Patterns of Niche Shift in Allopolyploid Adiantum viridimontanum (Pteridaceae) Across Habitat and Range Scales

This contribution is a study of the ecology of hybridization within the North American members of the Adiantum pedatum complex, a clade of maidenhair ferns; in the northeast part of its range, the clade comprises the diploids A. pedatum and A. aleuticum as well as their allotetraploid hybrid, A. viridimontanum. By utilizing fine-scale, field-collected data in concert with coarse-resolution climatic data, we characterized the realized ecological niche of the allotetraploid relative to its progenitors across habitat and range scales using a presence-only, envelope-based niche modeling approach. Our results demonstrate a pattern of niche intermediacy for A. viridimontanum across spatial scales and likewise at the habitat scale when the entire distribution of the three species in eastern North America is considered. However, the pattern of niche shift for the allotetraploid as characterized at the habitat scale is spatially variable; peripheral populations of the diploid species resolve in a portion of environmental space occupied only by the allotetraploid in the core portion of their range (where all three species co-occur). In geographic space, this pattern corresponds to the occupation of novel habitats by the allotetraploid in the core portion of its range, most notably serpentine mine barrens. These fine-scale results can be interpreted from the perspective of both niche conservatism and evolution, highlighting the importance of looking across spatial scales in studying ecological patterns.