Data from: The mismatch in distributions of vertebrates and the plants that they disperse

Little is known about how mutualistic interactions affect the distribution
of species richness on broad geographic scales. Because mutualism
positively affects the fitness of all species involved in the interaction,
one hypothesis is that the richness of species involved should be
positively correlated across their range, especially for obligate
relationships. Alternatively, if mutualisms are facilitative (e.g.,
involving multiple mutualistic partners), the distribution of mutualists
should not necessarily be related, and patterns in species distributions
might be more strongly correlated with environmental factors. In this
study, we compared the distributions of plants and vertebrate animals
involved in seed-dispersal mutualisms across the United States and Canada.
We compiled geographic distributions of plants dispersed by frugivores and
scatter-hoarding animals, and compared their distribution of richness to
the distribution in disperser richness. We found that the distribution of
animal dispersers shows a negative relationship to the distribution of the
plants that they disperse, and this is true whether the plants dispersed
by frugivores or scatter-hoarders are considered separately or combined.
In fact, the mismatch in species richness between plants and the animals
that disperse their seeds is dramatic, with plants species richness
greatest in the in the eastern United States and the animal species
richness greatest in the southwest United States. Environmental factors
were corelated with the difference in the distribution of plants and their
animal mutualists and likely are more important in the distribution of
both plants and animals. This study is the first to describe the
broad-scale distribution of seed-dispersing vertebrates and compare the
distributions to the plants they disperse. With these data, we can now
identify locations that warrant further study either to understand better
seed-dispersal mutualisms or the factors that influence the distribution
of the plants and animals involved in these mutualisms.