PARENT SESSION
Oral Session #29: Spatial Ecology and Disturbance Ecology.
Presiding: J. Ludwig
Tuesday, August 6. 8:00 AM to 11:30 AM. Coconino Meeting Room, TCC.
The persistence of rare species: demographic stochasticity and spatial effects.
Renault, Olivier1, Ferriere, Regis*,2,3,4, Dieckmann, Ulf4, 1 Laboratoire d'Ecologie des Populations et Communautes, Paris, France2 Laboratoire d'Ecologie, Paris, France3 Department of Ecology and Evolutionary Biology, Tucson, AZ4 Adaptive Dynamics Network, Laxenburg, Austria
ABSTRACT- Ecological theory is largely based on models that explicitely or implicitly assume that space is populated by infinitely many, randomly mixed 'individuals'. Here we address one issue where the discreteness of individuals, finiteness of populations and local nature of interactions may not be ignored: Given that rarity is perhaps the most common pattern of species abundance, and that many species are known to be persistently rare, what mechanisms acting at the individual level may offset the intrinsic hazard of rarity - demographic stochasticity? We use the framework of spatial density-dependent branching processes to show that limited dispersal and local interactions are significant influences of both population abundance and persistence. 'Persitent rarity' occurs when the mean population size is lower than carrying capacity, and mean persistence time is larger than in a well-mixed population. Persistently rare species are predicted to feature (i) high reproductive success, (ii) high sensitivity to competition, (iii) long-range interaction, (iv) dispersal on a spatial scale that exceeds the interaction range, and, as a consequence of (iii) and (iv), (v) overdispersed spatial patterns. Long-range interaction causes low abundance, and longer dispersal distance induces a 'rescue effect' that enhances persistence. Prediction (ii) and (v) agree with available empirical evidence; prediction (i) and (iii) oppose several ecological analyses of rare versus common species, but squares with insights from paleontological data. Prediction (iv) remains to be assessed.
KEY WORDS: rarity, dispersal, density dependence, extinction