Spatial sex segregation in the dioecious grass Poa ligularis in northern Patagonia: the role of environmental patchiness.

BERTILLER, M.B; SAIN, C.L; CORONATO, FR; ARES, J.O.; GRAFF, P

BIODIVERSITY AND CONSERVATION

SPRINGER

Lugar: Berlin; Año: 2002 vol. 11 p. 69 - 84

0960-3115

We examined the effect of environmental patchiness on the spatial segregation of the sexesin the dioecious anemophilus grass Poa ligularis. Because the species is sensitive to grazing, a betterunderstanding of environmental factors that control its spatial distribution and abundance could improveconservation efforts. We hypothesized that (i) males and females are spatially segregated in the microenvironments created by plant patches as the result of sexual specialization in habitat and/or resources use,(ii) sexual specialization is related to different tolerance to competition and reproductive costs of malesand females, and (iii) changes in patch structure affect the microenvironment and the intensity of spatialsegregation of the sexes. We analyzed the spatial distribution of sexes at three sites with different plantand micro-environmental patchiness and performed a controlled competition experiment with differentsubstitution of males and females. Our results showed that large plant patches created larger shelteredsoil fertility islands than small patches. As patch size and their area of influence increased, the densityand the spatial segregation of the sexes of P. ligularis also increased, resulting in biased habitat-specificsex ratios. In accordance with their higher reproductive costs, females were more frequent in sheltered(low air evaporative demand) and nitrogen-rich areas inside patch perimeters than males. Females werealso better able to tolerate inter-sexual competition than males. In contrast, males tolerated low nitrogenconcentration in soil and low sheltering, probably gaining advantage in pollen dispersal. Inter- and intrasexual competition, however, affected the reproductive output of both sexes. From the point of view ofconservation, environmental patchiness is important to the status of P. ligularis populations. The reductionof patch size limits the available microsites, biases the sex ratio towards males inside patches, increasesinter- and intra-sexual competition, and it might be expected to decrease overall seed and pollen productionand consequently potential recruitment.