TY  - JOUR
A1  - Wichmann, Matthias
A1  - Johst, Karin
A1  - Schwager, Monika
A1  - Jeltsch, Florian
A1  - Blasius, Bernd
T1  - Extinction risk, coloured noise and the scaling of variance
N2  - The impact of temporally correlated fluctuating environments (coloured noise) on the extinction risk of populations has become a main focus in theoretical population ecology. In this study we particularly focus on the extinction risk in strongly autocorrelated environments. Here, in contrast to moderate autocorrelation, we found the extinction risk to be highly dependent on the process of noise generation, in particular on the method of variance scaling. Such variance scaling is commonly applied to avoid variance-driven biases when comparing the extinction risk for white and coloured noise. In this study we found an often-used scaling technique to lead to high variability in the resulting variances of different time series for strong auto-correlation eventually leading to deviations in the projected extinction risk. Therefore, we present an alternative method that always delivers the target variance, even in the case of strong temporal correlation. Furthermore, in contrast to the earlier method, our very intuitive method is not bound to auto-regressive processes but can be applied to all types of coloured noises. We recommend the method introduced here to be used when the target of interest is the effect of noise colour on extinction risk not obscured by any variance effects.
Y1  - 2005
UR  - http://www.agnld.uni-potsdam.de/~bernd/papers/tpb1.pdf
ER  - 
TY  - JOUR
A1  - Jeltsch, Florian
A1  - Groeneveld, Jürgen
A1  - Wissel, Christian
A1  - Wucherer, W.
A1  - Dimeyeva, L.
T1  - Seed dispersal by cattle may cause shrub encroachment of Grewia flava on southern Kalahari rangelands
Y1  - 2005
SN  - 3-86537-386-0
ER  - 
TY  - JOUR
A1  - Wichmann, Matthias
A1  - Groeneveld, Jürgen
A1  - Jeltsch, Florian
A1  - Grimm, Volker
T1  - Mitigation of climate change impacts on raptors by behavioural adaptation : ecological buffering mechanisms
N2  - 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
Y1  - 2005
SN  - 0921-8181
ER  - 
TY  - JOUR
A1  - Grimm, Volker
A1  - Revilla, Eloy
A1  - Berger, Uta
A1  - Jeltsch, Florian
A1  - Mooij, Wolf M.
A1  - Railsback, Steven Floyd
A1  - Thulke, Hans-Hermann
A1  - Weiner, Jacob
A1  - Wiegand, Thorsten
A1  - DeAngelis, Donald L.
T1  - Pattern-oriented modeling of agend-based complex systems : lessons from ecology
N2  - Agent-based complex systems are dynamic networks of many interacting agents; examples include ecosystems, financial markets, and cities. The search for general principles underlying the internal organization of such systems often uses bottom-up simulation models such as cellular automata and agent-based models. No general framework for designing, testing, and analyzing bottom-up models has yet been established, but recent advances in ecological modeling have come together in a general strategy we call pattern-oriented modeling. This strategy provides a unifying framework for decoding the internal organization of agent-based complex systems and may lead toward unifying algorithmic theories of the relation between adaptive behavior and system complexity
Y1  - 2005
ER  - 
TY  - JOUR
A1  - Grimm, Volker
A1  - Revilla, Eloy
A1  - Groeneveld, Jürgen
A1  - Kramer-Schadt, Stephanie
A1  - Schwager, Monika
A1  - Tews, Jörg
A1  - Wichmann, Matthias
A1  - Jeltsch, Florian
T1  - Importance of buffer mechanisms for population viability analysis
Y1  - 2005
ER  - 
TY  - JOUR
A1  - Wichmann, Matthias
A1  - Groeneveld, Jürgen
A1  - Jeltsch, Florian
A1  - Grimm, Volker
T1  - Mitigation of climate change impacts on raptors by behavioural adaption : ecological buffering mechanism
Y1  - 2005
ER  -