Influence of substrate orientation on tadpoles feeding efficiency

In nature, tadpoles encounter food on substrates oriented at different angles (e.g. vertically along stems, horizontally on the bottom). We manipulated the orientation of food-covered surfaces to test how different orientations of surfaces affect tadpoles’ feeding efficiency. We studied taxa that differed in the oral morphology of their larvae and position in the water column. We hypothesized that species would differ in their ability to graze upon surfaces at different orientations and that differences in the tadpoles’ feeding ability would result in different growth rates for the species. The orientation of food-covered surfaces did not affect the growth rate of species with bottom-dwelling tadpoles (whose growth rate varied only between species). Among species with midwater tadpoles, some appear to have a generalist strategy and experienced a high relative growth rate on numerous substrate orientations whereas others achieved high growth rates only on flat substrates (i.e. at 0° and 180°). We conclude that oral morphology constrains tadpoles’ ability to feed at different substrate orientations, and this could lead to niche partitioning in structurally complex aquatic environments. Because physical parameters of the environment can affect tadpoles’ growth rate, characterizing these features might help us better understanding how competition structures tadpole assemblages.