The Upper Mississippi River System, including the Illinois River, has been invaded by a number of nonnative species including silver carp Hypophthalmichthys molitirx and bighead carp H. nobilis, collectively referred to here as Asian carps. Silver carp densities in the Illinois River have increased dramatically and now represent some of the highest densities of wild silver carp anywhere in the world. Asian carps have the potential to alter existing ecosystems by consuming planktonic resources and therefore, could have the ability to alter existing fish communities as most fishes are dependent on planktonic resources during early development. However, identifying the relationship of fish community structure to the establishment of Asian carps has yet to be thoroughly investigated. Using long-term fish community data collected by the Upper Mississippi River Restoration's Long Term Resource Monitoring element, we investigate changes in fish community structure pre-and post-establishment of Asian carps. Significant differences in the pre-and post-establishment communities were observed for the majority of gears and habitats. Species contributing to changes between establishment periods included most sportfish species and catostomids, which were less abundant post-establishment of Asian carps, while shortnose gar, grass carp, and emerald shiner were more abundant. While our analyses show Asian carps are likely contributing to major differences in fish community structure, future research and long-term monitoring should investigate the mechanisms and interactions responsible for community changes as well as identifying any potential concurrent or confounding factors such as changes in river hydrology or sedimentation.

Experiments with realistic scenarios of species loss from multitrophic ecosystems may improve insight into how biodiversity affects ecosystem functioning. Using 1000 L mesocoms, we examined effects of nonrandom species loss on community structure and ecosystem functioning of experimental food webs based on multitrophic tropical floodplain lagoon ecosystems. Realistic biodiversity scenarios were developed based on long-term field surveys, and experimental assemblages replicated sequential loss of rare species which occurred across all trophic levels of these complex food webs. Response variables represented multiple components of ecosystem functioning, including nutrient cycling, primary and secondary production, organic matter accumulation and whole ecosystem metabolism. Species richness significantly affected ecosystem function, even after statistically controlling for potentially confounding factors such as total biomass and direct trophic interactions. Overall, loss of rare species was generally associated with lower nutrient concentrations, phytoplankton and zooplankton densities, and whole ecosystem metabolism when compared with more diverse assemblages. This pattern was also observed for overall ecosystem multifunctionality, a combined metric representing the ability of an ecosystem to simultaneously maintain multiple functions. One key exception was attributed to time-dependent effects of intraguild predation, which initially increased values for most ecosystem response variables, but resulted in decreases over time likely due to reduced nutrient remineralization by surviving predators. At the same time, loss of species did not result in strong trophic cascades, possibly a result of compensation and complexity of these multitrophic ecosystems along with a dominance of bottom-up effects. Our results indicate that although rare species may comprise minor components of communities, their loss can have profound ecosystem consequences across multiple trophic levels due to a combination of direct and indirect effects in diverse multitrophic ecosystems.

No abstract

No abstract