@article{TielboergerKadmon1997,
  author    = {Tielb{\"o}rger, Katja and Kadmon, Ronen},
  title     = {Relationships between shrubs and annual communities in a sandy desert ecosystem : a three-year study},
  year      = {1997},
  abstract  = {A field study was designed to investigate the effect of shrubs on the dynamics and structure of annual plant communities in a sandy desert ecosystem. Densities of emerging and reproductive plants of all annual species were monitored in permanent quadrats located under shrubs and in open areas between shrubs during three successive years; a relatively dry one, a relatively wet one, and a very dry one. A total of 29 species were recorded in the study. Of these, 19 species did not show any evidence for differences in abundance between the two habitats. Nine species exhibited year-to-year variation in their responses to the shrub-opening gradient, being more common in a particular habitat during one year, and showing no response or even an opposite response during a different year. Only one species was consistently more abundant under shrubs throughout the whole study period, and no species was consistently more abundant in the openings. These findings contradict the hypothesis that annual species associated with desert shrub communities can be categorized into distinct groups based on their 'preference' for shrubs vs. openings. Ordination analyses of community-level patterns indicated that annual communities inhabiting the openings were more stable than those inhabiting the shrub habitat. The main lesson from this study is the importance of long-term observations in studies attempting to characterize community-level responses to environmental gradients.},
  language  = {en}
}
@article{TielboergerPrasseBornkammetal.2000,
  author    = {Tielb{\"o}rger, Katja and Prasse, R{\"u}diger and Bornkamm, Reinhard and Kadmon, Ronen and Tsoar, H.},
  title     = {Sukzessionsprozesse in einem Sandd{\"u}nengebiet nach Ausschluß von Beweidung},
  year      = {2000},
  language  = {de}
}
@article{TielboergerKadmonMuelleretal.2000,
  author    = {Tielb{\"o}rger, Katja and Kadmon, Ronen and M{\"u}ller, Monika and Jeltsch, Florian},
  title     = {Populationsdynamische Funktionen von Ausbreitung und Dormanz},
  year      = {2000},
  language  = {de}
}
@article{TielboergerKadmonMuelleretal.2000,
  author    = {Tielb{\"o}rger, Katja and Kadmon, Ronen and M{\"u}ller, Monika and Jeltsch, Florian},
  title     = {Raum-zeitliche Populationsdynamik von einj{\"a}hrigen W{\"u}stenpflanzen},
  year      = {2000},
  language  = {de}
}
@article{TielboergerKadmon2000,
  author    = {Tielb{\"o}rger, Katja and Kadmon, Ronen},
  title     = {Temporal environmental variation tips the balance between facilitation and interference in desert plants},
  year      = {2000},
  abstract  = {Recently, numerous studies have pointed to the importance of positive interactions in natural communities. There is now a broad consensus that the balance between negative and positive interactions should shift along environmental gradients, with competition prevailing under environmentally benign conditions and positive interactions dominating under harsh conditions. A commonly cited example of the importance of facilitation in harsh environments is the preference of desert annual plants for the areas under the canopy of shrubs. The recognition of apparently positive effects of desert shrubs on annuals, however, has been mostly based on density measurements, while fitness parameters of the understory plants have been ignored. Also, the temporal consistency of such effects has not been previously tested. Based on conceptual ideas about the balance between interference and facilitation, we predicted that positive effects of the shrubs on the understory should dominate in dry years, while in favorable years, negative effects would be stronger. We tested our hypothesis by measuring the direction and magnitude of the shrub effect on demographic responses of four desert annual plant species during four consecutive seasons of differing rainfall. The results contradicted our initial hypothesis. Depending on the species, the effect of the shrubs shifted from either negative to neutral or from neutral to positive with increasing annual rainfall. However, this trend was stronger for the effect of shrubs on plant reproductive success than on their densities. Our data highlight the importance of measuring fitness parameters in studies of plant-plant interactions. We suggest that the negative effects of shrubs on plant fitness were due to rainfall interception, while positive effects were related to increased nutrient availability beneath shrubs. However, the mechanisms by which the shrubs and annuals interact can only be resolved using an experimental approach. Our results contradict previous hypotheses about the relative importance of positive and negative interactions along environmental gradients. A simple conceptual model summarizing the proposed role of rainfall in determining the direction of shrub effects on their understory annuals is presented.},
  language  = {en}
}
@article{TielboergerKadmon2000,
  author    = {Tielb{\"o}rger, Katja and Kadmon, Ronen},
  title     = {Indirect effects in a desert plant community : is competition among annuals more intense under shrub canopies?},
  year      = {2000},
  abstract  = {An unresolved discussion in contemporary ecology deals with the relative importance of competition along environmental gradients. In deserts, local-scale differences in environmental productivity may be caused by the presence of shrubs, which represent a favorable habitat for annual populations within a nutrient-poor matrix. In this study, we attempted to test the hypothesis that facilitation of desert annuals by shrubs increase the intensity of competition among the annual plants. Such negative indirect effects have so far been ignored in studies about plant-plant interactions. We tested our hypothesis by measuring seedling survival and fecundity of four abundant annual plant species with and without neighbors in open areas and under shrub canopies in a sandy desert area. Our findings did not indicate indirect negative effects of shrubs on their understory annuals. Sensitivity to the presence of neighbors varied between species and surprisingly, the species with the smallest seeds was the only one which was not negatively affected by the presence of neighbors. In contrast to our hypothesis, there was no difference between the habitat types shrubs and openings in absolute and relative competition intensity. Our overall results suggest that negative indirect effects of shrubs are unimportant in determining demographic response of understory annual plants.},
  language  = {en}
}
@article{KadmonTielboerger1999,
  author    = {Kadmon, Ronen and Tielb{\"o}rger, Katja},
  title     = {Testing for source-sink population dynamics : an experimental approach exemplified with desert annuals},
  year      = {1999},
  abstract  = {Theoretical models indicate that natural populations may be structured in such a way that many individuals occur in habitats where reproduction is insufficient to balance mortality. The persistence of such 'sink' populations depends on immigration from neighboring 'source' habitats where local reproduction exceeds mortality. While source-sink dynamics has become a fundamental concept in ecological theory, there has been virtually no experimental test for the existence of sources and sinks in natural populations. This paper reports the results of a four-year study that was designed to experimentally test for source-sink population dynamics in desert annual communities. Based on evidence from a variety of desert ecosystems indicating that patchiness caused by the presence of shrubs is important in structuring desert annual communities, we distinguished between two types of habitats: areas beneath the canopy of shrubs and the open areas between the shrubs. If, as suggested in previous studies, source-sink dynamics is important in structuring such annual communities, one would expect that removal of populations from one habitat leads to extinction of some species in the other habitat. We tested this prediction using removal experiments. Specifically, we monitored density responses of annual populations inhabiting open areas to the repeated removal of conspecific populations from the shrubs and vice versa. Four years after establishment of the experiment, none of the studied 34 species responded to the removal treatments with habitat-specific extinction. Only one species exhibited a significant habitat-specific decrease in density in response to the removal of conspecific populations from the other habitat. These findings contradict our expectations and point to the importance of applying an experimental approach in studies of source-sink dynamics.},
  language  = {en}
}