Climate Exposure Relative to a Species' Climatic Niche

Quantifies projected climatic change relative to the climatic niche represented by a species' current distribution. A weighted current reference defines the niche centre and empirical radial boundary. Present and projected conditions at each location give local climatic displacement, signed change in niche distance, a derived non-radial reconfiguration term, and exceedance beyond the niche boundary. Occurrence records, range maps, and binary or continuous species distribution model outputs can define reference weights. Matrix and spatial workflows return location-level values, weighted summaries, maps and climatic-variable contributions.

climniche

Current-to-future climatic distance shows how much climate changes at a site, but not where projected conditions fall within the climatic niche represented by a species' current distribution. climniche calculates both the local displacement and the niche position reached.

Website: https://bohao0813.github.io/climniche/

Installation

Install the CRAN release:

install.packages("climniche")

Install the development version from GitHub:

install.packages("remotes")
remotes::install_github("Bohao0813/climniche")

Climate exposure relative to the current climatic niche

Non-negative location weights define the current climatic niche reference. These weights may come from occurrence records, range maps, binary SDMs or continuous suitability maps. At each site, projected climate is compared with both the local current climate and the shared niche centre and empirical radial boundary. Field names use snake case in R objects; figures and reports use the formal names below.

• Climatic Displacement (climate_change_amount): distance between current and future conditions at the same site under the fitted climatic metric.
• Niche Distance Shift (niche_distance_change): signed change in distance from the current climatic niche reference centre.
• Climatic Reconfiguration (climate_reconfiguration): non-radial component of Climatic Displacement that is not captured by Niche Distance Shift. It is derived from those two quantities.
• Niche Boundary Exceedance (niche_boundary_exceedance): positive excess of future niche distance beyond the empirical radial boundary of the current climatic niche reference.

Climatic Displacement, Niche Distance Shift and Climatic Reconfiguration obey the fitted geometric identity $D_i^2 = R_i^2 + C_i^2$. Climatic Reconfiguration is therefore not an independent exposure dimension. Niche Boundary Exceedance is a future boundary-relative state rather than a change in boundary status. Locations with similar Climatic Displacement can therefore be distinguished by where their projected climates fall within or beyond the current niche.

Workflow

Every input interface follows the same four steps.

1. Match current and projected climatic variables and locations, then convert species distribution data to non-negative reference weights.
2. Fit preprocessing and standardisation to current climate, construct the climatic distance and estimate the weighted niche centre and boundary.
3. Hold that fitted reference fixed while calculating the four reported quantities and climatic-variable contributions for projected conditions.
4. Return location-level values, weighted summaries, maps and reports from the same fitted niche reference.

fit_climniche() accepts numeric matrices and data frames. fit_climniche_raster() accepts RasterLayer, RasterStack and RasterBrick objects, whereas fit_climniche_terra() accepts SpatRaster objects. A fitted reference can also be created with fit_climniche_reference() and reused with project_climniche().

Basic use

library(climniche)

sim <- simulate_climniche()

fit <- fit_climniche(
  current = sim[["current"]],
  future = sim[["future_away"]],
  occupied = sim[["occupied"]],
  sensitivity = sim[["sensitivity"]]
)

climniche_summary(fit)
climniche_report(fit, species = "example species")
plot_climniche_summary_figure(fit)

fit_climniche_raster() and fit_climniche_terra() accept binary reference rasters and continuous SDM suitability rasters. Continuous values remain weights; occupied_threshold only sets values at or below the cutoff to zero. The supplied numerical scale is used as a relative weighting scale, not as an occurrence probability. domain limits the cells evaluated, while study_region adds an optional boundary to maps.

Through time

fit_climniche_series() holds the fitted current niche reference, climatic weighting matrix and empirical radial boundary fixed across ordered projections. For spatial series, future missing cells do not alter this reference; comparisons use cells available in every projection.

future <- lapply(c(0.25, 0.50, 0.75, 1), function(fraction) {
  sim[["current"]] + fraction *
    (sim[["future_away"]] - sim[["current"]])
})

series <- fit_climniche_series(
  current = sim[["current"]],
  future = future,
  time = c(2030, 2050, 2070, 2090),
  occupied = sim[["occupied"]],
  sensitivity = sim[["sensitivity"]]
)

climniche_range_summary(series)
departure <- climniche_departure(series)
plot_climniche_time(series)

Range summaries separate the Weighted Niche Boundary Exceedance Fraction from Conditional Relative Niche Boundary Exceedance. Their product is Range Mean Relative Niche Boundary Exceedance. These are weighted summaries of Niche Boundary Exceedance, not additional cell-level exposure metrics. Optional aggregation and raster cell area weights remain separate from the reference weights used to estimate the current climatic niche reference. climniche_departure() records the first supplied projection beyond the niche boundary and the fraction of supplied projections in which exceedance occurs. Persistent onset can be requested separately with persistence.

Ecological screening of climate exposure

climniche_priority() compares one climatic quantity with an ecological or management criterion using two-objective Pareto screening. The example below compares larger positive Niche Distance Shift with smaller Climatic Displacement in separate screens.

positive_shift <- climniche_priority(
  fit,
  exposure = "niche_distance_change",
  exposure_direction = "maximize"
)

low_displacement <- climniche_priority(
  fit,
  exposure = "climate_change_amount",
  positive_only = FALSE,
  exposure_direction = "minimize"
)

Each result retains the decision plane, Pareto fronts and spatial Pareto depth. Supply an external ecological or management layer through criterion when the second objective is intended to represent evidence independent of the reference weighting surface.

Climatic contributions

climniche_dominant_contribution() identifies the climate variable with the largest absolute contribution to squared niche distance change at each cell. Its dominance share measures how much of the total absolute contribution is assigned to that variable. These terms decompose the squared-distance change underlying Niche Distance Shift; they are not SDM variable importance.

contribution <- climniche_dominant_contribution(fit)
summary(contribution)

For a spatial fit, plot_climniche_dominant_contribution() maps the dominant variable and its share within the selected reference cells.

Worked example

The European anchovy example demonstrates the fitted geometry and radial boundary comparison in the Mediterranean Sea. The exposure through time example follows range-level exposure and persistent Niche Boundary Exceedance from 2030 to 2090. The ecological screening example contrasts larger positive Niche Distance Shift with lower Climatic Displacement. The climatic contribution example maps the fitted climate variables that account for squared niche distance change.

Contributor

Contributions are welcome. Please make a pull request or contact bohao.he@polimi.it.