Lit Review, 2. Assessment Strategies: The Central Debate

The central debate in the study of animal contests revolves around the assessment strategies employed by contestants. The two primary strategies discussed in the literature are mutual assessment and self-assessment (Arnott & Elwood, 2009). In mutual assessment, contestants gauge their own fighting ability or resource holding potential (RHP) relative to that of their opponent, and the contest outcome is determined by the difference in RHP between the two contestants (Enquist & Leimar, 1983). Conversely, in self-assessment, contestants make decisions based solely on their own RHP, without considering their opponent's abilities (Taylor & Elwood, 2003; Mesterton-Gibbons, 2019).
While mutual assessment was initially assumed to be the primary mechanism in animal contests, recent evidence suggests that self-assessment strategies may be more prevalent (Payne, 1998; Arnott & Elwood, 2009; Fawcett & Mowles, 2013). Fawcett & Mowles (2013) argue that complex cognitive mechanisms are not required for animals to base their contest decisions on their own or their opponent's fighting ability, and that simple mechanisms can account for observed patterns of contest behavior. They also suggest that the sequential assessment model (SAM), which assumes mutual assessment, may not always accurately represent the actual decision-making processes used by animals.
Critics of the mutual assessment paradigm argue that many studies have relied on correlational analyses of contest duration and RHP measures, which can lead to spurious conclusions about assessment strategies (Taylor & Elwood, 2003; Arnott & Elwood, 2009). These methodological challenges will be discussed in more detail in Section 3.
As alternatives to mutual assessment, several self-assessment models have been proposed, including the War of Attrition (WOA; Maynard Smith, 1974), the Energetic War of Attrition (E-WOA; Payne & Pagel, 1996; 1997), and the Cumulative Assessment Model (CAM; Payne, 1998). The CAM suggests that contestants accumulate costs during a contest and make decisions based on individual cost thresholds, without directly assessing their opponent's RHP. These models propose that contestants make decisions based on their own RHP and the costs they accumulate during the contest, without directly assessing their opponent's abilities.
Recent perspectives have suggested that assessment strategies may not be mutually exclusive and that animals may use a combination of self-assessment and mutual assessment depending on the context and the information available (Chapin et al., 2019; Briffa et al., 2020). This idea of a continuum of assessment strategies is supported by theoretical work, such as the game-theoretic model proposed by Mesterton-Gibbons (2019), which explores the variation between self-assessment and mutual assessment strategies.
In addition to the assessment of an opponent's RHP, the role of resource assessment in contest decisions has been increasingly recognized (Arnott & Elwood, 2009). Resource value can influence the costs that animals are willing to incur in a contest, and the integration of resource assessment with self and opponent assessment adds another layer of complexity to the study of animal contests.
In conclusion, while mutual assessment has been a dominant paradigm in the study of animal contests, recent evidence suggests that self-assessment strategies may be more prevalent than previously thought. The debate between mutual assessment and self-assessment has led to a more nuanced understanding of the potential for a continuum of assessment strategies and the role of contextual factors in shaping contest dynamics. The following sections will explore the empirical approaches used to test these alternative models (Section 3) and the various factors influencing contest decisions (Section 4), before considering the application of contest theory to group and social contexts (Section 5).