Evolutionary Implications of Wing and Size Variation in the Red-Winged Blackbird in Relation to Geographic and Climatic Factors: A Multiple Regression Analysis

Abstract

Power, Dennis M. (Royal Ontario Museum and Unive sity of Toronto, Torwto 5, Ont. Can.) 1969. Evolutionary implications of wing and size variation in the red-winged blackbird in relation to geographic and climatic factors: a multiple regression analysis. Syst. Zool., 18:363-373.-In red-winged blackbirds from central North America, geographic variation in wing length is a good indicator of geographic variation in body size. Multipli regression analysis is used to consider the relationship between geographic variation and eight geographic and climatic factors. Variation in males appears inversely related to two factors, latitude and July wet-bulb temperature, while variation in females is inversely related to only wet-bulb temperature. The statistical associations may indicate natural selection in terms of thermoregulatory efficiency. [Geographic variation. Thermoregulation. Multiple regression. Agelaius.] Speculation on the adaptive signifiance of' geographic variation is complicated by the fact that much of the genetic component of variation in a particular character may be the result of natural selection by more than one climatic, habitat, or biotic factor. Given a set of quantitative environmental factors which may be thought to relate in some way to variation in a character, a partial solution to the problem is in considering the statistical relationship between variation in the character and the enviromental factors by way of multiple regression analysis. The method yields, first, the multiple correlation coefficient which estimates the amount of variation