Realized niche and spatial pattern of native and exotic halophyte hybrids.

Interspecific hybridization is an important and common evolutionary mechanism, but field-based evaluations of changes in realized niches and zonation patterns of native and exotic hybrids relative to those of their parental plant species are rare. Would native hybrids forming hybrid zones between their parental species show realized niches similar to that of their parents, whereas would exotic hybrids show larger realized niches than their parents, and alter zonation patterns of native species? To address these questions, we examined key sediment characteristics in plots representing realized niches of native Sarcocornia hybrids, invasive Spartina hybrids and parental species in 14 salt marshes from four estuaries in the Gulf of Cadiz, Southwest Iberian Peninsula. In one representative marsh, the presence of plant taxa relative to intertidal plant zonation was recorded. Results documented that native and fertile hybrids of Sarcocornia had similar realized niche dimensions as their parental species and co-occurred with other plant species, supporting community diversity. However, exotic sterile hybrids of Spartina had realized niche dimensions lower than those of their parental species and occurred in monocultures. The native hybrids played a community structuring role, whereas the exotic Spartina hybrids were a disruptive influence that changed native halophyte zonation pattern and decreased diversity. This negative functional role could intensify if the sterile hybrids evolve and become fertile. Our study suggests the ecological niche dimension concept is an important tool for understanding species roles in ecosystems, incorporating many ideas from the individual to ecosystem levels.