Responses of Pancratium sickenbergeri to simulated bulb herbivory:: combining defence and tolerance strategies

1 We determined the effects of simulated bulb herbivory by the dorcas gazelle, Gazella dorcas, on the geophyte, Pancratium sickenbergeri (Amaryllidaceae), in the Negev desert, Israel. In a population with a high level of herbivory, we removed 0%, 25%, 50% and 75% of bulb tissue from plants. 2 Bulbs with an intermediate volume removed (50%) showed the highest re-growth capacity and fitness in relation to the other cutting treatments. The production of calcium oxalate defences increased in cut bulbs. 3 There was a trade-off between investment in storage and defence. Trade-offs were not found between growth and defence, between growth and reproduction or between reproduction and defence. 4 Control plants grew less, had lower levels of calcium oxalate, stored more energy and produced more flowers and fruits, but their current fitness was only slightly higher than in the intermediate cutting treatment (50%) because of the high abortion of fruits. 5 P. sickenbergeri showed a complex resource allocation pattern as the result of combining defence and tolerance of herbivory. Plants respond to high herbivory levels with a high re-growth capacity as a tolerant mechanism to maintain fitness.