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It has been shown that plant genotype can strongly affect not only individual herbivore performance, but also community composition and ecosystem function. Few studies, however, have addressed how plant genotype affects herbivore population dynamics. In this paper, we used a simulation modeling approach to ask how the genetic composition of a forest influences pest outbreak dynamics, using the example of aspen (Populus tremuloides) and forest tent caterpillars (FTC; Malacosoma disstria). Specifically, we examined how plant genotype, the relative size of genotypic patches, and the rate of insect dispersal between them, affect the frequency, amplitude, and duration of outbreaks. We found that coupling two different genotypes does not necessarily result in an averaging of insect dynamics. Instead, depending on the ratio of patch sizes, when dispersal rates are moderate, outbreaks in the two genotype case may be more or less severe than in forests of either genotype alone. Thres holds for different dynamic behaviors were similar for all genotypic combinations. Thus, the qualitative behavior of a stand of two different genotypes can be predicted based on the response of the insect to each genotype, the relative sizes of the two patches, and the scale of insect dispersal. [ABSTRACT FROM AUTHOR]

Individual variance in lifetime fecundity within populations is a life-history parameter of crucial evolutionary and ecological significance. However, knowledge of its magnitude and underlying mechanisms in natural populations is biased toward short-lived taxa. This paper summarizes results of a 23-year study on a population of the Mediterranean shrub Lavandula latifolia. We document the within-population pattern of individual variation in instantaneous and lifetime fecundity (as estimated by inflorescence production) and explore the mechanisms producing the lognormal distribution of individual fecundities by means of an individual-based simulation model. Throughout the study period, a few individuals consistently produced most inflorescences while the majority of plants exhibited moderate-to-low fecundities. The shape of yearly distributions of annual fecundities varied little across years, and most annual fecundity distributions did not depart significantly from a lognormal. The distribution of individual lifetime fecundity did not depart from lognormality. Despite the simplicity of the premises of our simulation model, it was remarkably successful at predicting the shapes of fecundity distributions and the early establishment of a persistent fecundity hierarchy. The agreement between model results and empirical data supports the view that multiplicative interactions of randomly varying environmental effects can play a central role in determining individual variation in lifetime fecundity in L. latifolia, and suggests that environmental stochasticity can be decisive in the genesis of strong fecundity hierarchies in long-lived plants. [ABSTRACT FROM AUTHOR]

We simulate species-area curves (SACs) using a spatially explicit neutral model. These display three distinct phases with the central phase being well approximated by a "power law" where species richness (S) is related to area (A) by S=cAz. If seeds are normally distributed in space about their parent, the power law phase of the SAC is unrealistically narrow, and implausibly large speciation rates are required to fit empirical data. However, if dispersal follows a more realistic "fat-tailed" distribution (where long-distance dispersal events are more likely) the SACs fit the empirical data better, have a power law that holds for a much broader range of areas, and require a dramatically smaller speciation rate than when dispersal is normally distributed. Neutral models with biologically plausible dispersal parameters and speciation rates lead to empirically realistic SACs. [ABSTRACT FROM AUTHOR]

Animals can attain fitness benefits by maintaining a positive net energy balance, including costs of movement during resource acquisition and the profits from foraging. Subterranean rodent burrowing provides an excellent system in which to examine the effects of movement costs on foraging behavior because it is energetically expensive to excavate burrows. We used an individual-based modeling approach to study pocket gopher foraging and its relationship to digging cost, food abundance, and food distribution. We used a unique combination of an individual-based foraging-behavior model and an energetic model to assess survival, body mass dynamics, and burrow configurations. Our model revealed that even the extreme cost of digging is not as costly as it appears when compared to metabolic costs. Concentrating digging in the area where food was found, or area-restricted search (ARS), was the most energetically efficient digging strategy compared to a random strategy. Field data show that natural burrow configurations were more closely approximated by the animals we modeled using ARS compared to random diggers. By using behavior and simple physiological principles in our model, we were able to observe realistic body mass dynamics and recreate natural movement patterns. [ABSTRACT FROM AUTHOR]

In contrast to competing explanations of species-area relationships (SARs), neutral theory is dynamic, meaning that it should explain patterns in both space and time. However, most empirical tests of neutral theory have relied on snapshots such as comparisons of observed and simulated SARs observed at one point in time. I used 35 years of data from permanent plots in Kansas grasslands to test the ability of strict and modified neutral models to reproduce observed species-area and species-time relationship (STRS). Holding species density to observed values, the models could generate realistic SARs or STRs, but not both simultaneously. Parameter combinations that simulated realistic STR5 led to SARs with extremely steep slopes. To examine the consequences of relaxing neutrality, I incorporated plant functional types into the model. More realistic dominance produced only limited improvement in the simulated results, and indicates that the models' primary flaw is their failure to reproduce rapid but spatially correlated changes in species composition. In these grasslands, characterized by large interannual variation in resources and many short-lived species, functional differences among species play a strong role in driving macroscopic patterns. The results emphasize the need to test neutral models, and other dynamic community models, with spatiotemporal data. [ABSTRACT FROM AUTHOR]

Individual genotypes, phenotypes, or species of plants can vary in their effects on herbivore population dynamics. In this study I used a simulation model to explore how the distribution of plant quality in a plant population affects the population dynamics of insect herbivores feeding on those plants. The model considers an herbivore population moving among patches (plants) with differing parameters for growth and carrying capacity. Observed population sizes across all patches were compared to the expectation that, if variance in parameters had no effect, population size should equal the sum of the carrying capacities of all plants. Results showed that variance in K alone, or in r and K together, strongly affected herbivore population size; increasing variance led to progressively stronger effects. The direction of the deviation of herbivore population size from the expectation in the absence of variance could be positive, negative, or both for different combinations of variance in r and K. Increasing skew also increased the deviation of observed population sizes from the expectation. Herbivore mobility increased the effect of variance in patch (plant) quality, whereas herbivore. selectivity decreased the effects of variance by decreasing herbivore movement. These results are consistent with observations from agricultural studies that polycultures can either increase or decrease herbivore population sizes relative to monocultures. [ABSTRACT FROM AUTHOR]