Abstract Detail



Ecology

Parker, V. T. [1], Stickrod, Morgan [2].

Phenological shifts in the Arbutoideae (Ericaceae) indicate important transitions in the evolutionary selective context for seed ecology.

The Arbutoideae, a basal subfamily in the Ericaceae, principally contains species found in summer-dry, fire-prone Mediterranean-climates, with lineages in this subfamily shifting from forest to shrubland. Life history changes that correspond with habitat shifts include fruit characters that have altered from principally bird-dispersed, succulent, red-orange fruit with unprotected seed in Arbutus, to dry drupes, with mealy mesocarps, and with stony endocarps in Arctostaphylos. Other genera exhibit combinations of these characters. Germination traits have also altered with Arbutus and other genera producing transient seed while Arctostaphylos produces dormant seed dependent on fire to stimulate germination. All genera produce species that resprout after fire, but in contrast, Arctostaphylos alone contains some taxa that have evolved obligate seeding. These changes in traits in the genera suggest two principal selective processes. One is that fire regime shifts have altered traits associated with reproduction; greater protection of seed or longer fire free intervals may result in most of the fruit trait changes. A second potential selective process is that changes in habitat-linked bird and rodent communities, both of which are important in seed dispersal and seed predation, through time also have influenced reproductive traits. To suggest whether seed predation or reproductive fire adaptation was the principal historic selective background, we scored herbarium sheets to determine phenological shifts; asking the questions: does phenology shift with origin of stony endocarps, loss of succulent mesocarps, or the origin of seed dormancy. We test these alternatives by comparing when shifts in fruit characters and the characteristic phenology of flowering and fruiting occurs. Our expectation is that any differences dominated by fire regimes alone would differentiate Arctostaphylos due to its seed dormancy and species with obligate seeding. Any differences principally influenced by seed predator/dispersal communities might occur at other phylogenetic divergences. Our results indicate that most shifts correlate with the development of a stony endocarp, suggesting defense of seeds against rodent seed predators. Thus, it appears that once this lineage adapted to closed-canopy shrub habitats, a different community of animal seed predators and seed dispersers began to influence fruit evolutionary responses. In the context of changing fire regimes, those fruit trait shifts later permitted changes in seed bank dynamics and the origin of obligate seeding in Arctostaphylos.


1 - San Francisco State University, Biology, 1600 Holloway Avenue, Department Of Biology, San Francisco, CA, 94132, United States
2 - San Francisco State University, Biology, 1600 Holloway Avenue, San Francisco, CA, 94132, USA

Keywords:
phenology
seed predation
Fire
Arbutoideae
Ericaceae.

Presentation Type: Oral Paper
Number: ECO1003
Abstract ID:75
Candidate for Awards:None


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