Williamson Drive: Herbivory from a north-central Texas flora of latest Pennsylvanian age shows discrete component community structure, expansion of piercing and sucking, and plant counterdefenses
Insect herbivory during the Pennsylvanian–Permian transition interval (late Gzhelian) was estimated from the Williamson Drive locality of north-central Texas, USA. We investigated vegetational composition and the response of host plants to herbivores by characterization of insect-damage patterns. The bulk flora consists of four major plant groups: lycophytes, sphenophytes, pteridophytes, and pteridosperms, as well as unaffiliated morphotypes. Forty-six distinctive damage types (DTs) were recognized from 17 herbivorized plant-host taxa that were categorized into the five functional feeding groups (FFGs) of external foliage feeding (20 DTs), oviposition (11 DTs), piercing and sucking (9 DTs), galling (5 DTs), and wood boring (1 DT). The distributional patterns of FFGs and DTs on the most herbivorized plant hosts indicate several generalized and specialized patterns and organization into distinctive component communities. The overall herbivory level in the flora is elevated compared to other Cisuralian floras of north-central Texas, based on separate analyses of foliar surface area removed (0.86%) and frequency of herbivorized leaves (19.83%). One ubiquitous plant host, Macroneuropteris scheuchzeri (Hoffmann) Cleal, Shute and Zodrow, is disproportionately consumed, representing 35.75% of all specimens, but contributing 84.38% of the total herbivorized surface area, 60.87% of DT richness, and 55.44% of the DT abundance from all plant species. A notable feature is the abundance of nine piercing-and-sucking DTs on several hosts, representing three of the four new DTs described in this flora and indicating the ecological expansion of this FFG by Paleodictyopteroidea and earliest Hemipteroidea. There is evidence for physical and chemical antiherbivore defense afforded by trichomes and resin ducts of two major host plants, but the absence of seed predation is curious. Analyses of herbivory at Williamson Drive and four younger Cisuralian floras of the region support Feeny's apparency hypothesis. The overwhelming dominance of M. scheuchzeri herbivory at Williamson Drive, absent in earlier, peat-substrated Pennsylvanian floras, is typical of Cisuralian mineral-substrated plants.
