Decomposing an elevational gradient in predation by insectivorous birds
Data files
Jan 30, 2024 version files 35.28 KB
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1_bird_code.R
14.05 KB
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2_climate_data.R
15.80 KB
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claycat_writing.csv
2.60 KB
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README.md
2.83 KB
Abstract
Insectivorous birds have ecologically important effects on prey abundance, behavior, and evolution, and through top-down control birds indirectly reduce herbivory and promote plant growth. While several studies sought to characterize biogeographic patterns in top-down control by birds, variation in bird predation along elevational gradients is not well characterized both in terms of its commonness and the mechanisms underlying such variation. Here we characterized variation in bird predation along a 700m montane elevation gradient using artificial clay caterpillars, assessing the roles of variation in aridity, other elevational effects not associated with aridity (e.g., most notably growing season length) and bird abundance and diversity. Multivariate models revealed attack rates increasing with aridity (when controlling for the effects of elevation) and elevation (when controlling for aridity). Because aridity declines with elevation, elevational patterns were not detectable in a univariate analysis. Bird abundance (but not diversity) decreased with elevation (but not aridity) and did not provide an explanation for our results, suggesting the underlying mechanisms were behaviorally based. We speculate that the declining abundance of insect prey with elevation and aridity leads to increased bird foraging efforts and thus the likelihood of attacking clay caterpillars. If widespread, these dynamics have important consequences for both the interpretation of predation bioassays generally and for our understanding of the multivariate drivers of variation top-down control by predators and predation risks experienced by prey.
README: Decomposing an elevational gradient in predation by insectivorous birds
Clay caterpillars were placed on aspen trees at 10 sites within a valley, at 5 valleys along an elevational gradient in the Rocky Mountains. Attack rates by birds were recorded from the clay caterpillars on either 3 or 4 separate dates per site. Data of attack are reported as a proportion of the 20 caterpillars at 1 site on 1 date that were attacked (76 total). We reported aridity as a PCA of temperature and precipitation.
We reported the bird community using eBird checklists from the same region as the valleys, and extracted this following "Best practices for Using eBird data". Data on the climate and on the bird community were sourced from public databases (PRISM and eBird respectively). The published code provides the parameters to which we extracted this data from these public sources, and also provides code for how these data were wrangled and thus used.
Description of the data and file structure
claycat_writing.csv- This file contains the data from the sites and date where attack rate was recorded.
Site: the site number (20 total, in each 5 valleys there are 4 sites)
Totalattack: the number of attacks out of 20 caterpillars at a site and date.
Drainage: the name of the valley
elevation_m: elevation in meters of each of the sites.
propattack: the proportion of caterpillars attacked out of 20 at a site and date.
DaysOut: The number of days between recording attacks that the caterpillars were exposed.
1_bird_code.R - Contains the code for extracting community data on eBird. We acquired checklists during the month of August 2020 as outlined in the code. This code also describes how we derived descriptive variables from this data (abundance and diversity) which were subsequently used in analyses.
2_climate_data.R - Contains the code for extracting the climate data for our study period from PRISM. We acquired the following variables for August 2020: the average precipitation (mm) for the month of august 2020 (when attack data was collected), the minimum temperature (degrees C) for the month of august 2020 (when attack data was collected), the maximum temperature (degrees C) for the month of august 2020 (when attack data was collected), the mean temperature (degrees C) for the month of august 2020 (when attack data was collected). Using this data, as outlined in the code, we created a PCA of these four variables and extracted the 1st principle component of this analyses, which was subsequently used in analyses as a metric of aridity.
Sharing/Access information
This is a section for linking to other ways to access the data, and for linking to sources the data is derived from, if any.
Data was derived from the following sources:
- ebird.org
- https://prism.oregonstate.edu/
Methods
Clay caterpillars were placed on aspen trees at 10 sites within a valley, at 5 valleys along an elevational gradient in the Rocky Mountains. Attack rates by birds were recorded from the clay caterpillars on either 3 or 4 seperate dates per site. Data of attack are reported as a proportion of the 20 caterpillars at 1 site on 1 date that were attacked (76 total). We reported aridity as a PCA of temperature and precipiation. We reported the bird community using eBird checklists from the same region as the valleys, and extracted this following "Best practices for Using eBird data".
Usage notes
R Studio