Individual fruit and crop size effects on seed dispersal differ between plant species offering contrasting rewards

Abstract

Intraspecific variation in plant traits, such as crop and fruit sizes, can affect frugivore attractiveness to individuals, ultimately influencing plant fitness. Different nutritional rewards offered by plants may attract different sets of seed dispersers, but we know little about how these differences can translate into dispersal effectiveness. Because seed dispersal interactions occur at the individual-level, downscaling from species to individual-based networks may help us link individual traits to plant fitness. Here, we tested whether crop and fruit sizes affected interactions between plant individuals and bird species using individual-based networks for two plant species offering contrasting nutritional rewards: the lipid-rich Xylopia aromatica and carbohydrate-rich Miconia rubiginosa. To this end, we sampled bird-fruit interactions in 10 individuals per plant species, representing a gradient of crop and fruit sizes in southeast Brazil. Then, we linked those traits to species-level network metrics, number of visits and quantitative effectiveness to examine their influence on seed dispersal. Miconia trees with larger fruit crops were more connected and attained higher quantitative effectiveness than trees with smaller fruit crops, whereas for Xylopia, trees producing larger fruits showed lower per capita fruit removal. Our findings suggest that traits that shape the selective pressures exerted by frugivores differ among plant species.