Countershading Case Study

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Discussion

The current study aimed to address whether countershaded prey are better protected from visually hunting predators compared to non-countershaded prey. The study also aimed to resolve these major differences in results from these previous research (Edmunds & Dewhist, 1994; Speed et al., 2005) on the effectiveness of countershading. The results from the current study partly addressed the aims indicating that countershaded prey had a better survival rate than non-background matched prey. The hypothesis that countershaded prey would be eaten less frequently than dark, light, or reverse countershaded prey was not supported. However, aspects of the functions of countershading was supported via the results and are discussed separately
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This supports the findings of previous research (Edmunds & Dewhist, 1994; Speed et al., 2005; Rowland et al., 2007). However, it should be noted that the orientation of prey with reverse countershading may effect the predation rate. It should also be noted, that various animals with this reverse countershading have been observed in up-side down orientations (Tinbergen, 1957; Chapman et al., 1994). For example, in prey such as caterpillars that are frequently positioned upside down (ventral surface pressed against leaf’s ventral surface) reduced predation rates have been demonstrated (Rowland et al., 2009). However, in the context of the current study’s experiment design, where the reverse countershaded prey was not oriented up-side down, the expected result of a higher predation rate than countershaded was indicated. This result, can be explain by both of the functions of countershading. Firstly, as countershaded prey matched the background when viewed (by bird species) from above, there would have less contrast, and therefore an increase in crypsis. Secondly, self-shadow concealment would only be present in countershaded prey items, and therefore a reduction in consumption of these could be due to the associated increase in crypsis. However, the function that is having the largest effect of increased crypsis in this comparison can not be clearly …show more content…
This supports the findings of Speed et al. (2007) experiment, however does not support the findings of other experiments (refer to: Edmunds & Dewhist, 1994; Rowland et al., 2007). This result indicates that the two functions of countershading are potentially not equally responsible for the increase in crypsis (and decrease in predation amount) in the previous two comparisons. This conclusion is based on the following reasons. Firstly, if self shadow concealment was the only cause of less predation in the previous comparisons of: 1) countershaded compared to reverse countershaded; and 2) countershaded compared to uniformly white, then the expected result in 3) countershaded compared to uniformly green would have resulted in significantly less eaten countershaded prey compared to that of uniformly green prey. However, if background matching was the cause of less predation in the previous comparisons (1, and 2) the expected result in this comparison (3) would be that uniform green prey would have a near equal probability of being eaten compared to countershaded. This is due to both prey items matching the background when viewed (by bird species) from above, having similar contrast, and therefore a similar level of crypsis. Importantly, both self shadow concealment and background matching of countershaded animals would only function correctly if the animal perceiving this is in

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