DOI: 10.5061/dryad.pc866t1s4
title: Agricultural margins could enhance landscape connectivity for pollinating insects across the Central Valley of California, U.S.A.

description: One of the defining features of the Anthropocene is eroding ecosystem
 services as a function of decreases in biodiversity and overall reductions
 in the abundance of once-common organisms, including many insects that
 play innumerable roles in natural communities and agricultural systems
 that support human society. It is now clear that the preservation of
 insects cannot rely solely on the legal protection of natural areas far
 removed from the densest areas of human habitation. Instead, a critical
 challenge moving forward is to intelligently manage areas that include
 intensively farmed landscapes, such as the Central Valley of California.
 Here we attempt to meet this challenge with a tool for modeling landscape
 connectivity for insects (with pollinators in particular in mind) that
 builds on available information including lethality of pesticides and
 expert opinion on insect movement. Despite the massive fragmentation of
 the Central Valley, we find that connectivity is possible, especially
 utilizing the restoration or improvement of agricultural margins which (in
 their summed-area) exceed natural areas. Finally, we highlight steps
 moving forward and the great many knowledge gaps that could be addressed
 in the field to improve future iterations of our modeling approach.
description: We used publicly-available land cover data and reported pesticide
 application rates to develop resistance-to-movement scenarios for
 pollinating insects in the Central Valley of California, U.S.A. The
 primary land cover datasets were LandIQ, NOAA C-CAP, and the USGS National
 Land Cover dataset. Additional minor datasets included Normalized
 Difference Vegetation Index (NDVI) from National Agriculture Imagery
 Program 2016 and the California Protected Areas Database. These datasets
 were combined to create a single static land cover map covering the entire
 Central Valley at 30-meter resolution. Reported pesticide application
 rates were obtained from the California Department of Pesticide Report
 Pesticide Use Reporting (PUR) for 2104, 2015, and 2016. Pesticide
 application rates were converted to LD<sub>50</sub>s (lethal
 doses) and were further converted to resistance-to-movement to create maps
 of resistance-to-movement under low, medium, and high pesticide
 application rates. We further tested three agricultural margin scenarios:
 current margins, all margins converted to natural habitat, and all margins
 converted to the nearest crop type. We crossed the three margin scenarios
 with the three resistance surfaces in a factorial manner and generated
 least-cost paths connecting 205 points along the eastern margin of the
 Central Valley with 205 points on the western margin of the Central
 Valley. We assessed the following metrics derived from the least-cost
 paths: 1) total path length of least-cost paths connecting the western and
 eastern sides of the study area, 2) unique path length in the inner area,
 3)  average distance to the nearest path in the inner area, 4) the average
 number of paths in the inner area. We repeated this process for a close-up
 study area within the Central Valley in addition to the larger Central
 Valley.
description: Shapefiles and GeoTIFF files can be opened and viewed in a wide
 range of Geographic Information System software including ArcGIS, QGIS, R,
 GRASS, ArcGIS Online, etc. Vector geographic data is in shapefile format.
 The following file types are associated with shapefiles: cpg, dbf, prj,
 sbn, sbx, shp, shp.xml, shx. These files should not be separated from one
 another. If moved, they may cause the data to be unable to be displayed.
 Raster geographic data is in geotiff format. The following file types are
 associated with geotiff: tfw, tif, tif.aux.xml, tif.ovr, tif.vat.cpg,
 tif.vat.dbf, tif.xml. These files should not be separated from one
 another. If moved, they may cause the data to be unable to be displayed.
 The coordinate system for all geographic data is NAD 1983 UTM Zone
 10N.