Functional diversity and coexistence of carnivorous and noncarnivorous
plants in wet, species-rich savannas
Abstract
1. Trait differences among plant species can favor species coexistence.
The role that such differences play in the assembly of diverse plant
communities maintained by frequent fires remains unresolved. This lack
of resolution results in part from the possibility that species with
similar traits may coexist because none has a significant fitness
advantage and in part from the difficulty of experimental manipulation
of highly diverse assemblages dominated by perennial species. 2. We
examined a 65-year chronosequence of losses of herbaceous species
following fire suppression (and subsequent encroachment by Pinus
elliottii) in three wet longleaf pine savannas. We used cluster
analysis, similarity profile permutation tests and k-R cluster analysis
to identify statistically significant functional groups. We then used
randomization tests to determine if the absence of functional groups
near pines was greater (or less) than expected by chance. We also tested
whether tolerant and sensitive species were less (or more) likely to
co-occur by chance in areas in savannas away from pines in accordance
with predictions of modern coexistence theory. 3. Functional group
richness near pines was lower than expected from random species
extirpations. Wetland perennials with thick rhizomes and high leaf water
content, spring-flowering wetland forbs (including Drosera tracyi),
orchids, Polygala spp., and club mosses were more likely to be absent
near pines than expected by chance. C3 grasses and sedges with seed
banks and tall, fall-flowering C4 grasses were less likely to be absent
near pines than expected by chance. Species sensitive to pine
encroachment were more likely to co-occur with other such species away
from pines at two of the three sites. 4. Results suggest that herb
species diversity in frequently-burned wet savannas is maintained in
part by a weak fitness (e.g., competitive) hierarchy among herbs, and
not as a result of trait differences among co-occurring species.