Changes in taxonomic and functional diversity of aquatic macroinvertebrates along a gradient of stream size and flow stability in the northeastern Colorado Rocky Mountains
Date
2018
Authors
Lafferty, M Holliday, author
Poff, N. LeRoy, advisor
Kondratieff, Boris, committee member
Kampf, Stephanie, committee member
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Abstract
While the pattern of aquatic macroinvertebrate communities along stream size gradients have been examined in past studies, it is usually in the context of the river continuum, moving along a stream network from the headwaters to large rivers. The effect of stream size among small headwater streams has received less attention. With increasing temperatures and decreasing snowfall predicted in the Colorado Rockies, streams in the area are likely to decrease in size and have an increased likelihood of flow cessation in especially dry years. To understand how these changes will affect aquatic macroinvertebrate communities, this study explored differences in species occurring in streams of differing size and flow stability. I examined the taxonomic and functional diversity of aquatic macroinvertebrates in 12 headwater streams in the Cache la Poudre watershed of northern Colorado. Each stream was assigned a stream “type” based on size (measured by discharge and drainage area) and the stability of the flow throughout the summer. My results show that size was positively correlated with both taxonomic and functional richness. I found that the large streams with intermediate stability and small streams with stable flow had greater taxa and functional richness than did the small streams with intermediate flow and small streams with unstable flow, illustrating that flow stability is also important in determining macroinvertebrate communities. Certain species functional traits, such as inhabiting erosional zones and filter-feeding were found to be associated with increasing stream size and stability. I calculated β-diversity across the size and stability gradient and found that replacement of taxa (turnover) better explained among-site differences than did addition of taxa (nestedness). The specific taxa that prefer smaller streams were identified with indicator species analysis. Overall, these results indicate that the hotter and drier summers predicted by climate change models may lead to decreases in overall macroinvertebrate taxa and functional richness and potentially cause displacement of taxa as the smallest headwater streams become less stable.
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Subject
macroinvertebrates
headwater
stream size