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Non-additive increases in sediment stability are generated by macroinvertebrate species interactions in laboratory streams.

Albertson LK, Cardinale BJ, Sklar LS - PLoS ONE (2014)

Bottom Line: Previous studies have shown that biological structures such as plant roots can have large impacts on landscape morphodynamics, and that physical models that do not incorporate biology can generate qualitatively incorrect predictions of sediment transport.However, work to date has focused almost entirely on the impacts of single, usually dominant, species.We then used this model to estimate potential bed movement in a natural stream for which we had measurements of channel geometry, grain size, and daily discharge.

View Article: PubMed Central - PubMed

Affiliation: Department of Ecology, Evolution, and Marine Biology, University of California Santa Barbara, Santa Barbara, CA, United States of America.

ABSTRACT
Previous studies have shown that biological structures such as plant roots can have large impacts on landscape morphodynamics, and that physical models that do not incorporate biology can generate qualitatively incorrect predictions of sediment transport. However, work to date has focused almost entirely on the impacts of single, usually dominant, species. Here we ask whether multiple, coexisting species of hydropsychid caddisfly larvae have different impacts on sediment mobility compared to single-species systems due to competitive interactions and niche differences. We manipulated the presence of two common species of net-spinning caddisfly (Ceratopsyche oslari, Arctopsyche californica) in laboratory mesocosms and measured how their silk filtration nets influence the critical shear stress required to initiate sediment grain motion when they were in monoculture versus polyculture. We found that critical shear stress increases non-additively in polycultures where species were allowed to interact. Critical shear stress was 26% higher in multi-species assemblages compared to the average single-species monoculture, and 21% greater than levels of stability achieved by the species having the largest impact on sediment motion in monoculture. Supplementary behavioral experiments suggest the non-additive increase in critical shear stress may have occurred as competition among species led to shifts in the spatial distribution of the two populations and complementary habitat use. To explore the implications of these results for field conditions, we used results from the laboratory study to parameterize a common model of sediment transport. We then used this model to estimate potential bed movement in a natural stream for which we had measurements of channel geometry, grain size, and daily discharge. Although this extrapolation is speculative, it illustrates that multi-species impacts could be sufficiently large to reduce bedload sediment flux over annual time scales in streams where multiple species of caddisfly are present.

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Effects of increasing critical shear stress on predicted bedload sediment transport flux for Convict Creek.The snowmelt hydrograph in Convict Creek for the 1992–1993 water year (which began on October 1, 1992) is represented by the thick black line. The thin black and colored lines represent the predicted cumulative bedload sediment transported for the four values of critical shear stress that correspond to our measurements for the four caddisfly treatments in the experiment: (1) no caddisflies, (2) Ceratopsyche monoculture, (3) Arctopsyche monoculture, (4) polyculture mixture of both species. Shading represents variation within one standard error.
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pone-0103417-g005: Effects of increasing critical shear stress on predicted bedload sediment transport flux for Convict Creek.The snowmelt hydrograph in Convict Creek for the 1992–1993 water year (which began on October 1, 1992) is represented by the thick black line. The thin black and colored lines represent the predicted cumulative bedload sediment transported for the four values of critical shear stress that correspond to our measurements for the four caddisfly treatments in the experiment: (1) no caddisflies, (2) Ceratopsyche monoculture, (3) Arctopsyche monoculture, (4) polyculture mixture of both species. Shading represents variation within one standard error.

Mentions: The snow-melt hydrograph for the 1993 water year in Convict Creek (Figure 5) shows a peak discharge that had a ∼4 year recurrence interval, which can be considered representative of conditions with moderate but substantial bedload sediment transport. Overlain on the hydrograph is the predicted cumulative bedload sediment flux calculated under four scenarios of critical shear stress (τ*crit) taken from the treatment values measured in the laboratory flume experiment; means are shown as solid lines and shading indicates the range within one standard error. As shown in Figure 5, increasing the critical shear stress would be expected to delay the onset of bed mobility by up to 40 days and reduce the cumulative bedload sediment flux from 3.7 to 2.3 kT for the polyculture scenario (τ*crit = 0.086) over the 140-day snow-melt hydrograph. The sensitivity of sediment flux to increasing critical shear stress is non-linear, with a small effect for the Ceratopsyche monoculture (2% reduction), a moderate effect for the Arctopsyche monoculture (21% reduction), but a large effect for the polyculture (37% reduction). Again, we caution that Figure 5 represents an extrapolation of results from laboratory flumes to the field and, in doing so, makes many unverified assumptions about the transferability of biological impacts to natural stream conditions. These results should only be viewed as an unverified, a priori hypothesis of what impacts caddisflies ‘might’ have in a stream like Convict Creek.


Non-additive increases in sediment stability are generated by macroinvertebrate species interactions in laboratory streams.

Albertson LK, Cardinale BJ, Sklar LS - PLoS ONE (2014)

Effects of increasing critical shear stress on predicted bedload sediment transport flux for Convict Creek.The snowmelt hydrograph in Convict Creek for the 1992–1993 water year (which began on October 1, 1992) is represented by the thick black line. The thin black and colored lines represent the predicted cumulative bedload sediment transported for the four values of critical shear stress that correspond to our measurements for the four caddisfly treatments in the experiment: (1) no caddisflies, (2) Ceratopsyche monoculture, (3) Arctopsyche monoculture, (4) polyculture mixture of both species. Shading represents variation within one standard error.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4125303&req=5

pone-0103417-g005: Effects of increasing critical shear stress on predicted bedload sediment transport flux for Convict Creek.The snowmelt hydrograph in Convict Creek for the 1992–1993 water year (which began on October 1, 1992) is represented by the thick black line. The thin black and colored lines represent the predicted cumulative bedload sediment transported for the four values of critical shear stress that correspond to our measurements for the four caddisfly treatments in the experiment: (1) no caddisflies, (2) Ceratopsyche monoculture, (3) Arctopsyche monoculture, (4) polyculture mixture of both species. Shading represents variation within one standard error.
Mentions: The snow-melt hydrograph for the 1993 water year in Convict Creek (Figure 5) shows a peak discharge that had a ∼4 year recurrence interval, which can be considered representative of conditions with moderate but substantial bedload sediment transport. Overlain on the hydrograph is the predicted cumulative bedload sediment flux calculated under four scenarios of critical shear stress (τ*crit) taken from the treatment values measured in the laboratory flume experiment; means are shown as solid lines and shading indicates the range within one standard error. As shown in Figure 5, increasing the critical shear stress would be expected to delay the onset of bed mobility by up to 40 days and reduce the cumulative bedload sediment flux from 3.7 to 2.3 kT for the polyculture scenario (τ*crit = 0.086) over the 140-day snow-melt hydrograph. The sensitivity of sediment flux to increasing critical shear stress is non-linear, with a small effect for the Ceratopsyche monoculture (2% reduction), a moderate effect for the Arctopsyche monoculture (21% reduction), but a large effect for the polyculture (37% reduction). Again, we caution that Figure 5 represents an extrapolation of results from laboratory flumes to the field and, in doing so, makes many unverified assumptions about the transferability of biological impacts to natural stream conditions. These results should only be viewed as an unverified, a priori hypothesis of what impacts caddisflies ‘might’ have in a stream like Convict Creek.

Bottom Line: Previous studies have shown that biological structures such as plant roots can have large impacts on landscape morphodynamics, and that physical models that do not incorporate biology can generate qualitatively incorrect predictions of sediment transport.However, work to date has focused almost entirely on the impacts of single, usually dominant, species.We then used this model to estimate potential bed movement in a natural stream for which we had measurements of channel geometry, grain size, and daily discharge.

View Article: PubMed Central - PubMed

Affiliation: Department of Ecology, Evolution, and Marine Biology, University of California Santa Barbara, Santa Barbara, CA, United States of America.

ABSTRACT
Previous studies have shown that biological structures such as plant roots can have large impacts on landscape morphodynamics, and that physical models that do not incorporate biology can generate qualitatively incorrect predictions of sediment transport. However, work to date has focused almost entirely on the impacts of single, usually dominant, species. Here we ask whether multiple, coexisting species of hydropsychid caddisfly larvae have different impacts on sediment mobility compared to single-species systems due to competitive interactions and niche differences. We manipulated the presence of two common species of net-spinning caddisfly (Ceratopsyche oslari, Arctopsyche californica) in laboratory mesocosms and measured how their silk filtration nets influence the critical shear stress required to initiate sediment grain motion when they were in monoculture versus polyculture. We found that critical shear stress increases non-additively in polycultures where species were allowed to interact. Critical shear stress was 26% higher in multi-species assemblages compared to the average single-species monoculture, and 21% greater than levels of stability achieved by the species having the largest impact on sediment motion in monoculture. Supplementary behavioral experiments suggest the non-additive increase in critical shear stress may have occurred as competition among species led to shifts in the spatial distribution of the two populations and complementary habitat use. To explore the implications of these results for field conditions, we used results from the laboratory study to parameterize a common model of sediment transport. We then used this model to estimate potential bed movement in a natural stream for which we had measurements of channel geometry, grain size, and daily discharge. Although this extrapolation is speculative, it illustrates that multi-species impacts could be sufficiently large to reduce bedload sediment flux over annual time scales in streams where multiple species of caddisfly are present.

Show MeSH
Related in: MedlinePlus