Facilitation drives local abundance and regional distribution of a rare plant in a harsh environment

• Published in: Ecology (Durham) 2006-11, Vol.87 (11), p.2728-2735
• Main Author: Freestone, Amy L.
• Format: Article
• Language: English
• Subjects: Analysis of Variance; Animal and plant ecology; Animal, plant and microbial ecology; Biological and medical sciences; Biomass; Bryopsida - physiology; California; competition; Conservation biology; Delphinium; Delphinium - physiology; Delphinium uliginosum; Didymodon tophaceus; Ecological competition; Ecology; Ecosystem; Endangered & extinct species; facilitation; Flowers & plants; Fundamental and applied biological sciences. Psychology; General aspects; geographical distribution; gradients; habitat specialist; Habitats; interspecific competition; Metapopulation ecology; moss; mosses and liverworts; Plant populations; Plants; population size; recruitment; Reproduction - physiology; scaling; seedlings; Seedlings - physiology; serpentine soils; serpentine wetland; soil toxicity; Soil water; soil water content; species diversity; Synecology; Wetland ecology; wetland plants; Wetlands
• ISSN: 0012-9658; 1939-9170
• DOI: 10.1890/0012-9658(2006)87[2728:FDLAAR]2.0.CO;2

The importance of facilitation to local community dynamics is becoming increasingly recognized. However, the predictability of positive interactions in stressful environments, the balance of competition and facilitation along environmental gradients, and the scaling of local positive interactions to regional distributions are aspects of facilitation that remain unresolved. I explored these questions in a habitat specialist, Delphinium uliginosum, and a moss, Didymodon tophaceus, both found in small serpentine wetlands. I tested three hypotheses: (1) moss facilitates germination, growth, and/or fecundity of D. uliginosum; (2) facilitation is stronger at the harsher ends of gradients in soil moisture, toxicity, and/or biomass; and (3) facilitation is reflected in positive associations at the levels of local abundance and regional occurrence. Although considerable competitive interactions occurred in later life stages, moss strongly facilitated D. uliginosum seedling emergence. There was no evidence that this facilitative effect weakened, or switched to competition, in benign environments. D. uliginosum was more locally abundant and more frequently present, across a large portion of its range, with than without moss, indicating a net facilitative effect in the face of competitive influences. Facilitated recruitment, possibly by seed retention, was found to be an important control on abundance and distribution in this rare species.