@article{StephTiedemannPrangeetal.2010, author = {Steph, Silke and Tiedemann, Ralph and Prange, Matthias and Groeneveld, J{\"u}rgen and Schulz, Michael Karl and Timmermann, Axel and N{\"u}rnberg, Dirk and R{\"u}hlemann, Carsten and Saukel, Cornelia and Haug, Gerald H.}, title = {Early Pliocene increase in thermohaline overturning : a precondition for the development of the modern equatorial Pacific cold tongue}, issn = {0883-8305}, doi = {10.1029/2008pa001645}, year = {2010}, abstract = {Unraveling the processes responsible for Earth's climate transition from an "El Nino-like state" during the warm early Pliocene into a modern-like "La Nina-dominated state" currently challenges the scientific community. Recently, the Pliocene climate switch has been linked to oceanic thermocline shoaling at similar to 3 million years ago along with Earth's final transition into a bipolar icehouse world. Here we present Pliocene proxy data and climate model results, which suggest an earlier timing of the Pliocene climate switch and a different chain of forcing mechanisms. We show that the increase in North Atlantic meridional overturning circulation between 4.8 and 4.0 million years ago, initiated by the progressive closure of the Central American Seaway, triggered overall shoaling of the tropical thermocline. This preconditioned the turnaround from a warm eastern equatorial Pacific to the modern equatorial cold tongue state about 1 million years earlier than previously assumed. Since similar to 3.6-3.5 million years ago, the intensification of Northern Hemisphere glaciation resulted in a strengthening of the trade winds, thereby amplifying upwelling and biogenic productivity at low latitudes.}, language = {en} } @article{JeltschGroeneveldWisseletal.2005, author = {Jeltsch, Florian and Groeneveld, J{\"u}rgen and Wissel, Christian and Wucherer, W. and Dimeyeva, L.}, title = {Seed dispersal by cattle may cause shrub encroachment of Grewia flava on southern Kalahari rangelands}, isbn = {3-86537-386-0}, year = {2005}, language = {en} } @article{EstherGroeneveldEnrightetal.2008, author = {Esther, Alexandra and Groeneveld, J{\"u}rgen and Enright, Neal J. and Miller, Ben P. and Lamont, Byron B. and Perry, George L. W. and Schurr, Frank Martin and Jeltsch, Florian}, title = {Assessing the importance of seed immigration on coexistence of plant functional types in a species-rich ecosystem}, issn = {0304-3800}, doi = {10.1016/j.ecolmodel.2008.01.014}, year = {2008}, abstract = {Modelling and empirical studies have shown that input from the regional seed pool is essential to maintain local species diversity. However, most of these studies have concentrated on simplified, if not neutral, model systems, and focus on a limited subset of species or on aggregated measures of diversity only (e.g., species richness or Shannon diversity). Thus they ignore more complex species interactions and important differences between species. To gain a better understanding of how seed immigration affects community structure at the local scale in real communities we conducted computer simulation experiments based on plant functional types (PFTs) for a species-rich, fire-prone Mediterranean-type shrubland in Western Australia. We developed a spatially explicit simulation model to explore the community dynamics of 38 PFTs, defined by seven traits - regeneration mode, seed production, seed size, maximum crown diameter, drought tolerance, dispersal mode and seed bank type - representing 78 woody species. Model parameterisation is based on published and unpublished data on the population dynamics of shrub species collected over 18 years. Simulation experiments are based on two contrasting seed immigration scenarios: (1) the 'equal seed input number' scenario, where the number of immigrant seeds is the same for all PFTs, and (2) the 'equal seed input mass' scenario, where the cumulative mass of migrating seeds is the same for all PFTs. Both scenarios were systematically tested and compared for different overall seed input values. Without immigration the local community drifts towards a state with only 13 coexisting PFTs. With increasing immigration rates in terms of overall mass of seeds the simulated number of coexisting PFTs and Shannon diversity quickly approaches values observed in the field. The equal seed mass scenario resulted in a more diverse community than did the seed number scenario. The model successfully approximates the frequency distributions (relative densities) of all individual plant traits except seed size for scenarios associated with equal seed input mass and high immigration rate. However, no scenario satisfactorily approximated the frequency distribution for all traits in combination. Our results show that regional seed input can explain the more aggregated measures of local community structure, and some, but not all, aspects of community composition. This points to the possible importance of other (untested) processes and traits (e.g., dispersal vectors) operating at the local scale. Our modelling framework can readily allow new factors to be systematically investigated, which is a major advantage compared to previous simulation studies, as it allows us to find structurally realistic models, which can address questions pertinent to ecological theory and to conservation management.}, language = {en} } @article{EstherGroeneveldEnrightetal.2011, author = {Esther, Alexandra and Groeneveld, J{\"u}rgen and Enright, Neal J. and Miller, Ben P. and Lamont, Byron B. and Perry, George L. W. and Tietjen, Britta and Jeltsch, Florian}, title = {Low-dimensional trade-offs fail to explain richness and structure in species-rich plant communities}, series = {Theoretical ecology}, volume = {4}, journal = {Theoretical ecology}, number = {4}, publisher = {Springer}, address = {Heidelberg}, issn = {1874-1738}, doi = {10.1007/s12080-010-0092-y}, pages = {495 -- 511}, year = {2011}, abstract = {Mathematical models and ecological theory suggest that low-dimensional life history trade-offs (i.e. negative correlation between two life history traits such as competition vs. colonisation) may potentially explain the maintenance of species diversity and community structure. In the absence of trade-offs, we would expect communities to be dominated by 'super-types' characterised by mainly positive trait expressions. However, it has proven difficult to find strong empirical evidence for such trade-offs in species-rich communities. We developed a spatially explicit, rule-based and individual-based stochastic model to explore the importance of low-dimensional trade-offs. This model simulates the community dynamics of 288 virtual plant functional types (PFTs), each of which is described by seven life history traits. We consider trait combinations that fit into the trade-off concept, as well as super-types with little or no energy constraints or resource limitations, and weak PFTs, which do not exploit resources efficiently. The model is parameterised using data from a fire-prone, species-rich Mediterranean-type shrubland in southwestern Australia. We performed an exclusion experiment, where we sequentially removed the strongest PFT in the simulation and studied the remaining communities. We analysed the impact of traits on performance of PFTs in the exclusion experiment with standard and boosted regression trees. Regression tree analysis of the simulation results showed that the trade-off concept is necessary for PFT viability in the case of weak trait expression combinations such as low seed production or small seeds. However, species richness and diversity can be high despite the presence of super-types. Furthermore, the exclusion of super-types does not necessarily lead to a large increase in PFT richness and diversity. We conclude that low-dimensional trade-offs do not provide explanations for multi-species co-existence contrary to the prediction of many conceptual models.}, language = {en} } @article{WichmannGroeneveldJeltschetal.2005, author = {Wichmann, Matthias and Groeneveld, J{\"u}rgen and Jeltsch, Florian and Grimm, Volker}, title = {Mitigation of climate change impacts on raptors by behavioural adaptation : ecological buffering mechanisms}, issn = {0921-8181}, year = {2005}, abstract = {The predicted climate change causes deep concerns on the effects of increasing temperatures and changing precipitation patterns on species viability and, in turn, on biodiversity. Models of Population Viability Analysis (PVA) provide a powerful tool to assess the risk of species extinction. However, most PVA models do not take into account the potential effects of behavioural adaptations. Organisms might adapt to new environmental situations and thereby mitigate negative effects of climate change. To demonstrate such mitigation effects, we use an existing PVA model describing a population of the tawny eagle (Aquila rapax) in the southern Kalahari. This model does not include behavioural adaptations. We develop a new model by assuming that the birds enlarge their average territory size to compensate for lower amounts of precipitation. Here, we found the predicted increase in risk of extinction due to climate change to be much lower than in the original model. However, this "buffering" of climate change by behavioural adaptation is not very effective in coping with increasing interannual variances. We refer to further examples of ecological "buffering mechanisms" from the literature and argue that possible buffering mechanisms should be given due consideration when the effects of climate change on biodiversity are to be predicted. (c) 2004 Elsevier B.V. All rights reserved}, language = {en} } @article{GrimmRevillaGroeneveldetal.2005, author = {Grimm, Volker and Revilla, Eloy and Groeneveld, J{\"u}rgen and Kramer-Schadt, Stephanie and Schwager, Monika and Tews, J{\"o}rg and Wichmann, Matthias and Jeltsch, Florian}, title = {Importance of buffer mechanisms for population viability analysis}, year = {2005}, language = {en} } @article{WichmannGroeneveldJeltschetal.2005, author = {Wichmann, Matthias and Groeneveld, J{\"u}rgen and Jeltsch, Florian and Grimm, Volker}, title = {Mitigation of climate change impacts on raptors by behavioural adaption : ecological buffering mechanism}, year = {2005}, language = {en} } @article{GroeneveldJohstKawaguchietal.2015, author = {Groeneveld, J{\"u}rgen and Johst, Karin and Kawaguchi, So and Meyer, Bettina and Teschke, Mathias and Grimm, Volker}, title = {How biological clocks and changing environmental conditions determine local population growth and species distribution in Antarctic krill (Euphausia superba): a conceptual model}, series = {Ecological modelling : international journal on ecological modelling and engineering and systems ecolog}, volume = {303}, journal = {Ecological modelling : international journal on ecological modelling and engineering and systems ecolog}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0304-3800}, doi = {10.1016/j.ecolmodel.2015.02.009}, pages = {78 -- 86}, year = {2015}, abstract = {The Southern Ocean ecosystem is characterized by extreme seasonal changes in environmental factors such as day length, sea ice extent and food availability. The key species Antarctic krill (Euphausia superba) has evolved metabolic and behavioural seasonal rhythms to cope with these seasonal changes. We investigate the switch between a physiological less active and active period for adult krill, a rhythm which seems to be controlled by internal biological clocks. These biological clocks can be synchronized by environmental triggers such as day length and food availability. They have evolved for particular environmental regimes to synchronize predictable seasonal environmental changes with important life cycle functions of the species. In a changing environment the time when krill is metabolically active and the time of peak food availability may not overlap if krill's seasonal activity is solely determined by photoperiod (day length). This is especially true for the Atlantic sector of the Southern Ocean where the spatio-temporal ice cover dynamics are changing substantially with rising average temperatures. We developed an individual-based model for krill to explore the impact of photoperiod and food availability on the growth and demographics of krill. We simulated dynamics of local krill populations (with no movement of krill assumed) along a south-north gradient for different triggers of metabolic activity and different levels of food availability below the ice. We also observed the fate of larval krill which cannot switch to low metabolism and therefore are likely to overwinter under ice. Krill could only occupy the southern end of the gradient, where algae bloom only lasts for a short time, when alternative food supply under the ice was high and metabolic activity was triggered by photoperiod. The northern distribution was limited by lack of overwintering habitat for krill larvae due to short duration of sea ice cover even for high food content under the ice. The variability of the krill's length-frequency distributions varied for different triggers of metabolic activity, but did not depend on the sea ice extent. Our findings suggest a southward shift of krill populations due to reduction in the spatial sea ice extent, which is consistent with field observations. Overall, our results highlight the importance of the explicit consideration of spatio-temporal sea ice dynamics especially for larval krill together with temporal synchronization through internal clocks, triggered by environmental factors (photoperiod and food) in adult krill for the population modelling of krill. (C) 2015 Elsevier B.V. All rights reserved.}, language = {en} } @article{MeliPalmqvistForbesetal.2014, author = {Meli, Mattia and Palmqvist, Annemette and Forbes, Valery E. and Groeneveld, J{\"u}rgen and Grimm, Volker}, title = {Two pairs of eyes are better than one: Combining individual-based and matrix models for ecological risk assessment of chemicals}, series = {Ecological modelling : international journal on ecological modelling and engineering and systems ecolog}, volume = {280}, journal = {Ecological modelling : international journal on ecological modelling and engineering and systems ecolog}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0304-3800}, doi = {10.1016/j.ecolmodel.2013.07.027}, pages = {40 -- 52}, year = {2014}, abstract = {Current chemical risk assessment procedures may result in imprecise estimates of risk due to sometimes arbitrary simplifying assumptions. As a way to incorporate ecological complexity and improve risk estimates, mechanistic effect models have been recommended. However, effect modeling has not yet been extensively used for regulatory purposes, one of the main reasons being uncertainty about which model type to use to answer specific regulatory questions. We took an individual-based model (IBM), which was developed for risk assessment of soil invertebrates and includes avoidance of highly contaminated areas, and contrasted it with a simpler, more standardized model, based on the generic metapopulation matrix model RAMAS. In the latter the individuals within a sub-population are not treated as separate entities anymore and the spatial resolution is lower. We explored consequences of model aggregation in terms of assessing population-level effects for different spatial distributions of a toxic chemical. For homogeneous contamination of the soil, we found good agreement between the two models, whereas for heterogeneous contamination, at different concentrations and percentages of contaminated area, RAMAS results were alternatively similar to IBM results with and without avoidance, and different food levels. This inconsistency is explained on the basis of behavioral responses that are included in the IBM but not in RAMAS. Overall, RAMAS was less sensitive than the IBM in detecting population-level effects of different spatial patterns of exposure. We conclude that choosing the right model type for risk assessment of chemicals depends on whether or not population-level effects of small-scale heterogeneity in exposure need to be detected. We recommend that if in doubt, both model types should be used and compared. Describing both models following the same standard format, the ODD protocol, makes them equally transparent and understandable. The simpler model helps to build up trust for the more complex model and can be used for more homogeneous exposure patterns. The more complex model helps detecting and understanding the limitations of the simpler model and is needed to ensure ecological realism for more complex exposure scenarios. (C) 2013 Elsevier B.V. All rights reserved.}, language = {en} } @article{RadchukJohstGroeneveldetal.2014, author = {Radchuk, Viktoriia and Johst, Karin and Groeneveld, J{\"u}rgen and Turlure, Camille and Grimm, Volker and Schtickzelle, Nicolas}, title = {Appropriate resolution in time and model structure for population viability analysis: Insights from a butterfly metapopulation}, series = {: an international journal}, volume = {169}, journal = {: an international journal}, publisher = {Elsevier}, address = {Oxford}, issn = {0006-3207}, doi = {10.1016/j.biocon.2013.12.004}, pages = {345 -- 354}, year = {2014}, abstract = {The importance of a careful choice of the appropriate scale for studying ecological phenomena has been stressed repeatedly. However, issues of spatial scale in metapopulation dynamics received much more attention compared to temporal scale. Moreover, multiple calls were made to carefully choose the appropriate model structure for Population Viability Analysis (PVA). We assessed the effect of using coarser resolution in time and model structure on population dynamics. For this purpose, we compared outcomes of two PVA models differing in their time step: daily individual-based model (dIBM) and yearly stage-based model (ySBM), loaded with empirical data on a well-known metapopulation of the butterfly Boloria eunomia. Both models included the same environmental drivers of population dynamics that were previously identified as being the most important for this species. Under temperature change scenarios, both models yielded the same qualitative scenario ranking, but they quite substantially differed quantitatively with dIBM being more pessimistic in absolute viability measures. We showed that these differences stemmed from inter-individual heterogeneity in dIBM allowing for phenological shifts of individual appearance. We conclude that a finer temporal resolution and an individual-based model structure allow capturing the essential mechanisms necessary to go beyond mere PVA scenario ranking. We encourage researchers to carefully chose the temporal resolution and structure of their model aiming at (1) depicting the processes important for (meta)population dynamics of the species and (2) implementing the environmental change scenarios expected for their study system in the future, using the temporal resolution at which such changes are predicted to operate.}, language = {en} }