A latitudinal gradient of plant-insect interactions during the late Permian in terrestrial ecosystems? New evidence from Southwest China

摘要

The Permian-Triassic transition is concerned with a critical time interval during the evolutionary history of terrestrial ecosystems. However, the ecological underpinnings of terrestrial ecosystems during this time interval are poorly understood due to an impoverished fossil record. One of the more understudied episodes in the history of life is the ecological state of terrestrial ecosystems immediately before the Permian-Triassic ecological crisis. We address this issue by a quantitative study of a floral assemblage and its herbivorous insect damage based on 1086 plant specimens from the uppermost Permian of Southwest China. This bulk flora comprises 25 genera and 36 species of plants representing a typical, tropical rainforest vegetation of the upper Permian. We record 171 insect damage occurrences belonging to 24 distinctive damage types (DTs) from six functional feeding groups that were recognised in the flora. Statistical analyses of the occurrence, richness, diversity and frequency of DTs reveal that gigantopterids are the principal host plants for insect herbivores in the flora. Compared with other late Permian floras, a significant distinction of the insect damage spectrum can be recognised palaeolatitudinally based on the global position of phytogeographic regions. Despite the different, major targeted plant hosts in these floras, the richness and diversity of insect DTs and their herbivory levels from mid- to high latitudinal floras are remarkably lower than those of low latitudinal to equatorial floras. Our study indicates that terrestrial ecosystems from lower latitudes have higher levels of ecological complexity, and a distinct latitudinal gradient that probably was well established in terrestrial ecosystems during the late Permian. This assessment provides the first comprehensive overview of the ecological relationships among plants and insects, as well as their representation in terrestrial ecosystems of the late Paleozoic Cathaysia Flora.