Ayres Abstracts

Reynolds, L.V., M.P. Ayres, T.G. Siccama, and R.T. Holmes.  2007. Climatic effects on caterpillar fluctuations in northern hardwood forestsCanadian Journal of Forest Research 37: 481-491pdf

Abstract.  Fluctuations in the abundance of Lepidoptera are common but inadequately understood. Here we show that caterpillar abundance in the White Mountains of New Hampshire has fluctuated by >20-fold from 1986-2005. We report tests of three possible causes: (H1) extreme winter cold; (H2) long, warm summers; and (H3) interannual variation in tree growth, which tends to correlate with phytochemistry. Caterpillar fluctuations from summers t to t+1 were uncorrelated or negatively correlated with minimum air temperature during the intervening winter (does not support H1), but were positively correlated with thermal sum during summer t (r = 0.49-0.56) (supports H2). There was limited interannual variation in the radial growth of two dominant tree species ( Acer saccharum and Betula alleghaniensis) and no correlation with caterpillar fluctuations (refutes H3). Thermal sum might influence caterpillar fluctuations through direct effects on insect development, indirect effects on susceptibility to natural enemies, and/or indirect effects on plant-insect interactions; the mechanisms are of particular interest because thermal sums have been increasing since local records began in 1957 (r = 0.41–0.45). In hardwoods forests of the northeastern U.S., there is some broad-scale driver related to summer temperatures that generates fluctuations in caterpillar abundance, which influences herbivory as well as higher level consumers, such as insectivorous birds.

Keywords: Climate, Dendroica, Geometridae, herbivore-based trophic system, herbivory, Hubbard Brook, insectivorous birds, Moran effect


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