TY  - JOUR
A1  - Schurr, Frank Martin
A1  - Dean, W. R. J.
A1  - Milton, Sue J.
A1  - Jeltsch, Florian
T1  - A conceptual model linking demography of the shrub species Grewia flava to the dynamics of Kalahari savannas
N2  - Environmental heterogeneity is a major determinant of plant population dynamics. In semi-arid Kalahari savannas, heterogeneity is created by savanna structure, i.e. by the spatial arrangement and temporal dynamics of woody plant and open grassland microsites. We formulate a conceptual model describing the effects of savanna dynamics on the population dynamics of the animal-dispersed shrub Grewia flava. From empirical results we derive model rules describing effects of savanna structure on several processes in Grewia's life cycle. By formulating the model, we summarise existing information on Grewia demography and identify gaps in this knowledge. Despite a number of such gaps, the model can be used to make certain quantitative predictions. As an example, we apply the model to investigate the role of seed dispersal in Grewia encroachment on rangelands. Model results show that cattle promote encroachment by depositing substantial numbers of seeds in open areas, where Grewia is otherwise dispersal-limited. Finally, we draw some general conclusions about Grewia's life history and population dynamics. Under natural conditions, concentrated seed deposition under woody plants appears to be a key process causing the observed association between Grewia and other woody plants. Furthermore, low rates of recruitment and high adult survival result in slow-motion dynamics of Grewia populations. As a consequence, Grewia populations interact with savanna dynamics on long temporal and short to intermediate spatial scales.
Y1  - 2004
ER  - 
TY  - JOUR
A1  - Jeltsch, Florian
A1  - Weber, Gisela
A1  - Paruelo, J.
A1  - Dean, W. R. J.
A1  - Milton, Sue J.
A1  - VanRooyen, N.
T1  - Beweidung als Degradationsfaktor in ariden und semiariden Weidesystemen
Y1  - 2000
ER  - 
TY  - JOUR
A1  - Jeltsch, Florian
A1  - Weber, Gisela
A1  - Dean, W. R. J.
A1  - Milton, Sue J.
A1  - VanRooyen, N.
A1  - O'Connor, Terry
A1  - Moloney, Kirk A.
T1  - Entstehung und Bedeutung räumlicher Vegetationsstrukturen in Trockensavannen : Baum-Graskoexistenz und Artenvielfalt
Y1  - 2000
ER  - 
TY  - JOUR
A1  - Jeltsch, Florian
A1  - Wichmann, Matthias
A1  - Dean, W. R. J.
T1  - Global change challenges the Tawny Eagle (Aquila rapax) : modelling extinction risk with respect to predicted climate and land use changes
Y1  - 2004
ER  - 
TY  - JOUR
A1  - Jeltsch, Florian
A1  - Wichmann, Matthias
A1  - Dean, W. R. J.
A1  - Moloney, Kirk A.
A1  - Wissel, Christian
T1  - Implications of climate change for the persistence of raptors in arid savannah
Y1  - 2003
ER  - 
TY  - JOUR
A1  - Wichmann, Matthias
A1  - Dean, W. R. J.
A1  - Jeltsch, Florian
T1  - Predicting the breeding success of large raptors in arid southern Africa : a first assessment
N2  - 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
Y1  - 2006
ER  -