Kenneth Farris

Document Type

Honors Thesis

Major

Zoology

Advisor(s)

Brian Olsen

Committee Members

Sabrina DeTurk, Jacquelyn Gill, Michael T. Kinnison

Graduation Year

May, 2025

Publication Date

2025

Abstract

The Niche Variation Hypothesis (NVH) states that an individual is limited in their ability to utilize the entirety of the population niche. This means that a population niche is not reflective of what an individual can utilize, but only a cumulation of all individual niches within it. This theoretical framework is key for modeling niche evolution, which requires the description of population-level means as a function of individual variation. When it was first introduced in 1965 the NVH was ultimately rejected by papers that had poor proxies and definitions of variation. The original studies in support of the NVH also benefited from examining populations with high intraspecific competition, which have increased between-individual variation as a means of niche partitioning, making the NVH more detectable. Eventually, as the use of proxies became more precise and accurate, the NVH was rejuvenated. I argue that with a greater focus on behavior, the niche variation hypothesis can be even more helpful in predicting niche evolution. Many published niche proxies (e.g., isotopic analysis, gut content, or morphology) are measurements of diet, which is directly impacted and controlled by behaviour. Reframing niche definitions around foraging behaviour instead of diet will allow us to use a wide range of niche proxies to investigate NVH and define the expected accuracy of each proxy as a function of its direct consequence of behaviour. To circumvent even more inaccuracy a direct examination of foraging behaviour should be implemented whenever possible. Another benefit of the use of behaviour is its relationship with niche evolution. Behavioural drive posits that for a morphological or physiological trait to change there may first have been a behavioural change that altered the selection pressure on the trait in question. While behaviour may seem to be an incredibly plastic trait, which would decrease the levels of between-individual variation, there are many behaviours that are both consistent and heritable (e.g., migration routes, aggression, exploration, or reactivity). The consistency of these behavioural traits and the effects of behavioural drive means that behaviour is both instrumental for niche evolution and is the best metric for investigating the NVH. Studies using the NVH as a framework and interindividual behavioural variation as the primary metric can become the cornerstone of our understanding of how niches evolve.

This manuscript is neither a comprehensive literature review nor a meta analysis. I instead discuss a select collection of papers aimed at supporting the development of more successful niche evolution models given the history of the niche variation hypothesis.

Download

Share