PARENT SESSION
Oral Session # 92: Biogeography IV: Dispersal.
Presiding: J Choo
Friday, August 8. 8:30 AM to 12:00 PM, SITCC Meeting Room 104.

Dispersal limitation in an early successional grassland.

Aschenbach, Todd^*,1, Kindscher, Kelly¹, Foster, Bryan¹, ¹ University of Kansas, Lawrence, KS

ABSTRACT- It is suggested that local species richness is limited by seed availability in low productivity environments and that this limitation becomes less important as productivity increases. To evaluate the role of propagule availability in regulating species richness along a natural nitrogen gradient, 30 prairie forb species were added to 80 plots in an early successional grassland in eastern Kansas over a two-year period. Species were seeded in spring 1999 and spring 2000. Treatments 1 and 4 received all 30 species, treatments 2 and 3 received 20 forb species, and the control plots (N=20) did not receive any forb species. Species richness of individual treatments and the control were paired along the nitrogen gradient and compared to evaluate the effect of seed additions relative to productivity. Data from fall and spring 2001 and 2002 are reported separately. Analyses indicate that seed additions result in significant increases in species richness (one-way ANOVA; P<0.001), however, the magnitude of this affect decreases with increasing soil nitrogen. In the absence of seed additions, species richness is positively correlated with soil nitrogen indicating that the range of productivity is characteristic of the left side of the classic hump shaped curve formed by the relationship between species richness and productivity. Results agree with the hypotheses that dispersal limitation is important in regulating rates of succession and species accumulation during early succession.

Key words: dispersal , productivity gradient, colonization, recruitment limitation