Multi-Layer Decomposition of Functional Community Restructuring

Implements the 'ASC-CFD' (Assemblage Shift Characterization - Community Functional Dynamics) framework for decomposing functional community restructuring into positional (centroid displacement), dispersive (functional dispersion), and boundary (convex hull volume) components. Tests each component against two null models: a sampling null model (individuals or replicates reassigned between communities) and a stratified trait-permutation null model, with a single global test when many communities are compared. Functional entities (species with similar traits) help detect replacement among similar species, and species-level leverage identifies the taxa driving functional shifts. Supports both temporal (paired) and spatial (pairwise) comparisons.

ascent: A multi-layer framework for decomposing functional community restructuring into positional, dispersive and boundary components

The ascent package implements the ASC-CFD (Assemblage Shift Characterization — Community Functional Dynamics) framework.

Most functional diversity metrics quantify how much communities differ, but provide little information about how those differences are organized within functional space.

Communities may exhibit identical levels of functional turnover while following completely different ecological trajectories, including directional shifts, internal reorganization, or expansion and contraction of functional boundaries.

The ascent package implements the ASC-CFD framework to explicitly decompose these processes.

ascent provides a multi-layer topological approach to decompose functional community restructuring into positional, dispersive, and boundary components, tested against sampling and trait null models.

Whether you are evaluating temporal perturbations (e.g., deforestation, climate change) or spatial beta-diversity gradients, ascent allows you to reconstruct the geometric trajectory of ecosystems and identify the specific taxa driving these shifts.

🧠 Core Architecture

The framework evaluates ecological dynamics by deconstructing them into three analytically distinct geometric layers within the retained functional space:

1. Positional Component ($\Delta C$): The net directional displacement of the community centroid. Measures the displacement of the community functional centroid within the retained trait space.
2. Dispersive Component ($\Delta FDis$): The internal demographic reorganization. Quantifies whether biomass is concentrating into central redundant strategies or expanding towards peripheral phenotypes.
3. Boundary Component ($\Delta FRic$): The multidimensional Convex Hull volume. Captures changes in the outer functional boundaries of communities through Convex Hull geometry. Because this metric depends exclusively on extreme species, it should be interpreted as a topological descriptor rather than a robust abundance-weighted estimate of functional change.

What does each layer measure?

ΔC → Where is the community moving? ΔFDis → How is biomass being redistributed? ΔFRic → Are functional boundaries expanding or collapsing?

Two Complementary Null Models

Each layer is tested against two null models that ask different questions:

• A (sampling): individuals — or whole samples, when both states have replicates — are reassigned at random between the states. Is the change larger than expected from sampling alone?
• B stratified (traits): trait positions are shuffled among the species of the contrast that have similar abundances (groups of stratum_size, default 5). Does the change depend on which traits the species have? For position, the lower tail flags compensation (less change than expected from the traits).

With functional entities (asc_entities()), A is also run on abundances summed by entity, and asc_transitions() splits the shift into a part between entities and a part within them: this is the recommended way to detect replacement among functionally similar species. For many communities (asc_pairwise()), asc_null() runs a single global test per layer instead of one p-value per pair.

Quick reading guide:

Species-level Functional Leverage

The asc_transitions() module projects species-specific abundance changes onto the observed ecosystem trajectory, identifying the taxa responsible for driving functional restructuring. This allows users to move beyond community-level metrics and directly quantify the contribution of individual species to directional ecosystem change.

Why not just use Functional Beta Diversity?

Current frameworks quantify the magnitude of functional turnover between communities. ascent instead decomposes restructuring into three distinct mechanisms:

🚀 Installation

Install the released version from CRAN:

install.packages("ascent")

Or the development version from GitHub:

# install.packages("devtools")
devtools::install_github("V3ndetta96/ascent")

💻 Quick Start

Here is a basic workflow evaluating the functional impact of deforestation on a bird community using mixed trait data (quantitative and binary).

library(ascent)

# 1. Define Traits and Abundances
# Note: Binary traits are set as factors to use the Gower metric.
traits <- data.frame(
  Body_Mass = c(15, 20, 30, 45, 60, 90, 150, 250, 400, 600),
  Frugivore = factor(c(0, 0, 1, 1, 1, 0, 1, 1, 1, 0))
)
rownames(traits) <- paste0("Sp", 1:10)

abund_time <- rbind(
  Reference = c( 0,  0, 10, 15, 25, 20, 10, 8, 4, 2), # Old-growth forest
  Impacted  = c(40, 35, 15,  5,  0,  0,  0, 0, 0, 0)  # Deforested
)

# 2. Execute the Paired Multi-Layer Framework
res <- asc_paired(
  traits = traits, abund = abund_time, 
  sites = c("Site1", "Site1"), time = c("Reference", "Impacted"),
  ref_time = "Reference", dist_method = "gower"
)

# 3. Evaluate the null models (A: sampling; B: traits)
res <- asc_null(res, n_perm = 999, seed = 123)

# 4. View Automated Ecological Diagnostic
summary(res)

Visualizing Dynamic Topology and Functional Leverage

ascent includes built-in ggplot2/patchwork methods to visualize the PCoA trajectory, the 2D Convex Hull boundaries, and the Functional Leverage (the specific taxa pulling or releasing the centroid).

plot(res, contrast = "Site1", type = "both", n_sp = 5)

🛠️ Package API Overview

📖 Documentation & Vignettes

For a comprehensive guide, including spatial network analyses and detailed ecological interpretations, please read the official vignette:

vignette("ascent_tutorial")

⚠️ Methodological Notes

FRic (Functional Richness)

FRic is computed as the volume of the convex hull in the retained PCoA space. Key considerations:

• Depends exclusively on extreme species. FRic captures the outer boundary of the functional space. It is insensitive to internal reorganization of biomass. A species that increases from 1% to 90% relative abundance will not alter FRic if it is not on the hull boundary.
• Not abundance-weighted. Unlike FDis or the centroid, FRic is a purely incidence-based metric within the framework. It should be interpreted as a topological descriptor of the functional boundary, not as a robust estimate of functional change.
• Requires N > k. When a community has fewer species than retained PCoA axes, the convex hull is geometrically undefined and FRic is reported as NA.

ΔFDis (Functional Dispersion Change)

• Not normalized. ΔFDis is an absolute difference in the retained PCoA space. Its magnitude depends on the trait scales, the number of retained axes, and the Gower distance matrix. Direct comparisons across studies with different species pools or trait sets should be made with caution.
• Normalized position: Only the positional component (rΔC%) is normalized by the regional functional diameter (Dmax_regional), enabling cross-study comparisons.

Null Model Scope

asc_null() evaluates each contrast (each site in asc_paired()) separately. A needs counts of individuals (whole numbers); with proportions only B is run. B shuffles traits only among the species present in the contrast. B is slightly liberal for dispersion (about 6.5 % false positives instead of 5 %) and when individuals are captured in groups (about 7 %): treat p-values close to 0.05 with caution.

Functional Leverage: Additive Property

The Functional Leverage satisfies a strict mathematical decomposition:

$$\sum_{i=1}^{S} \text{Leverage}_i = |\Delta C|$$

where $|\Delta C|$ is the absolute Euclidean distance between centroids. Each species' leverage is the product of its demographic change ($\Delta p_i$) and its projection, measured from a reference point (by default the midpoint between the two centroids), onto the unit direction of the centroid shift:

$$\text{Leverage}_i = \Delta p_i \cdot \text{proj}(\mathbf{f}_i, \hat{v})$$

This property ensures that the sum of all individual species contributions exactly reconstructs the total centroid displacement. Species with positive leverage drive the shift; species with negative leverage resist it.

✒️ Citation

While the official manuscript is in preparation, if you use ascent in your research, please cite the package directly:

Muñoz-Li, R. R. & F. Alvarez-Denis (2026). ascent: Multi-Layer Decomposition of Functional Community Restructuring. R package. https://doi.org/10.5281/zenodo.20388185

The entry for the installed version is given by citation("ascent").