Sex-related patterns of Poa ligularis in relation to shrub patch occurrence in northern Patagonia

BERTILLER, M.B; ARES, J.O.; GRAFF, P; BALDI, R.

JOURNAL OF VEGETATION SCIENCE

WILEY-BLACKWELL PUBLISHING, INC

Año: 2000 vol. 11 p. 9 - 14

1100-9233

Poa ligularis is a dioecious species and a valuableforage plant which is widespread in the arid steppe of northernPatagonia (Argentina). The vegetation in these areas consistsof a system of perennial plant patches alternating with baresoil areas defining contrasting micro-environments. We hypothesized that (1) male and female individuals of P. ligularisare spatially segregated in different micro-environments, (2)the intensity of spatial segregation of sexes depends on plantstructure and (3) spatial segregation of sexes is enhanced bycompetitive interactions between the sexes within the vegetation patches. We analysed the spatial distribution of female and male individuals in relation to the spatial pattern ofvegetation in two areas differing in their vegetation structure. The location of P. ligularis within patches whereeither male, female or both sexes occurred was also analysed. The results indicate that different patterns of spatialdistribution of sexes of P. ligularis may be found at thecommunity level depending on the dominant life forms andgeometric structure of plant patches. Where patches are ofa lower height, with a high internal patch cover, individualsof both sexes are concentrated within patch canopies. Insites characterized by large, tall patches and less internalpatch cover suitable microsites for female and male P.ligularis occur both within and outside the patch withmales located at further distances from the patch edge.Where the patch is large and tall enough to allow the establishment of males and females at relatively high numbers,males occupy the patch periphery or even colonize the interpatch bare soil. These spatial patterns are consistent withselective traits in which females better tolerate intraspecificcompetition than males, while males tolerate wider fluctuations in the physical environment (soil moisture, nitrogenavailability, wind intensity, etc.).