ON MODELS PREDICTING ABUNDANCE OF SPECIES AND ENDEMICS FOR THE DARWIN FINCHES IN THE GALÁPAGOS ARCHIPELAGO

Abstract

In a previous report to this journal (1963) we made conclusions on the processes of speciation and production of endemics among the Darwin finches in the Galapagos Archipelago. The conclusions were inferred from multiple-regression analysis wherein four independent variables of the insular environment were quantified and tested for respective abilities to predict species data. The analysis was an attempt by linear regression to discover (a) the environmental determinants of insular variation in the species numbers (Yi) and (b) the determinants of such variation for numbers of endemic subspecies (IY2). Insular area (X1) and number of land plant species (X2) presumably indexing ecologic and floristic diversity-were found lacking in power to push or move the dependent variables (the Y's). Isolation, measured by distance between islands (X3) and by distance from a given island to Indefatigable Island near the center of the archipelago (X4), was the major predictor of number of species and endemics for islands, with X3 being more important than X4 in terms of contribution to Y variances (My2). For both problem a and b, however, a component (Idy2) of the variance remained unaccounted for by regression of the Y's on the X's, and this was attributed to error inherent to the analysis, to factors not considered, or to both.