Optimism and pessimism: a concept for behavioural ecology

Abstract

Originating from human psychology, the concepts of "optimism" and "pessimism" were transferred to animal welfare science about 20 years ago to study emotional states in non-human animals. Over time, "optimism" and "pessimism" have developed into valuable welfare indicators, but little focus has been put on the ecological implications of this concept. Here, we aim to bridge this gap and underline the great potential for transferring it to behavioural ecology. We start by outlining why "optimism" and "pessimism" can be considered as aspects of animal personalities. Furthermore, we argue that considering "optimism"/"pessimism" in a behavioural ecology context can facilitate our understanding of individual adjustment to the environment. Specifically, we show how variation in "optimism"/"pessimism" can play a crucial role in adaptation processes to environmental heterogeneity, for example, niche choice and niche conformance. Building on these considerations, we hypothesise that "optimists" might be less plastic than "pessimists" in their behaviour, which could considerably affect the way they adjust to environmental change.

Keywords: animal personality; environmental change; individualised niche; optimism; pessimism; phenotypic plasticity.

Fig. 1

Principle of a judgement bias test for animals (modified after Mendl et al., 2009). CS+, conditioned stimulus indicating positive outcome; CS−, conditioned stimulus indicating negative outcome.

Fig. 2

“Optimism”/“pessimism” within an ecological framework. An individual may interpret an ambiguous situation in a biased way, leading to an either “optimistic” or “pessimistic” behavioural response. This response is dependent on environmental conditions, for example predator density in the habitat. The response can either constitute a match or a mismatch with the actual environment, resulting in positive or negative fitness consequences. Note that there is an asymmetry of costs and benefits in this simplified example: A false “optimistic” response would be much costlier than a false “pessimistic” one.