How the relative importance of community assembly processes varies with spatial scale is the focus of intensive debate, in part because inferring the scales at which specific niche-based processes act is difficult. One obstacle is that standard phylogenetic and functional diversity metrics may integrate the signals of multiple processes when combining separate niche axes into one variable (multiple-niche-axis metrics), potentially obscuring overlapping niche-based processes. We use simulations to evaluate the power of these metrics to detect competition and habitat filtering when these processes operate across multiple niche axes and vary in their relative importance. We then test for both processes at a range of spatial scales in a Neotropical bird assemblage. Simulations revealed that multiple-niche-axis metrics had low power to detect competition and habitat filtering when a mix of both processes acts across niche axes, whereas metrics focused on single-niche axes were better able to deal with this complexity. We found the same contrast in bird communities, where both competition and habitat filtering were detected at the scale of individual territories, but only by single-niche-axis metrics focused on specific niche axes (e.g., foraging traits). Our results suggest that multiple-niche-axis metrics may produce misleading evidence that niche-based processes are partitioned, particularly across scales, and highlight the importance of analyzing functional diversity patterns on individual niche axes when testing assembly models.
Wayqecha Peru Bird Community Census Data
Bird species presence/absence for 41 species at 72, 0.8 ha, survey points of radius 50 m, arranged 120 m apart on a 6 by 12 point grid across a grassland–forest ecotone (See publication Fig. 1 and Fig. A1). Species were recorded as present at a survey point if detected by either sight or song. Spatial grid references for survey points are also given. Y coordinates are grid rows and X coordinates grid columns. This enables the calculation of species presence/absence at larger spatial scales by grouping together neighboring survey points (e.g. grouping the data for two neighboring survey points creates a survey area of 1.6 ha). Data are in .csv format. Column headings: Site: 0.8 ha survey point names. X: X coordinate on survey grid. Y: Y coordinate on survey grid. Other columns are species names (genus and species separated by an underscore): 1= species presence, 0 = species absence.
Wayqecha Peru Bird Community Functional Traits
Species average bill, tail, wing and tarsus trait values for 41 primarily insectivorous bird species from a cloudforest–grassland ecotone at Wayqecha Biological Station, Peru. Please refer to main text for additional details on trait collection methods. Data are in .csv format. Column headings: Species: Species name. Taxonomy follows Remsen et al. (2011). Bill.nares: Average length of bill (mm) measured from bill tip to anterior edge of nares. Bill.width: Average bill width (mm) measured at anterior edge of nares. Bill.depth: Average bill depth (mm) measured at anterior edge of nares. Wing.length: Average wing length (mm) measured on unflattened wing. Tail.length: Average tail length (mm) measured from the tip of the longest rectrix to the point at which the two central rectrices protrude from the skin. Tarsus.length: Average tarsus length (mm) measured as the distance from the notch at the knee to the third crease at the ankle. Sample.size: Number of individuals measured. Measured.on.Site: Y = measurements taken on individuals captured within the survey site at Wayqecha. N = measurements taken on museum specimens.
Wayqecha Peru Bird Community Vegetation Data
Vegetation characteristics within a 20m x 20m square centered on each of the 72, 0.8 ha bird survey points from a cloudforest–grassland ecotone at Wayqecha Biological Station, Peru. Please refer to publication main text for additional details on vegetation data collection methods. Data are in .csv format. Column headings: Site: 0.8 ha survey point names. X: X coordinate on survey grid. Y: Y coordinate on survey grid. Max.canopy.height: Maximum canopy height in meters, estimated by eye. Percentage.grass.cover: Estimated by eye. Percentage.shrub.cover: Estimated by eye. Percentage.tree.cover: Estimated by eye.