Scale and macroecological patterns in seed dispersal mutualisms

Although some studies of seed dispersal mutualisms have documented adaptive relationships between fruits and frugivores, others have shown that adaptive patterns are constrained by phylogenetic, historical or climatic effects. Variable results among studies have thwarted attempts to find a paradigm to unite the field and direct research. Two recent studies in Global Ecology and Biogeography exemplify this dichotomy. One paper reported adaptive relationships between abundances of birds and fruits, while the other study found that bird-fruit abundance patterns were constrained by climatic effects. Almost paradoxically, both studies were conducted at the same locale. However, they focused on different spatio-temporal scales. These results are surprisingly consistent with several other recent studies that have taken a macroecological approach. They also indicate that mutualistic relationships between fruits and frugivores are scale dependent. When viewed together, recent work suggests that the conflicting results of previous studies may result from spatio-temporal variability of mutualistic relationships. This paper briefly reviews the emerging field of seed dispersal macroecology. A growing appreciation for scale appears to be leading the field in a new direction.