Dietary diversity in fruit-eating birds: a biogeographic comparison between New Zealand and Canada

If deterministic processes consistently structure ecological communities, similar patterns in species interactions should be observed in different geographic areas that experience similar environmental conditions. I tested for convergent patterns in dietary diversity of fruit-eating birds inhabiting similar latitude forests in the Northern and Southern hemispheres. I observed birds foraging for fruits over two fruiting seasons in both Nelson Lakes National Park, South Island, New Zealand, and the Pacific Rim National Park, Vancouver Island, Canada. I then conducted rarefaction analyses to compare community-level and species-level dietary diversity between geographic locales. Relationships between the size of each bird species and the average size of fruits consumed were also assessed. Results showed that the New Zealand bird community had greater overall dietary diversity than the Canadian community. However, similar levels of dietary diversity were observed among species within communities in both hemispheres. Positive relationships between bird size and fruit size were observed in New Zealand, but not in Canada. Therefore, while results showed some support for dietary convergence between hemispheres, several substantial differences were also observed, leading to mixed support for convergent patterns in the diets of fruit-eating birds between hemispheres.