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

Abstract

Ecological specialization is one of the most interesting and perplexing attributes of biological systems. While certain macroecological patterns, such as an increase in specialization at lower latitudes, have long been subjects of investigation, there is much yet to be learned about inter-specific variation in specialization within diverse communities. High levels of specialization have been documented for some dominant ecological interactions, such as parasitism and herbivory, but much less is known about the relative abundance of specialists and generalists within those broad functional groups. We examine untested assumptions about the positive association between local abundance and dietary specialization using a 17-year dataset of caterpillar-plant interactions in Ecuador. 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 1,917 morphospecies of Lepidoptera ("caterpillars") from 33 families. We find that more specialized caterpillars 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. At larger scales, 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 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. Statement of authorshipCS wrote the first draft of the manuscript. DMS, MLF and LAD contributed substantially to consequent drafts and revisions. LAD, TRW, SV and DMS collected field data. CS, MLF and LAD generated research questions and designed statistical analyses. CS, DMS, LAD and MLF conducted statistical analyses. Data statementData supporting the results and conclusions can be found on a website caterpillars.org. Statistical analyses supporting the results are available upon request.