Fish beta diversity responses to environmental heterogeneity and flood pulses are different according to reproductive guild

ABSTRACT In floodplain communities, beta diversity is influenced by different factors; however, environmental heterogeneity and floods are believed to be particularly influential. The influence of environmental heterogeneity and floods on beta diversity may vary among guilds that present different ecological traits. This study evaluated the correlation between the environmental heterogeneity and flood periods and the beta diversity of trophic and reproductive guilds of fish assemblages. Sampling was conducted quarterly between 2000 and 2012 in the upper Paraná River floodplain. The environmental heterogeneity and period (i.e., dry or flood) were associated with the beta diversity of each guild based on the results of generalized least squares linear models. Only guilds with parental care were influenced by the interaction between environmental heterogeneity and period. The beta diversity of the other guilds presented no relationship between environmental heterogeneity and period. It is likely that species with parental care presented less dispersal capacity, which increased the dissimilarity among assemblages. The higher dispersion rates of the other guilds may be responsible for the lack of relationship between the beta diversity and the environmental heterogeneity and period. In sum, these results suggest that reproductive guilds influence how environmental heterogeneity and floods affect beta diversity variation.

Rheophilic fish in oxbow lakes of the Warta River – the effect of environmental conditions on habitat selection

Oxbow lakes are typical elements of meandering watercourses and are considered to be key components of floodplains of natural rivers. A permanent connection with the river promotes the use of these water bodies by ichthyofauna as spawning grounds, shelter for fry, feeding and wintering grounds. The aim of this study was to determine which rheophilic species inhabit oxbow lakes and how environmental conditions affect habitat selection and fish behavior. Analyses were conducted on six oxbow lakes of the Warta River in the Koło-Poznań section. Fish and water samples were collected for three years, in spring, summer and late autumn. Variation in environmental conditions in the analyzed water bodies results in a considerable diversity of the ichthyofauna, including rheophilic species, in individual seasons of the year. In the course of the study, nine rheophilic fish species were recorded, including four from the lithophilic reproductive guild having the highest environmental requirements. Relative abundance of rheophilic species in the dominance structure ranged from 0 to 100%, depending on the reservoir and seasons, with an average of 7% for all catches. For comparison, their relative abundance in the adjacent parts of the river was 12 and 23%.

Influences of Human Stressors on Fish-Based Metrics for Assessing River Condition in Central Alberta

Economic developments in Alberta have resulted in widespread changes in land use that may deteriorate river conditions for fish. Fish assemblages were characterized with index of biological integrity metrics for the heavily-developed watershed of the Battle River, Alberta. Metric relationships with human stressors were quantified using regression and information theory methods. Although the fauna comprised 14 native species, 50% of the catch was white sucker (Catostomus commersoni Lacepede, 1803). Five statistically unrelated metrics were identified as being responsive to stressors: two trophic guilds, one habitat guild, one reproductive guild, and one measure of community structure. Regression showed that the cumulative effect of human developments, indexed as road density in the basin, was negatively linked to the relative abundance of lithophils and positively linked to the relative abundance of omnivores. Agriculture also threatened the integrity of fish assemblages. Stream sections with higher cattle densities in their basins had fewer lithophils and benthic invertivores; whereas stream sections with higher nutrient concentrations contained fewer species, as well as fewer top carnivores, but more true omnivores. Understanding effects of human footprints that are expanding in western Canada will be critical to the successful management of aquatic resources.

Spawning and Early Development of the River Blackfish, Gadopsis marmoratus Richardson (Gadopsiformes : Gadopsidae), in the McKenzie River, Victoria

Spawning and development of the river blackfish G. marmoratus were investigated at the McKenzie River in the Grampians, western Victoria. Eggs are deposited inside hollow logs. Removal of logs during some 'river improvement' schemes may have a deleterious effect on spawning. Some preliminary observations on the early development of the river blackfish are described. The species is tentatively classified as belonging to Balon's 'Speleophils' reproductive guild of fishes.