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Supporting Information Singer et al. 10.1073/pnas.1401949111 Field Experiment Testing the Enemy-Free Space Hypothesis Quercus rubra to Q. alba) was estimated to be equidistant between We conducted a bird exclusion experiment at three field sites in the tips and the Fagus/Quercus split (34 mya), i.e., at 17 mya. Middlesex County, Connecticut: Cockaponset State Forest, Hurd Branch lengths (in millions of years) were then calculated from the State Park, and Millers Pond State Park (see ref. 1 for more node ages. Following “phylogenetic host specificity” in Poulin et al. detail). The experiment encompassed the caterpillar communi- (3), HPD for each caterpillar species was calculated as the total ties of eight abundant tree taxa: Acer rubrum (red maple), Betula branch length (in millions of years) linking its host species along lenta (black birch), Carya spp. (Eucarya hickories), Hamamelis this phylogenetic tree; this was implemented using the Phyloge- virginiana (witch hazel), Prunus serotina (black cherry), Quercus netic Diversity (pd) command in the Picante package (7) in R (8). alba (white oak), Q. rubra (northern red oak), and Fagus gran- In our analyses, each caterpillar species represented a single difolia (American beech). These plant taxa show a gradient in data point with scores for HPD and bird predation log response the representation of dietary specialized caterpillars relative to ratio (LRR). After regressing the latter on the former using the dietary generalists (2). The 41 caterpillar species used in analyses raw data, we then accounted for the possible confounding effect were those with at least 10 observations over the 4-y study and of phylogenetic relationships of caterpillars on these two variables thus represent the most numerically dominant species over this via phylogenetically independent contrasts (PICs) (9). A com- time period (2,954 individual caterpillars out of 3,520 individual posite phylogeny for the 41 caterpillar species was constructed in caterpillars collected) (see Table S1 for the species list and Mesquite, version 2.75 (10), based on molecular phylogenetic sample sizes). According to a conventional categorical measure trees reported by Regier et al. (11), Zahiri et al. (12, 13), and of diet breadth based on plant taxonomy, 11 of these 41 cater- Sihvonen et al. (14). Expert opinion (David L. Wagner, Uni- pillar species are dietary specialists (host range of one plant versity of Connecticut, Storrs, CT) was then used to resolve family), whereas 30 caterpillar species are dietary generalists polytomies in three small clades. Further details on phylogeny (host range of more than one plant family). construction are given in Table S2. Two competing topologies We matched experimental and control branches in terms of were considered: a base tree in which (Nolidae + Erebidae) is tree species, tree size, height (1–3 m above ground), and hori- sister to Noctuidae (Fig. 1) and an alternative in which Nolidae is zontal spatial proximity, with the expectation that the pair of sister to (Noctuidae + Erebidae). Because branch lengths were branches would be within the foraging range of the same individual unknown, we tested branch lengths corresponding to all branches = birds and ovipositing female moths. To obtain independent mea- 1.0, Grafen’s arbitrary lengths, Pagel’s arbitrary lengths, Nee’s sures of bird predation across a range of microenvironments, pairs arbitrary lengths, and ln(Nee) lengths; these were generated in of experimental and control branches were replicated at two spatial Mesquite, version 2.75, using the PDAP package (15). Results scales: block and site. Each block was <1 ha, included all eight tree were broadly consistent across the combinations of phylogenetic taxa, and was separated from other blocks by at least 100 m. Each topologies and branch lengths; for simplicity, the results presented site was a relatively large tract of forest (>100 ha), separated from here reflect the base tree with ln(Nee) branch lengths. As a visual other sites by at least 10 km, and contained six complete blocks. In heuristic, caterpillar HPD was traced onto the base phylogeny each of 4 y (2008–2011), experimental and control branches were using the Parsimony Ancestral States method (16) (Fig. 1). We haphazardly selected (within the above constraints), and set up in then calculated standardized PICs using the PDAP module (17) May, at least 3 wk before sampling caterpillars from experimental of Mesquite (18), and regressed contrasts in bird predation LRR and control branches over 3–6 wk in June and early July, at the on contrasts in HPD. peak season of caterpillar abundance and insectivorous bird breeding (1). Antipredator Traits Associated with Diet Breadth Mean Body Length. We measured caterpillar body length as an Relationship Between Bird Predation and Herbivore Diet estimate of overall body size. Caterpillar body size has been shown Breadth: Accounting for Phylogeny to be associated with diet breadth, even when phylogeny is In addition to using a qualitative classification of diet breadth, we accounted for (19), such that dietary generalist species tend to be quantified the variation in herbivore diet breadth as host phy- larger than dietary specialist species (20). As such, it is important lodiversity (HPD) (3), the aggregate phylogenetic distance be- to account for caterpillar body size in analyses of bird predation tween hosts. Because we used only our own host plant records to because optimal foraging theory predicts that predators would calculate HPD, some generalists’ diet breadth is an underestimate choose large prey over small prey, all else being equal. In a re- of true diet breadth; i.e., it is a subset of the species they use more cent metaanalysis, Remmel et al. (21) present evidence that bird broadly. We believe this approach is superior to that of trying to predation of forest caterpillars tends to be biased toward larger quantify diet breadths more broadly, as the latter would include body size. In the bird exclusion experiment, when sampled cat- idiosyncratic errors due to an incomplete literature of host plant erpillars were brought back to the laboratory for rearing and records. We have high confidence in our records because we identification, we measured the length of each caterpillar using know that each caterpillar species has received the same sampling a ruler or digital calipers. Measurements taken with a ruler were effort; thus, our own estimates of diet breadth are comparable rounded to the nearest half-centimeter. In analyses, we used the among caterpillar species. In the broader literature, however, mean body length per caterpillar species calculated from samples sampling effort is idiosyncratic and some host records are not taken from bird-excluded branches only. reliable, thus introducing potential bias into quantitative measures of diet breadth. Stereotypy. We studied behavioral specialization by locating Phylogenetic topology of the eight host angiosperm species was caterpillars on their host plant by visual inspection. Each time we estimated from the Davies et al. (4) supertree via the Phylomatic located a caterpillar we noted its resting substrate and its behavior program (5) (Fig. S1). Node ages (in million years ago) were (e.g., walking, feeding, or resting). We grouped resting substrates obtained from Wikstrom et al. (6) (assuming the ACCTRAN op- into six categories: the upper surface of the leaf blade, the under timization). The single remaining undated node (that connecting surface of the leaf blade, the petiole, the leaf edge, within a shelter, Singer et al. www.pnas.org/cgi/content/short/1401949111 1of6 or woody tissue (including branches and the trunk). Most of our was present during all testing to monitor each participant. Before data on caterpillar behavior came from fieldwork each year from testing, each participant received a short introduction to cater- 2004 to 2007, although we continued to opportunistically locate pillar morphological diversity. During this talk, we showed pic- caterpillars and collect data while performing the bird exclusion tures of caterpillars in the families Sphingidae (hornworms), experiment (2008–2011). For species underrepresented in this Geometridae (loopers), Lycaenidae (hairstreaks), and Noto- dataset because of the difficulty of locating them in the wild, we dontidae (prominents). Participants were told to click on the transferred individual caterpillars encountered in beating samples caterpillars in the images as quickly and accurately as possible and to wild foliage and gave them ample time (10–20 min) to select that they were being timed. We did not inform participants about a resting place. The six categories of resting substrates formed the the specific hypotheses being tested. The Institutional Review six categories of resting location, and we assigned caterpillars to Board of Wesleyan University approved this research. The la- a category according to the substrate that they used most fre- tency until caterpillars were clicked was averaged across observers quently. We calculated stereotypy to measure the fidelity of each that successfully clicked on the caterpillar. In our analyses, latency caterpillar species to its most frequent resting substrate. Stereo- refers to the mean amount of time until discovery (in hundredths typy was the proportion of instances in which we located a cater- of a second) averaged across images of each caterpillar species. pillar species on its most frequently used resting substrate. We included