Diet is a primary factor used to characterize the ecological niches of species and populations, including classification along the generalist–specialist spectrum (Elton, 2001; Hutchinson, 1957). However, dietary generalism usually is coarsely characterized, with the role of nutrients in defining a species’ niche overlooked (Machovsky‐Capuska, Senior, Simpson, & Raubenheimer, 2016). This is problematic because nutrition plays a dominant role in determining which foods species consume, and thus which environments they inhabit (Raubenheimer, Simpson, & Tait, 2012). The field of nutritional ecology has demonstrated that, in particular, the macronutrients (protein, carbohydrate, and lipid) in the foods and diets of animals strongly influence their foraging behavior (Coogan et al., 2017; Rothman, Plumptre, Dierenfeld, & Pell, 2007) and ultimately fitness, including reproduction and longevity (Jensen et al., 2012; Solon‐Biet et al., 2014). Neglecting nutrition in niche theory might therefore limit our understanding of the ecological factors that determine the abundance and distribution of species.