Ecological, taxonomic, and life history correlates of seed mass among Indiana dune angiosperms

This study evaluated the ecological and taxonomic correlates of seed mass variation among 648 angiosperm species of the Indiana Dunes region (113 families, 507 genera in the original flora). The sample represented 50% of the species, 60% of the genera, and 67% of the families reported from the area. Species were chosen at random from the published flora. Each species was characterized by family membership, habitat, life history, phenological characters, and native vs. alien status, in order to determine the relationship among species between these variables and mean seed mass. Unique to this study are measurements of the effects of phenology and taxonomic family on seed mass. Each species occurred in @>1 of 13 habitat types described in the Intiana Dunes flora. To determine the effect of apparent water and light availability on seed mass, each habitat was assigned to one of four categories representing combinations of inferred water and light availability. Life histories or life forms represented were: annuals, biennials, herbaceous vines, parasites, perennials, short-lived perennials, shrubs, small trees, trees, and woody vines. Two phenological variables were available for most species: the time at which flowering begins (early, middle, or late), and the duration of flowering (short: 3 mo). The mean seed mass of each species was established by weighing samples from herbarium specimens in the United States National Herbarium. The frequency distribution of raw seed mass is highly skewed among species, so mean seed mass for each species was assigned to 1 of 14 seed mass classes based on a log scale (cf. Baker 1972). This transformation achieved a nearly normal distribution and made the data presentation comparable to that of Baker. One-way ANOVAs measured the effects of each factor across all other variables; two-way ANOVAs were conducted to detect significant interactions and strong associations between characters; multi-factorial ANOVAs were performed to measure the effect of each class variable independent of the others and to corroborate associations between characters suggested by the two-way ANOVAs. One-way ANOVAs revealed a statistically significant effect of all ecological and taxonomic factors on seed mass, with the exception of native vs. alien status. Seed mass variance was accounted for as follows: family, 30%; life history, 22%; habitat, 8%; water/light category, 5%; onset of flowering, 5%; and duration of flowering,