Taxonomic, phylogenetic and functional diversities of ferns and lycophytes along an elevational gradient depend on taxonomic scales

We evaluated the phylogenetic and functional diversities of ferns and lycophytes along an elevational gradient in central Japan and assessed the influence of taxonomic scales on the aforementioned diversities and support for the niche conservatism hypothesis. Our dataset was based on herbarium specimens and broad field sampling of ferns and lycophytes integrated into 300-m intervals of elevational gradient. Phylogenetic and functional diversities evaluated using the standardised effect sizes of the Rao quadratic entropy index depended on the phylogenetic scale, particularly the inclusiveness of lycophytes. In ferns only and polypods, phylogenetic diversity showed no trends with elevation, and functional diversity at lower and higher elevations showed over-dispersion and clustering, respectively; however, those diversities of ferns and lycophytes showed a contrasting pattern in ferns only and polypods, although taxonomic diversity showed similar patterns. These results suggest that phylogenetic and functional diversities were affected by the variable evolutionary history of included groups. The patterns of functional diversities of ferns only and polypods were supported by environmental filtering, although phylogenetic diversity showed no trends. This suggests that morphological and life-history traits examined in the present study independently evolved in various lineages. The decreasing pattern of the mean family age in ferns only along an elevational gradient supported the niche conservatism hypothesis; however, the patterns in ferns and lycophytes and polypods did not support this hypothesis. These results suggest that the mean family age is susceptible to taxon-specific history and focal taxonomic scale, although niche conservatism may contribute to biodiversity patterns along elevational gradients.