75/125 YEARS

Ecological Response to Habitat Heterogeneity in Extant Tree Ferns (Cyatheaceae): Implications for Plant Macroevolution

ARENS, Nan Crystal, and RUTHERFORD, Mateo Coto, Museum of Paleontology and Dept. of Integrative Biology, University of California, Berkeley, CA 94720-4780

Macroevolutionary pattern in vascular plants is assumed to be closely linked to ecological differentiation. Diversification within a lineage may be driven more by new ecological or life history strategies, than by morphological innovation. Extant tree ferns in the family Cyatheaceae offer a system for exploring these hypotheses. The cyatheoid ferns are a deeply rooted and species-rich clade with varied ecologies. In Neotropical montane cloud forests, a number of related species coexist, offering the opportunity to study patterns in ecological differentiation within a phylogenetic context.

Data from a mid-elevation cloud forest in southwestern Colombia show that tree fern species composition, growth and reproductive rates vary between habitats. Some species, such as Cyathea planadae, are limited to and reproduce under the closed forest canopy where light is limited; other species, such as Cyathea caracasana, have a wide tolerance to habitat heterogeneity and show accelerated growth and reproduction in high light, open habitats. These examples may represent extremes in ecological amplitude and habitat-use strategies that cyatheoid lineages explore through evolution. At a coarse phylogenetic scale (between monophyletic clades within the Cyatheaceae), this process may be reflected in habitat segregation between sister species at a single site.

High species richness of the cyatheoid ferns allows statistical consistency in these relationships to be established as more taxa are studied from other regions. Multivariate ordination of species composition in various regions of Latin America suggests study sites located in northwestern South America or southern Central America are appropriately comparable to southwestern Colombia. A phylogenetic hypothesis based on cpDNA and spore morphology is used to choose species for comparison permitting inference regarding directional and correlated evolutionary trends in these traits. This future research will employ transplants to determine whether morphological variation is controlled at the phenotype or genotype level and to assess niche breadth among species.

75/125 YEARS