0000000000901536
AUTHOR
Tommi Perälä
Workshop on ICES reference points (WKREF2)
The ICES Workshop on ICES reference points (WKREF2) was tasked review the WKREF1 report and based on the outcome develop updated guidelines for the ICES reference points system and recommendations for ACOM consideration. The WKREF1 report has suggested 5 key recommendations to simplify and harmonise the ICES reference points framework representing a major change to the current guidelines. At WKREF2, we detailed discussions and four key concerns were raised about the proposed approach. The first related to the simplification of rules to define Blim. Around two thirds of category 1 stocks would end up as WKREF1 “Blim Type 2” where Blim would be set as a fraction of B0. The Allee effect or “de…
Effects of temporal abiotic drivers on the dynamics of an allometric trophic network model
Current ecological research and ecosystem management call for improved understanding of the abiotic drivers of community dynamics, including temperature effects on species interactions and biomass accumulation. Allometric trophic network (ATN) models, which simulate material (carbon) transfer in trophic networks from producers to consumers based on mass-specific metabolic rates, provide an attractive framework to study consumer–resource interactions from organisms to ecosystems. However, the developed ATN models rarely consider temporal changes in some key abiotic drivers that affect, for example, consumer metabolism and producer growth. Here, we evaluate how temporal changes in carrying ca…
Calibrating Expert Assessments Using Hierarchical Gaussian Process Models
Expert assessments are routinely used to inform management and other decision making. However, often these assessments contain considerable biases and uncertainties for which reason they should be calibrated if possible. Moreover, coherently combining multiple expert assessments into one estimate poses a long-standing problem in statistics since modeling expert knowledge is often difficult. Here, we present a hierarchical Bayesian model for expert calibration in a task of estimating a continuous univariate parameter. The model allows experts' biases to vary as a function of the true value of the parameter and according to the expert's background. We follow the fully Bayesian approach (the s…
The effect of fish life-history structures on the topologies of aquatic food webs
Biological organisms can vastly change their ecological functionality due to changes in body size and diet across their life. Consequently, it has been increasingly recognized that to attain sufficient biological realism, food webs may need to include life-history structures. The objective of the work is to study theoretically whether and how the inclusion of life-history structures affects the food web topology. Topological research was done by applying network theory metrics for three different food web types with two different sizes that were generated by using the niche-model. The dynamical modeling was performed by using an allometric trophic network modeling approach. The different ty…
Species’ ecological functionality alters the outcome of fish stocking success predicted by a food-web model
Fish stocking is used worldwide in conservation and management, but its effects on food-web dynamics and ecosystem stability are poorly known. To better understand these effects and predict the outcomes of stocking, we used an empirically validated network model of a well-studied lake ecosystem. We simulate two stocking scenarios with two native fish species valuable for fishing. In the first scenario, we stock planktivorous fish (whitefish) larvae in the ecosystem. This leads to a 1% increase in adult whitefish biomasses and decreases the biomasses of the top predator (perch). In the second scenario, we also stock perch larvae in the ecosystem. This decreases the planktivorous whitefish an…
Figure S4 from Species' ecological functionality alters the outcome of fish stocking success predicted by a food-web model
Changes in the adult whitefish and perch biomasses in response to increased whitefish (Wht300; black) and perch stocking (Wht300+Per50; red) compared to the whitefish baseline (Wht200; gray) under Fmax = 0.4 (10% lower fishing pressure than in the main text), Fmax = 0.5 (fishing pressure in the main text), and under Fmax = 0.6 (10% higher fishing pressure than in the main text). Dashed lines indicate the time point when fishing was introduced to the simulations.
Environmentally‐induced noise dampens and reddens with increasing trophic level in a complex food web
Stochastic variability of key abiotic factors including temperature, precipitation and the availability of light and nutrients greatly influences species’ ecological function and evolutionary fate. Despite such influence, ecologists have typically ignored the effect of abiotic stochasticity on the structure and dynamics of ecological networks. Here we help to fill that gap by advancing the theory of how abiotic stochasticity, in the form of environmental noise, affects the population dynamics of species within food webs. We do this by analysing an allometric trophic network model of Lake Constance subjected to positive (red), negative (blue), and non‐autocorrelated (white) abiotic temporal …
Detection of Allee effects in marine fishes: analytical biases generated by data availability and model selection
The demographic Allee effect, or depensation, implies positive association between per capita population growth rate and population size at low abundances, thereby lowering growth ability of sparse populations. This can have far-reaching consequences on population recovery ability and colonization success. In the context of marine fishes, there is a widespread perception that Allee effects are rare or non-existent. However, studies that have failed to detect Allee effects in marine fishes have suffered from several fundamental methodological and data limitations. In the present study, we challenge the prevailing perception about the rarity of Allee effects by analysing nine populations of …
Figure S1 from Species' ecological functionality alters the outcome of fish stocking success predicted by a food-web model
Changes in the adult whitefish and perch catches (as biomass densities) in response to increased whitefish (Wht300; black) and perch stocking (Wht300+Per50; red) compared to the whitefish baseline (Wht200; gray) during the 100 year fishing period.
ESM - Material and Methods from Species' ecological functionality alters the outcome of fish stocking success predicted by a food-web model
Fish stocking is used worldwide in conservation and management, but its effects on food-web dynamics and ecosystem stability are poorly known. To better understand these effects and predict the outcomes of stocking, we used an empirically validated network model of a well-studied lake ecosystem. We simulate two stocking scenarios with two native fish species valuable for fishing. In the first scenario, we stock planktivorous fish (whitefish) larvae in the ecosystem. This leads to a 1% increase in adult whitefish biomasses and decreases the biomasses of the top predator (perch). In the second scenario, we also stock perch larvae in the ecosystem. This decreases the planktivorous whitefish an…
Return of the Apex Predator : How Brown Trout (Salmo trutta) Re-Establishment Shapes an Ecosystem
Re-establishment of a declined apex predator fish species in a lake ecosystem may have dramatic effects on other fish and plankton community already inhabiting the ecosystem. We studied mechanistically potential impacts of re-establishment of the brown trout (Salmo trutta) in the west-central European Lake Constance focusing on two commercially important fish species: whitefish and Eurasian perch. We compared simulation model outputs from two versions of an allometric trophic network model for Lake Constance, one with and one without the trout as the apex predator. The re-establishment of the declined brown trout reduced the perch population directly by predation and indirectly by increased…
Disentangling conditional effects of multiple regime shifts on Atlantic cod productivity
AbstractRegime shifts are increasingly prevalent in the ecological literature. However, definitions vary, and many detection methods are subjective. Here, we employ an operationally objective means of identifying regime shifts, using a Bayesian online change-point detection algorithm able to simultaneously identify shifts in the mean and(or) variance of time series data. We detected multiple regime shifts in long-term (59-154 years) patterns of coastal Norwegian Atlantic cod (>70% decline) and putative drivers of cod productivity: North Atlantic Oscillation (NAO); sea-surface temperature; zooplankton abundance; fishing mortality (F). The consequences of an environmental or climate-relate…
Figure S4 from Species' ecological functionality alters the outcome of fish stocking success predicted by a food-web model
Changes in the adult whitefish and perch biomasses in response to increased whitefish (Wht300; black) and perch stocking (Wht300+Per50; red) compared to the whitefish baseline (Wht200; gray) under Fmax = 0.4 (10% lower fishing pressure than in the main text), Fmax = 0.5 (fishing pressure in the main text), and under Fmax = 0.6 (10% higher fishing pressure than in the main text). Dashed lines indicate the time point when fishing was introduced to the simulations.
Figure S3 from Species' ecological functionality alters the outcome of fish stocking success predicted by a food-web model
Changes in the adult perch biomasses in response to perch stocking (Wht300+Per50 [red]; Wht300+Per25 [pink]; Wht300+Per75 [orange]) compared to the increased whitefish stocking (Wht300 [black]). Dashed lines indicate the time point when fishing was introduced to the simulations.
Figure S1 from Species' ecological functionality alters the outcome of fish stocking success predicted by a food-web model
Changes in the adult whitefish and perch catches (as biomass densities) in response to increased whitefish (Wht300; black) and perch stocking (Wht300+Per50; red) compared to the whitefish baseline (Wht200; gray) during the 100 year fishing period.
Figure S2 from Species' ecological functionality alters the outcome of fish stocking success predicted by a food-web model
Changes in the adult whitefish biomasses in response to increased whitefish stocking (Wht250 [light blue]; Wht300 [black]; Wht350 [dark blue]) compared to the whitefish baseline (Wht200 [light gray]). Dashed lines indicate the time point when fishing was introduced to the simulations.
Figure S2 from Species' ecological functionality alters the outcome of fish stocking success predicted by a food-web model
Changes in the adult whitefish biomasses in response to increased whitefish stocking (Wht250 [light blue]; Wht300 [black]; Wht350 [dark blue]) compared to the whitefish baseline (Wht200 [light gray]). Dashed lines indicate the time point when fishing was introduced to the simulations.
Temporary Allee effects among non‐stationary recruitment dynamics in depleted gadid and flatfish populations
Many considerably declined fish populations have not fully recovered despite reductions in fishing pressure. One of the possible causes of impaired recovery is the (demographic) Allee effect. To investigate whether low-abundance recruitment dynamics can switch between compensation and depensation, the latter implying the presence of the Allee effect, we analysed the stock–recruitment time series of 17 depleted cod-type and flatfish populations using a Bayesian change point model. The recruitment dynamics were represented with the sigmoidal Beverton–Holt and the Saila–Lorda stock–recruitment models, allowing the parameters of the models to shift at a priori unknown change points. Our synthes…
Fishing triggers trophic cascade in terms of variation, not abundance, in an allometric trophic network model
Trophic cascade studies often rely on linear food chains instead of complex food webs and are typically measured as biomass averages, not as biomass variation. We study trophic cascades propagating across a complex food web including a measure of biomass variation in addition to biomass average. We examined whether different fishing strategies induce trophic cascades and whether the cascades differ from each other. We utilized an allometric trophic network (ATN) model to mechanistically study fishing-induced changes in food web dynamics. Different fishing strategies did not trigger traditional, reciprocal trophic cascades, as measured in biomass averages. Instead, fishing triggered a varia…
Eco‐evolutionary dynamics driven by fishing : from single species models to dynamic evolution within complex food webs
Evidence of contemporary evolution across ecological time scales stimulated research on the eco‐evolutionary dynamics of natural populations. Aquatic systems provide a good setting to study eco‐evolutionary dynamics owing to a wealth of long‐term monitoring data and the detected trends in fish life‐history traits across intensively harvested marine and freshwater systems. In the present study, we focus on modelling approaches to simulate eco‐evolutionary dynamics of fishes and their ecosystems. Firstly, we review the development of modelling from single‐species to multispecies approaches. Secondly, we advance the current state‐of‐the‐art methodology by implementing evolution of life‐history…
Planetary well-being
Tensions between the well-being of present humans, future humans, and nonhuman nature manifest in social protests and political and academic debates over the future of Earth. The increasing consumption of natural resources no longer increases, let alone equalizes, human well-being, but has led to the current ecological crisis and harms both human and nonhuman well-being. While the crisis has been acknowledged, the existing conceptual frameworks are in some respects ill-equipped to address the crisis in a way that would link the resolving of the crisis with the pivotal aim of promoting equal well-being. The shortcomings of the existing concepts in this respect relate to anthropocentric norma…
ESM - Material and Methods from Species' ecological functionality alters the outcome of fish stocking success predicted by a food-web model
Fish stocking is used worldwide in conservation and management, but its effects on food-web dynamics and ecosystem stability are poorly known. To better understand these effects and predict the outcomes of stocking, we used an empirically validated network model of a well-studied lake ecosystem. We simulate two stocking scenarios with two native fish species valuable for fishing. In the first scenario, we stock planktivorous fish (whitefish) larvae in the ecosystem. This leads to a 1% increase in adult whitefish biomasses and decreases the biomasses of the top predator (perch). In the second scenario, we also stock perch larvae in the ecosystem. This decreases the planktivorous whitefish an…
Planetary well-being
Tensions between the well-being of present humans, future humans, and nonhuman nature manifest in social protests and political and academic debates over the future of Earth. The increasing consumption of natural resources no longer increases, let alone equalises, human well-being, but has led to the current ecological crisis and harms both human and nonhuman well-being. While the crisis has been acknowledged, the existing conceptual frameworks are in some respects ill-equipped to address the crisis in a way that would link the resolving of the crisis with the pivotal aim of promoting equal well-being. The shortcomings of the existing concepts in this respect relate to anthropocentric norma…
Comparison of Bayesian and numerical optimization-based diet estimation on herbivorous zooplankton
Consumer diet estimation with biotracer-based mixing models provides valuable information about trophic interactions and the dynamics of complex ecosystems. Here, we assessed the performance of four Bayesian and three numerical optimization-based diet estimation methods for estimating the diet composition of herbivorous zooplankton using consumer fatty acid (FA) profiles and resource library consisting of the results of homogeneous diet feeding experiments. The method performance was evaluated in terms of absolute errors, central probability interval checks, the success in identifying the primary resource in the diet, and the ability to detect the absence of resources in the diet. Despite …
Figure S3 from Species' ecological functionality alters the outcome of fish stocking success predicted by a food-web model
Changes in the adult perch biomasses in response to perch stocking (Wht300+Per50 [red]; Wht300+Per25 [pink]; Wht300+Per75 [orange]) compared to the increased whitefish stocking (Wht300 [black]). Dashed lines indicate the time point when fishing was introduced to the simulations.
Supplementary tables and figures from Detection of Allee effects in marine fishes: analytical biases generated by data availability and model selection
The demographic Allee effect, or depensation, implies positive association between per capita population growth rate and population size at low abundances, thereby lowering growth ability of sparse populations. This can have far-reaching consequences on population recovery ability and colonization success. In the context of marine fishes, there is a widespread perception that Allee effects are rare or non-existent. However, studies that have failed to detect Allee effects in marine fishes have suffered from several fundamental methodological and data limitations. In the present study, we challenge the prevailing perception about the rarity of Allee effects by analysing nine populations of A…
Allee effects and the Allee-effect zone in northwest Atlantic cod
According to the theory of compensatory dynamics, depleted populations should recover when the threat responsible for their decline is removed because per capita population growth is assumed to be highest when populations are at their smallest viable sizes. Yet, many seriously depleted fish populations have failed to recover despite threat mitigation. Atlantic cod (Gadus morhua) stocks off Newfoundland, despite 30 years of dramatically reduced fishing mortality and numerous fishery closures, have not recovered, suggesting that drivers other than fishing can regulate the growth of collapsed fish populations, inhibiting or preventing their recovery. Here, using Bayesian inference, we show str…
Supplementary tables and figures from Detection of Allee effects in marine fishes: analytical biases generated by data availability and model selection
The demographic Allee effect, or depensation, implies positive association between per capita population growth rate and population size at low abundances, thereby lowering growth ability of sparse populations. This can have far-reaching consequences on population recovery ability and colonization success. In the context of marine fishes, there is a widespread perception that Allee effects are rare or non-existent. However, studies that have failed to detect Allee effects in marine fishes have suffered from several fundamental methodological and data limitations. In the present study, we challenge the prevailing perception about the rarity of Allee effects by analysing nine populations of A…
Examining nonstationarity in the recruitment dynamics of fishes using Bayesian change point analysis
Marine ecosystems can undergo regime shifts, which result in nonstationarity in the dynamics of the fish populations inhabiting them. The assumption of time-invariant parameters in stock–recruitment models can lead to severe errors when forecasting renewal ability of stocks that experience shifts in their recruitment dynamics. We present a novel method for fitting stock–recruitment models using the Bayesian online change point detection algorithm, which is able to cope with sudden changes in the model parameters. We validate our method using simulations and apply it to empirical data of four demersal fishes in the southern Gulf of St. Lawrence. We show that all of the stocks have experience…
Generalist invasion in a complex lake food web
Invasive species constitute a threat not only to native populations but also to the structure and functioning of entire food webs. Despite being considered as a global problem, only a small number of studies have quantitatively predicted the food web-level consequences of invasions. Here, we use an allometric trophic network model parameterized using empirical data on species body masses and feeding interactions to predict the effects of a possible invasion of Amur sleeper (Perccottus glenii), on a well-studied lake ecosystem. We show that the modeled establishment of Amur sleeper decreased the biomasses o ftop predator fishes by about 10%–19%. These reductions were largely explained by inc…
Data from Detection of Allee effects in marine fishes: analytical biases generated by data availability and model selection
The demographic Allee effect, or depensation, implies positive association between per capita population growth rate and population size at low abundances, thereby lowering growth ability of sparse populations. This can have far-reaching consequences on population recovery ability and colonization success. In the context of marine fishes, there is a widespread perception that Allee effects are rare or non-existent. However, studies that have failed to detect Allee effects in marine fishes have suffered from several fundamental methodological and data limitations. In the present study, we challenge the prevailing perception about the rarity of Allee effects by analysing nine populations of A…
Data from: Environmentally-induced noise dampens and reddens with increasing trophic level in a complex food web
Stochastic variability of key abiotic factors including temperature, precipitation and the availability of light and nutrients greatly influences species’ ecological function and evolutionary fate. Despite such influence, ecologists have typically ignored the effect of abiotic stochasticity on the structure and dynamics of ecological networks. Here we help to fill that gap by advancing the theory of how abiotic stochasticity, in the form of environmental noise, affects the population dynamics of species within food webs. We do this by analysing an allometric trophic network model of Lake Constance subjected to positive (red), negative (blue), and non-autocorrelated (white) abiotic temporal …
Data from: Species’ ecological functionality alters the outcome of fish stocking success predicted by a food-web model
Fish stocking is used worldwide in conservation and management but its effects on food-web dynamics and ecosystem stability are poorly known. To better understand these effects and predict the outcomes of stocking, we used an empirically validated network model of a well-studied lake ecosystem. We simulate two stocking scenarios with two native fish species valuable for fishing. In the first scenario, we stock planktivorous fish (whitefish) larvae in the ecosystem. This leads to 1% increase in adult whitefish biomasses and decreases the biomasses of the top predator (perch). In the second scenario, we also stock perch larvae in the ecosystem. This decreases the planktivorous whitefish and t…