Trends in Ecology & Evolution
ReviewVisual Acuity and the Evolution of Signals
Section snippets
Sensory Acuity
Animal behavior is influenced by the information that an organism can perceive and process, which is in turn mediated by sensory systems. Thus, studies of how animals interact with both other animals and with the environment must consider the relevant perceptual systems. One way that individuals can extract information is via signals, which also form the basis for communication [1]; thus, signals are fundamental to the behavior and fitness of organisms. Though many definitions of ‘signal’
Incorporating Visual Acuity into Studies of Signaling
Including acuity in studies of animal signaling is important for several reasons. First, humans have exceptionally high acuity, surpassed only by a few predatory bird species, and thus researchers sometimes develop hypotheses regarding signal function that do not reflect what is seen by the intended viewer. Second, because acuity dictates what patterns can and cannot be resolved, it determines the spatial information that can be extracted from visual scenes by signal receivers (hereafter
The Effect of Eye Size and Type on the Perception of Signals in Interspecies Interactions
Interspecies interactions, from mutualism to parasitism to predation, are often mediated by signals. However, assumptions about which viewers can resolve the details of a signal are often untested. In interspecies interactions, heterospecifics can impose selection pressure on signals that impact the success or efficiency of an interaction [31]. In the common case where two animals interact but have different acuities (Box 3), signals can be more distinguishable by heterospecifics but not
Concluding Remarks and Future Directions
The human ability to both see and process spatial patterns is elite in the animal kingdom. Our high acuity allows us to resolve fine-scale details that are likely not resolvable by the vast majority of animal viewers, and at far greater distances. The examples presented here are by no means exhaustive, and illustrate the importance of considering acuity when making hypotheses about the function of animal visual signals. For example, predictions that deserve further attention include that: (i)
Acknowledgements
We thank three anonymous reviewers, Drs Eric Warrant, Stephen Nowicki, and Lorian Schweikert, as well as Kate Thomas and Sarah Solie for comments on earlier versions of this manuscript.
Glossary
- Cycles per degree (cpd)
- a measure of visual acuity; the number of black and white stripe pairs that an organism can discriminate within a single degree of visual angle.
- Minimum resolvable angle
- (αmin) another measure of visual acuity; the angular width of the narrowest black and white stripe pair that can be discerned. When given in degrees, its inverse is cpd.
- Visual acuity
- the ability of a visual system to resolve static spatial detail.
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