Competition is considered to rely on the value attributed to resources by animals, but the influence of extrinsic stressors on this value remains unexplored. Although natural or anthropogenic environmental stress often drives decreased competition, assumptions that this relies on resource devaluation are without formal evidence. According to theory, physiological or perceptual effects may influence contest behaviour directly, but motivational changes due to resource value are expected to manifest as behavioural adjustments only in interaction with attainment costs and resource benefits. Thus, we hypothesise that stressor-induced resource devaluations will impose greater effects when attainment costs are high, but not when resource benefits are higher. Noise may elicit such effects because it impacts the acoustic environment and imposes physiological and behavioural costs to animals. Therefore, we manipulated the acoustic environment using playbacks of artificial noise to test our hypotheses in the territorial male Siamese fighting fish, Betta splendens. Compared to a no-playback control, noise reduced defense motivation only when territory owners faced comparatively bigger opponents that impose greater injury costs, but not when territories also contained bubble nests that offer reproductive benefits. In turn, nest-size decreases were noted only after contests under noise treatment, but temporal nest-size changes relied on cross-contest variation in noise and comparative opponent size. Thus, the combined effects of noise are conditional on added attainment costs and offset by exceeding resource benefits. Our findings provide support for the hypothesised modulation of resource value under extrinsic stress and suggest implications for competition under increasing anthropogenic activity.

中文翻译：

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外在压力源调节资源评估：来自人工噪声下的地域性见解

人们认为竞争依赖于动物赋予资源的价值，但外在应激源对该价值的影响尚待探索。尽管自然的或人为的环境压力通常会导致竞争减少，但是这种依赖资源贬值的假设尚无正式证据。根据理论，生理或知觉效应可能会直接影响比赛行为，但是由于资源价值引起的动机变化预期仅在与获得成本和资源收益相互作用时才表现为行为调整。因此，我们假设，在获得成本高的情况下，压力导致的资源贬值将产生更大的影响，而在资源收益较高的情况下则不会。噪声可能会引起这种影响，因为它会影响声学环境，并给动物带来生理和行为上的损失。因此，我们使用人工噪声的回放来操纵声学环境，以在领土雄性暹罗斗鱼Betta splendens中检验我们的假设。与无回放控制相比，只有当领地拥有者面对相对更大的对手造成更大的伤害成本时，噪音才会降低防御动力，而当领地还包含提供生殖利益的泡泡巢时，噪音就不会降低。反过来，只有在经过噪音处理的比赛之后，才能看到巢大小的减少，但是暂时巢大小的变化依赖于交叉比赛中的噪音变化和相对的对手大小。因此，噪声的综合影响取决于获得成本的增加，并且可以通过超出资源收益来抵消。我们的发现为假设的外部压力下资源价值的调节提供了支持，并暗示了在人为活动增加下竞争的意义。