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- Cardinale, Massimiliano, et al.
(författare)
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Benchmark workshop on herring (Clupea harengus) in the Gulf of Bothnia (WKCLuB 2021)
- 2021
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The assessment for the Gulf of Bothnia herring (SD 3031) in 2019 was not accepted by the Advice Drafting Group and was changed from category 1 to 3. The assessment was not accepted based on the poor retrospective diagnostics where the Mohn’s rho values were above 20% for SSB, F and recruitment. The aim for the Benchmark was to evaluate a new model, Stock Synthesis (SS3) as a candidate for the assessment of Gulf of Bothnia Herring SD30–31 in order to minimize the retrospective pattern previously observed. Following the path of the Benchmark data related issues were revealed. This led to a situation that the benchmark was prolonged one year in order to correct the data related issues. Apart from a misspecification in the model about how the trapnet index was used (abundance index vs. biomass index), the data problem had been related to the acoustic survey. The acoustic survey index used in the assessment was thoroughly examined by the Baltic international fish survey working group (WGBIFS) in a meeting in December 2020. A number of model runs (six prior to meeting, and an additional 16 during the benchmark) were conducted for evaluation at this benchmark. The analysis presented extensive diagnostic tests including the standard ICES criterion related to retrospective patterns. This was considered an enhancement over using one method for accepting or rejecting an assessment. It was noted that the final retrospective pattern had low and acceptable values of Mohn’s rho. In general, the benchmark using the stock synthesis platform with the settings specified during the benchmark are considered acceptable for assessment and advice and have features that should ensure stability as new data are added (e.g. selectivity is assumed to be constant over time).
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- Cardinale, Massimiliano, et al.
(författare)
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Workshop on ICES reference points (WKREF1)
- 2022
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The ICES Workshop on ICES reference points (WKREF1) was tasked to provide a thorough review of the ICES reference points system as a basis to re-evaluate the process for estimating, updating and communicating reference points in the context of the ICES advice. As part of the preparation leading to WKREF1 a large database of the most recent assessment outputs for 78 Category 1 stocks were collated in the form `FLStock` objects, which formed the basis for several components of the presented analyses.
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- Gilljam, David, et al.
(författare)
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Adaptive rewiring aggravates the effects of species loss in ecosystems
- 2015
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Ingår i: Nature Communications. - : Nature Publishing Group. - 2041-1723. ; 6
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Tidskriftsartikel (refereegranskat)abstract
- Loss of one species in an ecosystem can trigger extinctions of other dependent species. For instance, specialist predators will go extinct following the loss of their only prey unless they can change their diet. It has therefore been suggested that an ability of consumers to rewire to novel prey should mitigate the consequences of species loss by reducing the risk of cascading extinction. Using a new modelling approach on natural and computer-generated food webs we find that, on the contrary, rewiring often aggravates the effects of species loss. This is because rewiring can lead to overexploitation of resources, which eventually causes extinction cascades. Such a scenario is particularly likely if prey species cannot escape predation when rare and if predators are efficient in exploiting novel prey. Indeed, rewiring is a two-edged sword; it might be advantageous for individual predators in the short term, yet harmful for long-term system persistence.
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- Gilljam, David
(författare)
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Environmental degradation amplifies species' responses to temperature variation in a trophic interaction
- 2019
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Ingår i: Journal of Animal Ecology. - : Wiley. - 0021-8790 .- 1365-2656. ; 88, s. 1657-1669
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Tidskriftsartikel (refereegranskat)abstract
- Land-use and climate change are two of the primary drivers of the current biodiversity crisis. However, we lack understanding of how single-species and multispecies associations are affected by interactions between multiple environmental stressors. We address this gap by examining how environmental degradation interacts with daily stochastic temperature variation to affect individual life history and population dynamics in a host-parasitoid trophic interaction, using the Indian meal moth, Plodia interpunctella, and its parasitoid wasp Venturia canescens. We carried out a single-generation individual life-history experiment and a multigeneration microcosm experiment during which individuals and microcosms were maintained at a mean temperature of 26 degrees C that was either kept constant or varied stochastically, at four levels of host resource degradation, in the presence or absence of parasitoids. At the individual level, resource degradation increased juvenile development time and decreased adult body size in both species. Parasitoids were more sensitive to temperature variation than their hosts, with a shorter juvenile stage duration than in constant temperatures and a longer adult life span in moderately degraded environments. Resource degradation also altered the host's response to temperature variation, leading to a longer juvenile development time at high resource degradation. At the population level, moderate resource degradation amplified the effects of temperature variation on host and parasitoid populations compared with no or high resource degradation and parasitoid overall abundance was lower in fluctuating temperatures. Top-down regulation by the parasitoid and bottom-up regulation driven by resource degradation contributed to more than 50% of host and parasitoid population responses to temperature variation. Our results demonstrate that environmental degradation can strongly affect how species in a trophic interaction respond to short-term temperature fluctuations through direct and indirect trait-mediated effects. These effects are driven by species differences in sensitivity to environmental conditions and modulate top-down (parasitism) and bottom-up (resource) regulation. This study highlights the need to account for differences in the sensitivity of species' traits to environmental stressors to understand how interacting species will respond to simultaneous anthropogenic changes.
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| 9. |
- Gilljam, David, et al.
(författare)
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High dynamic dimensionality promotes the persistence of ecological networks in a variable world
- 2016
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The long-term persistence of ecological communities depends on the strength of destabilizing stochastic forces relative to the strength of stabilizing feedbacks caused by interactions among and within species. What characteristics of a community that tip the balance of these forces in favour of persistence is not clear. Here we show that long-term persistence of a community is positively related to its dynamic dimensionality (DD). A high DD means that the system approaches the equilibrium from all directions at a similar rate. On the other hand, when DD is low the deterministic forces pulling the system towards equilibrium is weak in many directions compared to the stochastic forces pushing the system away from the equilibrium. As a consequence persistence decreases as DD decreases. This result illustrates the potential importance of dynamic dimensionality of ecosystems for their persistence in a variable world and by extension for their vulnerability to changes in the strength and patterns of climate variability caused by global warming.
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| 10. |
- Gilljam, David, et al.
(författare)
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Patterns of resource utilisation within and between species affect the dynamic dimensionality and stability of ecological communities
- 2016
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- In many ecological communities, individuals within species pass through a wide spectrum of sizes, spanning several orders of magnitude, during the independent part of their life cycle. Such a large size-variation within a species will affect the structure of its niche, since the size of an individual affects the type of prey it can consume as well as what predators will attack it. Here we use highly resolved individual-based empirical data to investigate patterns in the niche structure of several aquatic food webs. We quantify within and between species components of resource use in these webs and explore its consequences for dynamical dimensionality and community stability using simple food web models with stage-structured consumer species. Among the natural food webs there are webs where species overlap widely in their resource use while the resource use of size-classes within species differs. There are also webs where differences in resource use among species is relatively large and the niches of sizeclasses within species are more similar. Model systems with the former structure are found to have low dynamical dimensionality and to be less stable compared to systems with the latter structure. Thus, although differential resource use among individuals within a species is likely to decrease the intensity of intraspecific competition and favor individuals specializing on less exploited resources it can destabilize the community in which the individuals are embedded.
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