ORNITHOCOPROPHILOUS PLANTS OF MOUNT DESERT ROCK, A REMOTE BIRD-NESTING ISLAND IN THE GULF OF MAINE, USA

Plants growing on seabird-nesting islands are uniquely adapted to deal with guano-derived soils high in N and P. Such ornithocoprophilous plants found in isolated, oceanic settings provide useful models for ecological and evolutionary investigations. The current study explored the plants found on Mount Desert Rock (MDR), a small seabird-nesting, oceanic island 44 km south of Mount Desert Island (MDI), Hancock County, Maine, U.S.A. Twenty-seven species of vascular plants from ten families were recorded. Analyses of guano-derived soils from the rhizosphere of the three most abundant species from bird-nesting sites of MDR showed significantly higher (P < 0.05) NO3-, available P, extractable Cd, Cu, Pb, and Zn, and significantly lower Mn compared to soils from the rhizosphere of conspecifics on non-bird nesting coastal bluffs from nearby MDI. Bio-available Pb was several-fold higher in guano soils than for background levels for Maine. Leaf tissue elemental analyses from conspecifics on and off guano soils showed significant differences with respect to N, Ca, K, Mg, Fe, Mn, Zn, and Pb, although trends were not always consistent. Two-way ANOVA indicated a significant interaction between species and substrate for Ca, Mg, Zn, and Pb tissue accumulation, showing that for these four elements there is substantial differentiation among species found on and off of guano soil. A compilation of species lists from other important seabird-nesting islands in the region suggested an ornithocoprophilous flora for northeastern North America consisting of 168 species from 39 families, with Asteraceae (29 taxa; 17.3%), Poaceae (25 taxa; 14.9%), Polygonaceae (10 taxa; 5.95%), Caryophyllaceae (9 taxa; 5.4%), and Rosaceae (9 taxa; 5.4%) as the most species-rich families. The taxa were predominantly hermaphroditic (69%) and perennial (66%) species, native (60%) to eastern North America.