Lit Review, 4. Factors Influencing Contest Decisions

Beyond the core components of fighting ability (resource holding potential, RHP) and assessment strategies, a rich array of factors shape the strategic decisions animals make during contests. These include resource value perception, cognitive abilities and limitations, prior fight experiences, individual personality differences, morphological variation in weapons, and diversity in fighting styles. Accounting for these factors and their interactions with each other and with RHP asymmetries is crucial for building a comprehensive understanding of animal contest dynamics and evolution.
Resource Value Assessment
A key determinant of contest behavior and outcomes is the value each individual places on the contested resource. Contestants evaluate both RV and RHP asymmetries when deciding how to invest in a fight (Arnott & Elwood, 2008). An individual's subjective resource valuation can vary based on its physiological state, such as hunger or reproductive condition (Arnott & Elwood, 2008; Elwood & Arnott, 2012). For example, female dung beetles in superior breeding condition fight more aggressively for access to dung (Moczek, 1998). Resource value often interacts with fighting ability in complex ways. When RHP differences are small, RV tends to have a stronger influence on contest dynamics and outcomes. However, when RHP asymmetries exceed a certain threshold, the superior individual may win regardless of RV (Beacham, 1988; Dugatkin & Ohlsen, 1990). Effectively modeling animal contest decisions and outcomes therefore requires a nuanced consideration of the behavioral impacts of RV asymmetries and their relationship to RHP differences.
Cognition and Emotions
Cognitive processes and emotional states are increasingly recognized as important mediators of contest behaviors and decision rules. Information gathering and assessment during fights rely on cognitive abilities like perception, learning, memory, and opponent recognition (Reichert & Quinn, 2017). However, the level of cognitive sophistication required for different assessment strategies remains debated. Some argue that mutual assessment of fighting ability is too cognitively demanding for many species (Elwood & Arnott, 2012), while others suggest it could arise from relatively simple rules of thumb (Fawcett & Mowles, 2013). Cognitive performance during contests likely emerges through an interaction between an individual's cognitive abilities and contextual factors like stress and motivation (Reichert & Quinn, 2017).
Emotional state changes are also increasingly viewed as a key regulator of contest dynamics (Crump et al., 2020). Affective responses to contest events and appraisals of RHP, RV, and fight progress may guide strategic decisions via their effects on aggressive motivation and valence perception (Crump et al., 2020). Losers may experience a negative affective state akin to anxiety that promotes disengagement, while winners experience a positive state reinforcing aggressive persistence. Linking contest theory to concepts from animal cognition and emotion research is a promising direction for better understanding the proximate drivers of fighting behavior.
Winner-Loser Effects
An individual's prior fight record has a well-established influence on its subsequent contest performance via winner and loser effects. Victorious individuals tend to fight more aggressively and enjoy elevated chances of winning again in the near future, while losers become more submissive and likely to lose again (Hsu et al., 2006). Importantly, even a single fight outcome can measurably shift future behavior and success (Mesterton-Gibbons & Hardy, 2013). For instance, Mongolian gerbils with just one winning experience persisted longer in contests compared to naive individuals (Mesterton-Gibbons & Hardy, 2013). Winner-loser effects may arise through a combination of changes in actual fighting ability (e.g., injuries), information state about one's own RHP, endocrine responses, and cognitive-affective appraisals (Hsu et al., 2006; Crump et al., 2020). The duration of these effects varies between species and contexts, but they can help establish or maintain dominance hierarchies. How winner-loser effects accumulate over an individual's lifetime and fighting history to influence its assessment strategies remains an open question. As a feedback mechanism connecting past outcomes to future fighting decisions, winner-loser effects are an essential component of contest dynamics warranting further theoretical and empirical study.
Personalities and Morphological Variation
Consistent individual differences along behavioral axes like aggression, boldness, and sociality comprise animal personalities that can shape contest dynamics (Briffa et al., 2015). Aggressive and proactive behavioral types may be more motivated to initiate and escalate contests independent of RHP asymmetries. In hermit crabs, bolder individuals that recovered faster from startling were also more likely to initiate and win fights (Courtene-Jones & Briffa, 2014). Personality variation can thus generate differential likelihoods of escalation and persistence between contestants, and interact with RHP differences and winner-loser effects to affect fight outcomes.
Morphological traits used as weapons are another important source of individual variation in fighting behavior and ability. Variation in overall body size and weapon size can directly generate RHP asymmetries between opponents. Crucially though, the magnitude of a weapon's impact on fighting performance depends on how it scales with body size (Palaoro & Briffa, 2017). Weapons that exhibit positive allometry and disproportionately increase in size or striking power at larger body sizes violate the assumption of constant costs in many contest models. Accounting for the nonlinear effects of realistic weapon scaling relationships on RHP will be vital for predicting contest dynamics and trajectories (Palaoro & Briffa, 2017).
Fighting Style Diversity
Finally, diversity in fighting styles, both between and within species, introduces further complexity to contest dynamics. Species vary in their principal mode of agonistic engagement, such as striking, wrestling, biting or pushing, based on how their weapons and defenses are specialized (Palaoro & Peixoto, 2022). Contest dynamics will differ depending on whether a species relies more on displays or physical attacks to resolve conflicts (Palaoro & Peixoto, 2022). Species or individuals employing fighting tactics that can effectively counter the opponent's will likely have an advantage. This creates an intransitive ('rock-paper-scissors') dynamic where the relative efficacy of fighting styles matters more than differences in absolute fighting abilities. Even within a species, finer-scale behavioral patterns expressed during contests (e.g., displays, feints, attacks, blocks) may be important in opponent assessment, and their diversity and transition dynamics are an under-explored aspect of contest progression and resolution.
Conclusion
Integrating the multifaceted effects of resource value perception, cognitive abilities and constraints, prior fight experiences, individual personality differences, morphological variation in weapons, and the diversity of fighting styles into contest theory will be crucial for explaining variation within and between species in fighting behavior and decision rules. These factors interact with each other and with RHP asymmetries in complex ways to shape the information gathering, strategic decision making, and performance of individuals during fights. Studying their effects empirically across taxa and contexts, and incorporating them into theoretical models, is key to building a more comprehensive and predictive understanding of animal contest dynamics.
An exciting challenge is to unify these largely disparate bodies of knowledge into an integrative framework of contest decisions and outcomes. Achieving this will require drawing upon concepts and tools from research fields such as animal cognition, physiology, and morphology to enrich contest theory in interdisciplinary ways. For instance, as Reichert & Quinn (2017) propose, contest models could better capture the cognitive processes underlying fighting behavior by incorporating perception constraints, valuation and memory mechanisms, and speed-accuracy trade-offs. Considering additional layers of biological complexity, from gene expression changes to whole-organism performance capacities, could help elucidate the proximate pathways by which various internal and external factors influence an individual's fighting decisions and ability (Briffa & Lane, 2017). There is ample opportunity to expand contest models to encompass an array of understudied taxa, contexts, and fighting style combinations. By striving to reflect the true multidimensional complexity of animals' information processing and behavioral regulation, we can move toward a more holistic and realistic theory of conflict resolution in the natural world.