Conceptualizing and quantifying body condition using structural equation modelling: A user guide

Area of Science:

• Ecology
• Evolutionary Biology
• Behavioral Ecology

Background:

• Body condition is crucial in ecology, evolution, and conservation, often used as a proxy for individual performance and environmental impact.
• Current research typically uses univariate measures (e.g., fat storage) for body condition, overlooking its multidimensional health aspects (nutritional, immune, hormonal).
• Analyzing multivariate body condition presents statistical challenges, limiting comprehensive assessments.

Purpose of the Study:

• To introduce and explain Structural Equation Modelling (SEM) as a robust analytical tool for assessing the multivariate nature of body condition.
• To demonstrate SEM's utility in addressing challenges like variable reduction, conceptualization, and modeling condition-performance relationships.
• To compare SEM's predictive power against conventional statistical methods for body condition analysis.

Main Methods:

• Application of SEM to a real-world case study on body condition.
• Development of R-code examples for practical implementation of SEM.
• Comparative analysis of SEM against multiple regression and principal component analysis (PCA) using empirical data.

Main Results:

• SEM effectively handles the multidimensional aspects of body condition, enabling variable reduction and conceptualization.
• SEM allows for specifying relationships between body condition metrics and performance indicators, facilitating hypothesis testing.
• SEM demonstrated higher model performance, yielding more accurate and precise estimates than multiple regression and PCA.

Conclusions:

• SEM provides a flexible framework for analyzing the multivariate nature of body condition, enhancing our understanding of its impact on biological processes.
• SEM improves the predictive value of body condition proxies for organismal performance.
• The SEM approach is applicable to other multidimensional ecological concepts, including immunocompetence and environmental conditions.