Grazing effects on the sex ratio of a native dioecious grass depend on unpalatable neighbourhood

GRAFF, PAMELA; AGUIAR, MARTIN R.

Canberra, Australia

Conferencia; Ecological Society of Australia 2010 Conference (ESA10); 2010

Ecological Society of Australia

Dioecy makes plants particularly susceptible to anthropogenic disturbances. By changing the selective pressures on vegetation, domestic grazing could change gender performance and sex ratios with important repercussions on plant population dynamics. Understanding the mechanisms behind those changes can be of particular importance for rangeland management, especially when the species concerned support livestock production. We studied the impact of interspecific competition and herbivory on the sex performance of a perennial-native-dioecious grass (Poa ligularis). We linked the results of the process-based field experiments with fine-scale spatial patterns of naturally established plants at none, moderate and intense sheep grazing. We found that females were better defended against insects but had less competitive ability at exclosure conditions than males. This trade-off resulted in a microsite sex-biased spatial pattern, being females more segregated from unpalatable grasses than males. On the other hand, under domestic grazing, plants growing far from unpalatable grasses suffer higher levels of sheep grazing. The reduction in a 40-70% female density with grazing intensification results in a decrease of 53-83% flowering stems density. These results, plus the notion of recruitment limitation in field conditions, could strongly affect Poa population viability and livestock sustainability