Browsing by Author "Zipple, Matthew N"
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Item Open Access A comparison of dominance rank metrics reveals multiple competitive landscapes in an animal society.(Proceedings. Biological sciences, 2020-09-09) Levy, Emily J; Zipple, Matthew N; McLean, Emily; Campos, Fernando A; Dasari, Mauna; Fogel, Arielle S; Franz, Mathias; Gesquiere, Laurence R; Gordon, Jacob B; Grieneisen, Laura; Habig, Bobby; Jansen, David J; Learn, Niki H; Weibel, Chelsea J; Altmann, Jeanne; Alberts, Susan C; Archie, Elizabeth AAcross group-living animals, linear dominance hierarchies lead to disparities in access to resources, health outcomes and reproductive performance. Studies of how dominance rank predicts these traits typically employ one of several dominance rank metrics without examining the assumptions each metric makes about its underlying competitive processes. Here, we compare the ability of two dominance rank metrics-simple ordinal rank and proportional or 'standardized' rank-to predict 20 traits in a wild baboon population in Amboseli, Kenya. We propose that simple ordinal rank best predicts traits when competition is density-dependent, whereas proportional rank best predicts traits when competition is density-independent. We found that for 75% of traits (15/20), one rank metric performed better than the other. Strikingly, all male traits were best predicted by simple ordinal rank, whereas female traits were evenly split between proportional and simple ordinal rank. Hence, male and female traits are shaped by different competitive processes: males are largely driven by density-dependent resource access (e.g. access to oestrous females), whereas females are shaped by both density-independent (e.g. distributed food resources) and density-dependent resource access. This method of comparing how different rank metrics predict traits can be used to distinguish between different competitive processes operating in animal societies.Item Open Access Comparison of categorical color perception in two Estrildid finches(The American Naturalist) Caves, Eleanor M; Green, Patrick A; Zipple, Matthew N; Bharath, Dhanya; Peters, Susan; Johnsen, Sönke; Nowicki, StephenItem Open Access Influence of visual background on discrimination of signal-relevant colours in zebra finches (Taeniopygia guttata).(Proceedings. Biological sciences, 2022-06) Davis, Alexander; Zipple, Matthew N; Diaz, Danae; Peters, Susan; Nowicki, Stephen; Johnsen, SönkeColour signals of many animals are surrounded by a high-contrast achromatic background, but little is known about the possible function of this arrangement. For both humans and non-human animals, the background colour surrounding a colour stimulus affects the perception of that stimulus, an effect that can influence detection and discrimination of colour signals. Specifically, high colour contrast between the background and two given colour stimuli makes discrimination more difficult. However, it remains unclear how achromatic background contrast affects signal discrimination in non-human animals. Here, we test whether achromatic contrast between signal-relevant colours and an achromatic background affects the ability of zebra finches to discriminate between those colours. Using an odd-one-out paradigm and generalized linear mixed models, we found that higher achromatic contrast with the background, whether positive or negative, decreases the ability of zebra finches to discriminate between target and non-target stimuli. This effect is particularly strong when colour distances are small (less than 4 ΔS) and Michelson achromatic contrast with the background is high (greater than 0.5). We suggest that researchers should consider focal colour patches and their backgrounds as collectively comprising a signal, rather than focusing on solely the focal colour patch itself.Item Open Access Threshold assessment, categorical perception, and the evolution of reliable signaling.(Evolution; international journal of organic evolution, 2020-12) Peniston, James H; Green, Patrick A; Zipple, Matthew N; Nowicki, StephenAnimals often use assessment signals to communicate information about their quality to a variety of receivers, including potential mates, competitors, and predators. But what maintains reliable signaling and prevents signalers from signaling a better quality than they actually have? Previous work has shown that reliable signaling can be maintained if signalers pay fitness costs for signaling at different intensities and these costs are greater for lower quality individuals than higher quality ones. Models supporting this idea typically assume that continuous variation in signal intensity is perceived as such by receivers. In many organisms, however, receivers have threshold responses to signals, in which they respond to a signal if it is above a threshold value and do not respond if the signal is below the threshold value. Here, we use both analytical and individual-based models to investigate how such threshold responses affect the reliability of assessment signals. We show that reliable signaling systems can break down when receivers have an invariant threshold response, but reliable signaling can be rescued if there is variation among receivers in the location of their threshold boundary. Our models provide an important step toward understanding signal evolution when receivers have threshold responses to continuous signal variation.