TY - JOUR A1 - Scherer, Cedric A1 - Jeltsch, Florian A1 - Grimm, Volker A1 - Blaum, Niels T1 - Merging trait-based and individual-based modelling: An animal functional type approach to explore the responses of birds to climatic and land use changes in semi-arid African savannas JF - Ecological modelling : international journal on ecological modelling and engineering and systems ecolog N2 - Climate change and land use management practices are major drivers of biodiversity in terrestrial ecosystems. To understand and predict resulting changes in community structures, individual-based and spatially explicit population models are a useful tool but require detailed data sets for each species. More generic approaches are thus needed. Here we present a trait-based functional type approach to model savanna birds. The aim of our model is to explore the response of different bird functional types to modifications in habitat structure. The functional types are characterized by different traits, in particular body mass, which is related to life-history traits (reproduction and mortality) and spatial scales (home range area and dispersal ability), as well as the use of vegetation structures for foraging and nesting, which is related to habitat quality and suitability. We tested the performance of the functional types in artificial landscapes varying in shrub:grass ratio and clumping intensity of shrub patches. We found that an increase in shrub encroachment and a decrease in habitat quality caused by land use mismanagement and climate change endangered all simulated bird functional types. The strength of this effect was related to the preferred habitat. Furthermore, larger-bodied insectivores and omnivores were more prone to extinction due to shrub encroachment compared to small-bodied species. Insectivorous and omnivorous birds were more sensitive to clumping intensity of shrubs whereas herbivorous and carnivorous birds were most affected by a decreasing amount of grass cover. From an applied point of view, our findings emphasize that policies such as woody plant removal and a reduction in livestock stocking rates to prevent shrub encroachment should prioritize the enlargement of existing grassland patches. Overall, our results show that the combination of an individual-based modelling approach with carefully defined functional types can provide a powerful tool for exploring biodiversity responses to environmental changes. Furthermore, the increasing accumulation of worldwide data sets on species’ core and soft traits (surrogates to determine core traits indirectly) on one side and the refinement of conceptual frameworks for animal functional types on the other side will further improve functional type approaches which consider the sensitivities of multiple species to climate change, habitat loss, and fragmentation. KW - IBM KW - Functional types KW - Trait-based approach KW - Shrub encroachment KW - Birds Y1 - 2016 U6 - https://doi.org/10.1016/j.ecolmodel.2015.07.005 SN - 0304-3800 SN - 1872-7026 VL - 326 SP - 75 EP - 89 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Radchuk, Viktoriia A1 - Oppel, Steffen A1 - Groeneveld, Juergen A1 - Grimm, Volker A1 - Schtickzelle, Nicolas T1 - Simple or complex: Relative impact of data availability and model purpose on the choice of model types for population viability analyses JF - Ecological modelling : international journal on ecological modelling and engineering and systems ecolog N2 - Population viability analysis (PVA) models are used to estimate population extinction risk under different scenarios. Both simple and complex PVA models are developed and have their specific pros and cons; the question therefore arises whether we always use the most appropriate model type. Generally, the specific purpose of a model and the availability of data are listed as determining the choice of model type, but this has not been formally tested yet. We quantified the relative importance of model purpose and nine metrics of data availability and resolution for the choice of a PVA model type, while controlling for effects of the different life histories of the modelled species. We evaluated 37 model pairs: each consisting of a generally simpler, population-based model (PBM) and a more complex, individual-based model (IBM) developed for the same species. The choice of model type was primarily affected by the availability and resolution of demographic, dispersal and spatial data. Low-resolution data resulted in the development of less complex models. Model purpose did not affect the choice of the model type. We confirm the general assumption that poor data availability is the main reason for the wide use of simpler models, which may have limited predictive power for population responses to changing environmental conditions. Conservation biology is a crisis discipline where researchers learned to work with the data at hand. However, for threatened and poorly-known species, there is no short-cut when developing either a PBM or an IBM: investments to collect appropriately detailed data are required to ensure PVA models can assess extinction risk under complex environmental conditions. (C) 2015 Elsevier B.V. All rights reserved. KW - Model complexity KW - Individual-based model KW - Population-based model KW - Matrix model KW - Structured population model KW - Stage-based model Y1 - 2016 U6 - https://doi.org/10.1016/j.ecolmodel.2015.11.022 SN - 0304-3800 SN - 1872-7026 VL - 323 SP - 87 EP - 95 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Pavlova, Viola A1 - Grimm, Volker A1 - Dietz, Rune A1 - Sonne, Christian A1 - Vorkamp, Katrin A1 - Riget, Frank F. A1 - Letcher, Robert J. A1 - Gustavson, Kim A1 - Desforges, Jean-Pierre A1 - Nabe-Nielsen, Jacob T1 - Modeling Population-Level Consequences of Polychlorinated Biphenyl Exposure in East Greenland Polar Bears JF - Archives of environmental contamination and toxicology N2 - Polychlorinated biphenyls (PCBs) can cause endocrine disruption, cancer, immunosuppression, or reproductive failure in animals. We used an individual-based model to explore whether and how PCB-associated reproductive failure could affect the dynamics of a hypothetical polar bear (Ursus maritimus) population exposed to PCBs to the same degree as the East Greenland subpopulation. Dose-response data from experimental studies on a surrogate species, the mink (Mustela vision), were used in the absence of similar data for polar bears. Two alternative types of reproductive failure in relation to maternal sum-PCB concentrations were considered: increased abortion rate and increased cub mortality. We found that the quantitative impact of PCB-induced reproductive failure on population growth rate depended largely on the actual type of reproductive failure involved. Critical potencies of the dose-response relationship for decreasing the population growth rate were established for both modeled types of reproductive failure. Comparing the model predictions of the age-dependent trend of sum-PCBs concentrations in females with actual field measurements from East Greenland indicated that it was unlikely that PCB exposure caused a high incidence of abortions in the subpopulation. However, on the basis of this analysis, it could not be excluded that PCB exposure contributes to higher cub mortality. Our results highlight the necessity for further research on the possible influence of PCBs on polar bear reproduction regarding their physiological pathway. This includes determining the exact cause of reproductive failure, i.e., in utero exposure versus lactational exposure of offspring; the timing of offspring death; and establishing the most relevant reference metrics for the dose-response relationship. Y1 - 2016 U6 - https://doi.org/10.1007/s00244-015-0203-2 SN - 0090-4341 SN - 1432-0703 VL - 70 SP - 143 EP - 154 PB - Springer CY - New York ER - TY - JOUR A1 - Martin, Benjamin T. A1 - Czesny, Sergiusz A1 - Wahl, David H. A1 - Grimm, Volker T1 - Scale-dependent role of demography and dispersal on the distribution of populations in heterogeneous landscapes JF - Oikos N2 - Both dispersal and local demographic processes determine a population's distribution among habitats of varying quality, yet most theory, experiments, and field studies have focused on the former. We use a generic model to show how both processes contribute to a population's distribution, and how the relative importance of each mechanism depends on scale. In contrast to studies only considering habitat-dependent dispersal, we show that predictions of ideal free distribution (IFD) theory are relevant even at landscape scales, where the assumptions of IFD theory are violated. This is because scales that inhibit one process, promote the other's ability to drive populations to the IFD. Furthermore, because multiple processes can generate IFDs, the pattern alone does not specify a causal mechanism. This is important because populations with IFDs generated by dispersal or demography respond much differently to shifts in resource distributions. Y1 - 2016 U6 - https://doi.org/10.1111/oik.02345 SN - 0030-1299 SN - 1600-0706 VL - 125 SP - 667 EP - 673 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Horn, Juliane A1 - Becher, Matthias A. A1 - Kennedy, Peter J. A1 - Osborne, Juliet L. A1 - Grimm, Volker T1 - Multiple stressors: using the honeybee model BEEHAVE to explore how spatial and temporal forage stress affects colony resilience JF - Oikos N2 - The causes underlying the increased mortality of honeybee Apis mellifera colonies observed over the past decade remain unclear. Since so far the evidence for monocausal explanations is equivocal, involvement of multiple stressors is generally assumed. We here focus on various aspects of forage availability, which have received less attention than other stressors because it is virtually impossible to explore them empirically. We applied the colony model BEEHAVE, which links within-hive dynamics and foraging, to stylized landscape settings to explore how foraging distance, forage supply, and “forage gaps”, i.e. periods in which honeybees cannot find any nectar and pollen, affect colony resilience and the mechanisms behind. We found that colony extinction was mainly driven by foraging distance, but the timing of forage gaps had strongest effects on time to extinction. Sensitivity to forage gaps of 15 days was highest in June or July even if otherwise forage availability was sufficient to survive. Forage availability affected colonies via cascading effects on queen's egg-laying rate, reduction of new-emerging brood stages developing into adult workers, pollen debt, lack of workforce for nursing, and reduced foraging activity. Forage gaps in July led to reduction in egg-laying and increased mortality of brood stages at a time when the queen's seasonal egg-laying rate is at its maximum, leading to colony failure over time. Our results demonstrate that badly timed forage gaps interacting with poor overall forage supply reduce honeybee colony resilience. Existing regulation mechanisms which in principle enable colonies to cope with varying forage supply in a given landscape and year, such as a reduction in egg-laying, have only a certain capacity. Our results are hypothetical, as they are obtained from simplified landscape settings, but they are consistent with existing empirical knowledge. They offer ample opportunities for testing the predicted effects of forage stress in controlled experiments. Y1 - 2016 U6 - https://doi.org/10.1111/oik.02636 SN - 0030-1299 SN - 1600-0706 VL - 125 SP - 1001 EP - 1016 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Grimm, Volker A1 - Berger, Uta T1 - Robustness analysis: Deconstructing computational models for ecological theory and applications JF - Ecological modelling : international journal on ecological modelling and engineering and systems ecolog N2 - The design of computational models is path-dependent: the choices made in each step during model development constrain the choices that are available in the subsequent steps. The actual path of model development can be extremely different, even for the same system, because the path depends on the question addressed, the availability of data, and the consideration of specific expert knowledge, in addition to the experience, background, and modelling preferences of the modellers. Thus, insights from different models are practically impossible to integrate, which hinders the development of general theory. We therefore suggest augmenting the current culture of communicating models as working just fine with a culture of presenting analyses in which we try to break models, i.e., model mechanisms explaining certain observations break down. We refer to the systematic attempts to break a model as “robustness analysis” (RA). RA is the systematic deconstruction of a model by forcefully changing the model's parameters, structure, and representation of processes. We discuss the nature and elements of RA and provide brief examples. RA cannot be completely formalized into specific techniques and instead corresponds to detective work that is driven by general questions and specific hypotheses, with strong attention focused on unusual behaviours. Both individual modellers and ecological modelling in general will benefit from RA because RA helps with understanding models and identifying “robust theories”, which are general principles that are independent of the idiosyncrasies of specific models. Integrating the results of RAs from different models to address certain systems or questions will then provide a comprehensive overview of when certain mechanisms control system behaviour and when and why this control ceases. This approach can provide insights into the mechanisms that lead to regime shifts in actual ecological systems. KW - Sensitivity analysis KW - Ecological theory KW - Computational modelling KW - Robustness KW - Model analysis KW - Understanding Y1 - 2016 U6 - https://doi.org/10.1016/j.ecolmodel.2015.07.018 SN - 0304-3800 SN - 1872-7026 VL - 326 SP - 162 EP - 167 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Ayllon, Daniel A1 - Railsback, Steven Floyd A1 - Vincenzi, Simone A1 - Groeneveld, Juergen A1 - Almodoevar, Ana A1 - Grimm, Volker T1 - InSTREAM-Gen: Modelling eco-evolutionary dynamics of trout populations under anthropogenic environmental change JF - Ecological modelling : international journal on ecological modelling and engineering and systems ecolog N2 - Current rates of environmental change are exceeding the capacity of many populations to adapt to new conditions and thus avoid demographic collapse and ultimate extinction. In particular, cold-water freshwater fish species are predicted to experience strong selective pressure from climate change and a wide range of interacting anthropogenic stressors in the near future. To implement effective management and conservation measures, it is crucial to quantify the maximum rate of change that cold-water freshwater fish populations can withstand. Here, we present a spatially explicit eco-genetic individual-based model, inSTREAM-Gen, to predict the eco-evolutionary dynamics of stream-dwelling trout under anthropogenic environmental change. The model builds on a well-tested demographic model, which includes submodels of river dynamics, bioenergetics, and adaptive habitat selection, with a new genetic module that allows exploration of genetic and life-history adaptations to new environments. The genetic module models the transmission of two key traits, size at emergence and maturity size threshold. We parameterized the model for a brown trout (Salmo trutta L.) population at the warmest edge of its range to validate it and analyze its sensitivity to parameters under contrasting thermal profiles. To illustrate potential applications of the model, we analyzed the population's demographic and evolutionary dynamics under scenarios of (1) climate change-induced warming, and (2) warming plus flow reduction resulting from climate and land use change, compared to (3) a baseline of no environmental change. The model predicted severe declines in density and biomass under climate warming. These declines were lower than expected at range margins because of evolution towards smaller size at both emergence and maturation compared to the natural evolution under the baseline conditions. Despite stronger evolutionary responses, declining rates were substantially larger under the combined warming and flow reduction scenario, leading to a high probability of population extinction over contemporary time frames. Therefore, adaptive responses could not prevent extinction under high rates of environmental change. Our model demonstrates critical elements of next generation ecological modelling aiming at predictions in a changing world as it accounts for spatial and temporal resource heterogeneity, while merging individual behaviour and bioenergetics with microevolutionary adaptations. KW - Individual-based model KW - Eco-genetic modelling KW - Eco-evolution KW - Climate change KW - Brown trout KW - Next-generation modelling Y1 - 2016 U6 - https://doi.org/10.1016/j.ecolmodel.2015.07.026 SN - 0304-3800 SN - 1872-7026 VL - 326 SP - 36 EP - 53 PB - Elsevier CY - Amsterdam ER -