I understand that each animals respective environment and food supply contributes to its survival for certain amounts of time without food. But why? Wouldn’t it be beneficial for all animals to be able to go months or even years without food? Asking because I just saw a documentary on Nile crocodiles that feed around once or twice a year.
(I also understand that evolution is about reproduction and such, but if that’s the case, then why have varying capacities on how long an animal can survive without food?)
Life involves tradeoffs. For example, if you are weighed down by carrying more reserve energy, you are slower and more vulnerable to predators than your buddy who isn’t, and he will have more babies when you are dead.
Species evolve to carry whatever amount of energy stores, and at some point there is no advantage to having more that outweighs the disadvantages.
Two points:
Evolution doesn’t optimize for every possible beneficial traits. It just filters by what works. If a set of traits are good enough to persist, they probably will. If they aren’t, they won’t. Over long time periods, you’ll tend to drift towards being more optimized for an environment, but there’s no guarantee that any specific organism will ever develop any specific trait, even if it might be beneficial.
Second is that traits never really develop in isolation. There’s no variable that’s just “how long can you survive without food.” You need to take in enough food to offset your energy expenditure. Being able to go long periods without food generally means that you either go long periods without using much energy, or you can store a lot of energy for later use, or both.
But both of those have unavoidable physical consequences. Some body plans just inherently have higher baseline metabolic rates than others. Some strategies for survival require frequent expenditure of large amounts of energy. And carrying extra energy in, for example, fat stores means you have to physically carry around that extra bulk.
If something can reliably obtain enough food to operate at full capacity on a regular basis, it doesn’t really need to go long periods without eating. There’s no selection pressure for it. Would it be even better if it could operate exactly the same way except not need to eat as much? Sure, but generally speaking, that’s not physically possible to do.
It would need to change how it works and what it can do in order to add that extra ability, and frequently sacrificing things it’s good at in order to go longer without eating won’t necessarily help its survival. It may wind up impairing its ability to obtain food more than it extends the ability to go without, for example.
You've got it backwards. Evolution doesn't "dictate" anything. The environment does. The organisms best adapted to the environment thrive and reproduce more than those that aren't as well adapted.
In environments where food is scarce, organisms who would go longer periods of time without food had an upper hand, so they reproduced more and passed on the genes for those traits that let them go for long periods without food.
In an environment with plentiful food, there's no evolutionary pressure for that trait to be selected, and almost certainly a negative trade-off for that trait to be selected when it isn't necessary.
because feeding once or twice a year means you literally float around pretending to be a log the rest of the time.
If you move, you use energy. This includes thinking, and your heart beating, and a bunch of other stuff. Your only source of energy is your food. Evolution cant do jack about this fact.
So you can either choose, move less, or eat more. There is no "just do both."
in some rare situations its beneficial to not move and eat less.
But usually its better to move more and eat more.
Evolution isnt a 1 size fits all machine. it is a "what survives long enough to reproduce in this environment" machine. Its all about filling in gaps with good enough solutions. It doesnt even dictate things, it just finds out what works through trial and error.
I think an easier way to look at this is to say ok, what elements in a crocodiles existence would allow it to last a long time without food?
It's cold blooded, that lowers metabolism. They are big and the giant of their order. Generally the larger a species gets the lower it's metabolism is, brains take a lot of power and are kind of a fixed expense for species of similar type and intelligence. They are also semi aquatic, which generally lowers metabolism. Also they have fat reserves in various places, such as their tails, which provides energy when they don't have food available.
So you kind of take all of those elements and that's kind of how its able to survive. There is no why, what is, simply is.
Let's say you're a swallow. You eat tiny flying insects. They don't, individually, carry a lot of calories, so you need to eat a lot of them. But that's okay, because there are a lot of them, and they're easy to catch, since you're pretty good at tracking them and flying to keep up.
But you're not so good at storing energy in fat reserves - not compared with your cousin, anyway. Lucky b**d that he is, he only has to fly half the time you do.
Let's say you're an insect. Life is good, there's plenty of food, the only problem is there are a lot of giant kamikaze swallows around who snatch your cousins out of the air. You have a genetic glitch that makes you swerve suddenly whenever you're startled, so you've been able to survive so far. If you had brain 100 times smarter than an insect, you might appreciate this, but your brain just needs to help you find a mate and lay eggs in the next two weeks, which you do.
A hundred thousand years pass. You're a descendant of the swallow from the first paragraph. Lucky you're maneuverable in flight, since the insects are all a lot trickier nowadays. They dodge, they weave, they turn unpredictably. Your fat cousins couldn't keep up with that, and they starved to death 50,000 years ago. You're on the wing continually trying to get enough to eat, but you are, at least, alive.
How long an animal can go without food is directly related to how quickly it can act, how long it can sustain action, and how quickly it grows.
There are evolutionary advantages to being able to move quickly and sustain movement, and to grow fast.
But there are also evolutionary advantages to needing less food.
Different groups of animals have evolved to take advantage of both niches.
The animals that go weeks or months without food are generally cold blooded, that brings with it a big obvious advantage in that there's less pressure to eat more to survive but warm bloodededness brings with it a lot of advantages too. You as a warm blooded mammal have no idea how lucky you actually are not having to worry about just one day a fungal spore attaching itself to you, burrowing inside and then dissolving you from the inside out. We're simply too hot inside for that to happen, but that means we constantly need to eat a lot more for our bodies to maintain a warm internal temperature and, if we don't, we'll starve obviously.
Cold blooded animals have an advantage in not expending energy to warm themselves, that means they're less likely to starve in their environments, but look into frogs and amphibians in general facing massive extinction pressure (1/3 of amphibian species are threatened) from multiple factors but mainly the chytrid fungus which is running absolutely rampant. Hard to say warm vs cold blooded is "better", but each has their advantages and disadvantages.
One mistake you're making is thinking that evolution is about a species evolving to compete against other species, but the strongest competitor an animal needs to fight against are members of its own species.
If one cheetah can live longer without food than another cheetah, then it won't do him any good if the other cheetah catches all of the slow prey first because he's faster. He'll still starve.
So a species isn't just evolving to survive in the harshest conditions, it's also evolving to maximize acquisition and use of plentiful resources. If being able to survive longer without food requires a trade-off that makes it less competitive, it's going to be selected against. The tragedy of the commons predates humanity by billions of years.
You kind of covered it in your parentheses.
Other species didn't need to go that long without eating in order to reproduce, so they didn't evolve for it.
Beyond that your question about "why varying amounts" is the same as "why variable [anything]"? It's different the same reason any other trait is different. Different environment/conditions.
Here's my question back to you, question I often ask when people ask questions like why can't I eat all meat like a tiger or something like that...
Do YOU plan to live EXACTLY like a Nile crocodile?
🐊🐊 Do you plan to go into the river and lurk there for hours on end, barely moving at all, in order to have the calorie needs of a crocodile?
The cost of this comes in:
The TL;DR; is that nothing comes for free, and a lot of time the cost of such endurance is that you can't compete with the species that don't have this ability, that are optimized for the daily hunt.
Depends on how much energy one outputs on a regular basis. Crocodiles generally just float or sit in the same spot and then eat the nearest unsuspecting fool. Cats are another ambush predator that generally prefers waiting over chasing.
Ambush predators simply dont use much energy daily. Their meals go a very long way. Crocodiles eat HUGE animals whole so they get almost all the energy from their meal. Many other predators eat animals much smaller than themselves or dont eat the whole animal.
Humans and many other predators are hunters/seekers. We expend a great amount of energy just to eat one meal.
There's very little that can be done to reduce energy usage unless youre reducing movement and complexity of biology. There's a limit to how efficient metabolism can be. Not sure if we have hit it but clearly its not a trait that increases fitness significantly more than the efficiency we have now.
Also crocodiles are cold blooded and trade low capacity for exertion especially on cold environments for low dietary needs. Mammals need to eat a huge amount in comparison, but can be active all the time.
In addition to what others have said, it's worth mentioning for your specific example that crocodiles are ectotherms. Eating once or twice a year is pretty extreme, but the metabolic demands of an ectothermic organism are much lower than those of endothermic ones! So they're physiologically predisposed to developing that strategy.
Evolution isn't TRYING to make anything great.
Evolution is the process wherein random changes lead to some creatures performing better in an environment (longer life, more offspring) which cements those changes.
That's it.
Other animals don't have the semi hybernation state crocodiles live in, for the same reason crocodiles don't have the colourful wings of a butterfly.
Performing good enough to survive and pass on their genes, not necessarily better at anything. You can really see this in species where partner selection is influenced by arbitrary things like tail length (birds of paradise for example).
Yes. the "performing better" referred to longer life, or more offspring.
Thats all better is.
Tail length isn't arbitrary, it's animals using it as a primary or secondary sexual characteristic to choose a mate.
I think we are using the word arbitrary differently, but it doesn't matter. The point is evolution is driven as much by randomness as it is by selection. There are many kinds of drift.
See https://en.m.wikipedia.org/wiki/Genetic_drift