Can animals train to be noticeably stronger, faster, more agile... than other animals of the same species?
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.