Ecological correlates of range structure in rare and scarce British plants

1 The distribution patterns of 391 rare and scarce British plants (species recorded in 100 or fewer 10 × 10 km squares) were characterized by their distributional area (area of occupancy at 1‐km scale: AOO₁) and levels of aggregation (as reflected in fractal dimensions measured across two scales: D₁₋₁₀ and D₁₀₋₁₀₀). 2 Eighteen plant traits were tested for relationships to AOO, and to fractal dimension while controlling for AOO. These included both directly heritable traits (e.g. life‐form) and emergent properties that are, at most, indirectly heritable (e.g. typical local density). The latter set included an index of net distributional change and an index of range dynamism. 3 Only two traits, habitat preference and local abundance, were significantly related to AOO₁, but about half were associated with fractal dimension. 4 Relatively aggregated fine‐scale distributions (high D₁₋₁₀) were related to high local abundance, lack of specialized, long‐distance dispersal mechanisms, habitat preference and an increasing range size with relatively few local extinctions (i.e. a positive index of change with low dynamism). 5 Relatively aggregated coarse‐scale distributions (high D₁₀₋₁₀₀) were related to the use of insect pollinators, obligate outcrossing, habitat preference and relatively stable ranges (low dynamism). 6 Multivariate analyses of subsets of conceptually related variables showed that few variables interacted to affect distributional variables. 7 A highly significant negative relationship between dynamism and fractal dimension appears to be driven primarily by high rates of local extinction, leading to relatively scattered, diffuse range structures. Furthermore, it suggests that recent population trends may be inferred from snapshots of contemporary distribution patterns. 8 The role and interpretation of phylogenetically informed analyses in studies such as this are debatable. However, we found similar relationships in both phylogenetically informed and conventional analyses for all variables except pollination vector (a strongly conserved trait). 9 The spatial pattern of plant species distributions is associated with a range of ecological traits, particularly those describing past changes in distribution. The analysis of distribution patterns therefore has the potential to inform future conservation effort.