Temporal Changes in Community Assembly Processes and Food Web Structure in the Xingu River
Increasing hydropower expansion in hyper-diverse tropical river basins is currently threatening aquatic biodiversity on an unprecedented scale. Among the largest and most controversial of these projects is the Belo Monte Hydroelectric Complex being constructed on the Xingu River in Brazil.
The Xingu River is the largest clear water tributary to the Amazon, famously known for a 130 km expanse of rapids and braided channels known as the Volta Grande, or Big Bend. This section of the Xingu contains over 450 species of fishes, with at least 26 species of micro-endemics found only in the rapids. The Xingu River supports a large ornamental fishery surrounding the high diversity of rheophilic species, many of which possess numerous adaptions to life in high velocity habitats that may make them particularly vulnerable to environmental impacts.
Our understanding of this diverse ichthyofauna is limited to taxonomic assessments, with almost no data available on habitat use, feeding ecology, and niche relationships. The Belo Monte Hydroelectric Complex will divert a significant portion of the river’s flow to a series of man-made canals and reservoirs. This design will result in the flooding of the upper portion of the Volta Grande and the dewatering of the lower portion, significantly altering flow dynamics. With construction nearing completion, baseline data on the functional ecology, trophic structure, and factors driving community assembly of these fishes are critically needed.
My dissertation research uses functional traits-based approaches, null model comparisons, and stable isotope analysis in order to understand temporal changes in the functional and trophic relationships among fishes within the Xingu rapids and provide baseline data for ongoing monitoring efforts.
This research is part of the iXingu Project, a large collaborative effort to inventory the aquatic biodiversity of the Lower Xingu Rapids prior to completion of the Belo Monte Dam. Many people of the iXingu team have helped with aspects of this research: Mark Sabaj and John Lundberg (Academy of Natural Sciences of Philadelphia and Drexel University), Nathan Lujan (Royal Ontario Museum), Lucia Rapp Py-Daniel, Jansen Zuanon, and Alany Gonçalves (Instituto Nacional de Pesquisas da Amazônia), Leandro Sousa and Tommaso Giarrizzo (Universidade Federal do Pará), and Kirk Winemiller (Texas A&M University).
The rocky formations and maze of channels of the Xingu are best seen from above. During fieldwork in February 2015, Unmanned Aerial Vehicle (UAV) technology was used to capture aerial imagery and videos of the Xingu River.
Below is one of the videos that I filmed using a GoPro attached to the UAV. The aerial footage shows the iXingu team at work sampling in the Xingu River near the mouth of the Iriri River.
Global Patterns of Non-native Freshwater Fishes are Consistent with Biotic Resistance
The idea that diverse communities should be more resistant to biological invasions has a long history in ecology. While experiments often find a negative relationship between invasion success and native species richness, large-scale comparative studies tend to find a positive relationship. This discrepancy has been referred to as the invasion paradox.
Biotic resistance requires interactions on a local level; yet, regional studies often use checklists of species at the watershed or country scale. This causes a mismatch between the question and the scale of previous tests of the theory. In addition, differences in competitive environments across regions may confound tests of biotic resistance based solely on native species richness of the invaded community.
Using global and regional datasets for fishes in river and stream reaches, we demonstrated that global distributions of non-native fishes are consistent with biotic resistance. In addition to a negative relationship between native and non-native species richness in local assemblages at the global scale, nearly all non-native species originated from regions with higher native species richness than the invaded region.
These findings imply that coevolved ecological interactions in species-rich systems inhibit establishment of generalist non-native species from less diverse communities. Distinct evolutionary histories in different regions strongly influence invasion of intact communities that are relatively un-impacted by human actions, and may explain the conflicting evidence for biotic resistance found at different spatial scales.
This research was conducted with Kirk Winemiller (Texas A&M University) and Michi Tobler (Kansas State University).