2002
Sabo, John L.; Power, Mary E.
River-watershed exchange: Effects of riverine subsidies on riparian lizards and their terrestrial prey Journal Article
In: Ecology, vol. 83, no. 7, pp. 1860-1869, 2002, ISSN: 0012-9658.
Abstract | Links | BibTeX | Tags: APPARENT COMPETITION, AQUATIC INSECTS, BENTHIC-PELAGIC LINKS, COMMUNITIES, FOOD-WEB, invertebrates, ISLANDS, MARINE, SECONDARY PRODUCTION, STREAM
@article{Sabo2002,
title = {River-watershed exchange: Effects of riverine subsidies on riparian lizards and their terrestrial prey},
author = {John L. Sabo and Mary E. Power},
url = {https://angelo.berkeley.edu/wp-content/uploads/sites/59/River-watershed-exchange-Effects-of-riverine-subsidies-on-riparian-lizards-and-their-terrestrial-prey_Sabo_2002.pdf},
issn = {0012-9658},
year = {2002},
date = {2002-07-00},
journal = {Ecology},
volume = {83},
number = {7},
pages = {1860-1869},
abstract = {Resource subsidies from external habitats can enhance the performance or population density of local consumers, altering their effects on in situ prey. Indirect effects of subsidies may be either positive or negative depending on the behavior of the shared consumer. Here we document strong links between riverine insects, riparian lizards (Sceloporus occidentalis), and terrestrial invertebrates. We hypothesized that aquatic insects subsidize riparian lizard populations leading to higher growth rates of these lizards in near-river habitats, and that subsidies exert short-term positive effects on terrestrial resources as a result of diet shifts by lizards to aquatic insects. To test these hypotheses, we used 2 m high fences, or "subsidy shields," to experimentally reduce aquatic insect flux to large (91 m 2) enclosures of lizards. Subsidy shields reduced aquatic insect flux by 55-65%. Growth rates of lizards were 7X higher in subsidized (no-shield) enclosures during the early summer but were not significantly different later in the summer, when ambient fluxes of aquatic insects dropped to 20% of their early season levels. Within the watershed, lizard growth rates (in mass) were positively correlated with the numerical abundance of aquatic insects. Thus, lizard growth rates tracked both seasonal and spatial availability of riverine insect subsidies during our experiment. Subsidies also had indirect effects on the ground-dwelling, terrestrial prey of lizards. Declines of diurnal terrestrial invertebrates Were significantly higher in shield than no-shield enclosures, and the most common ground spider (Arctosa sp. [Lycosidae]) disappeared completely from shield enclosures by the end of the experiment. Declines in terrestrial invertebrate abundance did not differ between no-shield enclosures and lizard exclosures. These data suggest that riverine insects subsidize riparian Sceloporus and, in the short term, reduce their predation on terrestrial arthropods.},
keywords = {APPARENT COMPETITION, AQUATIC INSECTS, BENTHIC-PELAGIC LINKS, COMMUNITIES, FOOD-WEB, invertebrates, ISLANDS, MARINE, SECONDARY PRODUCTION, STREAM},
pubstate = {published},
tppubtype = {article}
}
Resource subsidies from external habitats can enhance the performance or population density of local consumers, altering their effects on in situ prey. Indirect effects of subsidies may be either positive or negative depending on the behavior of the shared consumer. Here we document strong links between riverine insects, riparian lizards (Sceloporus occidentalis), and terrestrial invertebrates. We hypothesized that aquatic insects subsidize riparian lizard populations leading to higher growth rates of these lizards in near-river habitats, and that subsidies exert short-term positive effects on terrestrial resources as a result of diet shifts by lizards to aquatic insects. To test these hypotheses, we used 2 m high fences, or “subsidy shields,” to experimentally reduce aquatic insect flux to large (91 m 2) enclosures of lizards. Subsidy shields reduced aquatic insect flux by 55-65%. Growth rates of lizards were 7X higher in subsidized (no-shield) enclosures during the early summer but were not significantly different later in the summer, when ambient fluxes of aquatic insects dropped to 20% of their early season levels. Within the watershed, lizard growth rates (in mass) were positively correlated with the numerical abundance of aquatic insects. Thus, lizard growth rates tracked both seasonal and spatial availability of riverine insect subsidies during our experiment. Subsidies also had indirect effects on the ground-dwelling, terrestrial prey of lizards. Declines of diurnal terrestrial invertebrates Were significantly higher in shield than no-shield enclosures, and the most common ground spider (Arctosa sp. [Lycosidae]) disappeared completely from shield enclosures by the end of the experiment. Declines in terrestrial invertebrate abundance did not differ between no-shield enclosures and lizard exclosures. These data suggest that riverine insects subsidize riparian Sceloporus and, in the short term, reduce their predation on terrestrial arthropods.
2001
Power, Mary E.
Prey exchange between a stream and its forested watershed elevate predator densities in both habitats Journal Article
In: Proceedings of the National Academy of Sciences of the United States of America, vol. 98, no. 1, pp. 14-15, 2001, ISSN: 0027-8424.
Abstract | Links | BibTeX | Tags: AQUATIC INSECTS, ISLANDS, MARINE, terrestrial food webs
@article{Power2001c,
title = {Prey exchange between a stream and its forested watershed elevate predator densities in both habitats},
author = {Mary E. Power},
url = {https://angelo.berkeley.edu/wp-content/uploads/sites/59/PNAS-2001-Power-14-5.pdf},
doi = {10.1073/pnas.98.1.14},
issn = {0027-8424},
year = {2001},
date = {2001-01-02},
journal = {Proceedings of the National Academy of Sciences of the United States of America},
volume = {98},
number = {1},
pages = {14-15},
abstract = {On the 27th of March, 2000, ecology lost two leaders who leave important legacies to the study of food webs. Shigeru Nakano, whose paper with Masashi Murakami appears in this issue of PNAS (1), was visiting Gary Polis at his field site in Baja California. Polis, Nakano, and three other colleagues perished when their boat capsized in a violent, unexpected storm offshore from Bahia de Los Angeles in the Sea of Cortez.},
keywords = {AQUATIC INSECTS, ISLANDS, MARINE, terrestrial food webs},
pubstate = {published},
tppubtype = {article}
}
On the 27th of March, 2000, ecology lost two leaders who leave important legacies to the study of food webs. Shigeru Nakano, whose paper with Masashi Murakami appears in this issue of PNAS (1), was visiting Gary Polis at his field site in Baja California. Polis, Nakano, and three other colleagues perished when their boat capsized in a violent, unexpected storm offshore from Bahia de Los Angeles in the Sea of Cortez.
1997
Kupferberg, Sarah J.
Facilitation of periphyton production by tadpole grazing: functional differences between species Journal Article
In: Freshwater Biology, vol. 37, no. 2, pp. 427-439, 1997.
Abstract | Links | BibTeX | Tags: AQUATIC INSECTS, bottom-up, competition, epiphytes, food webs, herbivores, nutrient, stream periphyton, top-down, trophic cascades
@article{Kupferberg1997c,
title = {Facilitation of periphyton production by tadpole grazing: functional differences between species},
author = {Sarah J. Kupferberg},
url = {https://angelo.berkeley.edu/wp-content/uploads/sites/59/KUPFERBERG_Freshwater_Biology1997.pdf},
year = {1997},
date = {1997-04-00},
journal = {Freshwater Biology},
volume = {37},
number = {2},
pages = {427-439},
abstract = {1. This study examined how interactions between resources that vary in edibility, and herbivores that vary in ability to acquire resources, control primary productivity. In a northern California river, grazing on Cladophora glomerata, a relatively inedible filamentous green alga, and its more nutritious epiphytic diatoms, was manipulated by exposing cobbles to tadpoles (Rana boylii or Hyla regilla) or excluding tadpoles.
2. Rana indirectly facilitated Cladophora by removing diatoms, whereas Hyla did not significantly change biomass relative to controls. Algal ash-free dry mass on cobbles in Rana treatments was 65 and 72% greater than on controls in two years of investigation (1991 and 1993). Rana decreased epiphytic diatom biovolume by 56% and detritus by 87%.
3. Because nitrogen excretion rates of Hyla and Rana were similar, the differences in effect between the two species were probably due to their roles as consumers rather than as recyclers.
4. The net effect of Rana on periphyton was a 10% increase in areal specific primary productivity (mg O-2 h(-1) m(-2)); Hyla caused an 18% decrease. Rana decreased biomass-specific productivity (mg O-2 h(-1) g(-1)) 44%; Hyla had no effect.
5. In tadpole exclosures, grazers such as baetid mayfly larvae (mostly Centroptilum sp.) were 4.7 (1991) and 1.8 (1993) times more abundant, and midge larvae (Chironomidae) were 2.5 (1991) and 2 (1993) times more abundant than in Rana enclosures. Invertebrate assemblages in Hyla enclosures, however, were similar to exclosures. Few predatory insects and fish colonized Rana enclosures. Path analyses indicated that Rana affected macroinvertebrates via both interference and exploitation of epiphytic diatoms.},
keywords = {AQUATIC INSECTS, bottom-up, competition, epiphytes, food webs, herbivores, nutrient, stream periphyton, top-down, trophic cascades},
pubstate = {published},
tppubtype = {article}
}
1. This study examined how interactions between resources that vary in edibility, and herbivores that vary in ability to acquire resources, control primary productivity. In a northern California river, grazing on Cladophora glomerata, a relatively inedible filamentous green alga, and its more nutritious epiphytic diatoms, was manipulated by exposing cobbles to tadpoles (Rana boylii or Hyla regilla) or excluding tadpoles.
2. Rana indirectly facilitated Cladophora by removing diatoms, whereas Hyla did not significantly change biomass relative to controls. Algal ash-free dry mass on cobbles in Rana treatments was 65 and 72% greater than on controls in two years of investigation (1991 and 1993). Rana decreased epiphytic diatom biovolume by 56% and detritus by 87%.
3. Because nitrogen excretion rates of Hyla and Rana were similar, the differences in effect between the two species were probably due to their roles as consumers rather than as recyclers.
4. The net effect of Rana on periphyton was a 10% increase in areal specific primary productivity (mg O-2 h(-1) m(-2)); Hyla caused an 18% decrease. Rana decreased biomass-specific productivity (mg O-2 h(-1) g(-1)) 44%; Hyla had no effect.
5. In tadpole exclosures, grazers such as baetid mayfly larvae (mostly Centroptilum sp.) were 4.7 (1991) and 1.8 (1993) times more abundant, and midge larvae (Chironomidae) were 2.5 (1991) and 2 (1993) times more abundant than in Rana enclosures. Invertebrate assemblages in Hyla enclosures, however, were similar to exclosures. Few predatory insects and fish colonized Rana enclosures. Path analyses indicated that Rana affected macroinvertebrates via both interference and exploitation of epiphytic diatoms.
2. Rana indirectly facilitated Cladophora by removing diatoms, whereas Hyla did not significantly change biomass relative to controls. Algal ash-free dry mass on cobbles in Rana treatments was 65 and 72% greater than on controls in two years of investigation (1991 and 1993). Rana decreased epiphytic diatom biovolume by 56% and detritus by 87%.
3. Because nitrogen excretion rates of Hyla and Rana were similar, the differences in effect between the two species were probably due to their roles as consumers rather than as recyclers.
4. The net effect of Rana on periphyton was a 10% increase in areal specific primary productivity (mg O-2 h(-1) m(-2)); Hyla caused an 18% decrease. Rana decreased biomass-specific productivity (mg O-2 h(-1) g(-1)) 44%; Hyla had no effect.
5. In tadpole exclosures, grazers such as baetid mayfly larvae (mostly Centroptilum sp.) were 4.7 (1991) and 1.8 (1993) times more abundant, and midge larvae (Chironomidae) were 2.5 (1991) and 2 (1993) times more abundant than in Rana enclosures. Invertebrate assemblages in Hyla enclosures, however, were similar to exclosures. Few predatory insects and fish colonized Rana enclosures. Path analyses indicated that Rana affected macroinvertebrates via both interference and exploitation of epiphytic diatoms.
Parker, Michael S.; Power, Mary E.
Effect of stream flow regulation and absence of scouring floods on trophic transfer of biomass to fish in Northern California rivers Journal Article
In: Technical Completion Report, University of California Water Resources Center, vol. UCAL-WRC-W-825, no. 825, 1997.
Abstract | Links | BibTeX | Tags: algae, AQUATIC INSECTS, Benthos, Fish Ecology, Flood Control, geomorphology, River Beds, Water Diversion, Watershed Management
@article{111bp,
title = {Effect of stream flow regulation and absence of scouring floods on trophic transfer of biomass to fish in Northern California rivers},
author = {Michael S. Parker and Mary E. Power},
url = {https://angelo.berkeley.edu/wp-content/uploads/sites/59/parker-power-flow-regulation-food-webs-tech-report-1997-copy-1.pdf},
year = {1997},
date = {1997-01-01},
urldate = {1997-01-01},
journal = {Technical Completion Report, University of California Water Resources Center},
volume = {UCAL-WRC-W-825},
number = {825},
abstract = {Scouring winter floods strongly influence the structure and dynamics of food webs in rivers with winter flood, summer drought hydrographs. Reduction or elimination of scouring floods, in addtition to altering physical conditions within rivers, may negatively affect salmonid populations by reducing energy flow to them from lower trophic levels. We compared food webs of two northern California rivers with drastically different flow regimes to assess the effects of differences in food web structure on the distribution and growth of juvenile steelhead trout. The upper Mad River has a highly regulated flow regime and rarely experiences scouring winter floods, while the upper Van Duzen River is free-flowing and experiences frequent scouring floods. Thrroughout spring and summer 1994 densities of the large, grazing caddisfly Dicosmoecus gilvipes exceeded 801m2 in the Mad River, but were < 21m2 in the Van Duzen. Consequently, filamentous green algae was nearly absent in the Mad from June through September, but was relatively abundant in the Van Duzen. Densities of other stream-dwelling insects (primarily Chironomids and mayflies, which are the preferred prey of juvenile salmonids) and juvenile steelhead were consistently mlich lower in the Mad than the Van Duzen. At the end of the summer, Dicosmoecus pupated, and thus became inactive, which resulted in a large bloom of filamentous green algae (primarily Oedogonium and Cladophora) and a several-fold increase in the densities of Chironomids and mayflies in the Mad but not the Van Duzen. River flows in 1995 were much higher than in 1994 and both rivers experienced a number of scouring floods. As a consequence, Dicosmoecus densities were reduced to < 21m2 in both rivers throughout the spring and summer. The Mad experienced a large Cladophora bloom, and densities of Chironomids and mayflies were several times higher in 1995 than 1994. These observations support our hypothesis that eliminating scouring floods favors large, slow-growing benthic insect taxa over smaller, faster-growing taxa whose populations build up rapidly after floods. Since the former are invulnerable to predation by juvenile salmonids, energy flow is reduced and juvenile salmonid populations decline.
Experimental manipulation of juvenile steelhead in artificial channels with and without Dicosmoecus allowed us to test this hypothesis more directly and without potential influences from factors other than food web structure that may have varied between regulated and unregulated rivers. Experimental results revealed that Dicosmoecus significantly reduced the availability of small prey, which resulted in negative juvenile steelhead growth. Together, our surveys and experimental results show that elimination of scouring floods alters energy pathways in river food webs resulting in reduced biomass available to fish populations. Modifying flow regimes regulated by dams, so they more closely resemble natural hydrographs, may be an important step in restoring salmonid populations in some rivers.},
keywords = {algae, AQUATIC INSECTS, Benthos, Fish Ecology, Flood Control, geomorphology, River Beds, Water Diversion, Watershed Management},
pubstate = {published},
tppubtype = {article}
}
Scouring winter floods strongly influence the structure and dynamics of food webs in rivers with winter flood, summer drought hydrographs. Reduction or elimination of scouring floods, in addtition to altering physical conditions within rivers, may negatively affect salmonid populations by reducing energy flow to them from lower trophic levels. We compared food webs of two northern California rivers with drastically different flow regimes to assess the effects of differences in food web structure on the distribution and growth of juvenile steelhead trout. The upper Mad River has a highly regulated flow regime and rarely experiences scouring winter floods, while the upper Van Duzen River is free-flowing and experiences frequent scouring floods. Thrroughout spring and summer 1994 densities of the large, grazing caddisfly Dicosmoecus gilvipes exceeded 801m2 in the Mad River, but were < 21m2 in the Van Duzen. Consequently, filamentous green algae was nearly absent in the Mad from June through September, but was relatively abundant in the Van Duzen. Densities of other stream-dwelling insects (primarily Chironomids and mayflies, which are the preferred prey of juvenile salmonids) and juvenile steelhead were consistently mlich lower in the Mad than the Van Duzen. At the end of the summer, Dicosmoecus pupated, and thus became inactive, which resulted in a large bloom of filamentous green algae (primarily Oedogonium and Cladophora) and a several-fold increase in the densities of Chironomids and mayflies in the Mad but not the Van Duzen. River flows in 1995 were much higher than in 1994 and both rivers experienced a number of scouring floods. As a consequence, Dicosmoecus densities were reduced to < 21m2 in both rivers throughout the spring and summer. The Mad experienced a large Cladophora bloom, and densities of Chironomids and mayflies were several times higher in 1995 than 1994. These observations support our hypothesis that eliminating scouring floods favors large, slow-growing benthic insect taxa over smaller, faster-growing taxa whose populations build up rapidly after floods. Since the former are invulnerable to predation by juvenile salmonids, energy flow is reduced and juvenile salmonid populations decline.
Experimental manipulation of juvenile steelhead in artificial channels with and without Dicosmoecus allowed us to test this hypothesis more directly and without potential influences from factors other than food web structure that may have varied between regulated and unregulated rivers. Experimental results revealed that Dicosmoecus significantly reduced the availability of small prey, which resulted in negative juvenile steelhead growth. Together, our surveys and experimental results show that elimination of scouring floods alters energy pathways in river food webs resulting in reduced biomass available to fish populations. Modifying flow regimes regulated by dams, so they more closely resemble natural hydrographs, may be an important step in restoring salmonid populations in some rivers.
Experimental manipulation of juvenile steelhead in artificial channels with and without Dicosmoecus allowed us to test this hypothesis more directly and without potential influences from factors other than food web structure that may have varied between regulated and unregulated rivers. Experimental results revealed that Dicosmoecus significantly reduced the availability of small prey, which resulted in negative juvenile steelhead growth. Together, our surveys and experimental results show that elimination of scouring floods alters energy pathways in river food webs resulting in reduced biomass available to fish populations. Modifying flow regimes regulated by dams, so they more closely resemble natural hydrographs, may be an important step in restoring salmonid populations in some rivers.