Fossil insect folivory tracks paleotemperature for six million years

Abstract

Abstract. Paleoecological studies enhance our understanding of biotic response to climate change because they consider timescales not accessible through laboratory or ecological studies. From 60 to 51 million years ago (Ma), global temperatures gradually warmed to the greatest sustained highs of the last 65 million years. Superimposed on this gradual warming is a transient spike of high temperature and pCO 2 (partial pressure of carbon dioxide in the atmosphere; the Paleocene-Eocene Thermal Maximum 55.8 Ma) and a subsequent short-term cooling event (;54 Ma). The highly resolved continental fossil record of the Bighorn Basin, Wyoming, USA, spans this interval and is therefore uniquely suited to examine the long-term effects of temperature change on the two dominant groups in terrestrial ecosystems, plants and insect herbivores. We sampled insect damage on fossil angiosperm leaves at nine well-dated localities that range in age from 52.7 to 59 Ma. A total of 9071 leaves belonging to 107 species were examined for the presence or absence of 71 insect-feeding damage types. Damage richness, frequency, and composition were analyzed on the bulk floras and individual host species. Overall, there was a strong positive correlation between changes in damage richness and changes in estimated temperature, a weak positive relationship for damage frequency and temperature, and no significant correlation for floral diversity. Thus, insect damage richness appears to be more sensitive to past climate change than to plant diversity, although plant diversity in our samples only ranges from 6 to 25 dicot species. The close tracking of the richness of herbivore damage, a presumed proxy for actual insect herbivore richness, to both warming and cooling over a finely divided, extended time interval has profound importance for interpreting the evolution of insects and plant-insect associations in the context of deep time. Our results also indicate that increased insect herbivory is likely to be a net long-term effect of anthropogenic warming.

Examining plant physiological responses to climate change through an evolutionary lens

“…First, higher temperatures may accelerate insect population growth rates, potentially increasing the frequency and severity of plant damage (Liu et al, 2011;Mitton and Ferrenberg, 2012). Indeed, foliar damage from insect herbivores increased dramatically with mean annual temperature across millions of years in the fossil record (Currano et al, 2010). Warmer winter temperatures also may reduce overwinter mortality among herbivores (Bale et al, 2002) and increase foraging opportunities during prolonged growing seasons (Brodie et al, 2012).…”

Insect Leaf-Chewing Damage Tracks Herbivore Richness in Modern and Ancient Forests

“…However, this relationship has not been systematically addressed, and the consistent correlation in the fossil record of total and endophytic DTR strongly suggests that it may be significant [3], [9]. The few actualistic studies of insect-damaged leaves to date, while helpful, did not include insect sampling [26], [27].…”

Why Did Terrestrial Insect Diversity Not Increase During the Angiosperm Radiation? Mid-Mesozoic, Plant-Associated Insect Lineages Harbor Clues

“…Long-term projects with multiple colleagues were initiated to examine diverse preangiospermous, gymnosperm-dominated floras (Labandeira 2006;Ding et al 2014). Current preliminary studies of Mesozoic herbivory use a similar methodology as those for the early Permian (Labandeira and Allen 2007;Schachat et al 2014), the CretaceousPaleogene (K-Pg) boundary Wilf et al 2006), and the mid-Paleogene climate events (Wilf et al 2005;Wappler et al 2012;Currano et al 2009). In addition, studies of mid-Mesozoic pollination have centered principally on the preangiospermous mid-Mesozoic (Ren et al 2009;Labandeira 2010;Peñalver et al 2012).…”