Fitness is foundational for our understanding of ecological responses. Fitness allows researchers to describe how successful an organism is in its environment. It is often described as an organism’s contribution to the next generation through survival and reproduction, but exactly how fitness is defined or measured is not strictly laid out and differs greatly between researchers. Such a vital concept being poorly measured or defined can muddle it to the point of uselessness. In order to investigate the use of the concept of fitness, I performed a meta-analysis and asked, (1) How is fitness defined and used by researchers? (2) Are all measures of fitness created equal? Through an article analysis, I was able to see how researchers in the fields of ecology and evolutionary biology define, use, and measure fitness. I did this by reading 522 papers published between 2012-2016 in the Web of Science categories of ecology and evolutionary biology. In addition, through an experiment using garden peas, I was able to determine a plant’s change in biomass and allocation in response to a gradient of nutrient concentration and potting media, as well as the relationship between biomass and reproductive yield.
Results/Conclusions
In a preliminary analysis of the journal articles, fitness was only defined 36% of the time. There were 29 different definitions of fitness though only 3 were common (found in >5% of papers). In my experiment, two common plant fitness measurements, biomass and reproduction, are unimodally related. While this means that fitness is indeed a function of vegetative biomass, the unimodal relationship means that: 1) the plants with the most reproductive output are intermediate in size, and; 2) for any unique amount of reproduction there is both a small and a large plant with identical reproductive output. Two things emerge from the meta-analysis and the experiment: first, one must be clear about the expected relationship between proxy measurements and fitness, as it may not be linear. Second, we do not advocate any one definition of fitness over another, but we think that given the many definitions that exist, researchers should be clear about which one they are using.