[Paper Review] Eco-evolutionary "fitness" in 3 dimensions: absolute growth, absolute efficiency, and relative competitiveness

Joanna Masel|arXiv (Cornell University)|Jul 3, 2014

Evolutionary Game Theory and Cooperation65 references3 citations

TL;DR

This paper proposes a three-dimensional framework for eco-evolutionary fitness by integrating absolute growth (r), absolute efficiency (K), and relative competitiveness (c), disentangling these previously conflated traits. It reinterprets r/K-selection theory to resolve contradictions in ecological and evolutionary models, providing a unified model that supports Grime's universal adaptive strategy theory through a geometric rotation of the fitness space.

ABSTRACT

Competitions can occur on an absolute scale, to be faster or more efficient, or they can occur on a relative scale, to "beat" one's competitor in a zero-sum game. Ecological models have focused on absolute competitions, in which optima exist. Classic evolutionary models such as the Wright-Fisher model, as well as more recent models of travelling waves, have focused on purely relative competitions, in which fitness continues to increase indefinitely, without actually progressing anywhere. This manuscript proposes a new way to describe both at the same time. It begins with a revised version of r/K-selection theory. r continues to describe maximum reproductive speed, but the new version of K, with a different subscript, now describes parsimoniousness in territory use, a group-selected, anti-tragedy-of-the-commons trait. A third dimension c of fitness is then added to this novel system, one which is unitless and normalized, and hence capable of capturing the population genetics concept w of a strictly relative, genetically-limited competitive race. MacArthur's original version of r/K-selection theory is shown to confound parsimoniousness K with competitive ability c, despite the fact that available data suggests a negative correlation between the two; here they are disentangled. A rotation of the resulting three-dimensional system provides a population genetic underpinning for Grime's universal adaptive strategy theory of ruderals (selected for high r), stress tolerators (selected for a combination of high r and high K), and competitors (selected for a combination of high r and high c).

Motivation & Objective

• To resolve the conceptual conflict between ecological models emphasizing absolute performance and evolutionary models focused on relative competitive advantage.
• To disentangle the historically conflated traits of K-selection (efficiency) and competitive ability (c) in r/K-selection theory.
• To provide a geometric, three-dimensional representation of fitness that integrates ecological and population genetic perspectives.
• To offer a theoretical foundation for Grime's universal adaptive strategy theory using a rotated fitness space.
• To formalize the concept of fitness in eco-evolutionary dynamics by introducing a unitless, normalized competitive metric (c).

Proposed method

• Reformulates r/K-selection theory by redefining K as a measure of parsimonious territory use, distinct from competitive ability.
• Introduces a third dimension, c, representing relative competitiveness, normalized and unitless to align with population genetics fitness (w).
• Constructs a three-dimensional fitness space with axes r (absolute growth), K (absolute efficiency), and c (relative competitiveness).
• Applies a geometric rotation to the 3D fitness space to align with Grime's ruderal, stress-tolerator, and competitor strategies.
• Uses mathematical modeling to demonstrate that the new framework resolves inconsistencies in prior models, particularly the negative correlation between K and c.
• Employs population genetics principles to ground the relative fitness metric c in evolutionary dynamics.

Experimental results

Research questions

• RQ1 How can ecological fitness, defined by absolute performance, be reconciled with evolutionary fitness, defined by relative competitive success?
• RQ2 Why has the traditional r/K-selection model failed to account for the observed negative correlation between K and c?
• RQ3 Can a three-dimensional fitness framework unify ecological and evolutionary perspectives on fitness?
• RQ4 How does the new model support or extend Grime's universal adaptive strategy theory?
• RQ5 What is the mathematical and biological role of the normalized, unitless competitive metric c in fitness dynamics?

Key findings

• The paper successfully disentangles K (efficiency) from c (competitive ability), resolving a long-standing conceptual confusion in r/K-selection theory.
• The three-dimensional fitness space, with axes r, K, and c, provides a geometric framework that captures both ecological and evolutionary fitness dimensions.
• The model demonstrates that the negative empirical correlation between K and c is biologically plausible and not a contradiction when properly separated.
• A rotation of the 3D fitness space aligns the axes with Grime's three universal strategies: ruderals (high r), stress tolerators (high r and K), and competitors (high r and c).
• The normalized competitive metric c provides a direct population-genetic interpretation of fitness (w), bridging ecological and evolutionary theory.
• The revised framework supports the existence of evolutionary optima in ecological contexts while preserving the relative fitness dynamics central to population genetics.