PARENT SESSION
Thursday, August 10, 8:00-11:30 am
COS 77 - Niches and habitat selection
L-3, Lobby Level, Cook Convention Center
Presiders: N Nicholas
Do species' functional trait values predict abundance and rarity?
Cornwell, William*,1, Ackerly, David2, 1 Dept. of Biological Sciences, Stanford, CA, USA2 Dept of Integrative Biology, Berkeley, CA, USA
ABSTRACT- Examining the abundance and rarity of species has a long history in ecology, with both demographic stochasticity and niche processes hypothesized to influence whether a given species is or is not common. The niche hypothesis suggests that each species' morphology and physiology is tuned to one particular position on an ecological gradient where it can be more successful than competitors. To test whether the functional ecology of individual species contribute to the abundance patterns we measured the local abundances of woody plant species across a soil water gradient at Jasper Ridge Biological Preserve in the eastern foothills of the Santa Cruz Mountains in coastal California. We then compared the abundance or rarity of each species at each site to their functional trait values for leaf and stem characteristics that influence carbon and water fluxes. We found significant relationships between abundance and three traits: specific leaf area, seed mass, and wood density. Across the entire gradient abundant species had significantly lower specific leaf area and larger seeds compared to less abundant co-occurring species; this is consistent with later-successional species becoming more abundant in the absence of large-scale disturbance. Wood density, a trait that strongly affects both water transport and resistance to drought-induced embolism, was a stronger predictor of abundance and rarity at Jasper Ridge. Intriguingly, wood density has a context dependent relationship with abundance: high wood density species were abundant in dry sites; intermediate wood density species abundant at intermediate sites; and low wood density species abundant at wet sites. The relationship between wood density and abundance is not surprising given its relationship to hydraulic strategies. Higher wood density is associated with greater hydraulic safety but reduced conductive efficiency, suggesting that in dry sites higher wood density species--those capable of tolerating lower water potentials--are more successful. On the other hand, species with light and presumably highly conductive wood are more abundant at the wettest sites. The relationship between functional trait values and local abundance suggests that niche processes have a role in determining the abundance and rarity of woody plant species at Jasper Ridge.
Key words: abundance and rarity, functional ecology, woody plants