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.
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Behnke, R. H., Scoones, I. & Kerven, C. (eds). 1993. Range ecology at disequilibrium: new models of natural variability and pastoral adaptation in African savannas. Overseas Development Institute, London.
Boeken, B. & Shachak, M. 1998. The dynamics of abundance and incidence of annual plant species during colonization in a desert. Ecography 21: 63–73.
Bowers, M. A. 1987. Precipitation and the relative abundances of desert winter annuals: a 6-year study in the northern Mohave desert. J. Arid Environ. 12: 141–150.
Collins, S. L. & Glenn, S. M. 1991. Importance of spatial and temporal dynamics in species regional abundance and distribution. Ecology 72: 654–664.
Dawkins, R. & Krebs, J. R. 1979. Arms races between and within species. Proc. Roy. Soc. London B 205: 489–511.
Eberhardt, L. L. & Thomas, J. M. 1991. Designing environmental field studies. Ecol. Monogr. 61: 53–74.
Ellis, J. E. & Swift, D. M. 1988. Stability of African pastoral ecosystems: alternate paradigms and implications for development. J. Range Manage. 41: 450–459.
Friedel, M. H., Foran, B. D. & Stafford Smith, M. 1990. Where the creeks run dry or ten feet high: pastoral management in arid Australia. Proc. Ecol. Soc. Austr. 16: 185–194.
Fuls, E. R. 1992. Semi-arid and arid rangelands: a resource under siege due to patch-selective grazing. J. Arid Environ. 22:191–193.
Gillison, A. N. & Brewer, K. R. W. 1985. The use of gradient directed transects or gradsects in natural resource surveys. J. Environ. Manag. 20: 103–127.
Goldberg, D. E. & Turner, R. M. 1986. Vegetation change and plant demography in permanent plots in the Sonoran desert. Ecology 67: 695–712.
Guo, Q. & Brown, J. H. 1996. Temporal fluctuations and experimental effects in desert plant communities. Oecologia 107: 568–577.
Gutierrez, J. R. & Whitford, W. G. 1987. Responses of Chihuahuan Desert herbaceous annuals to rainfall augmentation. J. Arid Environ. 12: 127–139.
Hoffman, M. T. & Cowling, R. M. 1990. Vegetation change in the semi-arid Karoo over the last 200 years: an expanding Karoo -fact or fiction ? S. Afr. J. Sci. 86: 286–294.
Kellner, K. & Bosch, O. J. H. 1992. Influence of patch formation in determining the stocking rate for southern African grassland. J. Arid Environ. 22: 99–105.
Kelt, D. A. & Valone, T. J. 1995. Effects of grazing on the abundance and diversity of annual plants in Chihuahuan desert scrub habitat. Oecologia 103: 191–195.
Lawes, M. J. & Nanni, R. F. 1992. The density, habitat use and social organization of the dorcas gazelles (Gazella dorcas) in the Makhtesh Ramon, Negev desert, Israel. J. Arid Environ. 24: 177–196.
Loria, M. & Noy-Meir, I. 1979. Dynamics of some annual populations of a desert loess plain. Isr. J. Bot. 28: 211–225.
Maynard Smith, J. 1989. Evolutionary genetics. Oxford University Press, Oxford.
McAuliffe, J. R. 1990. A rapid survey method for the estimation of density and cover in desert plant communities. J. Veg. Sci. 1: 653–656.
Milchunas, D. G., Lauenroth, W. K., Chapman, P. L. & Kazempour, K. 1989. Effects of grazing, topography, and precipitation on the structure of a semi-arid grassland. Vegetatio 80: 11–23.
Milton, S. J. 1994. Growth, flowering and recruitment of shrubs in grazed and protected rangeland in the arid Karoo. Vegetatio 111: 17–27.
Milton, S. J. & Hoffman, M. T. 1994. The application of stateand-transition models to rangeland research and management in arid succulent and semi-arid grassy Karoo, South Africa. Afr. J. Range Forage Sci. 11: 18–26.
Morton, S. R. 1990. The impact of European settlement on the vertebrate animals in arid Australia: a conceptual model. Proc. Ecol. Soc. Aust. 16: 201–213.
O'Connor, T. G. 1985. A synthesis of field experiments concerning the grass layer in the savanna regions of southern Africa. S. Afr. Nat. Sci. Prog. Rep. 114. CSIR, Pretoria.
Parsons, D. A. B., Shackleton, C. M. & Scholes, R. J. 1997. Changes in herbaceous layer condition under contrasting land use systems in the semi-arid lowveld, South Africa. J. Arid Environ. 37: 319–329.
Saltz, D. & Rubinstein, D. I. 1995. Population dynamics of a reintroduced Asiatic wild ass (Equus hemionus) herd. Ecol. Appl. 5: 327–335.
Saltz, D., Schmidt, H., Rowen, M., Karnieli, A., Ward, D. & Schmidt, I. 1999. The feasibility of applying remote-sensing techniques for assessing grazing impacts in hyper-arid environments. J. Range Manag. 52: 500–507.
Saltz, D. & Ward, D. 2000. Responding to a three-pronged attack: desert lilies subject to herbivory by dorcas gazelles. Plant Ecol. 148: 127–138.
Seely, M. K. & Louw, G. 1980. A first approximation of the effects of rainfall on the ecology and energetics of a Namib desert dune ecosystem. J. Arid Environs 3: 25–54.
Sullivan, S. 1996. Towards a non-equilibrium ecology: perspectives from an arid land. J. Biogeog. 23: 1–5.
Tapson, D. R. 1993. Biological sustainability in pastoral systems: The kwaZulu case. p. 118–135. In: Behnke, R. H., Scoones, I. & Kerven, C. (eds), Range ecology at disequilibrium. New models of natural variability and pastoral adaptation in African savannas. ODI/IIED/Commonwealth Secretariat, London.
Venter, J., Liggitt, B., Tainton, N. M. & Clarke, G. P. M. 1989. The influence of different land use practices on soil erosion, herbage production, and grass species richness and diversity. J. Grassl. Soc. S. Afr. 6: 89–98.
Ward, D. & Olsvig-Whittaker, L. 1993. Plant species diversity at the junction of two desert biogeographic zones. Biodivers. Lett. 1: 172–185.
Ward, D., Olsvig-Whittaker, L. & Lawes, M. 1993. Vegetationenvironment relationships in a Negev Desert erosion cirque. J. Veg. Sci. 4: 83–94.
Ward, D. & Saltz, D. 1994. Foraging at different spatial scales: dorcas gazelles foraging for lilies in the Negev desert. Ecology 75: 48–58.
Ward, D., Spiegel, M. & Saltz, D. 1997. Gazelle herbivory and interpopulation differences in calcium oxalate content of leaves of a desert lily. J. Chem. Ecol. 23: 333–346.
Ward, D., Ngairorue, B. T., Kathena, J., Samuels, R. & Ofran, Y. 1998a. Land degradation is not a necessary outcome of communal pastoralism in arid Namibia. J. Arid Environs 40: 357–371.
Ward, D., Saltz, D., Rowen, M. & Schmidt, I. 1998b. Effects of grazing by re-introduced Equus hemionus on the vegetation in a Negev desert erosion cirque. J. Veg. Sci. 10: 579–586.
Werner, W. 1994. Land tenure issues in Namibia: interactions with sustainable resource management. Pp. 27–41. In: S. Wolters (ed.). Proceedings of Namibia's national workshop to combat desertification. Desert Research Foundation of Namibia, Windhoek, Namibia.
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Ward, D., Saltz, D. & Olsvig-Whittaker, L. Distinguishing signal from noise: Long-term studies of vegetation in Makhtesh Ramon erosion cirque, Negev desert, Israel. Plant Ecology 150, 27–36 (2000). https://doi.org/10.1023/A:1026529126729
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DOI: https://doi.org/10.1023/A:1026529126729