Insights on the Climatic Constraints on the Beetle Fauna of Coastal Alaska, U.S.A., Derived from the Mutual Climatic Range Method of Paleoclimate Reconstruction

Abstract

The Mutual Climatic Range (MCR) method of paleoclimate reconstruction uses the climatic parameters associated with the modern range of species to produce climate envelopes for taxa found in fossil assemblages. The overlap of these climate envelopes produces a mutual climatic range for fossil assemblages. The method employs predatory and scavenging beetle species found in fossil assemblages. By comparing observed versus predicted mean summer and winter temperatures from MCR, we developed a set of calibration equations for fossil beetle assemblages in Alaska and the Yukon Territory. These equations showed that MCR predictions fit the observed mean temperatures of the warmest month (TMAX) reasonably well, but the predictions of mean temperatures for the coldest month (TMIN) for coastal sites were consistently below the observed values. Thus the beetle communities living in coastal Alaska today are indicative of colder winter temperatures than are indicated by the observed TMIN, and such lack of correlation is a difficulty in applying the MCR method and in estimating paleoclimates in Beringia. We postulate that periods of severely cold weather in coastal regions are sufficiently common to eliminate species adapted to maritime climates. Instead we find in coastal localities more cold-resistant species whose principal ranges are in interior regions. These species are adapted to continental climates (with extreme seasonality of temperatures), rather than maritime climates (with reduced seasonality).Another difficulty in estimating paleoclimates of Beringia is that the coastal geography has changed with each glacial/interglacial cycle. Glacial and interstadial sites that lie near the modern coast were subject to continental, rather than maritime climates.