Volume 77 - Issue 1 (March 2012)

ABSTRACT Effective conservation requires an understanding of the genetic interactions among populations and individuals of a species, particularly those with fragmented, isolated distributions. Alnus maritima (seaside alder) is a rare tree species with an extremely fragmented distribution of highly isolated populations in the Delmarva Peninsula, Georgia, and Oklahoma. We conducted a mating system study to estimate the outcrossing rate, inbreeding coefficient, biparental inbreeding rate, and correlation of paternity in progeny from a Georgia and an Oklahoma population to investigate the effects of isolation on the A. maritima mating system. Data from nine microsatellite loci showed similarly high multilocus outcrossing rates in both populations (tm50.94). Individual tree outcrossing rates were also high (tm50.873–1.047). There was no significant biparental inbreeding in either population, but there was significantly higher correlated paternity in the Oklahoma population. Results showed the high outcrossing expected for a wind-pollinated,monoecious species that can promote the maintenance of genetic variation detected in A. maritima seed pools and standing populations. Likewise, pollen flow among Oklahoma populations may promote maintenance of regional genetic variation. However, despite the genetic diversity in the seed pool generated by A. maritima’s highly outcrossed mating system, failure of new individuals to be recruited into populations from seed presents an obstacle that will need to be considered when developing conservation strategies for this rare species.

ABSTRACT Harperella (Ptilimnium nodosum) is a federally endangered plant species with a large population along Sideling Hill Creek, Allegany and Washington Counties, Maryland. Monitoring of this species is difficult owing to the unpredictable flood events that change the distribution and composition of stream substrates of its rocky shoal habitat. We characterized substrate types in 80 quadrats using two methods of nonmetric multidimensional scaling (NMS and MDS). We employed multiple-response permutation procedure (MRPP) to examine differences in substrate composition between habitats occupied (N 5 52) and unoccupied (N 5 28) by Harperella. The NMS and MDS ordinations show that Harperella cover and amount of fine sediments are positively associated. Harperella occupies specific microhabitat with high cover of fine sediments, often held in crevices of exposed bedrock. The MRPP results demonstrated that substrate composition in occupied versus unoccupied habitats differ significantly. This difference is chiefly attributable to cover of fine sediments in occupied habitats and cobble, gravel, and sand in unoccupied habitats. We conclude that the local distribution and abundance of Harperella patches in Sideling Hill Creek is constrained by the abundance of appropriate substrate microhabitat in any given year and recommend that annual census be modified to focus on large persistent patches.