OOS 5-9
Sleeping with the enemy: Short- and long-term effects of resprouting shrubs on the performance of a post-fire recruiting, carnivorous plant
The stress-gradient hypothesis predicts that facilitation becomes a more frequent process in community interactions as abiotic stress increases. However, debate exists as to whether, at high levels of stress, competition remains prominent. We address this question using Drosophyllum lusitanicum (L.) Link (Drosophyllaceae), a rare carnivorous plant endemic to fire-prone Mediterranean heathlands in the Iberian Peninsula. This species copes with abiotic stress (nutrient limitation) by investing in prey-capture structures at the expense of photosynthesis and growth. Adults are killed by fire and populations regenerate by fire-triggered seed germination. Post-fire recruits are then exposed to seasonal (summer) water stress. In the absence of direct competition for nutrients, they may benefit from neighboring, resprouting shrubs which may facilitate summer survival, although they may also overgrow Drosophyllum. To test positive/negative effects of neighboring shrubs on recruitment success of Drosophyllum, we buried seeds in recently burned (open microsites and close to resprouting shrubs) and unburned patches and recorded germination and seedling survival/growth. To explore possible negative effects of mature shrubs on established Drosophyllum individuals as water stress decreases, we placed potted, greenhouse-reared juvenile plants in burned (open & close to shrubs) and unburned patches (in gaps and underneath shrubs) and recorded prey capture.
Results/Conclusions
Our results support the stress-gradient hypothesis and indicate that facilitation has a strong effect on establishment of Drosophyllum in disturbed habitats under high levels of abiotic stress. Germination of D. lusitanicum seeds was significantly higher in burned patches. Comparing microsites within burned patches, both germination and seedling survival were significantly higher close to resprouting shrubs while growth was not affected by proximity to shrubs. Mature shrubs in unburned patches had a marked negative effect on the amount of prey captured, whereas proximity to shrubs did not affect prey capture in burned patches. Therefore, in early post-fire habitats, surrounding resprouting shrubs do not impact growth and have a strong nursing effect on seedlings of poor competitive species by providing a favorable microhabitat. In late post-fire habitats, mature shrubs inhibit recruitment and limit nutrient intake (prey capture) of Drosophyllum. However, indirect competition may be a price worth paying because the facilitative effects of the surrounding community in initial post-disturbance stages can outweigh these future costs.