PARENT SESSION
Oral Session #1: Conservation Ecology: Threatened and Endangered Species. Presiding: W. Bond.
Monday, August 6, 2001. 8:00 AM to 12:15 PM. Madison Ballroom C.
The effects of habitat loss and isolation on a rare salt marsh plant.
THORPE, ANDREA1, DIFFENDORFER, JAMES1, 1
ABSTRACT- We explored the effects of habitat loss and isolation on Lasthenia glabrata ssp. coulteri (Coulter's goldfields, Asteraceae), a rare species, endemic to the southern California salt marsh. Three populations ("connected"), while from the same lagoon, had been exposed to different levels of human-induced impacts. Two populations ("isolated") were located in separate lagoons. Seed germination tests and allozyme electrophoresis was used to test for population divergence, reduced fitness parameters, and differences in genetic diversity. As salinity increased, the final proportion of germination decreased (P<0.001). Furthermore, the two isolated populations exhibited the lowest final germination (P<0.001). Salinity and moisture interacted to affect the rate of germination (P<0.001), however, this interaction was strongly driven by salinity. Populations also differed in their rate of germination (P=0.007) and seed set. Allozyme analyses suggest genetic divergence. The smallest population (N=7 in 2000) in the connected lagoon, which has been subjected to extreme anthropogenic perturbations in recent years, had approximately 1/5 the heterozygosity of the other populations. These results indicate that populations have diverged in both fitness-related and genetic traits. While this divergence may be historical, the declining population sizes and reduced seed set of the most impacted populations suggest that anthropogenic habitat loss, alteration, and fragmentation may be responsible for observed population declines, and could ultimately lead to the extinction of some populations.
KEY WORDS: germination, genetic diversity, habitat loss, habitat isolation