Jack-of-all-trades paradigm meets long-term data: Generalists are more widespread and locally less abundant

Background/Question/Methods

Ecological specialization is one of the most interesting and perplexing attributes of natural systems, and while strong macroecological patterns are known, such as an increase of specialization in the tropics, there is much to be learned about patterns of specialization in nature. High levels of specialization have been documented for some dominant ecological interactions, such as parasitism or herbivory, but almost nothing is known about relative abundances of specialists and generalists in terrestrial communities. We examine assumptions about the positive association between local abundance and dietary specialization using a 17-year dataset of caterpillar-plant interactions in Ecuador and Bayesian linear models. Our long-term data consist of experimental verification of caterpillar-plant associations and include standardized plot-based samples as well as general, regional collections of caterpillars, allowing for investigations across spatial scales and using different indices of abundance for 1917 morphospecies of Lepidoptera from 33 families.

Results/Conclusions

We find that specialists are locally more abundant than generalists, consistent with a key component of the "jack of all trades, master of none" hypothesis, which has otherwise received poor to mixed support from previous studies that have mostly involved fewer species and shorter time series. Generalists achieve greater prevalence across the landscape, and we find some evidence for geographic variation in the abundance-diet breadth relationship, in particular among elevational bands. Interspecific variation in abundance also had a negative relationship with diet breadth, with specialists having more variable abundances across species. The interesting result that more specialized species can be both rare and common highlights the ecological complexity of specialization.