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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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Experimental methods.(A) The two caddisfly (Trichoptera: Hydropsychidae) species used in the experiment. These caddisflies have a fully aquatic larval life-stage during which time individuals spin nets in the benthic substrate to filter feed. Arctopsyche is, on average, twice as long and 7 times as heavy as Ceratopsyche (Figure S1). (B)The flume mesocosms used in the experiment (1.2-m long × 0.15-m wide × 0.20-m deep). A motor attached to a shaft and propeller recirculates water through the flume and over the sediment patch. Grey shading along the flume bottom represents the plexiglass false-bottom leading up to and behind the working patch of sediments.
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pone-0103417-g001: Experimental methods.(A) The two caddisfly (Trichoptera: Hydropsychidae) species used in the experiment. These caddisflies have a fully aquatic larval life-stage during which time individuals spin nets in the benthic substrate to filter feed. Arctopsyche is, on average, twice as long and 7 times as heavy as Ceratopsyche (Figure S1). (B)The flume mesocosms used in the experiment (1.2-m long × 0.15-m wide × 0.20-m deep). A motor attached to a shaft and propeller recirculates water through the flume and over the sediment patch. Grey shading along the flume bottom represents the plexiglass false-bottom leading up to and behind the working patch of sediments.

Mentions: The species that we studied were hydropsychid caddisflies (Trichoptera:Hydropsychidae), a group of insects that live in streams (Figure 1A). As larvae, the hydropsychid family of caddisflies live in the benthic habitat where they construct nets composed of silk threads across the interstitial spaces between sediment particles to capture food. They often occur in high densities (>103 m−2) in riffle habitats [21], [22], where bed sediments typically remain immobile until flow depth approaches bank-full. Previous studies have shown that these silk nets can bind sediments together, thereby increasing the critical shear stress required for incipient motion during high discharge events [22]–[24]. Although hydropsychid caddisflies are a geographically diverse group [25], no studies to date have explicitly monitored whether caddisflies in streams that contain multiple species have the same impact on sediment mobility as those that contain just one species. Given their life-history characteristics, there are several a priori reasons to hypothesize that multi-species assemblages might impact incipient motion differently than single species assemblages. First, body size differs considerably between species, leading to differences in the size of rocks, pore spaces, and flow velocities in which they construct nets [26], [27]. Second, when densities are high, caddisflies are aggressive, and compete intensely for suitable space to construct their nets [28], [29]. Taken together, the potential exists for competition to drive differential use of benthic habitat by species that differ in body size.


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

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

Experimental methods.(A) The two caddisfly (Trichoptera: Hydropsychidae) species used in the experiment. These caddisflies have a fully aquatic larval life-stage during which time individuals spin nets in the benthic substrate to filter feed. Arctopsyche is, on average, twice as long and 7 times as heavy as Ceratopsyche (Figure S1). (B)The flume mesocosms used in the experiment (1.2-m long × 0.15-m wide × 0.20-m deep). A motor attached to a shaft and propeller recirculates water through the flume and over the sediment patch. Grey shading along the flume bottom represents the plexiglass false-bottom leading up to and behind the working patch of sediments.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0103417-g001: Experimental methods.(A) The two caddisfly (Trichoptera: Hydropsychidae) species used in the experiment. These caddisflies have a fully aquatic larval life-stage during which time individuals spin nets in the benthic substrate to filter feed. Arctopsyche is, on average, twice as long and 7 times as heavy as Ceratopsyche (Figure S1). (B)The flume mesocosms used in the experiment (1.2-m long × 0.15-m wide × 0.20-m deep). A motor attached to a shaft and propeller recirculates water through the flume and over the sediment patch. Grey shading along the flume bottom represents the plexiglass false-bottom leading up to and behind the working patch of sediments.
Mentions: The species that we studied were hydropsychid caddisflies (Trichoptera:Hydropsychidae), a group of insects that live in streams (Figure 1A). As larvae, the hydropsychid family of caddisflies live in the benthic habitat where they construct nets composed of silk threads across the interstitial spaces between sediment particles to capture food. They often occur in high densities (>103 m−2) in riffle habitats [21], [22], where bed sediments typically remain immobile until flow depth approaches bank-full. Previous studies have shown that these silk nets can bind sediments together, thereby increasing the critical shear stress required for incipient motion during high discharge events [22]–[24]. Although hydropsychid caddisflies are a geographically diverse group [25], no studies to date have explicitly monitored whether caddisflies in streams that contain multiple species have the same impact on sediment mobility as those that contain just one species. Given their life-history characteristics, there are several a priori reasons to hypothesize that multi-species assemblages might impact incipient motion differently than single species assemblages. First, body size differs considerably between species, leading to differences in the size of rocks, pore spaces, and flow velocities in which they construct nets [26], [27]. Second, when densities are high, caddisflies are aggressive, and compete intensely for suitable space to construct their nets [28], [29]. Taken together, the potential exists for competition to drive differential use of benthic habitat by species that differ in body size.

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