Causes and consequences of niche differentiation between color morphs of pygmy grasshoppers

Abstract: In this thesis, I used the color polymorphic pygmy grasshopper, Tetrix subulata, as a model system in order to investigate the degree of niche differentiation between alternative color morphs that are present within a single population. First, I hypothesized that individuals belonging to different color morphs differ in their innate food preference due to somewhat dissimilar physiology, and in their actual food consumption due in part to differential habitat use. I found that alternative morphs differ in their preferred food (multiple-choice experiment in the lab), and in long-term consumption of food in the wild (stable isotopes analysis). Next, I investigated what kind of ecological constraints may result in differential habitat use? Firstly, by painting grasshoppers either black or white in order to influence their thermal properties, I demonstrated that thermoregulatory behavior results in differential microhabitat use in a way that may increase fitness. Secondly, in computer based experiments in which human ‘predators’ were asked to detect images of grasshoppers implemented in images of various environments, I further demonstrated that the degree to which a specific body coloration supply protection, changes across backgrounds, and that no single color pattern provides superior protection against all visual backgrounds. Thus, predator avoidance behavior may result in differential habitat use as well. Can these findings translate into an advantage of polymorphic relative to monomorphic populations?  I then evaluated one prediction from theory that posits that more variable founder groups will be more successful in establishing population in new environments. Indeed, I found higher number of individuals the following year in more variable founder groups in semi-natural conditions in field experiment. This thesis demonstrates, niche differentiation along several dimensions between alternative color morph in a generalist invertebrate. It provides experimental evidence supporting the notion that visual predation may be driving force behind evolutionary change in morph frequencies, and points to a possible advantage for color polymorphic relative to monomorphic groups in terms of a higher establishment success.