1. ¹Department of Plant Biology, 2502 Plant Sciences Building, University of Georgia, Athens, GA 30602-7271, USA
2. ²Department of Plant Biology, 2502 Plant Sciences Building, University of Georgia, Athens, GA 30602-7271, USA

Correspondence: JL Hamrick, Department of Plant Biology, 2502 Plant Sciences Building, University of Georgia, Athens, GA 30602-7271, USA. E-mail: hamrick@plantbio.uga.edu

Received 4 November 2003; Accepted 1 October 2004; Published online 16 February 2005.

Abstract

We estimate gene flow and patterns of genetic diversity in Albizia lebbeck, an invasive leguminous tree in the dry forest of southwestern Puerto Rico. Genetic diversity estimates calculated for 10 populations of 24 trees each indicated that these populations may have been formed from multiple introductions. The presence of unique genotypes in the northernmost populations suggests that novel genotypes are still immigrating into the area. This combination of individuals from disparate locations led to high estimates of genetic diversity (H_e=0.266, P=0.67). Indirect estimates of gene flow indicate that only 0.69 migrants per generation move between populations, suggesting that genetic diversity within populations should decrease due to genetic drift. Since migration–drift equilibrium was not found, however, this estimate needs to be viewed with caution. The regular production of pods in this outcrossing species (t_m=0.979) indicates that sufficient outcross pollen is received to insure successful reproduction. Direct estimates of gene flow indicate that between 44 and 100% of pollen received by trees in four small stands of trees (n<11) was foreign. The role of gene flow in facilitating the spread of this invasive plant species is discussed.