Humans have a huge variation in physical ability because of exercise differences. Olympic athletes are a number of times stronger than average people on the street. It seems that variation in animals is very small, but I am wondering if one could force an animal to follow a specific program and eat specific food to get a lot stronger, agile, etc. than an average animal of the same species.
When I visited the Cheetah Outreach Center in South Africa, the guides there told us that their captive cheetahs couldn't run nearly as fast as wild ones, and that wild ones were much more muscular than the ones in the center; their point was that actually having to run full-out or starve caused much more rigorous training than occasionally jogging after a fake rabbit on a string. That's supported by this article:
The cheetahs being studied didn’t come close to the speeds reported for wild cheetahs — the zoo animals reached 38 mph (61 kph), while the greyhounds topped out at 43 mph (68 kph).
The researchers said this was probably because the captive-born cheetahs have never really gotten the chance to let loose in the wild and run full throttle.
"They have lived in a zoo for several generations and have never had to run to catch food. They have probably never learned to run, particularly," Wilson said.
Can animals train to be noticeably stronger, faster, more agile.. than other animals of the same species?
Yes, of course!
Humans are animals, so yes! But even in non-human animals. You can look for example in a tutorial on how to train a dog (or a horse) for specific skills (speed, high jump, long jump, etc...).
It seems that variation in animals is very small
Such a general statement can only be wrong. Consider dogs as an example. The fastest dogs go at 72 km/h (~45 mph) while many dog breeds barely reach 5 km/h (~3 mph; and they're all considered as the same species). So, there is a lot of genetic variation among dogs.
Now when it comes to variation caused by training it is a little harder to estimate. Consider having a look at Guy and Snow (1977), McKeever et al. (1987), Evans and Rose (1987) and Rivero and Piercy (2008). For what it is worth, note for example that trained racing horse can go up to 70km/h while most horses can go only up to 40-45 km/h. There are a number of studies showing the effect of training on horses.
Definitely when it comes to horses. They are selectively bred for generations to work in different sports: dressage, show jumping, endurance, racing and so on. As one example: to train a horse for olympic level dressage takes ten years or more in order to build muscles and coordination.
Some example of horse sports, several of them describes how horses are trained: https://en.wikipedia.org/wiki/List_of_equestrian_sports#Olympic_disciplines
Wild animals may have less variation in traits such as speed of running, if they predominantly eat similar diets, and if the slow ones are regularly getting eaten and failing to breed. Wild animals likely run at around the optimal speed for their environment.
The process of training implies some level of domestication - humans protecting the animals, perhaps modifying their diet, and expecting them to perform a service in return. In this situation, the animal's day-to-day activities would likely change, together with the change in diet. Animals' physiology tends to be able to change substantially in response to these kinds of environmental and behavioural changes (phenotypic plasticity).
So I guess the answer is yes to whether animals can be trained to perform differently, but the question of whether they would want to is maybe open.
There are actually two questions here:
- Can animals train to be noticeably stronger, faster, more agile... than other animals of the same species?'
As a couple of others have stated, yes. This is, in fact, evident in horse racing, dog racing, dog agility course competitions, and a few other similar competitions. If animals couldn't be trained to become stronger/faster then those sports would not exist as they are.
- Is there natural variation in strength/agility/speed/etc in animals they way there is in humans?
This question is implied by your statement "It seems that variation in animals is very small..." In fact, statistical analysis asserts that virtually every measurable difference between organisms falls on a Normal Distribution (see also Bell Curve). However, this only works if we compare like populations, or "apples with apples". For example, I certainly would not compare a bull dog's running speed with that of a whippet (racing dog similar to a greyhound, and a cool Devo song). But if I compared all whippets then they would be normally distributed. Now, if I had a trained whippet vs a non-trained whippet then we are again going to run into problems (see point 1).
Here is the thing with the normal distribution though, 68% of the population lies within 1 standard deviation of the average. This means that over 2/3 of the population is pretty close to average. Further, 95% of the population lies within 2 standard deviations of the average.
Here is a slightly more realistic example of this: The average height of men worldwide is roughly 5'10" and the standard deviation is roughly 3". Thus 68% of men worldwide are between 5'7" and 6'1" tall. (Yes, I'm rounding these numbers a bit but you get the point.) You can do something similar with weight, strength, etc, though certain attributes are difficult to measure.
What does this really mean? Well, the natural speed of say a cheetah in the wild is normally distributed. That is, if we could measure them all. However, in the wild, not all cheetahs survive. As part of survival, only the fastest and strongest survive so what we actually have is a much smaller set. This is why animals might appear to have less variation.
If you look then you can see the variations in nature. Go to a park and stop and look at the pigeons. Some are actually quite fat while others are not.