Understanding variation in resource specialization is important for progress on issues that include coevolution, community assembly, ecosystem processes, and the latitudinal gradient of species richness. Herbivorous insects are useful models for studying resource specialization, and the interaction between plants and herbivorous insects is one of the most common and consequential ecological associations on the planet. However, uncertainty persists regarding fundamental features of herbivore diet breadth, including its relationship to latitude and plant species richness. Here, we use a global dataset to investigate host range for over 7,500 insect herbivore species covering a wide taxonomic breadth and interacting with more than 2,000 species of plants in 165 families. We ask whether relatively specialized and generalized herbivores represent a dichotomy rather than a continuum from few to many host families and species attacked and whether diet breadth changes with increasing plant species richness toward the tropics. Across geographic regions and taxonomic subsets of the data, we find that the distribution of diet breadth is fit well by a discrete, truncated Pareto power law characterized by the predominance of specialized herbivores and a long, thin tail of more generalized species. Both the taxonomic and phylogenetic distributions of diet breadth shift globally with latitude, consistent with a higher frequency of specialized insects in tropical regions. We also find that more diverse lineages of plants support assemblages of relatively more specialized herbivores and that the global distribution of plant diversity contributes to but does not fully explain the latitudinal gradient in insect herbivore specialization.

Bell Museum and Department of Plant Biology University of Minnesota St Paul MN 55108 1095

Departamento de Zoologia Universidade de Brasília Brasília Distrito Federal Brazil 70 910 900;

Department of Biological Sciences George Washington University Washington DC 20052;

Department of Biological Sciences Wright State University Dayton OH 45435; Sección Invertebrados Museo Ecuatoriano de Ciencias Naturales Quito Ecuador;

Department of Biology and Whitney R Harris World Ecology Center University of Missouri St Louis St Louis MO 63121;

Department of Biology Chiba University Chiba 263 8522 Japan;

Department of Biology Program in Ecology Evolution and Conservation Biology and

Department of Biology Program in Ecology Evolution and Conservation Biology and Sección Invertebrados Museo Ecuatoriano de Ciencias Naturales Quito Ecuador;

Department of Biology University of Ostrava 710 00 Ostrava Czech Republic;

Department of Biology Wesleyan University Middletown CT 06459;

Department of Ecology and Evolutionary Biology Tulane University New Orleans LA 70118;

Department of Ecology and Evolutionary Biology University of Connecticut Storrs CT 06269;

Department of Mathematics and Statistics University of Nevada Reno NV 89557;

Department of Zoology University of Oxford Oxford OX1 3PS United Kingdom;

Faculty of Science University of South Bohemia 370 05 Ceske Budejovice Czech Republic; Biology Centre Czech Academy of Science 370 05 Ceske Budejovice Czech Republic;

Faculty of Science University of South Bohemia 370 05 Ceske Budejovice Czech Republic; Biology Centre Czech Academy of Science 370 05 Ceske Budejovice Czech Republic; Department of Zoology University of Oxford Oxford OX1 3PS United Kingdom;

Faculty of Science University of South Bohemia 370 05 Ceske Budejovice Czech Republic; Biology Centre Czech Academy of Science 370 05 Ceske Budejovice Czech Republic; New Guinea Binatang Research Center Madang Papua New Guinea;

Faculty of Science University of South Bohemia 370 05 Ceske Budejovice Czech Republic; Smithsonian Tropical Research Institute Apartado 0843 03092 Balboa Ancon Panama;

J F Blumenbach Institute of Zoology and Anthropology Göttingen University 37073 Göttingen Germany;

National Museum of Natural History Smithsonian Institution Washington DC 20013 7012;

New Guinea Binatang Research Center Madang Papua New Guinea; Department of Biology University of Papua New Guinea Port Moresby Papua New Guinea;

New Guinea Binatang Research Center Madang Papua New Guinea; Environmental Futures Research Institute Griffith University Queensland 4111 Australia;

Sección Invertebrados Museo Ecuatoriano de Ciencias Naturales Quito Ecuador;

Sección Invertebrados Museo Ecuatoriano de Ciencias Naturales Quito Ecuador; Department of Biology Colorado Mesa University Grand Junction CO 81507; and

Smithsonian Tropical Research Institute Apartado 0843 03092 Balboa Ancon Panama; Department of Biology University of Utah Salt Lake City UT 84112 0840;

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