Vertebrate‐Dispersed Plants of the Iberian Peninsula: A Study of Fruit Characteristics

Abstract

This study examines the characteristics of ripe fruits of 111 species (35 families, 62 genera) of vertebrate—dispersed plants (with fleshy fruits) native to the Iberian Peninsula. The sample included 58% of the species, 87% of the genera, and 95% of the families of fleshy—fruit—producing plants occurring in the area. Species were characterized by 23 variables related to the design of the fruit (size, mass of seeds and pulp, number of seeds, seed size) and the organic and inorganic chemical constituents of pulp (water, lipids, protein, fiber, non—structural carbohydrate, ash, Ca, Na, Mg, K, P, Fe, Cu, Zn, Mn). Qualitative variables related to geographical distribution at two different scales (northern temperate vs. southern mediterranean; mediterranean lowlands vs. highlands), growth form, fruit color, and display type of the infructescence, were used to categorize species and perform comparisons of fruit characteristics. Factor analysis (FA) was used to examine trait covariation and identify major independent trends of variation in fruit structure and pulp composition. Factor scores of species were used to examine patterns related to taxonomic affiliation and ecological characteristics of species. With increasing fruit size, pulp mass increased more slowly than seed mass, and thus the pulp/seed mass ratio decreased. The ratio of pulp to seed was greatest in small—seeded fruits. Trees tended to produce the greatest amount of pulp per seed, and herbs the smallest amount. In the species with the smallest seeds the biomass of the pulp exceeded that of the seeds. Major trends of interspecific variation in fruit design included: (1) fruit size (54.5% of variance); (2) inverse relationship between number of seeds/fruit with mass of single seeds and mass of pulp allocated to each seed (23.1%); (3) variation in pulp/seed mass ratio (16.6%). Fruit size, seed size, and pulp/seed mass ratio tended to vary independently of each other. There was significant heterogeneity in factor source of species differing in geographical distribution, growth form, fruit color, and display type. Interspecific patterns in fruit design were strongly influenced by phylogeny, although no predictable relationship existed between fruit structure and taxonomic affiliation. Water was the dominant constituent of fresh pulp (range = 19.3—91.1%, mean = 70.8%). On a dry mass basis, nonstructural carbohydrate (NSC) represented 25.9—93.5% (mean = 67.0%), fiber 2.6—52.0% (16.3%), lipids 0.2—58.8% (6.9%), and protein 0.9—27.7% (5.0%). Based on factor analysis, there was a strong negative correlation between NSC and lipids (Factor 1, 46.5% of variance), and a complementary variation of NSC and fiber (Factor 2, 25.5%). Factors 3 (14.8%) and 4 (11.5%) corresponded to variation in protein and water, respectively. No significant heterogeneity in factor scores existed among groups of species based on geographical distribution or type of display. Heterogeneity did exist with regard to fruit color and plant growth form. No predictable relationship existed between phylogeny and pulp organic composition, although taxonomic diversity had some influence on interspecific variability. With the single exception of the joint occurrence of Ca and Mg, the concentration of any mineral element in the pulp of a species was not predictably associated with the amounts of other elements in the pulp. Composition of the inorganic fraction was not significantly related to either geographical distribution of the species of type of fruit display. Species groups based on fruit color or growth form differed significantly in total mineral content. No phylogenetic correlates were apparent in the constitution of the inorganic fraction of fruit pulp. The broadest patterns revealed by this study were of a "null type". The few "positive" ones have rather restricted implications as to the overall constitution of fruits, and only one—third of these seem attributable to the selective action of frugivores on fruit traits. The study failed to reveal any overwhelming influence of the disperser/dispersal environment on the characteristics of Iberian fruits taken as a whole, particularly with reference to interspecific variation. Phylogeny, architectural constraints, and species—specific energy and nutrient allocation patterns, seemed most important in explaining observed variation in fruit constitution.