Recommended
Recommended
More Related Content
Recently uploaded
Recently uploaded (20)
Featured
Featured (20)
Do novel ecosystems follow predictable trajectoires? Testing the trophic surge hypothesis in reservoirs using fish
- 8. 5y 4y 14y 9y
- 9. Life history traits Trophic position Age at first reproduction Habitat selection Movement Filling time Eco-regions
- 10. P < 0.001 R2 = 0.29 P = 0.01 R2 = 0.13
- 11. Ostrofsky 1978 Balon and Coche 1974 Straskraba et al. 1993
Editor's Notes
- Thanks everyone for taking the time to hear what I have to say about fish community dynamics in large reservoirs. What I will present you today are results from my postdoc at McGill University in collaboration with Hydro-Québec as an industrial partner through a Mitacs Elevate scholarship. In this postdoc, I am looking at the effects of river impoundment on fish community dynamics using a multi-scale approach. If you want to learn more about my research interests, I invite you to have a look at my webpage.
- To see what is happening at the population level over time following impoundment, I decided to revisit the Trophic surge hypothesis. The TSH makes predictions about how the increase in phosphorus loading from the leaching and decomposition of organic matter from newly flooded terrestrial areas would affect productivity in reservoirs How this can be translated biologically, During the surge, the large influx of allochthonous inorganic nutrients and organic detritus from the flooded area should translated quickly into high primary production The rapid expansion of littoral habitat from the inundated terrestrial area would create new ecological niches, and coupled with high primary production, should result in high zooplankton and benthos productivity. Increases in primary production and secondary consumers should lead to a peak in fish recruitment followed by an increase in adults a few years. After the surge, the reservoir should experience a trophic depression, when available nutrients and detritus stocks are exhausted. The non-equilibrium phase should be then followed by a new trophic equilibrium where the reservoir stabilizes toward a steady “lake-type” ecosystem (Grimard and Jones 1982). We evaluated the prevalence of a hump-shaped pattern (i.e., surge and then depression during the trophic non-equilibrium phase) in 40 recruitment and 109 adult fish time series that came from seven different reservoirs in boreal and temperate ecosystems. This analysis was perform at the global scale. To test if the TSH was supported by each individual time series, we compared the fit of the data to alternative scenarios corresponding to plausible general abundance patterns that could be observed for the period covering before impoundment, during reservoir filling and after impoundment. Specifically, we tested for the presence of 1) no pattern over time (flat line function), 2) a linear increasing pattern; 3) a linear decreasing pattern, 4) a non-linear decreasing trend (negative exponential function), 5-6) two non-linear increasing pattern (negative exponential and quadratic polynomial functions), 7-8) two hump-shaped patterns suggested to capture the whole trophic surge hypothesis (using either Ricker and negative quadratic polynomial functions; Table S1, Fig. S1).
- To see what is happening at the population level over time following impoundment, I decided to revisit the Trophic surge hypothesis. The TSH makes predictions about how the increase in phosphorus loading from the leaching and decomposition of organic matter from newly flooded terrestrial areas would affect productivity in reservoirs How this can be translated biologically, During the surge, the large influx of allochthonous inorganic nutrients and organic detritus from the flooded area should translated quickly into high primary production The rapid expansion of littoral habitat from the inundated terrestrial area would create new ecological niches, and coupled with high primary production, should result in high zooplankton and benthos productivity. Increases in primary production and secondary consumers should lead to a peak in fish recruitment followed by an increase in adults a few years. After the surge, the reservoir should experience a trophic depression, when available nutrients and detritus stocks are exhausted. The non-equilibrium phase should be then followed by a new trophic equilibrium where the reservoir stabilizes toward a steady “lake-type” ecosystem (Grimard and Jones 1982). We evaluated the prevalence of a hump-shaped pattern (i.e., surge and then depression during the trophic non-equilibrium phase) in 40 recruitment and 109 adult fish time series that came from seven different reservoirs in boreal and temperate ecosystems. This analysis was perform at the global scale. To test if the TSH was supported by each individual time series, we compared the fit of the data to alternative scenarios corresponding to plausible general abundance patterns that could be observed for the period covering before impoundment, during reservoir filling and after impoundment. Specifically, we tested for the presence of 1) no pattern over time (flat line function), 2) a linear increasing pattern; 3) a linear decreasing pattern, 4) a non-linear decreasing trend (negative exponential function), 5-6) two non-linear increasing pattern (negative exponential and quadratic polynomial functions), 7-8) two hump-shaped patterns suggested to capture the whole trophic surge hypothesis (using either Ricker and negative quadratic polynomial functions; Table S1, Fig. S1).
- If a time series support the TSH, we should statistically detect a hump-shaped pattern A hump-shaped trend was the predominant pattern identified across individual recruitment time series based on curve fitting
- If a time series support the TSH, we should statistically detect a hump-shaped pattern A hump-shaped trend was the predominant pattern identified across individual recruitment time series based on curve fitting When we merged (combined) all the time series – very midl support Let’s explore this variation – One
- To go a step further to undersand what can cause variability in our ability to detect the surge and on the duration and magnitude and extract generalities, we we extracted 5 TSH metrics that could be used in a predictive framework. These TSH metrics were: 1) the occurrence of the TSH (i.e., detection of a hump-shaped pattern or not), 2) the duration of the trophic non-equilibrium phase in years (i.e., the time needed for abundance values to either come back to values comparable to pre-impoundment or to reach a stable state), 3) the duration of the surge in years (i.e., time needed to reach the peak in abundance from t0), 4-5) the magnitude of the peak in abundance in relation to t0BF and t0EF, and 5-6) the timing of the peak (i.e., year at which the peak occurred) in relation to t0BF and t0EF. We defined the duration of the trophic non-equilibrium and surge phases based on visual inspection of the time series whereas the magnitude of the peak was extracted by dividing the actual observed value at the peak for a given time series by the mean value of abundance before impoundment.
- Based on earlier studies, it has been suggested that the duration, magnitude of the surge, and the time to reach the trophic equilibrium, will vary as a function of several key attributes. Specifically, the following predictors have been proposed: 1) reservoir characteristics such as area flooded, depth, water residency time, geographic location (Dillon 1975, Ostrofsky 1978, Straškraba et al. 1993), 2) the degree of alteration in the hydrological regime and reservoir management, including the magnitude and timing of drawdown, reservoir filling options, mitigation measures (Grimard and Jones 1982, Pegg et al. 2015), 3), the land use and the amount of nutrient loading in the watershed (Ostrofsky 1978, Grimard and Jones 1982), 4) the species life history traits and the strength of trophic interactions (Cherry and Guthrie 1975), and 5) other external factors such as stocking, species introductions and fishing (Balon and Coche 1974, Kimmel and Groeger 1986, Pivnička 1992, Costa-Pierce 1997, Tessier et al. 2016). However, we have very little direct empirical evidence of the TSH, and a limited temporal perspective on the ecological consequences of creating a reservoir. analyse d'ajustement de courbe
- Here, you have two examples of TSH metrics from our 149 time series. In panel a) you have the duration of the TNE and in panel b, you have the duration of the surge As a first observation, there is quite a lot of variation among time series The trophic non-equilibrium phase lasted about nine years after filling in recruits for both ecoregions, but can last about at least 14 y in adult fish in boreal ecosystems. This is very conservative because many time series did not convincingly reach the equilibrium phase at the end of the dataset. The surge lasted about four years in recruits and about 5y in adults suggesting that the increase in abundance is fast and the depression took longer The next step
- Based on earlier studies, it has been suggested that the duration, magnitude of the surge, and the time to reach the trophic equilibrium, will vary as a function of several key attributes. Specifically, the following predictors have been proposed: 1) reservoir characteristics such as area flooded, depth, water residency time, geographic location (Dillon 1975, Ostrofsky 1978, Straškraba et al. 1993), 2) the degree of alteration in the hydrological regime and reservoir management, including the magnitude and timing of drawdown, reservoir filling options, mitigation measures (Grimard and Jones 1982, Pegg et al. 2015), 3), the land use and the amount of nutrient loading in the watershed (Ostrofsky 1978, Grimard and Jones 1982), 4) the species life history traits and the strength of trophic interactions (Cherry and Guthrie 1975), and 5) other external factors such as stocking, species introductions and fishing (Balon and Coche 1974, Kimmel and Groeger 1986, Pivnička 1992, Costa-Pierce 1997, Tessier et al. 2016). However, we have very little direct empirical evidence of the TSH, and a limited temporal perspective on the ecological consequences of creating a reservoir. analyse d'ajustement de courbe
- Based on earlier studies, it has been suggested that the duration, magnitude of the surge, and the time to reach the trophic equilibrium, will vary as a function of several key attributes. Specifically, the following predictors have been proposed: 1) reservoir characteristics such as area flooded, depth, water residency time, geographic location (Dillon 1975, Ostrofsky 1978, Straškraba et al. 1993), 2) the degree of alteration in the hydrological regime and reservoir management, including the magnitude and timing of drawdown, reservoir filling options, mitigation measures (Grimard and Jones 1982, Pegg et al. 2015), 3), the land use and the amount of nutrient loading in the watershed (Ostrofsky 1978, Grimard and Jones 1982), 4) the species life history traits and the strength of trophic interactions (Cherry and Guthrie 1975), and 5) other external factors such as stocking, species introductions and fishing (Balon and Coche 1974, Kimmel and Groeger 1986, Pivnička 1992, Costa-Pierce 1997, Tessier et al. 2016). However, we have very little direct empirical evidence of the TSH, and a limited temporal perspective on the ecological consequences of creating a reservoir. analyse d'ajustement de courbe
- Testing the TSH on fish was a first step. The next logical step would be to test the generality of the TSH on biogeochemical processes (e.g., phosphorus budget, sedimentation, GHG emissions) and other organisms from different trophic levels (e.g., primary producers, zooplankton, zoobenthos) across geographic latitudes. Then, we could develop a general framework exploring the ecological interactions between the different components (e.g., distance and lag between the peaks in abundance) from a bottom-up perspective. Interestingly, Ostrofsky (1978), Straškraba et al. (1993), and Kimmel and Groeger (1986) graphically explored the trajectory of several factors relevant to reservoir aging and dam closure (e.g., water conductivity, oxygen, total phosphorus, phytoplankton biomass, fish landings) and noted that many relationships were clearly hump-shaped. Based on these trajectories, long-term management recommendations should be not formulated before convincing evidence that the reservoir reached its new trophic equilibrium.
- Measures descriptives