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2016 |
Uno, Hiromi Spatial and temporal linkage of stream-riparian food webs by seasonal migration of mayfly Ephemerella maculata PhD Thesis University of California, Berkeley, 2016, ISBN: 978-1-369-05549-8. Abstract | BibTeX | Tags: Aquatic insect, Aquatic-terrestrial linkage, Biological sciences, food web, Spatial heterogeneity, subsidy, Temporal heterogeneity @phdthesis{Uno2016, title = {Spatial and temporal linkage of stream-riparian food webs by seasonal migration of mayfly Ephemerella maculata}, author = {Hiromi Uno}, isbn = {978-1-369-05549-8}, year = {2016}, date = {2016-05-30}, school = {University of California, Berkeley}, abstract = {Stream environments are spatially and temporally heterogeneous. Mainstem rivers are often wide, sunlit, warm and productive, while tributaries are shaded by riparian trees, unproductive, and remain cool in summer. Within mainstem rivers themselves there is substantial spatial heterogeneity in habitat structure and physical conditions, such as water temperature. River environments also change dramatically with season. Organisms that live in the riverine environment respond to and take advantage of such heterogeneous environments by moving between microhabitats or shifting their phenology. I studied the life cycle of a riverine mayfly, Ephemerella maculata (Ephemerellidae), in a northern California river system, its responses to spatial and temporal heterogeneity, and how its movements connect stream and riparian food webs in space and time. I discovered that E. maculata migrates between the mainstem and tributaries of rivers during its life cycle, thereby linking food webs in these two habitats, and enhancing predator growth in unproductive tributaries. The resource subsidy from productive but warm rivers to cool, unproductive tributaries associated with the mayfly migration increase the growth of stenothermic predators like juvenile salmonids in otherwise food-limited, cool thermal refuges, and increase their resilience to future warming. Furthermore, I examined the resilience of E. maculata to changes in water temperature using field surveys and lab rearing experiments. I discovered that different life stages of E. maculata have different thermal responses, and they shift their phenology depending on the water temperature, allowing each life stage to occur in the most desirable thermal condition. Therefore, as long as the natural seasonal pattern of the water temperature is sustained, E. maculata can resist temperature changes by shifting their phenology. Finally, I have shown that thermal spatial heterogeneity of rivers desynchronizes mayfly emergence timing, prolonging the subsidy period to riparian predators, and changing the predators’ responses to this subsidy.}, keywords = {Aquatic insect, Aquatic-terrestrial linkage, Biological sciences, food web, Spatial heterogeneity, subsidy, Temporal heterogeneity}, pubstate = {published}, tppubtype = {phdthesis} } Stream environments are spatially and temporally heterogeneous. Mainstem rivers are often wide, sunlit, warm and productive, while tributaries are shaded by riparian trees, unproductive, and remain cool in summer. Within mainstem rivers themselves there is substantial spatial heterogeneity in habitat structure and physical conditions, such as water temperature. River environments also change dramatically with season. Organisms that live in the riverine environment respond to and take advantage of such heterogeneous environments by moving between microhabitats or shifting their phenology. I studied the life cycle of a riverine mayfly, Ephemerella maculata (Ephemerellidae), in a northern California river system, its responses to spatial and temporal heterogeneity, and how its movements connect stream and riparian food webs in space and time. I discovered that E. maculata migrates between the mainstem and tributaries of rivers during its life cycle, thereby linking food webs in these two habitats, and enhancing predator growth in unproductive tributaries. The resource subsidy from productive but warm rivers to cool, unproductive tributaries associated with the mayfly migration increase the growth of stenothermic predators like juvenile salmonids in otherwise food-limited, cool thermal refuges, and increase their resilience to future warming. Furthermore, I examined the resilience of E. maculata to changes in water temperature using field surveys and lab rearing experiments. I discovered that different life stages of E. maculata have different thermal responses, and they shift their phenology depending on the water temperature, allowing each life stage to occur in the most desirable thermal condition. Therefore, as long as the natural seasonal pattern of the water temperature is sustained, E. maculata can resist temperature changes by shifting their phenology. Finally, I have shown that thermal spatial heterogeneity of rivers desynchronizes mayfly emergence timing, prolonging the subsidy period to riparian predators, and changing the predators’ responses to this subsidy. |
2013 |
Atlas, William I; Palen, Wendy J; Courcelles, Danielle M; Munshaw, Robin G; Monteith, Zachary L Dependence of stream predators on terrestrial prey fluxes: food web responses to subsidized predation Journal Article Ecosphere , 4 (6), pp. 1-16, 2013. Abstract | Links | BibTeX | Tags: food web, stream predators, terrestrial preys @article{Atlas2013, title = {Dependence of stream predators on terrestrial prey fluxes: food web responses to subsidized predation}, author = {William I. Atlas and Wendy J. Palen and Danielle M. Courcelles and Robin G. Munshaw and Zachary L. Monteith}, url = {https://angelo.berkeley.edu/wp-content/uploads/Atlas_2013_Ecosphere.pdf}, doi = {10.1890/ES12-00366.1}, year = {2013}, date = {2013-06-06}, journal = {Ecosphere }, volume = {4}, number = {6}, pages = {1-16}, abstract = {Resource subsidies in the form of energy, materials, and organisms can support the productivity of recipient ecosystems. When subsidies increase the abundance of top predators, theory predicts that top-down interactions will be strengthened. However, the degree to which subsidies intensify predation should be constrained by the strength of interactions between predators and their prey. To test the potential for subsidies to drive strong top-down control by two stream predators, steelhead (Oncorhynchus mykiss) and Pacific giant salamander (Dicamptodon tenebrosus) we reduced terrestrial prey and manipulated the presence of predators in 32 stream reaches. Prey subsidies supported elevated growth of predatory steelhead in our study system and in the absence of allochthonous prey steelhead experienced a 187% reduction in growth. Despite the high biomass of subsidized predators, there was little support for strong top-down control of herbivore biomass, or a trophic cascade as measured by changes in AFDM and chlorophyll-a. This result was consistent across subsidy treatments, suggesting that predatory steelhead are unable to increase exploitation of aquatic prey in the absence of terrestrial prey subsidies. The potential for top-down control was apparently limited by the fact that most (82%) herbivores in our study system were armored and relatively invulnerable to predation. These results demonstrate the potential importance of behavioral and morphological adaptations that can temper predator prey interactions in highly subsidized ecosystems.}, keywords = {food web, stream predators, terrestrial preys}, pubstate = {published}, tppubtype = {article} } Resource subsidies in the form of energy, materials, and organisms can support the productivity of recipient ecosystems. When subsidies increase the abundance of top predators, theory predicts that top-down interactions will be strengthened. However, the degree to which subsidies intensify predation should be constrained by the strength of interactions between predators and their prey. To test the potential for subsidies to drive strong top-down control by two stream predators, steelhead (Oncorhynchus mykiss) and Pacific giant salamander (Dicamptodon tenebrosus) we reduced terrestrial prey and manipulated the presence of predators in 32 stream reaches. Prey subsidies supported elevated growth of predatory steelhead in our study system and in the absence of allochthonous prey steelhead experienced a 187% reduction in growth. Despite the high biomass of subsidized predators, there was little support for strong top-down control of herbivore biomass, or a trophic cascade as measured by changes in AFDM and chlorophyll-a. This result was consistent across subsidy treatments, suggesting that predatory steelhead are unable to increase exploitation of aquatic prey in the absence of terrestrial prey subsidies. The potential for top-down control was apparently limited by the fact that most (82%) herbivores in our study system were armored and relatively invulnerable to predation. These results demonstrate the potential importance of behavioral and morphological adaptations that can temper predator prey interactions in highly subsidized ecosystems. |
2010 |
Holomuzki, Joseph R; Feminella, Jack W; Power, Mary E Biotic interactions in freshwater benthic habitats Journal Article Journal of the North American Benthological Society, 29 (1), pp. 220-244, 2010. Abstract | Links | BibTeX | Tags: food web, freshwater benthic habitat @article{Holomuzki2010, title = {Biotic interactions in freshwater benthic habitats}, author = {Joseph R. Holomuzki and Jack W. Feminella and Mary E. Power}, url = {https://angelo.berkeley.edu/wp-content/uploads/Holomuzki_2010_JoNorthBenthoSoc.pdf}, doi = {10.1899/08-044.1}, year = {2010}, date = {2010-03-01}, journal = {Journal of the North American Benthological Society}, volume = {29}, number = {1}, pages = {220-244}, abstract = {We summarized studies on the impacts and scale effects of negative (competition, predation, parasitism, herbivory) and positive (mutualism, commensalism, indirect facilitation) species interactions in freshwater benthic habitats since ,1986 and focused on organisms with mainly or entirely aquatic life cycles. Benthologists publishing in J-NABS have contributed robustly to our overall knowledge of predation and herbivory but less so of other species interactions. Predators can limit the abundance of benthic prey and affect prey size or age structure, behavior, and morphology, and these effects can be transmitted through food webs and ecosystems. Herbivores can limit biomass of benthic algae, alter physiognomy, species composition and diversity, and stoichiometry, and exert strong indirect effects within food webs and nutrient cycles. Parasites can alter host behavior or morphology, but few studies have shown that lethal/sublethal effects of parasites on their hosts have population- or community-scale consequences. Fishes and macroinvertebrates occasionally experience competition, but the effect of competition on demographies and assemblages appears restricted to local scales, perhaps because competition can be modulated by many biotic (bioenergetic efficiency, parasitism, predation) and abiotic (floods, drought, resource distribution) factors. Positive interactions have been the least studied species interaction by benthologists, but interest is growing. Future study of population-scale positive interactions and nontraditional interactions at larger scales (e.g., riparian effects on benthic habitat stabilization, crosssystem recruitment of different life stages) will improve our understanding of freshwater benthic ecosystems and their conservation. We urge benthologists to explore how populations evolve in response to biotic interactions embedded in benthic communities and to assess how these responses might redefine trophic and community structure and their emergent properties.}, keywords = {food web, freshwater benthic habitat}, pubstate = {published}, tppubtype = {article} } We summarized studies on the impacts and scale effects of negative (competition, predation, parasitism, herbivory) and positive (mutualism, commensalism, indirect facilitation) species interactions in freshwater benthic habitats since ,1986 and focused on organisms with mainly or entirely aquatic life cycles. Benthologists publishing in J-NABS have contributed robustly to our overall knowledge of predation and herbivory but less so of other species interactions. Predators can limit the abundance of benthic prey and affect prey size or age structure, behavior, and morphology, and these effects can be transmitted through food webs and ecosystems. Herbivores can limit biomass of benthic algae, alter physiognomy, species composition and diversity, and stoichiometry, and exert strong indirect effects within food webs and nutrient cycles. Parasites can alter host behavior or morphology, but few studies have shown that lethal/sublethal effects of parasites on their hosts have population- or community-scale consequences. Fishes and macroinvertebrates occasionally experience competition, but the effect of competition on demographies and assemblages appears restricted to local scales, perhaps because competition can be modulated by many biotic (bioenergetic efficiency, parasitism, predation) and abiotic (floods, drought, resource distribution) factors. Positive interactions have been the least studied species interaction by benthologists, but interest is growing. Future study of population-scale positive interactions and nontraditional interactions at larger scales (e.g., riparian effects on benthic habitat stabilization, crosssystem recruitment of different life stages) will improve our understanding of freshwater benthic ecosystems and their conservation. We urge benthologists to explore how populations evolve in response to biotic interactions embedded in benthic communities and to assess how these responses might redefine trophic and community structure and their emergent properties. |
2006 |
Howard, J K; Cuffey, K M The functional role of native freshwater mussels in the fluvial benthic environment Journal Article Freshwater Biology, 51 (3), pp. 460-474, 2006. Abstract | Links | BibTeX | Tags: benthic, biodeposit, California, fluvial, food web, freshwater mussels, functional role, trophic @article{Howard2006, title = {The functional role of native freshwater mussels in the fluvial benthic environment}, author = {J.K. Howard and K.M. Cuffey}, url = {https://angelo.berkeley.edu/wp-content/uploads/Howard_2006_FreshBio.pdf}, doi = {10.1111/j.1365-2427.2005.01507.x}, year = {2006}, date = {2006-02-10}, journal = {Freshwater Biology}, volume = {51}, number = {3}, pages = {460-474}, abstract = {1. Freshwater mussels are the dominant consumer biomass in many fluvial systems. As filter feeding grazers, mussels can remove large amounts of particulate matter from the water column and transfer these resources to the substrate as biodeposits (agglutinated mussel faeces and pseudofaeces). Mussel biodeposits are a nutrient rich and easily assimilated food source and therefore may have significant relevance to benthic community structure. This study examines the functional role of Margaritifera falcata in the South Fork Eel River, California. 2. We addressed two main questions: (i) Do mussels increase benthic resources in this system? (ii) If so, does this alter macroinvertebrate community structure? 3. Measurements and enclosure experiments in the South Fork Eel River show that mussels can play a significant role in local food webs by increasing available fine particulate matter (both organic and inorganic) on the substrate. We document increased benthic macroinvertebrate biomass for predators and collectors (Leptophlebidae) in the presence of mussels, but only in late summer.}, keywords = {benthic, biodeposit, California, fluvial, food web, freshwater mussels, functional role, trophic}, pubstate = {published}, tppubtype = {article} } 1. Freshwater mussels are the dominant consumer biomass in many fluvial systems. As filter feeding grazers, mussels can remove large amounts of particulate matter from the water column and transfer these resources to the substrate as biodeposits (agglutinated mussel faeces and pseudofaeces). Mussel biodeposits are a nutrient rich and easily assimilated food source and therefore may have significant relevance to benthic community structure. This study examines the functional role of Margaritifera falcata in the South Fork Eel River, California. 2. We addressed two main questions: (i) Do mussels increase benthic resources in this system? (ii) If so, does this alter macroinvertebrate community structure? 3. Measurements and enclosure experiments in the South Fork Eel River show that mussels can play a significant role in local food webs by increasing available fine particulate matter (both organic and inorganic) on the substrate. We document increased benthic macroinvertebrate biomass for predators and collectors (Leptophlebidae) in the presence of mussels, but only in late summer. |
McNeely, C; Clinton, S M; Erbe, J M Landscape variation in C sources of scraping primary consumers in streams Journal Article Journal of the North American Benthological Society, 25 (4), pp. 787-799, 2006. Abstract | Links | BibTeX | Tags: carbon source, diet, drainage area, Eel River drainage, epilithon, fine particulate organic matter, food web, Glossosoma, Heptageniidae, scrapers, Stable carbon isotopes @article{McNeely2006, title = {Landscape variation in C sources of scraping primary consumers in streams}, author = {C. McNeely and S. M. Clinton and J.M. Erbe}, url = {https://angelo.berkeley.edu/wp-content/uploads/McNeely_2006_Benth.pdf}, doi = {10.1899/0887-3593(2006)025[0787:LVICSO]2.0.CO;2}, year = {2006}, date = {2006-01-01}, journal = {Journal of the North American Benthological Society}, volume = {25}, number = {4}, pages = {787-799}, abstract = {We studied variation in C and energy flow in stream food webs by examining primary consumer diets and potential food sources at 8 sites of different drainage areas in the South Fork Eel River drainage. Both heptageniid mayfly nymphs and Glossosoma caddisfly larvae are considered scrapers in traditional functional feeding group classification, but past studies suggested that they differed in their relative use of terrestrial and algal C in some streams. In our study, microscopic examination and stable C isotope ratios (δ13C) suggested an increasing contribution of algae to both epilithic biofilms and fine particulate organic matter as stream drainage area and productivity increased. The proportion of algal cells in biofilms of small, unproductive streams was low, and biofilm δ13C values were similar to those of terrestrial detritus, suggesting that biofilms were composed primarily of heterotrophic microorganisms. Glossosoma larvae fed selectively on algae where it was scarce within the biofilms of small forested streams. In contrast, heptageniid mayfly nymphs did not appear to feed selectively on algae, but consumed algae and other materials in proportion to their abundance in the environment. These feeding patterns may have consequences for energy flow through food webs. Heptageniid mayflies feeding on biofilms in unproductive streams may augment the flow of dissolved organic C from terrestrial sources through food webs. In contrast, selective feeding by abundant Glossosoma larvae may reduce the flow of algal C through food webs because they are resistant to aquatic predators.}, keywords = {carbon source, diet, drainage area, Eel River drainage, epilithon, fine particulate organic matter, food web, Glossosoma, Heptageniidae, scrapers, Stable carbon isotopes}, pubstate = {published}, tppubtype = {article} } We studied variation in C and energy flow in stream food webs by examining primary consumer diets and potential food sources at 8 sites of different drainage areas in the South Fork Eel River drainage. Both heptageniid mayfly nymphs and Glossosoma caddisfly larvae are considered scrapers in traditional functional feeding group classification, but past studies suggested that they differed in their relative use of terrestrial and algal C in some streams. In our study, microscopic examination and stable C isotope ratios (δ13C) suggested an increasing contribution of algae to both epilithic biofilms and fine particulate organic matter as stream drainage area and productivity increased. The proportion of algal cells in biofilms of small, unproductive streams was low, and biofilm δ13C values were similar to those of terrestrial detritus, suggesting that biofilms were composed primarily of heterotrophic microorganisms. Glossosoma larvae fed selectively on algae where it was scarce within the biofilms of small forested streams. In contrast, heptageniid mayfly nymphs did not appear to feed selectively on algae, but consumed algae and other materials in proportion to their abundance in the environment. These feeding patterns may have consequences for energy flow through food webs. Heptageniid mayflies feeding on biofilms in unproductive streams may augment the flow of dissolved organic C from terrestrial sources through food webs. In contrast, selective feeding by abundant Glossosoma larvae may reduce the flow of algal C through food webs because they are resistant to aquatic predators. |
2002 |
Sabo, John L; Power, Mary E Numerical response of riparian lizards to aquatic insects and the short-term consequences for alternate terrestrial prey Journal Article Ecology, 83 (11), pp. 3023-3036, 2002. Abstract | Links | BibTeX | Tags: Carabidae, food web, indirect effects, insect, lizard, Lycosidae, numerical response, Riparian, river–watershed exchange, Sceloporus occidentalis, subsidy, Western fence lizard @article{Sabo2002, title = {Numerical response of riparian lizards to aquatic insects and the short-term consequences for alternate terrestrial prey}, author = {John L. Sabo and Mary E. Power}, url = {https://angelo.berkeley.edu/wp-content/uploads/Numerical-response-of-riparian-lizards-to-aquatic-insects-and-the-short-term-consequences-for-alternate-terrestrial-prey_Sabo_2002.pdf}, doi = {10.2307/3071839}, year = {2002}, date = {2002-00-00}, journal = {Ecology}, volume = {83}, number = {11}, pages = {3023-3036}, abstract = {Spatial subsidies, or inputs of resources from more productive donor habitats, can cause numerical responses in consumer populations via behavioral and demographic mechanisms. In addition, subsidies may have indirect effects on the in situ prey of these consumers. These indirect effects can be either negative (e.g., apparent competition) or positive (e.g., via diet shifts) depending on the relative strength of the predator’s functional and numerical responses to prey subsidies. Here we report a numerical response by a lizard (Western fence lizard, Sceloporus occidentalis) to experimental reductions in the flux of river-derived insects. Initially, equal densities of lizards declined significantly faster in plots in which aquatic insect abundance was reduced by nearly 50% (season average) relative to controls. Abundance and biomass of terrestrial arthropods declined significantly between the start and end of the experiment across treatments. Despite consistently lower lizard abundance in plots with reduced subsidy levels, however, relative declines in the abundance and biomass of in situ terrestrial arthropods (all taxa combined) were not significantly different between reduced- and ambient-subsidy plots. Relative declines in spider biomass differed significantly between treatments and were higher in reduced-subsidy than ambient-subsidy plots, but only over one of three 3-wk sampling intervals. Thus, over the biologically active summer season, aquatic subsidies exerted brief positive or no significant indirect effects on the in situ prey of riparian lizards. These results suggest that, although aquatic insect prey may determine the spatial distribution and local abundance of riparian predators, the effects of increased predator density on in situ prey may be offset by higher per capita predation by these consumers on in situ prey in subsidy-poor relative to subsidy-rich habitats. Numerical response of lizards to aquatic insects and short-term consequences for terrestrial prey. }, keywords = {Carabidae, food web, indirect effects, insect, lizard, Lycosidae, numerical response, Riparian, river–watershed exchange, Sceloporus occidentalis, subsidy, Western fence lizard}, pubstate = {published}, tppubtype = {article} } Spatial subsidies, or inputs of resources from more productive donor habitats, can cause numerical responses in consumer populations via behavioral and demographic mechanisms. In addition, subsidies may have indirect effects on the in situ prey of these consumers. These indirect effects can be either negative (e.g., apparent competition) or positive (e.g., via diet shifts) depending on the relative strength of the predator’s functional and numerical responses to prey subsidies. Here we report a numerical response by a lizard (Western fence lizard, Sceloporus occidentalis) to experimental reductions in the flux of river-derived insects. Initially, equal densities of lizards declined significantly faster in plots in which aquatic insect abundance was reduced by nearly 50% (season average) relative to controls. Abundance and biomass of terrestrial arthropods declined significantly between the start and end of the experiment across treatments. Despite consistently lower lizard abundance in plots with reduced subsidy levels, however, relative declines in the abundance and biomass of in situ terrestrial arthropods (all taxa combined) were not significantly different between reduced- and ambient-subsidy plots. Relative declines in spider biomass differed significantly between treatments and were higher in reduced-subsidy than ambient-subsidy plots, but only over one of three 3-wk sampling intervals. Thus, over the biologically active summer season, aquatic subsidies exerted brief positive or no significant indirect effects on the in situ prey of riparian lizards. These results suggest that, although aquatic insect prey may determine the spatial distribution and local abundance of riparian predators, the effects of increased predator density on in situ prey may be offset by higher per capita predation by these consumers on in situ prey in subsidy-poor relative to subsidy-rich habitats. Numerical response of lizards to aquatic insects and short-term consequences for terrestrial prey. |
1999 |
Berlow, Eric L; Navarrete, Sergio A; Briggs, Cheryl J; Power, Mary E; Menge, Bruce A Quantifying variation in the strengths of species interactions Journal Article Ecology, 80 (7), pp. 2206-2224, 1999, ISSN: 0012-9658. Abstract | Links | BibTeX | Tags: density dependence, food web, functional response, interaction strength, keystone species, per capita effects, predator–prey interaction, simulation, species impact, species interactions @article{Berlow1999, title = {Quantifying variation in the strengths of species interactions}, author = {Eric L. Berlow and Sergio A. Navarrete and Cheryl J. Briggs and Mary E. Power and Bruce A. Menge}, url = {https://angelo.berkeley.edu/wp-content/uploads/QUANTIFYING-VARIATION-IN-THE-STRENGTHS-OF-SPECIES-INTERACTIONS_Berlow_1999.pdf}, doi = {10.1890/0012-9658(1999)080[2206:QVITSO]2.0.CO;2}, issn = {0012-9658}, year = {1999}, date = {1999-10-00}, journal = {Ecology}, volume = {80}, number = {7}, pages = {2206-2224}, abstract = {Understanding how the strengths of species interactions are distributed among species is critical for developing predictive models of natural food webs as well as for developing management and conservation strategies. Recently a number of ecologists have attempted to clarify the concepts of "strong-" and "weak-interactors" in a community, and to derive techniques for quantifying interaction strengths in the field, using metrics that are consistent, comparable, and of relevance to theoreticians. In this paper we examine potential biases in different empirical approaches to quantifying variation in interaction strengths within and among natural communities. Using both simulated and published data, we explore the behavior of four commonly used or recently proposed empirical measures of the strength of consumer-prey interactions. The type of index used, the experimental protocol, and the underlying model of predator-prey interaction all strongly influence one's perception of both (1) the distribution of interaction strengths among species (e.g., presence of "keystone" species), and (2) the specific identity of the interactions that appear to be most important. Raw treatment differences tend to emphasize effects on very abundant prey, while the three proportional indices tend to emphasize effects on extremely rare prey. Two of the proportional indices are inherently asymmetric about zero, and they inflate positive or negative effects, respectively. When predators exhibit a saturating functional response, the three proportional measures of per capita effect are biased toward a skewed distribution of interaction strengths dominated by effects on the rarest prey. Predator interference causes the per capita measures to emphasize the effects of rare predators. Estimates of per capita effects are also problematic when (1) the per capita effects are back-calculated from experiments designed to measure collective effects (e.g., predator exclusions), and (2) the collective effect of a predator is constant across a wide range of predator densities, as may be common for keystone predators. Finally, since all of the indices show time-dependent behavior, they are differentially suited fur different experimental protocols (e.g., short-term vs, long-term results, or community initially near vs. far from equilibrium). All the indices explored here have the potential to provide useful, complementary information about ecological impacts of species in natural communities. In this analysis, we attempt to clarify what each index actually measures and the conditions under which each is most revealing.}, keywords = {density dependence, food web, functional response, interaction strength, keystone species, per capita effects, predator–prey interaction, simulation, species impact, species interactions}, pubstate = {published}, tppubtype = {article} } Understanding how the strengths of species interactions are distributed among species is critical for developing predictive models of natural food webs as well as for developing management and conservation strategies. Recently a number of ecologists have attempted to clarify the concepts of "strong-" and "weak-interactors" in a community, and to derive techniques for quantifying interaction strengths in the field, using metrics that are consistent, comparable, and of relevance to theoreticians. In this paper we examine potential biases in different empirical approaches to quantifying variation in interaction strengths within and among natural communities. Using both simulated and published data, we explore the behavior of four commonly used or recently proposed empirical measures of the strength of consumer-prey interactions. The type of index used, the experimental protocol, and the underlying model of predator-prey interaction all strongly influence one's perception of both (1) the distribution of interaction strengths among species (e.g., presence of "keystone" species), and (2) the specific identity of the interactions that appear to be most important. Raw treatment differences tend to emphasize effects on very abundant prey, while the three proportional indices tend to emphasize effects on extremely rare prey. Two of the proportional indices are inherently asymmetric about zero, and they inflate positive or negative effects, respectively. When predators exhibit a saturating functional response, the three proportional measures of per capita effect are biased toward a skewed distribution of interaction strengths dominated by effects on the rarest prey. Predator interference causes the per capita measures to emphasize the effects of rare predators. Estimates of per capita effects are also problematic when (1) the per capita effects are back-calculated from experiments designed to measure collective effects (e.g., predator exclusions), and (2) the collective effect of a predator is constant across a wide range of predator densities, as may be common for keystone predators. Finally, since all of the indices show time-dependent behavior, they are differentially suited fur different experimental protocols (e.g., short-term vs, long-term results, or community initially near vs. far from equilibrium). All the indices explored here have the potential to provide useful, complementary information about ecological impacts of species in natural communities. In this analysis, we attempt to clarify what each index actually measures and the conditions under which each is most revealing. |
1996 |
Wootton, Timothy J; Parker, Michael S; Power, Mary E The effect of disturbance on river food webs Journal Article Science, 273 (5281), pp. 1558-1561, 1996. Abstract | Links | BibTeX | Tags: disturbance, food web, model @article{Wootton1996, title = {The effect of disturbance on river food webs}, author = {J. Timothy Wootton and Michael S. Parker and Mary E. Power}, url = {https://angelo.berkeley.edu/wp-content/uploads/Wootton_Science1996.pdf}, doi = {10.1126/science.273.5281.1558}, year = {1996}, date = {1996-09-13}, journal = {Science}, volume = {273}, number = {5281}, pages = {1558-1561}, abstract = {A multitrophic model integrating the effects of flooding disturbance and food web interactions in rivers predicted that removing floods would cause increases of predator-resistant grazing insects, which would divert energy away from the food chain leading to predatory fish. Experimental manipulations of predator-resistant grazers and top predators, and large-scale comparisons of regulated and unregulated rivers, verified the model predictions. Thus, multitrophic models can successfully synthesize a variety of ecological processes, and conservation programs may benefit by taking a food web perspective instead of concentrating on a single species.}, keywords = {disturbance, food web, model}, pubstate = {published}, tppubtype = {article} } A multitrophic model integrating the effects of flooding disturbance and food web interactions in rivers predicted that removing floods would cause increases of predator-resistant grazing insects, which would divert energy away from the food chain leading to predatory fish. Experimental manipulations of predator-resistant grazers and top predators, and large-scale comparisons of regulated and unregulated rivers, verified the model predictions. Thus, multitrophic models can successfully synthesize a variety of ecological processes, and conservation programs may benefit by taking a food web perspective instead of concentrating on a single species. |
1994 |
Parker, Michael S Feeding Ecology of Stream-Dwelling Pacific Giant Salamander Larvae (Dicamptodon tenebrosus) Journal Article Copeia, 1994 (3), pp. 705–718, 1994. Links | BibTeX | Tags: ecology, food web @article{Parker1994, title = {Feeding Ecology of Stream-Dwelling Pacific Giant Salamander Larvae (Dicamptodon tenebrosus)}, author = {Michael S. Parker}, url = {https://angelo.berkeley.edu/wp-content/uploads/ParkerMS_FeedEcolGiantSalamander_Copeia1994.pdf}, year = {1994}, date = {1994-00-00}, journal = {Copeia}, volume = {1994}, number = {3}, pages = {705–718}, keywords = {ecology, food web}, pubstate = {published}, tppubtype = {article} } |
1993 |
Parker, Michael S Predation by Pacific giant salamander larvae on juvenile steelhead trout Journal Article Northwestern Naturalist, 74 (3), pp. 77-81, 1993, ISSN: 10511733, 19385315. Links | BibTeX | Tags: ecology, food web @article{Parker1993, title = {Predation by Pacific giant salamander larvae on juvenile steelhead trout}, author = {Michael S. Parker}, url = {https://angelo.berkeley.edu/wp-content/uploads/ParkerMS_PredGiantSalamanderSteelhead_NorthNat1993.pdf}, issn = {10511733, 19385315}, year = {1993}, date = {1993-01-01}, journal = {Northwestern Naturalist}, volume = {74}, number = {3}, pages = {77-81}, keywords = {ecology, food web}, pubstate = {published}, tppubtype = {article} } |
1992 |
Power, M E Top down and bottom up forces in food webs: do plants have primacy? Journal Article Ecology, 73 (3), pp. 733-746, 1992. Links | BibTeX | Tags: food web, primacy @article{Power1992, title = {Top down and bottom up forces in food webs: do plants have primacy?}, author = {M.E. Power}, url = {https://angelo.berkeley.edu/wp-content/uploads/Power_1992_Eco2.pdf}, doi = {10.2307/1940153}, year = {1992}, date = {1992-06-00}, journal = {Ecology}, volume = {73}, number = {3}, pages = {733-746}, keywords = {food web, primacy}, pubstate = {published}, tppubtype = {article} } |