Meta-analysis Shows a Consistent and Strong Latitudinal Pattern in Fish Omnivory Across Ecosystems

Abstract

Several studies have demonstrated a latitudinal gradient in the proportion of omnivorous fish species (that is, consumers of both vegetal and animal material) in marine ecosystems. To establish if this global macroecological pattern also exists in fresh and brackish waters, we compared the relative richness of omnivorous fish in freshwater, estuarine, and marine ecosystems at contrasting latitudes. Furthermore, we sought to determine the main environmental correlates of change in fish omnivory. We conducted a meta-analysis of published data focusing on change in the relative richness of omnivorous fishes in native fish communities along a broad global latitudinal gradient, ranging from 41°S to 81.5 N°including all continents except for Antarctica. Data from streams, rivers, lakes, reservoirs, estuaries, and open marine waters (ca. 90 papers covering 269 systems) were analyzed. Additionally, the relationship between the observed richness in omnivory and key factors influencing trophic structure were explored. For all ecosystems, we found a consistent increasing trend in the relative richness of omnivores with decreasing latitude. Furthermore, omnivore richness was higher in freshwaters than in marine ecosystems. Our results suggest that the observed latitudinal gradient in fish omnivory is a global ecological pattern occurring in both freshwater and marine ecosystems. We hypothesize that this macroecological pattern in fish trophic structure is, in part, explained by the higher total fish diversity at lower latitudes and by the effect of temperature on individual food intake rates; both factors ultimately increasing animal food limitation as the systems get warmer.

The effect of temperature on herbivory by the omnivorous ectotherm snail Lymnaea stagnalis

“…This pattern is consistent with increased plant consumption at lower latitudes by invertebrates as well (Pennings et al, 2009;Schemske et al, 2009;González-Bergonzoni et al, 2012). However, it is debated which factors drive this pattern (González-Bergonzoni et al, 2012;Ho & Pennings, 2013). Ambient temperature, the evolutionary time to adapt to plant consumption, and food availability have been evoked as important explanatory factors (González-Bergonzoni et al, 2012).…”

“…The prevalence of herbivory (planteating) varies with latitude: in fish communities, the level of herbivory strongly increases toward the equator (Floeter et al, 2005;Moss, 2010). This pattern is consistent with increased plant consumption at lower latitudes by invertebrates as well (Pennings et al, 2009;Schemske et al, 2009;González-Bergonzoni et al, 2012). However, it is debated which factors drive this pattern (González-Bergonzoni et al, 2012;Ho & Pennings, 2013).…”

“…In aquatic systems, most animals consuming vascular plants are omnivorous, including both plant and animal material in their diet (González-Bergonzoni et al, 2012;Gross & Bakker, 2012;Wood et al, 2012). The prevalence of herbivory (planteating) varies with latitude: in fish communities, the level of herbivory strongly increases toward the equator (Floeter et al, 2005;Moss, 2010).…”

“…However, it is debated which factors drive this pattern (González-Bergonzoni et al, 2012;Ho & Pennings, 2013). Ambient temperature, the evolutionary time to adapt to plant consumption, and food availability have been evoked as important explanatory factors (González-Bergonzoni et al, 2012). At higher temperatures ectotherm animals, such as fish, can better digest plant material (Clements et al, 2009).…”

Frog and toad larvae become vegetarian when it is hot

“…This finding suggests that the influence of temperature on the feeding preferences of ectotherms may be noticeable temporally within the same community, and not only along latitudinal gradients, as discovered in omnivorous fishes. 5 The changes in tadpole survival and life-history traits demonstrated that temperature induced changes in the relative quality of diets. While performance on animal diets strongly decreased at higher temperatures, performance on plant diets increased slightly, which may justify the shifts toward a greater assimilation of plant material during the heat waves.…”