Selection caused by abiotic factors may vary across ecosystems due to variation in habitat properties (Table 1) and the strength of environmental gradients. For example, abiotic gradients can vary between different types of media (e.g., air vs water) due to differences in density, viscosity and heat capacities (Table 1). In addition, it has been suggested there is overall greater environmental structure on land than in freshwater systems (Herfindal et al. 2022). However, some gradients may be stronger in water than on land, such as for light, which can promote niche differentiation in freshwater habitats (Stompet al. 2007). Possibly as a result of these differences, there is evidence that species sorting–when species tend to be found in local communities matching their environmental preferences (Heino et al. 2015; Govaert et al. 2021)–tends to be stronger on land. For example, species sorting appears to be weakest in lakes compared to riverine and terrestrial habitats (Soininen 2014), possibly due to their isolation (Heino et al. 2015). Finally, differences between ecosystems in environmental structure also have major implications for the evolution of thermal niches (Steele et al. 2018; Sundayet al. 2019) and suggest the ability of species to track thermal optima in response to climate change may differ across realms (Burrowset al. 2011).