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PLANT–ANIMAL INTERACTIONS IN RANDOM ENVIRONMENTS: HABITAT-STAGE ELASTICITY, SEED PREDATORS, AND HURRICANES

PLANT–ANIMAL INTERACTIONS IN RANDOM ENVIRONMENTS: HABITAT-STAGE ELASTICITY, SEED PREDATORS, AND HURRICANES,10.1890/04-1187,Ecology,Carol C. Horvitz,Sh

PLANT–ANIMAL INTERACTIONS IN RANDOM ENVIRONMENTS: HABITAT-STAGE ELASTICITY, SEED PREDATORS, AND HURRICANES   (Citations: 20)
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When environments change stochastically, the question arises how to eval- uate the effects of a plant-animal interaction on the fitness of the plant, where plant fitness is measured by the stochastic growth rate. We develop the concept of habitat-stage elasticity, , which gives the proportional sensitivity of the stochastic growth rate to perturbations S E b of stage transition rates in each state ( b) of the habitat. We employ it to understand why a specialist gall-making seed predator has relatively low impact on the fitness of a sub- tropical shrub. The plant lives in a forest characterized by patchy, recurrent disturbances caused by hurricanes. Both predation rate and plant demography vary with canopy openness. In the most closed-canopy state, the seed predator destroys 90% of the fruits, and demo- graphic quality, the dominant eigenvalue of that state's matrix, is low, while in the most open-canopy state, predation is negligible and demographic quality high. The seed predator is locally extirpated by strong hurricanes, recolonization taking several years. The effect of the predator on the stochastic growth rate is negligible at both low and high hurricane frequency. Its effect peaks (6%) at an intermediate hurricane frequency. The stochastic growth rate varies in its sensitivity to the predator in different states of the habitat due to a product of two factors: the frequency of the state in the environment and the contribution of fecundity to its elasticity. The latter factor encapsulates the expected se- quence of future states of the habitat. In our system, the contribution of fecundity to elasticity of the darkest state increases with hurricane frequency, even though the probability of encountering that state decreases, because today's dark habitats are more likely to become lighter ones. The contribution of fecundity to the two lightest states does not vary with hurricane frequency. In contrast, its contribution in intermediate states at intermediate hurricane frequencies is most dynamic, since uncolonized states may become colonized states and insensitive states may become sensitive states. The effects of an animal on plant fitness is determined by the disturbance regime in addition to its impact on vital rates in each environmental state.
Journal: Ecology , vol. 86, no. 12, pp. 3312-3322, 2005
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    • ...Because all natural populations experience stochastic variation in vital rates, stochastic demography models (Tuljapurkar et al. 2003; Horvitz et al. 2005; Boyce et al. 2006; Gotelli and Ellison 2006) provide an appropriate framework for analyzing the effects of directional changes in environmental conditions and of changes in the disturbance regime on population dynamics...
    • ...To accommodate such shifts in vital rates, information about disturbance regime and rates of recovery after disturbance should be combined with data on the correlation between vital rates and environmental state in analysis of population dynamics (Horvitz et al. 2005)...
    • ...In this study, we employ a recently proposed method to predict population viability in environments that undergo directional change (Horvitz et al. 2005), based on the limited demographic and environmental data typically available for natural systems...
    • ...Horvitz, personal communication) and followed the methods suggested by Tuljapurkar et al. (2003) and Horvitz et al. (2005)...
    • ...individual life-history transitions for population growth rate (Caswell 2001; Horvitz et al. 2005)...
    • ...Habitat elasticity is the sum of all E S for a given habitat, and reflects its relative frequency (Horvitz et al. 2005)...
    • ...The magnitude of a given habitat-stage elasticity is a function of the habitat elasticity, and the relative contribution of individual lifehistory transition rates to the habitat elasticity (Horvitz et al. 2005)...

    Per Toränget al. Linking environmental and demographic data to predict future populatio...

    • ...In many ways, herbicide management is analogous to the impacts of natural disturbances, such as hurricanes (Horvitz, Tuljapurkar & Pascarella 2005), floods (Menges 1990) and fires (Schultz and Crone 1998; Menges and Quintana-Ascencio 2003)...

    Elizabeth E. Croneet al. Nontarget effects of broadleaf herbicide on a native perennial forb: a...

    • ...A ˚ berg 1992b; Benton and Grant 1996; Dixon et al. 1996; Caswell and Kaye 2001; Pavia et al. 2002; Tuljapurkar et al. 2003; Horvits et al. 2005; Smith et al. 2005; see also examples calculated from previously published results in Sect...

    Carl Johan Svenssonet al. Robustness in life history of the brown seaweed Ascophyllum nodosum (F...

    • ...McGraw & Furedi (2005) Panax quinquefolius deer grazing perennial herb D in l: 0.05 Horvitz et al. (2005) Ardisia escallonioides insect: flower gall perennial shrub D in l: 6% reduction in l under historic hurricane frequency Shea et al. (2005) Cirsium nutans biocontrol insects: prdsp and meristem damage monocarpic herb D in l: 0.662 and 1.1...

    John L. Maronet al. Herbivory: effects on plant abundance, distribution and population gro...

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