Abstract
Patterns and drivers of the spatio-temporal distribution of herbivores are key elements of their ecological and evolutionary impacts on plant populations. Herbivore spatial distributions may be influenced by increased (RCH: resource concentration hypothesis) or decreased (RDH: resource dilution hypothesis) resource densities, but the effect of temporal variations in resource densities on such distributions remains poorly documented. We used a survey of a masting tree species and its seed predators in Southeastern France to address the effect of a host’s pulsed resource on the spatio-temporal distributions of highly specialized insect herbivores feeding on seeds. Variations in both resource and seed predator densities were assessed by estimating seed production and seed infestation rates in focus trees during 10 consecutive years. We found increasing seed infestation rates with decreasing host tree densities in years of low seed production, indicating a RDH pattern of seed predators. However, such pattern was not persistent in years of high seed production during which seed infestation rates did not depend on host tree densities. We showed that temporal variations in resource density can lead to transience of seed predator spatial distribution. This study highlights how predictions of plant-herbivore interactions in natural ecosystems may rely on temporal components underlying RCH and RDH hypotheses.
Highlights
Patterns and drivers of the spatio-temporal distribution of herbivores are key elements of their ecological and evolutionary impacts on plant populations
The computation of masting metrics based on seed production data supported a strong masting pattern in this cedar population, i.e. high coefficients of variation at both population (CVp = 1.64) and individual (CVi = 1.34) levels and a high coefficient of synchrony (r = 0.70)
One central finding of this 10-year longitudinal survey was that both spatial and temporal patterns of the resource provided by a masting tree population dynamically drive the relative distribution of seed predators
Summary
Patterns and drivers of the spatio-temporal distribution of herbivores are key elements of their ecological and evolutionary impacts on plant populations. We used a survey of a masting tree species and its seed predators in Southeastern France to address the effect of a host’s pulsed resource on the spatio-temporal distributions of highly specialized insect herbivores feeding on seeds Variations in both resource and seed predator densities were assessed by estimating seed production and seed infestation rates in focus trees during 10 consecutive years. Taking into account both spatial and temporal dynamics of resource availability is of critical importance to understand herbivore distributions, and more importantly to assess whether observed distributions are transient or persistent when resource distribution display consistent variations that do not result from herbivory itself Occurrences of both RCH and RDH patterns have been primarily documented in agricultural crop-insect pest systems[31,41,42], while knowledge remains limited regarding wild systems such as prairie fields[38,43] or forests[28,44]. The aim of this study was to assess the impact of temporal variation in resource density, i.e. masting, on the spatial distribution of seed predators in a natural forest ecosystem
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