Integrating gradient with scale in ecological and evolutionary studies

Abstract

Gradient and scale are two key concepts in ecology and evolution that are closely related but inherently distinct. While scale commonly refers to the dimensional space of a specific ecological/evolutionary (eco–evo) issue, gradient measures the range of a given variable. Gradient and scale can jointly and interactively influence eco–evo patterns. Extensive previous research investigated how changing scales may affect the observation and interpretation of eco–evo patterns; however, relatively little attention has been paid to the role of changing gradients. Here, synthesizing recent research progress, we suggest that the role of scale in the emergence of ecological patterns should be evaluated in conjunction with considering the underlying environmental gradients. This is important because, in most studies, the range of the gradient is often part of its full potential range. The difference between sampled (partial) versus potential (full) environmental gradients may profoundly impact observed eco–evo patterns and alter scale–gradient relationships. Based on observations from both field and experimental studies, we illustrate the underlying features of gradients and how they may affect observed patterns, along with the linkages of these features to scales. Since sampled gradients often do not cover their full potential ranges, we discuss how the breadth and the starting and ending positions of key gradients may affect research design and data interpretation. We then outline potential approaches and related perspectives to better integrate gradient with scale in future studies.

Efficient sampling designs to assess biodiversity spatial autocorrelation : should we go fractal ?

“…There are many empirical questions related to species distributions that involves monotonic environmental gradient in space: the effect of latitudinal gradient and associated climatic trends across a biogeo-graphic region, the effect of altitude on a mountaine slope, the effect of salinity in an estuarine river etc. When studying the effect of this kind of variables, the sparsity of fractal designs turned out to be advantageous, as conjectured by Guo et al (2023). Moderately increasing the contraction parameter yielded a higher standard deviation of the covariate in the design compared to hybrid designs, hence leading to lower error of the estimated effect.…”

“…our asymptotic analysis of error on γ for short autocorrelation range). Reducing the sampling area necessarily contributes to reduce the environmental variation, particularly for monotonic environmental covariates (see Guo et al (2023) for a discussion on this point).…”

“…It should also be noted that we evaluated designs on a simple scenario with a parsimonious autocorrelation structure (only positive autocorrelation, steadily decreasing in space with a single well-defined range). However, biological patterns often stem from heterogeneous drivers acting at different scales (Ricklefs, 2008; Thuiller et al, 2015; Guo et al, 2023). For instance, when studying the distribution of a species in space, competition among conspecifics may drive negative autocorrelation (i.e.…”

Dealing with area‐to‐point spatial misalignment in species distribution models

“…By doing so, we assumed that the effect of area‐to‐point misalignment depends on a ratio between the covariate grain and the environmental spatial heterogeneity (Gotway and Young 2002, Naimi et al 2014). Indeed, we expect a greater loss of information when coarsening the covariate in heterogeneous environments (low spatial range ρ) than in homogeneous ones (high spatial range ρ) (Guo et al 2023, Lu and Jetz 2023).…”

Macroecological correlates of richness, body size, and species range size in terrestrial vertebrates across the world

“…High species richness can lead to stronger biotic interactions (competition, predation) at lower latitudes (than at higher latitudes), and could thus limit species range size and range expansion (Paquette andHargreaves 2021, Matysioková andRemeš 2022). Also, areas across the tropics usually have higher environmental heterogeneity than higher latitudes, thus across a given extent of area (i.e., same spatial scale), more habitat types (and species) will be found, and the size of each habitat type would be smaller (Guo et al 2023a). Consequently, the ranges of many component species would be smaller as well.…”