Most amphipods are detritivores or scavengers, with some being grazers of algae, omnivores or predators of small insects and crustaceans. Food is grasped with the front two pairs of legs, which are armed with large claws. More immobile species of amphipods eat higher quantities of less nutritious food rather than actively seeking more nutritious food. This is a type of compensatory feeding. This behaviour may have evolved to minimise predation risk when searching for other foods. "Ampithoe longimana", for example, is more sedentary than other species and have been observed to remain on host plants longer. In fact, when presented with both high- and low-nutrition food options, the sedentary species "Ampithoe longimana" does not distinguish between the two options. Other amphipod species, such as "Gammarus mucronatus" and "Elasmopus levis", which have superior predator avoidance and are more mobile, are better able to pursue different food sources. In species without the compensatory feeding ability, survivorship, fertility, and growth can be strongly negatively affected in the absence of high-quality food. Compensatory feeding may also explain the year-round presence of "A. longimana" in certain waters. Because algal presence changes throughout the year in certain communities, the evolution of flexible feeding techniques such as compensatory feeding may have been beneficial to survival.