Precipitation drives the abundance and distribution of Arctia virginalis: A 40-year study

Ecology seeks to understand the abundance and distribution of species. Ecologists typically collect either long-time series without knowledge of the drivers or short-term experimental results, which may not scale up. We surveyed the annual population dynamics of Arctia virginalis for 40 years and conducted experiments examining the relative roles of abiotic conditions, host plants, predation, parasitoids, and viral infection. Rather than finding a single limiting factor, these factors were all important at some times or places. Annual densities varied by 1000-fold and showed evidence of a regime shift around 2002, coincident with changing precipitation. Wet sites and wet years supported higher densities, and precipitation interacted with most of the factors considered. Population control was context-dependent, but water availability was generally the relevant context. Precipitation appears to be important for other Lepidoptera in western North America. Studies that include experimental ..., , # Data from: Precipitation drives the abundance and distribution of Arctia virginalis: A 40-year study

Dataset DOI: [10.5061/dryad.05qfttfgs](https://doi.org/10.5061/dryad.05qfttfgs)

## Description of the data and file structure

We estimated the density of late instar *Arctia virginalis* caterpillars on ten bushes of *Lupinus arboreus* across from the main lab at the Bodega Marine Reserve. Surveys were conducted during the last week in March from 1986-2025.

### Files and variables

#### File: Woolies_on_Lupine_1986_2025.xlsx

**Description:** The first column lists the year and the next 10 columns provide the densities of caterpillars on each bush. Densities are number of caterpillars per m^2^ of ground area covered by the leaves of each bush.

## Code/software

Data are provided in Microsoft Excel.
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