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  • 1
    Electronic Resource
    Electronic Resource
    Distinguishing signal from noise: Long-term studies of vegetation in Makhtesh Ramon erosion cirque, Negev desert, Israel (2000)
    Springer
    Plant ecology 150 (2000), S. 27-36 
    Details
    ISSN: 1573-5052
    Keywords: Asiatic wild asses ; Deserts ; Gazelles ; Herbivory ; Lilies ; Long-term plant population dynamics ; Negev
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We consider three case studies of long-term plant population dynamics in Makhtesh Ramon erosion cirque in the central Negev desert of Israel. We show that rainfall is the major driving variable in this system, and that it creates large temporal and spatial variation in plant species diversity and vegetation community composition. This variability makes it extremely difficult to distinguish `signal' (= pattern in vegetation) from `noise' (random spatial and temporal variance). Our long-term vegetation studies in permanent plots arranged along the length of the cirque, initiated in 1990 and continuing, show that there is high spatial and temporal variance in plant species' incidences and abundances. This is particularly true of annual plant species. However, using pairs of fenced and unfenced plots arranged along the major abiotic gradient, altitude (which mirrors changes in rainfall), we were able to tease apart the effects of variance in rainfall and herbivory. We found significant negative effects of herbivory by the re-introduced Asiatic wild ass (Equus hemionus) on plant cover and on vegetation community composition. In a study of the effects of herbivory by dorcas gazelles (Gazella dorcas) on the lily Pancratium sickenbergeri, we found that there was little inter-annual fluctuation in lily population size in two sand dunes in Makhtesh Ramon in spite of the high percentage of lilies that is removed by the gazelles and the almost complete herbivory of flowers by these herbivores. This result indicates that the dune lily populations may be maintained by dispersal of seed from other lily populations elsewhere in Makhtesh Ramon where gazelles are rare or absent.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1026529126729
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  • 2
    Electronic Resource
    Electronic Resource
    Responding to a three-pronged attack: desert lilies subject to herbivory by dorcas gazelles (2000)
    Springer
    Plant ecology 148 (2000), S. 127-138 
    Details
    ISSN: 1573-5052
    Keywords: Herbivory ; Coevolution ; Lilies ; Plant defences ; Desert ; Israel ; Gazelles ; Growth strategies
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We examined the effects of herbivory by the dorcas gazelle, Gazella dorcas, on different phenological stages of the lily Pancratium sickenbergeri from 1990–1996 in the Negev desert, Israel. We placed particular emphasis on the role of gazelle herbivory on selecting for plant defences and the effectiveness of these defences against subsequent herbivory. In the summer months, the gazelles dig in the sand to remove all or part of the bulb of the lily. Plants with partially-consumed bulbs were less likely to produce leaves the following winter and probably have lower lifetime flower production. Herbivory has resulted in greater downward growth of the bulb in populations with herbivory than those without herbivory, which reduces the probability that the entire plant will be consumed. Gazelles eat the leaves in the winter; this herbivory has a negative impact on leaf growth rates. However, the production of calcium oxalate limits gazelle consumption to the tips, and consequently reduces the effects of leaf herbivory. In the fall, the gazelles consumed virtually all flowers, yet we found no defence or growth strategy that might ameliorate this impact, with the possible exception of forgoing the output of a second flower stalk after the first has been consumed. The results of this study suggest that lilies employ different strategies to resist gazelle herbivory, and that these strategies are dependent on the phenological stage that is eaten. Avoidance by defence is the strategy in the leaves, avoidance by escape is utilized in bulbs. Forgoing the output of a second flower stalk after the first has been consumed can be considered as a form of escape based on a bet-hedging strategy or a shift in energy allocation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1009895512145
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  • 3
    Electronic Resource
    Electronic Resource
    From snapshot information to long-term population dynamics of Acacias by a simulation model (2000)
    Springer
    Plant ecology 150 (2000), S. 97-114 
    Details
    ISSN: 1573-5052
    Keywords: Acacia raddiana ; Individual-based ; Negev desert ; Pattern and process ; Permutation index ; Rare recruitment ; SAM ; Size frequency distributions ; Spatially-explicit simulation model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The African Acacia species A. raddiana is believed to be endangered in the Negev desert of Israel. The ecology of this species is not well understood. The main idea of our study is to learn more about the long-term population dynamics of these trees using snapshot information in the form of size frequency distributions. These distributions are highly condensed indices of population dynamics acting over many years. In this paper, we analyse field data on recruitment, growth, and mortality and use an existing simulation model of the population dynamics of A. raddiana (SAM) to produce contrasting scenarios of these live history processes that are based on the analysed field evidence. The main properties of simulated as well as observed tree size frequency distributions are characterised with Simpson's index of dominance and a new permutation index. Finally, by running the SAM model under the different scenarios, we study the effect of these different processes on simulated size frequency distributions (pattern) and we compare them to size distributions observed in the field, in order to identify the processes acting in the field. Our study confirms rare recruitment events as a major factor shaping tree size frequency distributions and shows that the paucity of recruitment has been a normal feature of A. raddiana in the Negev over many years. Irregular growth, e.g., due to episodic rainfall, showed a moderate influence on size distributions. Finally, the size frequency distributions observed in the Negev reveal the information that, in this harsh environment, mortality of adult A. raddiana is independent of tree size (age).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1026574303048
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    Paper (German National Licenses)
    Fulltext
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