Background/Question/Methods The direct effects of invasions by Bythotrephes longimanus in north-t... more Background/Question/Methods The direct effects of invasions by Bythotrephes longimanus in north-temperate lakes have now been reasonably well documented. Reductions in pelagic zooplankton species richness and abundance regularly occur and these changes typically divert resources away from native predators at higher trophic levels. Indirect effects of such invasions, even in the pelagic zone of lakes, have been much more difficult to demonstrate, but some evidence has recently emerged to document such effects on rotifer and phytoplankton communities in these systems. Aquatic ecologists have also recently been investigating the prevalence of benthic-pelagic coupling in lakes because of its potential consequences for influencing nutrient cycling, predator-prey interactions, and food web dynamics. We hypothesize that habitat coupling may result in an extension of the impacts of this invasive predator beyond the pelagic zone and into the littoral. The pre- and post-invasion biology of li...
In a seven-year long fish biomanipulation experiment, we successfully reduced the biomass of plan... more In a seven-year long fish biomanipulation experiment, we successfully reduced the biomass of planktivorous fish in one lake (Mouse Lake) while increasing planktivorous fish biomasses in another (Ranger Lake). A previous analysis (Yan et al. 2001) showed that the total biomass of crustacean zooplankton was unaffected by these changes in planktivore biomass and density but that significant changes were observed in zooplankton community composition and average body size. In Mouse Lake, the zooplankton community shifted from one dominated by small-bodied copepods to one with primarily large-bodied Cladocera. In Ranger Lake, a community with large-bodied Cladocera was replaced by smaller-bodied copepods. This pattern of zooplankton responses (and non-responses) suggested that the range of predator biomass in our whole-lake experiment was sufficient to affect only the size-structure and species composition and was not enough to influence total zooplankton biomass. However, a detailed anal...
Original Abstract: Larvae of the phantom midge, Chaoborus spp., are often the dominant invertebra... more Original Abstract: Larvae of the phantom midge, Chaoborus spp., are often the dominant invertebrate planktivore in temperate lakes. Chaoborus population dynamics may be influenced from the top-down by fish planktivory and in turn, may strongly influence the dynamics of their zooplankton prey. We analyzed this trophic cascade from planktivorous fish, through Chaoborus, to zooplankton using a seven-year study of fish biomanipulation in two oligotrophic lakes, located near Dorset, Ontario. This paper is one of a series of publications based on "The Dorset Project". Each paper focuses on different aspects of the whole-system experiment, from water chemistry to fish. Ranger Lake had a high biomass of piscivores (largemouth bass) and few planktivorous fish, while Mouse Lake with no obligate piscivores had an abundance of fish planktivores. After three years of initial study (1991-1993) the bass were removed from Ranger Lake and transferred to Mouse Lake. The entire communities o...
We developed a new simulation model approach to estimating secondary production of Chaoborus in o... more We developed a new simulation model approach to estimating secondary production of Chaoborus in order to determine the pathways and rates of energy flow between zooplankton, Chaoborus, and planktivorous fish. The model is applied to data from a seven-year long study of fish biomanipulation. A lake with high fish planktivore biomass and a second lake with high piscivore biomass were studied for three years (1991-1993), after which the piscivores were transferred to the high planktivore lake, and the two lakes were studied for a further four years (1994-1997). We found that the effects of fish on Chaoborus are complex, non-intuitive, and could not be elucidated from just studying patterns of zooplankton, Chanborus, and fish biomass. When predation from planktivorous fish is high, the well-known effects on the Chaoborus assemblage are a switch towards smaller-bodied species and a reduction in total Chaoborus biomass, while low fish predation is typified by high biomass and a predominan...
The Fluoroprobe (FP, bbe Moldaenke) is increasingly being used to determine the composition and e... more The Fluoroprobe (FP, bbe Moldaenke) is increasingly being used to determine the composition and extent of algal communities, providing total chlorophyll a concentrations (chl), pigment concentrations for 4 phytoplankton classes, and yellow substances (i.e. chromophoric dissolved organic matter). Evaluations of the instrument have been mixed, and extensive comparisons between in situ FP-measured chl (FP-chl), chl obtained by acetone extraction (AE-chl), and abundance using microscope counts are lacking. Using data from Severn Sound and inland lakes, we examine the accuracy of the FP in estimating chl, and whether this accuracy varies over space and time, or is influenced by sample complexity (composite vs. discrete samples). The FP's ability to distinguish phytoplankton groups is assessed by comparisons to microscope counts. Overall, in situ FP-chl correlated reasonably well with AE-chl (r 2 =0.57 for Severn Sound sites, r 2 =0.74 for inland lakes). The strength of the relationsh...
This file summarizes the basic findings of the Prairie Drought Project. Please see individual lak... more This file summarizes the basic findings of the Prairie Drought Project. Please see individual lake files, methods and land-use reports for additional details.
Proceedings. Biological sciences / The Royal Society, Jan 7, 2015
Calcium (Ca) concentrations are decreasing in softwater lakes across eastern North America and we... more Calcium (Ca) concentrations are decreasing in softwater lakes across eastern North America and western Europe. Using long-term contemporary and palaeo-environmental field data, we show that this is precipitating a dramatic change in Canadian lakes: the replacement of previously dominant pelagic herbivores (Ca-rich Daphnia species) by Holopedium glacialis, a jelly-clad, Ca-poor competitor. In some lakes, this transformation is being facilitated by increases in macro-invertebrate predation, both from native (Chaoborus spp.) and introduced (Bythotrephes longimanus) zooplanktivores, to which Holopedium, with its jelly coat, is relatively invulnerable. Greater representation by Holopedium within cladoceran zooplankton communities will reduce nutrient transfer through food webs, given their lower phosphorus content relative to daphniids, and greater absolute abundances may pose long-term problems to water users. The dominance of jelly-clad zooplankton will likely persist while lakewater C...
A Bayesian network model was developed to assess the combined influence of nutrient conditions an... more A Bayesian network model was developed to assess the combined influence of nutrient conditions and climate on the occurrence of cyanobacterial blooms within lakes of diverse hydrology and nutrient supply. Physicochemical, biological, and meteorological observations were collated from 20 lakes located at different latitudes and characterized by a range of sizes and trophic states. Using these data, we built a Bayesian network to (1) analyze the sensitivity of cyanobacterial bloom development to different environmental factors and (2) determine the probability that cyanobacterial blooms would occur. Blooms were classified in three categories of hazard (low, moderate, and high) based on cell abundances. The most important factors determining cyanobacterial bloom occurrence were water temperature, nutrient availability, and the ratio of mixing depth to euphotic depth. The probability of cyanobacterial blooms was evaluated under different combinations of total phosphorus and water temperature. The Bayesian network was then applied to quantify the probability of blooms under a future climate warming scenario. The probability of the ''high hazardous'' category of cyanobacterial blooms increased 5% in response to either an increase in water temperature of 0.88C (initial water temperature above 248C) or an increase in total phosphorus from 0.01 mg/L to 0.02 mg/L. Mesotrophic lakes were particularly vulnerable to warming. Reducing nutrient concentrations counteracts the increased cyanobacterial risk associated with higher temperatures.
Proceedings. Biological sciences / The Royal Society, Jan 7, 2014
Although competing species are expected to exhibit compensatory dynamics (negative temporal covar... more Although competing species are expected to exhibit compensatory dynamics (negative temporal covariation), empirical work has demonstrated that competitive communities often exhibit synchronous dynamics (positive temporal covariation). This has led to the suggestion that environmental forcing dominates species dynamics; however, synchronous and compensatory dynamics may appear at different length scales and/or at different times, making it challenging to identify their relative importance. We compiled 58 long-term datasets of zooplankton abundance in north-temperate and sub-tropical lakes and used wavelet analysis to quantify general patterns in the times and scales at which synchronous/compensatory dynamics dominated zooplankton communities in different regions and across the entire dataset. Synchronous dynamics were far more prevalent at all scales and times and were ubiquitous at the annual scale. Although we found compensatory dynamics in approximately 14% of all combinations of ...
Population dynamics are influenced by drivers acting from outside and from within an ecosystem. E... more Population dynamics are influenced by drivers acting from outside and from within an ecosystem. Extrinsic forces operating over broad spatial scales can impart synchronous behavior to separate populations, while internal, system-specific drivers often lead to idiosyncratic behavior. Here, we demonstrate synchrony in community-level dynamics among phytoplankton and bacteria in six north temperate humic lakes. The influence of regional meteorological factors explained much of the temporal variability in the phytoplankton community, and resulted in synchronous patterns of community change among lakes. Bacterial dynamics, in contrast, were driven by system-specific interactions with phytoplankton. Despite the importance of intrinsic factors for determining bacterial community composition and dynamics, we demonstrated that biological interactions transmitted the signal of the regional extrinsic drivers to the bacterial communities, ultimately resulting in synchronous community phenologies for bacterioplankton communities as well. This demonstrates how linkages between the components of a complex biological system can work to simplify the dynamics of the system and implies that it may be possible to predict the behavior of microbial communities responsible for important biogeochemical services in the landscape.
Proceedings of the National Academy of Sciences, 2003
Six high-resolution climatic reconstructions, based on diatom analyses from lake sediment cores f... more Six high-resolution climatic reconstructions, based on diatom analyses from lake sediment cores from the northern prairies of North America, show that shifts in drought conditions on decadal through multicentennial scales have prevailed in this region for at least the last two millennia. The predominant broad-scale pattern seen at all sites is a major shift in moisture regimes from wet to dry, or vice versa (depending on location), that occurred after a period of relative stability. These large-scale shifts at the different sites exhibit spatial coherence at regional scales. The three Canadian sites record this abrupt shift between anno Domini 500 and 800, and subsequently conditions become increasingly variable. All three U.S. sites underwent a pronounced change, but the timing of this change is between anno Domini 1000 and 1300, thus later than in all of the Canadian sites. The mechanisms behind these patterns are poorly understood, but they are likely related to changes in the shape and location of the jet stream and associated storm tracks. If the patterns seen at these sites are representative of the region, this observed pattern can have huge implications for future water availability in this region.
JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, a... more JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.
2006. A comparison of the species Á/time relationship across ecosystems and taxonomic groups. Á/ ... more 2006. A comparison of the species Á/time relationship across ecosystems and taxonomic groups. Á/ Oikos 112: 185 Á/195.
Insight into the causes and consequences of changes in aquatic biodiversity requires an improved ... more Insight into the causes and consequences of changes in aquatic biodiversity requires an improved understanding of the nature of the relationships between species richness and ecosystem function over a much longer temporal perspective than we currently possess. We used high-resolution paleoecological records from two prairie lakes to show that diatom species richness (as fossil frustules) was negatively correlated (r 2 ϭ 0.09-0.24, p Ͻ 0.001) with diatom production (as fossil pigments) during the past 2,000 yr. By comparing analyses from intervals of fresh and saline waters, we demonstrate that these significant richness-production relationships arose during freshwater periods (r 2 ϭ 0.13-0.45, p Ͻ 0.001) and could be eliminated (r 2 Ͻ 0.02, p Ͼ 0.1) by abiotic disturbances such as droughts. Procrustes analyses of the concordance of species change within freshwater communities and the change in richnessproduction relationships through time revealed that shifts in diatom community composition could have a large influence in determining the negative relationship between richness and production. Finally, significant correlations (r 2 ϭ 0.09-0.24, p Ͻ 0.0001) between past diatom species richness and ratios of stable isotopes (primarily ␦ 15 N) suggested that C and N biogeochemical cycles are also linked to changes in algal biodiversity. Taken together, these analyses suggest that the ongoing disruption of climate and biogeochemical systems by humans may obscure the relationship between aquatic biodiversity and ecosystem function in the future.
Background/Question/Methods The direct effects of invasions by Bythotrephes longimanus in north-t... more Background/Question/Methods The direct effects of invasions by Bythotrephes longimanus in north-temperate lakes have now been reasonably well documented. Reductions in pelagic zooplankton species richness and abundance regularly occur and these changes typically divert resources away from native predators at higher trophic levels. Indirect effects of such invasions, even in the pelagic zone of lakes, have been much more difficult to demonstrate, but some evidence has recently emerged to document such effects on rotifer and phytoplankton communities in these systems. Aquatic ecologists have also recently been investigating the prevalence of benthic-pelagic coupling in lakes because of its potential consequences for influencing nutrient cycling, predator-prey interactions, and food web dynamics. We hypothesize that habitat coupling may result in an extension of the impacts of this invasive predator beyond the pelagic zone and into the littoral. The pre- and post-invasion biology of li...
In a seven-year long fish biomanipulation experiment, we successfully reduced the biomass of plan... more In a seven-year long fish biomanipulation experiment, we successfully reduced the biomass of planktivorous fish in one lake (Mouse Lake) while increasing planktivorous fish biomasses in another (Ranger Lake). A previous analysis (Yan et al. 2001) showed that the total biomass of crustacean zooplankton was unaffected by these changes in planktivore biomass and density but that significant changes were observed in zooplankton community composition and average body size. In Mouse Lake, the zooplankton community shifted from one dominated by small-bodied copepods to one with primarily large-bodied Cladocera. In Ranger Lake, a community with large-bodied Cladocera was replaced by smaller-bodied copepods. This pattern of zooplankton responses (and non-responses) suggested that the range of predator biomass in our whole-lake experiment was sufficient to affect only the size-structure and species composition and was not enough to influence total zooplankton biomass. However, a detailed anal...
Original Abstract: Larvae of the phantom midge, Chaoborus spp., are often the dominant invertebra... more Original Abstract: Larvae of the phantom midge, Chaoborus spp., are often the dominant invertebrate planktivore in temperate lakes. Chaoborus population dynamics may be influenced from the top-down by fish planktivory and in turn, may strongly influence the dynamics of their zooplankton prey. We analyzed this trophic cascade from planktivorous fish, through Chaoborus, to zooplankton using a seven-year study of fish biomanipulation in two oligotrophic lakes, located near Dorset, Ontario. This paper is one of a series of publications based on "The Dorset Project". Each paper focuses on different aspects of the whole-system experiment, from water chemistry to fish. Ranger Lake had a high biomass of piscivores (largemouth bass) and few planktivorous fish, while Mouse Lake with no obligate piscivores had an abundance of fish planktivores. After three years of initial study (1991-1993) the bass were removed from Ranger Lake and transferred to Mouse Lake. The entire communities o...
We developed a new simulation model approach to estimating secondary production of Chaoborus in o... more We developed a new simulation model approach to estimating secondary production of Chaoborus in order to determine the pathways and rates of energy flow between zooplankton, Chaoborus, and planktivorous fish. The model is applied to data from a seven-year long study of fish biomanipulation. A lake with high fish planktivore biomass and a second lake with high piscivore biomass were studied for three years (1991-1993), after which the piscivores were transferred to the high planktivore lake, and the two lakes were studied for a further four years (1994-1997). We found that the effects of fish on Chaoborus are complex, non-intuitive, and could not be elucidated from just studying patterns of zooplankton, Chanborus, and fish biomass. When predation from planktivorous fish is high, the well-known effects on the Chaoborus assemblage are a switch towards smaller-bodied species and a reduction in total Chaoborus biomass, while low fish predation is typified by high biomass and a predominan...
The Fluoroprobe (FP, bbe Moldaenke) is increasingly being used to determine the composition and e... more The Fluoroprobe (FP, bbe Moldaenke) is increasingly being used to determine the composition and extent of algal communities, providing total chlorophyll a concentrations (chl), pigment concentrations for 4 phytoplankton classes, and yellow substances (i.e. chromophoric dissolved organic matter). Evaluations of the instrument have been mixed, and extensive comparisons between in situ FP-measured chl (FP-chl), chl obtained by acetone extraction (AE-chl), and abundance using microscope counts are lacking. Using data from Severn Sound and inland lakes, we examine the accuracy of the FP in estimating chl, and whether this accuracy varies over space and time, or is influenced by sample complexity (composite vs. discrete samples). The FP's ability to distinguish phytoplankton groups is assessed by comparisons to microscope counts. Overall, in situ FP-chl correlated reasonably well with AE-chl (r 2 =0.57 for Severn Sound sites, r 2 =0.74 for inland lakes). The strength of the relationsh...
This file summarizes the basic findings of the Prairie Drought Project. Please see individual lak... more This file summarizes the basic findings of the Prairie Drought Project. Please see individual lake files, methods and land-use reports for additional details.
Proceedings. Biological sciences / The Royal Society, Jan 7, 2015
Calcium (Ca) concentrations are decreasing in softwater lakes across eastern North America and we... more Calcium (Ca) concentrations are decreasing in softwater lakes across eastern North America and western Europe. Using long-term contemporary and palaeo-environmental field data, we show that this is precipitating a dramatic change in Canadian lakes: the replacement of previously dominant pelagic herbivores (Ca-rich Daphnia species) by Holopedium glacialis, a jelly-clad, Ca-poor competitor. In some lakes, this transformation is being facilitated by increases in macro-invertebrate predation, both from native (Chaoborus spp.) and introduced (Bythotrephes longimanus) zooplanktivores, to which Holopedium, with its jelly coat, is relatively invulnerable. Greater representation by Holopedium within cladoceran zooplankton communities will reduce nutrient transfer through food webs, given their lower phosphorus content relative to daphniids, and greater absolute abundances may pose long-term problems to water users. The dominance of jelly-clad zooplankton will likely persist while lakewater C...
A Bayesian network model was developed to assess the combined influence of nutrient conditions an... more A Bayesian network model was developed to assess the combined influence of nutrient conditions and climate on the occurrence of cyanobacterial blooms within lakes of diverse hydrology and nutrient supply. Physicochemical, biological, and meteorological observations were collated from 20 lakes located at different latitudes and characterized by a range of sizes and trophic states. Using these data, we built a Bayesian network to (1) analyze the sensitivity of cyanobacterial bloom development to different environmental factors and (2) determine the probability that cyanobacterial blooms would occur. Blooms were classified in three categories of hazard (low, moderate, and high) based on cell abundances. The most important factors determining cyanobacterial bloom occurrence were water temperature, nutrient availability, and the ratio of mixing depth to euphotic depth. The probability of cyanobacterial blooms was evaluated under different combinations of total phosphorus and water temperature. The Bayesian network was then applied to quantify the probability of blooms under a future climate warming scenario. The probability of the ''high hazardous'' category of cyanobacterial blooms increased 5% in response to either an increase in water temperature of 0.88C (initial water temperature above 248C) or an increase in total phosphorus from 0.01 mg/L to 0.02 mg/L. Mesotrophic lakes were particularly vulnerable to warming. Reducing nutrient concentrations counteracts the increased cyanobacterial risk associated with higher temperatures.
Proceedings. Biological sciences / The Royal Society, Jan 7, 2014
Although competing species are expected to exhibit compensatory dynamics (negative temporal covar... more Although competing species are expected to exhibit compensatory dynamics (negative temporal covariation), empirical work has demonstrated that competitive communities often exhibit synchronous dynamics (positive temporal covariation). This has led to the suggestion that environmental forcing dominates species dynamics; however, synchronous and compensatory dynamics may appear at different length scales and/or at different times, making it challenging to identify their relative importance. We compiled 58 long-term datasets of zooplankton abundance in north-temperate and sub-tropical lakes and used wavelet analysis to quantify general patterns in the times and scales at which synchronous/compensatory dynamics dominated zooplankton communities in different regions and across the entire dataset. Synchronous dynamics were far more prevalent at all scales and times and were ubiquitous at the annual scale. Although we found compensatory dynamics in approximately 14% of all combinations of ...
Population dynamics are influenced by drivers acting from outside and from within an ecosystem. E... more Population dynamics are influenced by drivers acting from outside and from within an ecosystem. Extrinsic forces operating over broad spatial scales can impart synchronous behavior to separate populations, while internal, system-specific drivers often lead to idiosyncratic behavior. Here, we demonstrate synchrony in community-level dynamics among phytoplankton and bacteria in six north temperate humic lakes. The influence of regional meteorological factors explained much of the temporal variability in the phytoplankton community, and resulted in synchronous patterns of community change among lakes. Bacterial dynamics, in contrast, were driven by system-specific interactions with phytoplankton. Despite the importance of intrinsic factors for determining bacterial community composition and dynamics, we demonstrated that biological interactions transmitted the signal of the regional extrinsic drivers to the bacterial communities, ultimately resulting in synchronous community phenologies for bacterioplankton communities as well. This demonstrates how linkages between the components of a complex biological system can work to simplify the dynamics of the system and implies that it may be possible to predict the behavior of microbial communities responsible for important biogeochemical services in the landscape.
Proceedings of the National Academy of Sciences, 2003
Six high-resolution climatic reconstructions, based on diatom analyses from lake sediment cores f... more Six high-resolution climatic reconstructions, based on diatom analyses from lake sediment cores from the northern prairies of North America, show that shifts in drought conditions on decadal through multicentennial scales have prevailed in this region for at least the last two millennia. The predominant broad-scale pattern seen at all sites is a major shift in moisture regimes from wet to dry, or vice versa (depending on location), that occurred after a period of relative stability. These large-scale shifts at the different sites exhibit spatial coherence at regional scales. The three Canadian sites record this abrupt shift between anno Domini 500 and 800, and subsequently conditions become increasingly variable. All three U.S. sites underwent a pronounced change, but the timing of this change is between anno Domini 1000 and 1300, thus later than in all of the Canadian sites. The mechanisms behind these patterns are poorly understood, but they are likely related to changes in the shape and location of the jet stream and associated storm tracks. If the patterns seen at these sites are representative of the region, this observed pattern can have huge implications for future water availability in this region.
JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, a... more JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.
2006. A comparison of the species Á/time relationship across ecosystems and taxonomic groups. Á/ ... more 2006. A comparison of the species Á/time relationship across ecosystems and taxonomic groups. Á/ Oikos 112: 185 Á/195.
Insight into the causes and consequences of changes in aquatic biodiversity requires an improved ... more Insight into the causes and consequences of changes in aquatic biodiversity requires an improved understanding of the nature of the relationships between species richness and ecosystem function over a much longer temporal perspective than we currently possess. We used high-resolution paleoecological records from two prairie lakes to show that diatom species richness (as fossil frustules) was negatively correlated (r 2 ϭ 0.09-0.24, p Ͻ 0.001) with diatom production (as fossil pigments) during the past 2,000 yr. By comparing analyses from intervals of fresh and saline waters, we demonstrate that these significant richness-production relationships arose during freshwater periods (r 2 ϭ 0.13-0.45, p Ͻ 0.001) and could be eliminated (r 2 Ͻ 0.02, p Ͼ 0.1) by abiotic disturbances such as droughts. Procrustes analyses of the concordance of species change within freshwater communities and the change in richnessproduction relationships through time revealed that shifts in diatom community composition could have a large influence in determining the negative relationship between richness and production. Finally, significant correlations (r 2 ϭ 0.09-0.24, p Ͻ 0.0001) between past diatom species richness and ratios of stable isotopes (primarily ␦ 15 N) suggested that C and N biogeochemical cycles are also linked to changes in algal biodiversity. Taken together, these analyses suggest that the ongoing disruption of climate and biogeochemical systems by humans may obscure the relationship between aquatic biodiversity and ecosystem function in the future.
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Papers by James Rusak