Population dynamics of clonal plants in fragmented landscapes: Empirical analyses and simulation models

Habitat fragmentation is a topic of growing concern to ecologists. Fragmentation reduces habitat area and increases isolation, making colonization less likely, and local extinction more likely. Because of their immobility, plants are particularly affected by habitat fragmentation. However, some plant species can "move" via clonal, vegetative dispersal. Clonal plant populations are two-tiered. Genets are derived from seeds, while ramets are vegetative propagules. I used plant census data from a long-term, experimental study of habitat fragmentation to explore the effects of patch size on within-patch population dynamics of Solidago canadensis and Aster prealtus. These two species exhibited contrasting effects of patch size that varied over time. Allozymes were used to distinguish genets of S. canadensis. There were no patch size effects on genet population sizes. There were more genets in patch interiors than edges. Wright's F-statistics revealed population subdivision between edge and interior subpopulations and nonrandom mating within subpopulations. Finally, I developed a cell-based, spatially explicit model of clonal growth to simulate the effects of habitat fragmentation on clonal plant population dynamics. The components of the model were (1) genet recruitment from seed, (2) vegetative growth, (3) local disturbance (ramet death), (4) three patch sizes, (5) edge-mowing, and (6) equal-area subsampling to compare results in different-sized patches. When genet recruitment continued for the entire simulation, genet and ramet populations remained large and population sizes differed with patch size and ramet mortality rate. In all scenarios, small patches had the fewest genets though ramet populations did not differ. When recruitment ended after five years, genet attrition occurred. Small patches had the smallest genet population sizes while ramet populations remained high. When patch edges were "mowed" and there was little ramet death, medium patches had larger genet populations than large patches. This study indicates that habitat fragmentation affects the population dynamics of clonal, herbaceous plants. In particular, patch size and differences between patch edges and interiors affect local population persistence, genet population size, and genetypic variation in the population. Model results suggest that patch size effects clonal plant population dynamics and has implications for the study of invasive clonal plant species.