Temporal variation, dormancy, and coexistence: A field test of the storage effect

Abstract

Theoretical models suggest that overlapping generations, in combination with a temporally f luctuating environment, may allow the persistence of competitors that otherwise would not coexist. Despite extensive theoretical development, this ''storage effect'' hypothesis has received little empirical attention. Herein I present the first explicit mathematical analysis of the contribution of the storage effect to the dynamics of competing natural populations. In Oneida Lake, NY, data collected over the past 30 years show a striking negative correlation between the water-column densities of two species of suspension-feeding zooplankton, Daphnia galeata mendotae and Daphnia pulicaria. I have demonstrated competition between these two species and have shown that both possess long-lived eggs that establish overlapping generations. Moreover, recruitment to this long-lived stage varies annually, so that both daphnids have years in which they are favored (for recruitment) relative to their competitor. When the long-term population growth rates are calculated both with and without the effects of a variable environment, I show that D. galeata mendotae clearly cannot persist without the environmental variation and prolonged dormancy (i.e., storage effect) whereas D. pulicaria persists through consistently high per capita recruitment to the long-lived stage.The long-term persistence of competitors without competitive exclusion has led to numerous explanations for the maintenance of species diversity (1-3). Included among these hypotheses are those that posit resource partitioning and spatial or temporal separation of potential competitors at equilibrium (4-6). Alternatively, nonequilibrium theory suggests that a fluctuating environment may promote the coexistence of competitors (2, 7-9). Although variation alone cannot prevent the inevitable fixation of a single genotype or species (10, 11), Chesson and colleagues (2, 12-18) have proposed a way in which temporal recruitment fluctuations among species can lead to the stable coexistence of competitors. Their mechanism called the ''storage effect,'' may occur as long as each competitor can increase from low densities. One way in which this criterion is met is when each taxon has a long-lived stage that is immune to the effects of competition and is able to carry the population through periods of poor recruitment. In an environment where recruitment is occasionally low, this longlived stage buffers competitors against exclusion in a way that is not possible in models with nonoverlapping generations.In its original form, the storage effect results from three components: interspecific competition, a persistent long-lived stage, and temporal variation in recruitment to this long-lived stage. More recently, the theory has been expanded and can now be expressed as the outcome of three ingredients: species-specific responses to the environment, covariance between environment and competition, and subadditive growth rates (16-18). Comprehensive reviews of the general theory are av...

Quantifying and testing coexistence mechanisms arising from recruitment fluctuations

“…Warner and Chesson (1985) developed a method for partitioning long-term population growth rates into components due to recruitment fluctuations and components due to other factors, and this technique was applied most notably to testing the storage effect for coexisting Daphnia species (Caceres, 1997). Although this technique reveals the effects of recruitment fluctuations on the dynamics of an individual species, it does not directly address interactions between species.…”

Temporal niche promotes biodiversity during adaptive radiation

“…The theory of temporal niche dynamics (TND) suggests that temporal variation in niche availability allows the storage effect to operate, buffering species against extinction 4,5 . Increased species coexistence in fluctuating environments has been documented for both natural [6][7][8] and experimental 9,10 communities, and has, in a few cases, been explicitly linked to TND 6,11 . In parallel, diversification under fluctuating selection has been of much interest for evolutionary biologists [12][13][14] .…”

Aging alters interspecific competition between two sympatric insect–parasitic nematode species

“…The importance of dormant stages for promoting species coexistence has been well established both theoretically and empirically (Cáceres 1997; Angert et al. 2009).…”