability. There were no clear differences in the results based on watercourse and overland distances. The variability in metacommunity structuring among basins was not related to the differences in the environmental heterogeneity and spatial extent. Our study emphasized that (1) environmental control is prevailing in stream metacommunities, (2) dispersal mode may have an important effect on metacommunity structuring, and (3) some factors other than spatial extent or environmental heterogeneity contributed to the differences among the basins.

Spatial predictors of fish species composition in European lowland lakes

Composition of animal communities can be shaped by both local and regional processes. Among others, dispersal of organisms links local and regional patterns and determines the similarity of communities at increasing spatial distances. Unique and shared spatial and environmental contributions to fish community composition were calculated for watercourse distances between 49 hydrologically connected lakes in the German lowland area. Variation partitioning indicated a dominant unique effect of spatial predictors on fish community composition, whereas the effects of lake morphometry and productivity were weaker. The spatial effect was attributable to an uneven occurrence of small, littoral fish species found even at the small spatial extension covered here (maximum spatial distance ˜550 km). Distance decay of community similarity was moderate, but significant, if all 31 fish species were considered, but the slope of the decay function became steeper if only 11 small‐sized, primarily littoral species were included. These results suggest that fish in European lowland lakes can be considered a metacommunity with limited dispersal along watercourse connections in particular for small‐sized species. The analysis supports that for an appropriate evaluation of spatial effects on fish community similarity, reliable estimates of local richness are required which include in particular also rare, small‐sized species occurring primarily in littoral areas. Furthermore, watercourse distance is a more reliable approximation than Euclidean distance to the real spatial dimension of fish dispersal.

Influence of connectivity, habitat quality and invasive species on egg and larval distributions and local abundance of crucian carp in Japanese agricultural landscapes

The quality of habitat at and around a spawning site, and the availability of movement between spawning and nonspawning habitats are likely to be important determinants for population persistence in a degraded and fragmented landscape. We assessed the influence of habitat connectivity, habitat quality and invasive species for distributions and local abundance of eggs and larvae of crucian carp ( Crassius auratus complex, which is listed as “data deficient” on the Japanese Red List) in agricultural landscapes surrounding Lake Mikata, Japan, where drainage ditches and paddy fields are extensively utilised for spawning (lake or river shores are also used). We investigated the presence and abundance of eggs and larvae of crucian carp and habitat components at 146 sites across a range of presumed spawning habitats. Egg presence was affected strongly by connectivity to the lake (watercourse distance from the lake), and egg abundance was significantly influenced by both connectivity and habitat quality. In contrast, larval presence was primarily related to habitat quality. Larval abundance was influenced by connectivity and habitat quality, but the effect of connectivity was relatively low. Furthermore, larval abundance was negatively related to the presence of the invasive species red swamp crayfish ( Procambarus craki) and bullfrog ( Rana catesbeiana). Our findings indicate that connectivity, habitat quality and the presences of invasive species are crucial in determining suitable spawning and nursery habitats, but their relative importance may vary depending on egg and larval life stages. We suggest that restoring connectivity, improving habitat quality and removal of invasive species could be effective conservation strategies for the declining populations of crucian carp in agricultural landscapes.

Spatial eigenfunction analyses in stream networks: do watercourse and overland distances produce different results?

SUMMARY1. The use of spatial variables is a common procedure in ecological studies. The techniqueis based on the definition of a connectivity⁄distance matrix that conceptually defines thedispersal of organisms. The shortest distance between two points is a straight line. Despitethe fact that a straight line may not represent the easiest dispersal path for many kinds oforganisms, straight-line distances are often used to detect patterns. We argue that othertypes of connectivity⁄distance matrices will better represent dispersal paths, such as thewatercourse distance for aquatic organisms (e.g. fish, shrimps).2. We used empirical and simulated community data to evaluate the usefulness of spatialvariables generated from watercourse and overland (straight-line) distances.3. Spatial variables based on watercourse distances captured patterns that straight-linedistances did not, and provided better representations of the spatial patterns generated bydispersal along a dendritic network. Keywords: community, dispersal, overland, stream networks, watercourse

Predicting the spatial distribution of the invasive piscivorous chub (Opsariichthys uncirostris uncirostris) in the irrigation ditches of Kyushu, Japan: a tool for the risk management of biological invasions

The piscivorous chub (Opsariichthys uncirostris uncirostris) has widely invaded Kyushu Island in Japan, and its presence in irrigation ditches known as creeks around Ariake Bay has caused particular concern because various native freshwater fishes are also known to exist in the region. In order to examine the habitat characteristics that are related to its occurrence, we developed a species distribution model for piscivorous chub that inhabits creeks in the Kase river catchment by using geographic and habitat variables that were both biotic and abiotic. We then evaluated the model by using a different data set from the adjacent Chikugo river catchment. The resulting multiple logistic regression model, whose performance was supported by a high value of 0.881 for the area under the receiver operating characteristics curve (AUC), indicated that the occurrence of piscivorous chub was strongly affected by the watercourse distance from the source populations in the Kase river. The model’s performance was still high (AUC = 0.792) when tested with the data set from the Chikugo river catchment. We also produced a GIS map that projects the predicted distribution of piscivorous chub across all creeks within the Kase river catchment. The result is likely to reflect the connectivity between static and lentic habitat and is not merely a question of the simple distance from the source populations. We also discuss how the potential distribution map can be applied to the management of piscivorous chub.

THE ROLE OF ENVIRONMENTAL AND SPATIAL PROCESSES IN STRUCTURING LAKE COMMUNITIES FROM BACTERIA TO FISH

We assessed the relative roles of local environmental conditions and dispersal on community structure in a landscape of lakes for the major trophic groups. We use taxonomic presence-absence and abundance data for bacteria, phytoplankton, zooplankton, and fish from 18 lakes in southern Quebec, Canada. The question of interest was whether communities composed of organisms with more limited dispersal abilities, because of size and life history (zooplankton and fish) would show a different effect of lake distribution than communities composed of good dispersers (bacteria and phytoplankton). We examine the variation in structure attributable to local environmental (i.e., lake chemical and physical variables) vs. dispersal predictors (i.e., overland and watercourse distances between lakes) using variation partitioning techniques. Overall, we show that less motile species (crustacean zooplankton and fish) are better predicted by spatial factors than by local environmental ones. Furthermore, we show that for zooplankton abundances, both overland and watercourse dispersal pathways are equally strong, though they may select for different components of the community, while for fish, only watercourses are relevant dispersal pathways. These results suggest that crustacean zooplankton and fish are more constrained by dispersal and therefore more likely to operate as a metacommunity than are bacteria and phytoplankton within this studied landscape.