Lit Review, 3. Empirical Approaches to Studying Assessment Strategies

Empirical studies of assessment strategies in animal contests have employed a variety of methodological approaches to test the predictions of different theoretical models. However, these approaches come with their own considerations and challenges. This section will review the main empirical methods used to study assessment strategies, discuss their limitations, and highlight recent frameworks and meta-analytical techniques that offer new avenues for analyzing contest data.
One of the most common approaches has been to examine the relationship between contest duration and measures of resource holding potential (RHP), such as body size or weapon size (Taylor & Elwood, 2003; Arnott & Elwood, 2009). However, these correlational analyses can be problematic and may not accurately reflect the assessment strategies used by the animals. Taylor & Elwood (2003) demonstrated that a negative relationship between RHP difference and contest duration, often considered evidence for mutual assessment, can arise even when contestants only assess their own RHP.
To address these challenges, several authors have proposed alternative approaches. Taylor & Elwood (2003) suggest examining the relationships between contest duration and winner and loser RHP separately, rather than relying on composite measures of RHP difference. Briffa & Elwood (2009) argue that staged contests between size-matched individuals can provide a more powerful tool for studying assessment strategies, as the correlational approach is only valid when opponents are randomly matched. Arnott & Elwood (2009) recommend using experimental manipulations of RHP components to test the predictions of different assessment models and focusing on examining the contest dynamics and behavior of both winners and losers, rather than relying solely on contest duration.
Recent frameworks offer new avenues for analyzing and interpreting contest data. Chapin et al. (2019) introduce a repeated-testing approach that allows for the identification of individual-level variation in assessment strategies within populations. This approach recognizes that assessment strategies can vary within individuals and across contexts, providing a more nuanced understanding of contest dynamics. Briffa et al. (2020) demonstrate how ternary plots can be used to visualize the relative contribution of self-assessment, opponent assessment, and resource assessment in contest decisions. These plots offer a novel way to represent the multidimensional nature of assessment strategies and to compare strategies across different taxa and contexts.
Meta-analytical approaches have also been used to test predictions of different assessment models across species. Pinto et al. (2019) compiled data from 36 species and examined the relationship between contest duration and winner and loser RHP, as well as the relationship between escalation patterns and RHP asymmetry. Their results provided stronger support for self-assessment strategies than mutual assessment. Vieira & Peixoto (2013) conducted a meta-analysis of contest studies in arthropods, highlighting the need to control for differences in resource value and prior experience when investigating RHP asymmetries.
Empirical studies of assessment strategies have been conducted across a wide range of taxa, providing insights into the prevalence of different strategies:
# Invertebrates: Studies on crustaceans and insects have been particularly informative. For example, Payne (1998) proposed the cumulative assessment model (CAM) based on work in the portunid crab Necora puber, suggesting that contestants assess their own state and the damage inflicted by their opponent during the contest.
# Fish: Studies on various fish species have provided evidence for both mutual and self-assessment strategies. Morrell et al. (2005) investigated assessment strategies in the fiddler crab Uca mjoebergi, finding support for mutual assessment, as contests were more likely to escalate when size asymmetry was low.
# Reptiles and amphibians: Reichert & Quinn (2017) manipulated the acoustic signals of male gray tree frogs to test the role of mutual assessment in territorial contests.
# Mammals: Studies on mammals have been less common but have provided some insights into assessment strategies. For example, Jennings et al. (2012) investigated assessment strategies in fallow deer, finding evidence for mutual assessment based on the relationship between contest duration and winner and loser RHP.
Incorporating contest dynamics and temporal patterns has been a key focus in empirical studies of assessment strategies. Examining the temporal dynamics of contests, such as changes in the intensity or frequency of aggressive behaviors over time, can help distinguish between different assessment models (Briffa & Elwood, 2009; Palaoro & Peixoto, 2022). The cumulative assessment model (CAM) proposed by Payne (1998) emphasizes the importance of considering the temporal dynamics of contests, as the relative importance of self-assessment and opponent-inflicted damage may change over the course of the interaction.
In conclusion, empirical studies of assessment strategies have employed a range of methodological approaches to overcome challenges and distinguish between different models. By combining experimental manipulations, detailed behavioral analyses, physiological measurements, and meta-analytical techniques, researchers have gained insights into the assessment strategies used by a variety of taxa. Incorporating contest dynamics and temporal patterns can further enhance our understanding of how animals gather and use information during contests. Future research should focus on developing more rigorous experimental designs, controlling for potential confounding factors, and integrating multiple approaches to provide a more comprehensive understanding of assessment strategies in animal contests.