caa a22 4500 469097396 CHVBK 20180323133035.0 cr unu---uuuuu 170328e19920801xx s 000 0 eng 10.1007/BF00317238 doi (NATIONALLICENCE)springer-10.1007/BF00317238 Contrasting demography of two Patagonian shrubs under different conditions of sheep grazing and resource supply [Elektronische Daten] [R. Fernández, A. Nuñez, A. Soriano] Summary: Two shrub species, dominant in western Patagonia, Argentina, exhibited different demographic behaviors under the effect of sheep grazing and of manipulated resource levels. Senecio filaginoides showed an increase in cover under increasing grazing pressures; the rise was explained by an increasing number of individuals and not by larger plants; this trend was reversed when no grazing took place. Mulinum spinosum showed a slight decrease in cover and density at increasing grazing pressures, and no change in plant size. In a field experiment in which water was added (30 mm in early summer) and the dominant grasses removed, both factors substantially augmented the number of 1-year-old seedlings of Senecio recruited; the only noticeable response of Mulinum was an increase in seedling emergence because of grass removal. Six years after this last treatment, Senecio exhibited a ten fold increase in density, and its population structure showed a peak in younger classes; Mulinum remained unaffected. In seedling surveys conducted within an exclsure and in its surroundings, the emergence of Senecio was similar in these areas in the two years of the study, whereas the emergence of Mulinum was higher inside the exclosure for one of the years. The emergence of Senecio in the wetter year was 3 times larger than in the drier one. Grazing did not affect first-year survival of any species; the major source of seedlign death in this case, as well as in the manipulative experiment, was desiccation during summer drought. We conclude that the contrasting responses of the two species to grazing are mostly due to the greater ability of Senecio to benefit from any increase in resources, including those not used by grazed plants. The difference might also be due to a reduction in the seed availability of Mulinum caused by sheep preference for its fruits. The dissimilar abilities of the two shrubs to employ the resources freed by grazing would derive more from their contrasting demographic potential (i.e. the ability to rapidly increase biomass/m2) than from a difference in their niche overlap with palatable species. Springer-Verlag, 1992 Grazing nationallicence Life histories nationallicence Patagonia nationallicence Resource levels nationallicence Shrubs nationallicence Fernández R. Departmento de Ecología-IFEVA, Facultad de Agronomía, Universidad de Buenos Aires, 1417, Buenos Aires, Argentina aut Nuñez A. Departmento de Ecología-IFEVA, Facultad de Agronomía, Universidad de Buenos Aires, 1417, Buenos Aires, Argentina aut Soriano A. Departmento de Ecología-IFEVA, Facultad de Agronomía, Universidad de Buenos Aires, 1417, Buenos Aires, Argentina aut Oecologia Springer-Verlag 91/1(1992-08-01), 39-46 0029-8549 91:1<39 1992 91 442 https://doi.org/10.1007/BF00317238 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/BF00317238 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Fernández R. Departmento de Ecología-IFEVA, Facultad de Agronomía, Universidad de Buenos Aires, 1417, Buenos Aires, Argentina aut NATIONALLICENCE 700 1- Nuñez A. Departmento de Ecología-IFEVA, Facultad de Agronomía, Universidad de Buenos Aires, 1417, Buenos Aires, Argentina aut NATIONALLICENCE 700 1- Soriano A. Departmento de Ecología-IFEVA, Facultad de Agronomía, Universidad de Buenos Aires, 1417, Buenos Aires, Argentina aut NATIONALLICENCE 773 0- Oecologia Springer-Verlag 91/1(1992-08-01), 39-46 0029-8549 91:1<39 1992 91 442 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer