Visual predator

Temporal and spatial shifts in the abundance of chemically undefended algae and cyanobacteria may leave grazers with few dietary options except to consume low-quality, chemically defended food items. While some herbivores may be able to either tolerate or inactivate these toxins (Samelle and Wilson 2005), species that lack tolerance may be faced with the dilemma of either remaining on a low-quality patch or migrating to a different patch, thus increasing their risk of predation by visual predators (Krivan and Vrkoc 2000). In systems that experience seasonal... 

S. Johnsen, E.A. Widder (2001). Ultraviolet absorption in transparent zooplankton and its implications for depth distributon and visual predation. Mar. Biol, 138, 717-730. 

Abstract For most mammals, the ability to detect odours and discriminate between them is necessary for survival. Information regarding the availability of food, the presence of predators and the sex, age and dominance status of conspecifics is odour mediated. Probably because of this extraordinary reliance upon odour cues, mice and rats have developed the ability to learn and remember information associated with olfactory cues as effectively as primates recall visually related cues. As a result, these rodents have become the model of choice to study the neural and cognitive processes involved in olfactory discrimination. In this paper, we describe some of the more ethologically based tasks used in assessing olfactory discrimination and the advantages and disadvantages of the different methodologies employed. 

The predators discussed up to this point search for prey by using their ability to perceive certain chemical clues. Some unusual predators have evolved the ability to attract their prey with scents that mimic the odor of a valuable resource (see reviews of chemical mimicry in refs. 9 and 39). Several groups of spiders lure male insect prey with scents that mimic the sex pheromone scents of females of the prey species (see reviews in refs. 9,13,40, and 41). To the best of our knowledge, these spiders are the only predators that mimic sex pheromones. However, the spiders share some similarities with the diverse orchids which mimic insect sex pheromones to lure pollinators (9, 42, 43) and with the predatory fireflies, which practice elaborate mimicry of visual sexual signals to lure their prey heterospecific male fireflies (44). 

On the other hand there are also assumptions built into our perception, which are, for example, the basis of our visual illusions. Thus we perceive the moon moving against the clouds, since we hypothesize that objects move in a static environment, which fits to our immediate earthly environment. Here it is important to spot a moving object, be it a predator or prey, in minimum time. That we fall prey to an illusion, when we look up at the sky, does not really matter. In addition we know that we categorize and thus impose an order onto and into what we perceive. Colour perception is a good example. 

When disturbed or molested, these insects release small droplets of hemo-lymph from the tibio-femoral joints of their legs, and it is now well established that the deterrency exhibited by many species of coccinellids towards potential predators results from the presence of repellent and bitter alkaloids in that fluid [ 12,13]. In ladybirds, this unpalatability is associated with a bright aposematic coloration and a characteristic smell due to 3-alkyl-2-methoxypyrazines [14, 15]. The beetles use these molecules not only to reinforce the visual alerting signal on an olfactory level, but also as aggregation pheromones [16]. 

A non-toxic species of salamander may derive protection from predators by visually resembling a toxic form so closely that predators cannot distinguish between them Batesian mimicry). Free-ranging birds avoid both the toxic red eft Notophthalmus viridescens) and the similar-looking non-toxic red morph of the red-backed salamander Plethodon cinereus). The red-striped morph of P. cinereus, which does not resemble the red eft, is eaten (Brodie and Brodie, 1980). 

Tadpoles of the two closely related frog species Rana lessonae and Rana esculenta respond more to chemical cues of their predator, the pike E. lucius, than to visual and tactile ones. The strongest swimming, resting, and edge-use behaviors - all considered antipredator responses - occurred to a combination of... 

Alino, P. M., Sammarco, P. W., and Coll, J. C., Toxic prey discrimination in highly specialised predators visual v. chemical cues as determinants, J. Exp. Mar. Biol. Ecol., 164, 209, 1992. 

---