D3367: Thermal tolerance of saproxylic arthropods in a temperate deciduous forest

Temperature is a key abiotic condition that limits the distribution of arthropods. Whereas some arthropods can escape local thermal extremes, less vagile organisms (e.g., insect larvae) are at the mercy of local microclimatic conditions. Here, we quantified thermal tolerances of three species of beetle larvae (Dendroides canadensis, Lucanus elaphus, and Odontotaenius disjunctus) and a millipede (Euryurus leachii), that inhabit coarse woody debris (CWD) in temperate forests of eastern North America. We determined how their critical thermal maxima (CT_max) varied with body size (mass), and measured the thermal profiles of CWD representing the range of their occupied microhabitats. We also explored how CT_max varies with season and sex in E. leachii. Beetle thermal tolerance increased with mass intraspecifically, and average CT_max differed among species. CT_max did not vary predictable with mass or sex, but appeared to be seasonally plastic in E. leachii. Temperatures within relatively dry CWD occasionally exceeded the tolerance limits of the beetle species and millipedes, and deeper portions of CWD were cooler. The results suggest that some species are excluded from highly exposed CWD due to extreme thermal conditions. Understanding such patterns in forested systems will help predict potential shifts in community composition and ecosystem processes due to disturbance and climatic change.