Data and code for "Resource gradients drive the distribution and photobiont characteristics of two lichen species in a subarctic lava field"

This project described how the distribution and morphology of two species of lichen varied along a transect perpendicular to Lake Myvatn in Iceland. All data were collected in a recent (1729) lava field and we focused on two species Flavocetraria cucullata and Peltigera leucophlebia. Lake Myvatn is famous for large midge (Diptera: Chironomidae) emergences of which many are deposited on land. Thus, the transect reflects variation in midge deposition. P. leucophlebia contains both green algae and cynaobacterial endosymbionts and thus is able to fix atmospheric nitrogen, while F. cucullata contains only green algae and is therefore dependent on environmental nutrients. We suspected that these species differed in their response to the midge-derived nutrient gradient.

We measured the distribution of each lichen along a 400 x 15 m transect perpendicular to the lake, characterized their surrounding vegetation, and took thin sections of thalli on which we characterized photobiont thickness and chlorophyll-a concentrations using images taken with a near infrared camera.

The data are housed in the Data folder. FLG_Transect_Points.csv contains the location and names of each lichen plot. FLG_Surrounding_Vegetation.csv contains the vegetation inside each plot. Lichen_IR.csv contains the ENDVI, our metric of chlorophyll-a concentration, and photobiont thickness, in units of pixels taken using a standardized zoom.

All scripts associated with the project are housed in the Analysis folder. IRProcessing.R contains the code used to calculate the chlorophyll-a concentration and thickness from each of the photographs of the lichen thin sections. Myv_analysis.R contains all the code used for the statistical analyses and to generate figures. GOLichenAnalysis2019.Rproj is the RStudio project, which sets the relative locations of files. See https://support.posit.co/hc/en-us/articles/200526207-Using-RStudio-Projects for more information on .Rproj files.