Range-size, local abundance and germination niche-breadth in Mediterranean plants of two life-forms

The relationships between rarity (i.e., range-size, local abundance) and niche-breadth can be important to assess the risks the species face under global change, namely those resulting from fire regime change. In fire areas, germination is critical for establishing after fire for many species. We examined the relationships between rarity and germination niche-breadth for 53 plant species of two life-forms (chamaephytes and hemicryptophytes) growing in Eastern Spain. Rarity was measured as geographic range-size and as local abundance. Local abundance was evaluated at two sites differing in their post-fire successional status (a recently burned area and a long-unburned one). Germination niche-breadth was measured as the mean germination evenness index from four germination experiments that subjected the seeds to various germinating conditions characteristics of fire environments. Correlations between rarity (range-size, local abundance) and niche-breadth were calculated in cross-species mode or by way of phylogenetically independent contrasts, and either for the 53 species (all-species set) or for each of two life-form groups (chamaephytes, hemicryptophytes). In general, no significant correlations were found between the rarity measures and germination niche-breadth for the all-species set. However, significant correlations emerged when the analyses were done separating species by life-forms. Germination niche-breadth was positively correlated with range-size for chamaephytes, and negatively for hemicryptophytes. In addition, germination niche-breadth was uncorrelated, or negatively so, with local abundance for chamaephytes and hemicryptophytes, respectively. While no correlation between range-size and local abundance was found for chamaephytes, a negative one was obtained for hemicryptophytes. We conclude that rarity/germination-niche relationships varied by life-form. This pattern of relationships was obscured when all species were joined in a single group. Based on the contrasting patterns of correlations obtained for each life-form we argue that the changes in the germinating environment caused by alterations in fire regime are likely to differentially affect these two groups of species.