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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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Shifts in net distribution in mono.- vs. polyculture suggest a likely mechanism leading to differences in critical shear stress.(A) A kernel density plot shows the density of nets at a given depth. Ceratopsyche (blue) and Arctopsyche (green) build at relatively similar depths in monoculture, although the smaller species, Ceratopsyche, is capable of building at a significantly deeper depth. Dotted lines represent the mean net depth for each species. (B) When placed together in polyculture, Arctopsyche shifts to build its nets at a shallower depth and Ceratopsyche shifts to build its nets at a deeper depth.
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pone-0103417-g003: Shifts in net distribution in mono.- vs. polyculture suggest a likely mechanism leading to differences in critical shear stress.(A) A kernel density plot shows the density of nets at a given depth. Ceratopsyche (blue) and Arctopsyche (green) build at relatively similar depths in monoculture, although the smaller species, Ceratopsyche, is capable of building at a significantly deeper depth. Dotted lines represent the mean net depth for each species. (B) When placed together in polyculture, Arctopsyche shifts to build its nets at a shallower depth and Ceratopsyche shifts to build its nets at a deeper depth.

Mentions: Our behavioral study of the vertical distributions of caddisfly net locations suggests that the observed non-additive increase in critical shear stress may have resulted from competitive interactions that caused both species to shift their habitat use and net locations when in polyculture. When the two species were in monoculture, Ceratopsyche nets were built, on average, at significantly deeper depths than Arctopsyche nets, at 29±1.3 mm and 22±1.1 mm (mean ± SEM) below the surface, respectively (Figure 3A, t-test: t = −4.1, p<0.001). When the two species were placed together and forced to interact, both species shifted the depth at which they built nets (Figure 3B). In polyculture, Arctopsyche nets were shallower than in monoculture (t-test: t = 2.9, p = 0.004) with a mean net depth of 18±1.0 mm. Ceratopsyche nets were deeper than in monoculture (t-test: t = −2.2, p = 0.03) with a mean net depth of 33±1.6 mm.


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

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

Shifts in net distribution in mono.- vs. polyculture suggest a likely mechanism leading to differences in critical shear stress.(A) A kernel density plot shows the density of nets at a given depth. Ceratopsyche (blue) and Arctopsyche (green) build at relatively similar depths in monoculture, although the smaller species, Ceratopsyche, is capable of building at a significantly deeper depth. Dotted lines represent the mean net depth for each species. (B) When placed together in polyculture, Arctopsyche shifts to build its nets at a shallower depth and Ceratopsyche shifts to build its nets at a deeper depth.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0103417-g003: Shifts in net distribution in mono.- vs. polyculture suggest a likely mechanism leading to differences in critical shear stress.(A) A kernel density plot shows the density of nets at a given depth. Ceratopsyche (blue) and Arctopsyche (green) build at relatively similar depths in monoculture, although the smaller species, Ceratopsyche, is capable of building at a significantly deeper depth. Dotted lines represent the mean net depth for each species. (B) When placed together in polyculture, Arctopsyche shifts to build its nets at a shallower depth and Ceratopsyche shifts to build its nets at a deeper depth.
Mentions: Our behavioral study of the vertical distributions of caddisfly net locations suggests that the observed non-additive increase in critical shear stress may have resulted from competitive interactions that caused both species to shift their habitat use and net locations when in polyculture. When the two species were in monoculture, Ceratopsyche nets were built, on average, at significantly deeper depths than Arctopsyche nets, at 29±1.3 mm and 22±1.1 mm (mean ± SEM) below the surface, respectively (Figure 3A, t-test: t = −4.1, p<0.001). When the two species were placed together and forced to interact, both species shifted the depth at which they built nets (Figure 3B). In polyculture, Arctopsyche nets were shallower than in monoculture (t-test: t = 2.9, p = 0.004) with a mean net depth of 18±1.0 mm. Ceratopsyche nets were deeper than in monoculture (t-test: t = −2.2, p = 0.03) with a mean net depth of 33±1.6 mm.

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