PARENT SESSION
Oral Session # 4: Forest Ecology I: Diversity, Suppression, and Release.
Presiding: B Schamp
Monday, August 4. 8:00 AM to 11:30 AM, SITCC Meeting Room 103.
Stabilizing biodiversity with random individual effects.
Clark, James*,1, Dietze, Mike1, Govindarajan, Sathish2, Agarwal, Pankaj2, 1 Duke University, Durham, NC, USA2 Duke University, Durham, NC, USA
ABSTRACT- Ecological theory and analysis suggest that potentially high diversity of tree species depends on tradeoffs. 'Colonization-competition' tradeoffs involve the capacity to colonize new sites vs the ability to hold them (competition). Different 'successional niches' involve tradeoffs between species capable of exploiting high resource availability following disturbance vs. others that can survive long after disturbances, when resources are scarce. Stochasticity can promote coexistence, provided that species differ in their colonization success, because long life span can buffer population growth against variable recruitment (the 'storage effect'). Tradeoffs are still implied, because stochastic recruitment only promotes diversity if correlation among species, in terms of recruitment success, is not too large. In short, to explain high diversity, models typically require precise parameter combinations that imply tradeoffs. In most models, species lacking these tradeoffs are rapidly excluded. We demonstrate that tradeoffs are less critical for coexistence than is often thought, because variability within populations can overwhelm species differences, and because this individual variation can have a stabilizing effect on diversity. In models, stochasticity is typically implemented as variability in time that applies to entire populations. The stabilizing effect we explore occurs when variability is packaged in the bodies of individual organisms. Analysis suggests that the theoretical need for tradeoffs and the empirical support for those tradeoffs can be overemphasized. We present empirical and theoretical analysis to illustrate both points. Using hierarchical Bayes demographic models, we demonstrate 1) that high variability within species is a source of massive stochasticity that has low correlation among species, and 2) that parameter tradeoffs are generally not evident among many coexisting species. Using models that incorporate the individual effects parameterized from field data, we demonstrate its stabilizing effect on diversity.
Key words: coexistence, hierarchical Bayes, competition, computation