PARENT SESSION
Oral Session #57: Plant Competition I.
Presiding: T. Seastedt
Wednesday, August 7. 8:00 AM to 11:30 AM. Grand Ballroom Central, Radisson.

Overgrowth competition and sex ratio dynamics using a spatially explicit sub-indiviual-based (SESUB) model.

STIEHA, CHRISTOPHER^*,1, CROWLEY, PHILIP¹, MCLETCHIE, NICHOLAS¹, ¹ T.H. Morgan School of Biological Sciences, Lexington, Kentucky

ABSTRACT- As a key component of our ongoing studies on sex-ratio dynamics in a bryophyte metapopulation, we have developed a high-resolution, two-dimensional model of the dioecious liverwort Marchantia inflexa. Marchantia ramets grow by extending ribbon-like thalli over rock or bark substrate, and over other thalli from the same or different ramets. Patches can thus contain tangled mats of physiologically independent but physically interwoven ramets. Our model represents discrete growth increments of thalli as rectangles (sub-individual modules); when overgrowth forces some of the rectangular modules into energetic deficit, they are jettisoned by the ramet, resulting in fragmentation into smaller ramets. Incorporating this mechanism, we address overgrowth competition between the separate male and female genets and ramets based on their general growth form. We find that between-sex overgrowth competition is approximately logistic within patches, with no sign of a stable two-sex equilibrium, consistent with previous modeling analyses and with the frequency of single-sex patches in the field. But taking the growth form into account generally reduces the contributions of within-patch sexual and asexual reproduction to the patch dynamics, relative to results obtained from geometrically simpler representations. We are currently re-formatting the model to run on a supercomputer, allowing the analysis of larger patches (>1 m²) over longer time intervals (>10 years).

KEY WORDS: overgrowth competition, sub-individual-based (SESUB) model, sex-ratio dynamics, metapopulation