Wtf! That is so NOT fitness!

For several weeks now I have been doing in depth literature searches on different topics. Today I began my literature search on plant body size and fitness, and I’m having some issues with how people define “fitness”. Let’s look at how some common sources define fitness. In fact, let’s do a simple google search for “define: fitness”- take a look below. The image is a bit small so google this yourself and follow along with my red marks.

Figure 1: Google search for "define:fitness"

Ok, well clearly we aren’t talking about monthly based women’s health magazines or our abilities to “traverse the seas” (whatever that means...). But take a look at the definitions with check marks beside them. 

I guess Wikipedia is more reliable then we think. It tells us the definition of fitness is:

“Fitness (often denoted in population genetics models) is a central idea in evolutionary theory. It describes the capability of an individual of certain genotype to reproduce, and usually is equal to the proportion of the individual's genes in all the genes of the next generation”

Those pesky, but apparently rather bright Americans tell us that fitness is (USDA):

“The ability to survive to reproductive age and produce viable offspring; fitness also describes the frequency distribution of reproductive success for a population of sexually mature adults”

Ok! Perfect! So we understand what fitness is, right? It’s measured by the ability of one individual to transmit its genes into the next generation. GENES= VIABLE OFFSPRING! Like... real living things that can reproduce themselves. Imagine you had a child... a living, breathing child! That’s fitness! The more children you have that are capable of reproduction, the higher your fitness is! I think I made my point. 

It may seem clear to us now what fitness actually is, but apparently a large portion of the plant ecology community thinks it is ok to make direct conclusions about fitness based on data that has little or even NOTHING to do with fitness. 

Common Mistakes

If there is one area of plant ecology that has been done and done and done again, then done and done and re-done and essentially killed, it’s the relationship between the amounts of vegetation a plant allocates to growth versus the amount of vegetation it allocates to reproduction, otherwise known as reproductive allocation (bet you never would have guessed that’s what it’s called, eh). I think I have read 50 papers in the last week that I thought would be about reproductive size threshold (aka what I am interested in)... that really ended up being another rehashing of this ridiculous reproductive allocation stuff. 

Another really irritating thing throughout these papers is the synonymous use of the term reproductive effort with reproductive output. Reproductive output is definitely a decent measure of fitness. Measuring reproductive output and thus fitness in humans is a bit different than plants. You can monitor a man and see how many women he impregnates- that’s creepy but feasible I suppose. However, in the wild when a plant disperses its seeds, you can’t really keep track of where they all go, and how many will be viable. To make this easier to understand, let’s return to the idea of monitoring people having sex...x-rated blog today I know. You monitor who a man sleeps with and you can get a pretty good idea of who he impregnates and how many babies each woman will give birth to. In the plant world, this is similar to counting all the seeds of the plants before they disperse them. Although there is no chance all of them will live, it gives you an idea of the maximum, and the chances of at least one of those successfully living is pretty high. 

Reproductive effort however is known as the proportion of total resources invested in some seed or reproductive organ production. Reproductive effort... I have no idea how to compare this to a human. Well....we have a plant for example it says “oh I’m going to allocate 30% of my resources to reproduction” -maybe that’s the same as someone saying “ I want to get pregnant but I need energy for other things so I’ll have sex twice a week”... maybe that’s stretching it a bit. Still, however you look at it, reproductive effort cannot be interchanged with reproductive output. And the number of times you have sex per week has nothing to do with your fitness... keep that in mind, guys. 

I won’t use any specific examples in case I one day end up crossing paths with one of these people, I honestly have no idea how I would fair in a fight, but I will provide some general examples of this from the literature-many people assume the same things:

-Dumb Plant Ecologist 1: Omg! If a plant allocates more vegetation to reproduction that means it has higher fitness. 

-Me (Smart Plant Ecologist): No, it doesn’t. Think about fitness. That’s not a measure of fitness at all! You need some measure of an output in there... fecundity maybe? You cannot translate how much you allocate to reproduction into fitness. 

-Dumb Plant Ecologist 2: Bigger plants have higher reproductive effort, so they have more offspring! Higher fitness!

-Me (Smart Plant Ecologist): Sorry. Trying reaaaaallllly, reaaaaalllllly hard to produce offspring and putting more resources into your efforts does not give you higher fitness by definition. Go read Chambers and Aarssen- that might clarify things for you.  In fact, for those of you who haven’t... if you want a real, natural experiment that is BANG ON in how it describes and predicts fitness check out my blog post about bigger not being better!

I think it’s time I end my rant about fitness, which somehow got intertwined with promiscuous males and such. I really wrote this blog to open people’s eyes to not believing everything you read. It’s funny how many times I cited these papers in my undergrad thesis and really, they weren’t what I was looking for at all, because of how they defined that one word: fitness. I’m just glad I can now say with certainty when I defend my Master’s that my measures of fitness (which are TBA still but soon won’t be) are correct. And now if any of you ever question what is and isn't a measure of fitness... you can say with certainty "Wtf! That is so NOT fitness!"