@article{vonderLippeBullockKowariketal.2013, author = {von der Lippe, Moritz and Bullock, James M. and Kowarik, Ingo and Knopp, Tatjana and Wichmann, Matthias}, title = {Human-mediated dispersal of seeds by the airflow of vehicles}, series = {PLoS one}, volume = {8}, journal = {PLoS one}, number = {1}, publisher = {PLoS}, address = {San Fransisco}, issn = {1932-6203}, doi = {10.1371/journal.pone.0052733}, pages = {10}, year = {2013}, abstract = {Human-mediated dispersal is known as an important driver of long-distance dispersal for plants but underlying mechanisms have rarely been assessed. Road corridors function as routes of secondary dispersal for many plant species but the extent to which vehicles support this process remains unclear. In this paper we quantify dispersal distances and seed deposition of plant species moved over the ground by the slipstream of passing cars. We exposed marked seeds of four species on a section of road and drove a car along the road at a speed of 48 km/h. By tracking seeds we quantified movement parallel as well as lateral to the road, resulting dispersal kernels, and the effect of repeated vehicle passes. Median distances travelled by seeds along the road were about eight meters for species with wind dispersal morphologies and one meter for species without such adaptations. Airflow created by the car lifted seeds and resulted in longitudinal dispersal. Single seeds reached our maximum measuring distance of 45 m and for some species exceeded distances under primary dispersal. Mathematical models were fit to dispersal kernels. The incremental effect of passing vehicles on longitudinal dispersal decreased with increasing number of passes as seeds accumulated at road verges. We conclude that dispersal by vehicle airflow facilitates seed movement along roads and accumulation of seeds in roadside habitats. Dispersal by vehicle airflow can aid the spread of plant species and thus has wide implications for roadside ecology, invasion biology and nature conservation.}, language = {en} } @article{WichmannDeanJeltsch2006, author = {Wichmann, Matthias and Dean, W. R. J. and Jeltsch, Florian}, title = {Predicting the breeding success of large raptors in arid southern Africa : a first assessment}, year = {2006}, abstract = {Raptors are often priorities for conservation efforts and breeding success is a target measure for assessing their conservation status. The breeding success of large raptors in and southern Africa is thought to be higher in years of high rainfall. While this correlation has been found in several studies, it has not yet been shown for data from a wider geographical area. In conservation research, it is important to explore the differences between spatially- separated populations to estimate and to compare their conservation status, and to deduce specific management strategies. Using a theoretical approach, we develop a simplistic model to explain the breeding success-rainfall relationship in large African raptors at larger spatial scales. Secondly, we validate this model and we show that the inclusion of field data leads to consistent predictions. In particular, we recommend that the average size of the 'effective territory' should be included in the relationship between annual rainfall and breeding success of raptors in and southern Africa. Accordingly, we suggest that breeding success is a function of precipitation and inter- nest distance. We present a new measure of territory quality depending on rainfall and territory size. We suggest that our model provides a useful first approach to assess breeding success in large raptors of and southern Africa. However, we strongly emphasise the need to gather more data to further verify our model. A general problem in conservation research is to compare the status of populations assessed in different study areas under changing environmental conditions. Our simplistic approach indicates that this problem can be overcome by using a weighted evaluation of a target measure (i.e. breeding success), taking regional differences into account}, language = {en} } @article{EccardDeanWichmannetal.2006, author = {Eccard, Jana and Dean, W. Richard J. and Wichmann, Matthias and Huttunen, S. M and Eskelinen, Eeva-Liisa and Moloney, Kirk A. and Jeltsch, Florian}, title = {Use of large Acacia trees by the cavity dwelling Black-tailed Tree Rat in the southern Kalahari}, issn = {0140-1963}, doi = {10.1016/j.jaridenv.2005.06.019}, year = {2006}, abstract = {Recent extensive harvesting of large, often dead Acacia trees in and savanna of southern Africa is cause for concern about the conservation status of the arid savanna and its animal community. We mapped vegetation and nests of the Black-tailed Tree Rat Thallomy's nigricauda to assess the extent to which the rats depend on particular tree species and on the existence of dead, standing trees. The study was conducted in continuous Acacia woodland on the southern and eastern edge of the Kalahari, South Africa. Trees in which there were tree rat nests were compared with trees of similar size and vigour to identify the characteristics of nest sites. Spatial analysis of tree rat distribution was conducted using Ripley's-L function. We found that T nigricauda was able to utilize all available tree species, as long as trees were large and old enough so that cavities were existing inside the stem. The spatial distribution of nest trees did not show clumping at the investigated scale, and we therefore reject the notion of the rats forming colonies when inhabiting continuous woodlands. The selection of a particular tree as a nest site was furthermore depending on the close proximity of the major food plant, Acacia mellifera. This may limit the choice of suitable nest sites. since A. mellifera was less likely to grow within a vegetation patch containing a large trees than in patches without large trees.}, language = {en} } @article{WichmannJohstSchwageretal.2005, author = {Wichmann, Matthias and Johst, Karin and Schwager, Monika and Jeltsch, Florian and Blasius, Bernd}, title = {Extinction risk, coloured noise and the scaling of variance}, year = {2005}, abstract = {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.}, 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{JeltschWichmannDean2004, author = {Jeltsch, Florian and Wichmann, Matthias and Dean, W. R. J.}, title = {Global change challenges the Tawny Eagle (Aquila rapax) : modelling extinction risk with respect to predicted climate and land use changes}, year = {2004}, language = {en} } @article{JeltschTewsBroseetal.2004, author = {Jeltsch, Florian and Tews, J{\"o}rg and Brose, Ulrich and Grimm, Volker and Tielb{\"o}rger, Katja and Wichmann, Matthias and Schwager, Monika}, title = {Animal species diversity driven by habitat heterogeneity/diversity : the importance of keystone structures}, year = {2004}, abstract = {In a selected literature survey we reviewed studies on the habitat heterogeneity-animal species diversity relationship and evaluated whether there are uncertainties and biases in its empirical support. We reviewed 85 publications for the period 1960-2003. We screened each publication for terms that were used to define habitat heterogeneity, the animal species group and ecosystem studied, the definition of the structural variable, the measurement of vegetation structure and the temporal and spatial scale of the study. The majority of studies found a positive correlation between habitat heterogeneity/diversity and animal species diversity. However, empirical support for this relationship is drastically biased towards studies of vertebrates and habitats under anthropogenic influence. In this paper we show that ecological effects of habitat heterogeneity may vary considerably between species groups depending on whether structural attributes are perceived as heterogeneity or fragmentation. Possible effects may also vary relative to the structural variable measured. Based upon this, we introduce a classification framework that may be used for across-studies comparisons. Moreover, the effect of habitat heterogeneity for one species group may differ in relation to the spatial scale. In several studies, however, different species groups are closely linked to 'keystone structures' that determine animal species diversity by their presence. Detecting crucial keystone structures of the vegetation has profound implications for nature conservation and biodiversity management.}, language = {en} } @article{JeltschWichmannJohstetal.2003, author = {Jeltsch, Florian and Wichmann, Matthias and Johst, J. and Moloney, Kirk A. and Wissel, Christian}, title = {Extinction risk in periodically fluctuating environments}, year = {2003}, language = {en} }