1. The fast-slow plant economics spectrum predicts that because of evolutionary and biophysical constraints, different plant organs must be coordinated to converge in a unique ecological strategy within a continuum that shifts from fast to slow resource acquisition and conservation. Therefore, along a gradient of aridity, taxa with different strategies will be expected to be successful because selection pressures for slow resource acquisition become stronger as the environment becomes drier. In extremely arid and seasonal environments, however, a slow strategy may become disadvantageous because slow traits are costly to maintain.Additionally, as the availability of water decreases, selection pressures increase, reducing the variation in ecological strategies.2. Using shrub assemblages along an aridity gradient in the Atacama Desert, we test the hypothesis that selection pressures imposed by hyper-aridity act simultaneously on the variation and coordination of trait attributes, leading to an inverse pattern in the fast-slow plant economics spectrum, where strategies shift from slow to fast as the environment becomes drier.3. We established 20-22 plots at each of four sites along the gradient to estimate plant community structure and functional variation. For all species recorded, we quantified a set of leaf, stem, and root traits. 4. Results revealed an inverse pattern of the fast-slow economics spectrum for leaf and stem traits, but not for root traits; that is, as aridity further increased, aboveground traits exhibited a shift from a slow to a fast strategy with some level of coordination. Below-ground traits, however, did not shift accordingly with our prediction, rather they showed more complex pattern of shift and coordination with above-ground traits along the gradient. We also found that trait variation showed an idiosyncratic pattern of variation along the gradient, indicating that ecological strategies are driven by local processes within sites. 5. Synthesis. Our results increase our understanding of the fast-slow plant economics spectrum by showing that environmental gradients, as well as local process can K E Y W O R D S Additional supporting information may be found online in the Supporting Information section at the end of the article. How to cite this article: Carvajal DE, Loayza AP, Rios RS, Delpiano CA, Squeo FA. A hyper-arid environment shapes an inverse pattern of the fast-slow plant economics spectrum for above-, but not below-ground resource acquisition strategies. J

We examined the effect of seed dispersal by Purplish Jays (Cyanocorax cyanomelas; pulp consumers) and the Chestnut-eared Araçari (Pteroglossus castanotis; "legitimate" seed dispersers) on population growth of the small tree Guettarda viburnoides (Rubiaceae) in northeastern Bolivian savannas. Because each bird species differs with respect to feeding and post-feeding behavior, we hypothesized that seed dispersal by each species will contribute differently to the rate of increase of G. viburnoides, but that seed dispersal by either species will increase population growth when compared to a scenario with no seed dispersal. To examine the effects of individual dispersers on the future population size of G. viburnoides, we projected population growth rate using demographic models for G. viburnoides that explicitly incorporate data on quantitative and qualitative aspects of seed dispersal by each frugivore species. Our model suggests that seed dispersal by C. cyanomelas leads to positive population growth of G. viburnoides, whereas seed dispersal by P. castanotis has a detrimental effect on the population growth of this species. To our knowledge, this is the first study to report negative effects of a "legitimate" seed disperser on the population dynamics of the plant it consumes. Our results stress the importance of incorporating frugivore effects into population projection matrices, to allow a comprehensive analysis of the effectiveness of different dispersers for plant population dynamics.

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