PS 7-60
Effect of competition on water-use traits and photosynthetic traits observed in leaf morphology during ancient plant diversity transitions
Under current conditions of climate change, floral response to perturbation is of particular significance to humanity given our dependence on crops and other plant products, yet this response is not well understood. The Big Five mass extinction events were associated with significant faunal diversity losses; however, the plant record is not as clear. Though evidence of mass floral extinction is observed at the Permo-Triassic boundary, only taxa transitions and localized extinctions lacking significant global plant diversity losses are observed in the remaining mass extinction events. Geologic perturbations of this magnitude affect the ecological space, or ecomorphospace, available for exploitation. This research investigates the effect of competition on floral communities during geologic perturbations, which significantly impact ecomorphospace, and the associated biologic response of those communities. During recovery and the early phases of radiation (low competition), niche expansion is the dominant selective force driving plant evolution; however, as space becomes limited (high competition), the dominant selective force appears to shift to niche partitioning. By investigating quantifiable leaf morphological traits, floral shifts between niche partitioning and niche exploitation can be compared. Quantifiable traits include stomatal density, vein density, cuticle structure, evaporative controls of stomata openings, and leaf margin circumference versus leaf surface area ratios. Field localities across accepted geologic perturbation events and associated trait groups were identified for study as appropriate to the paleoenvironment and floral diversity. Existing collections also were used where available. Paleoenvironments were defined through sedimentary and stratigraphic interpretation in the field and through the literature.
Results/Conclusions
The shift from niche partitioning to niche exploitation drives plant ecomorphology such that ecomorphological leaf traits are narrow and specialized during partitioning, but broad and non-specialized during exploitation. Preliminary analysis suggests different trait distributions are associated with different competitive pressures driven by the limits of ecomorphospace. If it is possible to quantify the extent and timing of niche utilization shifts, it may be possible to develop models predicting not only the extent and duration of floral response to geologic perturbations, but also the associated rates of change of these shifts in the context of anthropogenic climate change.