Group of variables Variable Type and levels Influences the dispersal-range size relationship because…
Dispersal departure/transfer
Clade
categorical: plants, animals
…plants, as sessile and passive dispersers, may be more affected by dispersal limitation than animals.
Dispersal type
categorical: passive, active, mixed
…passive dispersers, being dependent on external sources for their dispersal, may be more affected by dispersal limitation than active dispersers.
Realm categorical: terrestrial, marine, freshwater …species in marine systems are less affected by dispersal limitation than those in terrestrial/freshwater systems, because marine systems might have higher connectivity.
settlement
Temperature regulation
categorical: endotherm, ectotherm
…endotherms are less affected by niche limitation than ectotherms due to broad thermal tolerances, allowing them to attain and persist in larger ranges more easily.
Biogeographical region size continuous …species in regions with less available (niche) space (e.g., smaller regions) may be less affected by dispersal limitation than species with more space available, because in smaller regions even less dispersive species may have attained maximum range sizes.
Habitat correction categorical: single habitat, yes, no. …available niche space rather than colonization ability may be the limiting factor when it comes to dispersal.
Available space correction categorical: unique site, yes, no. …dispersal limitation and (maximum) range sizes may differ between regions or habitats of difference sizes (also see ‘Biogeographical region size’ for specific predictions).
Evolution evolutionary history
Species age
categorical: considered, no considered
…time for range expansion rather than dispersal ability may be the limiting factor when it comes to understanding differences in range sizes across species.
Phylogenetic correction categorical: considered, not considered …dispersal ability and range size may be phylogenetically and temporally correlated, thus correcting for phylogenetic dependence might reduce or remove the effect of evolution on the relationship.
past dynamics
Latitude
categorical: tropical, subtropical, temperate, multiple latitudes
…species in tropical regions may be less affected by dispersal limitation because of long-term environmental stability (e.g., lack of glaciations), thus more time for range expansion. Tropical species may therefore have had more opportunity to attain and persist in their maximum range sizes, compared with temperate regions.
Latitude correction categorical: unique latitudinal zone, yes, no. …dispersal limitation and (maximum) range sizes may differ between latitudes (also see ‘Latitude’ for specific predictions).
Methodology dispersal approximation
Number of dispersal-related traits
continuous
…the dispersal process may not be accurately approximated when including only few traits that lack the components of dispersal most relevant for range expansion.
range size definition
Range size metric
categorical: extent of occurrence, area of occupancy
…area of occupancy can underestimate range size by excluding discontinuities in the spatial distribution of taxa, resulting in a mismatch between range size and dispersal.
Range size completeness categorical: partial, complete …partial ranges may underestimate true range sizes.
taxonomic delimitation
Taxonomic unit
categorical: species, non-species
…using higher taxonomic levels as units of analysis (e.g., ‘genus’, ‘family’) ignores species-level variation in dispersal ability and range size.
Taxonomic breadth categorical: genus, family, order, class, phylum/division …identifying universal dispersal-related traits associated with range size at very broad taxonomic levels (e.g., ‘phylum’, ’division’) may be difficult.
Number of species continuous … a higher number of species increases statistical power, captures a higher trait and range size variation, and may be less biased by incomplete sampling of species within the study system.