While litter size can affect many aspects of delivering and raising puppies, it doesn't actually affect the size of individual puppies. The parents' genes, the puppy's breed, and the mother's health and nutrition determine the puppy's size at birth. The dog's breed is the biggest determinant of litter size. In general, large dogs have larger litters because, biologically, they can safely carry more puppies.
Whether Fluffy has three or ten puppies depends largely on their breed. Some breeds are known to produce large litters, while others are more conservative. As a general rule, you should expect smaller litters in smaller dog breeds and larger litters in larger dog breeds. Breeders will tell you that they get larger litters if x, smaller litters if y, that they will never mate with a dog if z.
A mother at her best and at the peak of her reproductive age will be a mother most likely to have a large litter of healthy puppies, and as with any given breed of dog, a mother's litter those younger than two years old or one approaching the onset of old age will likely have a smaller litter. You may be planning a breeding and wondering how you can increase the litter size, or you may have already bred and wonder how you can figure out the litter size ahead of time. A dwarf or one or two noticeably smaller and weaker puppies are also more likely to appear in a large litter, but this may only be because the contrast between larger and stronger puppies and weaker puppies is more noticeable when there are many other puppies to compare them with. So to answer the question, no, dwarves aren't likely to be more aggressive than the other puppies in the litter.
The average number of puppies in a litter of German Shorthaired Pointer ranges from 8 to 12 puppies, but smaller and larger litters are expected. If a pregnant litter contains a very large number of puppies, more than the mother's body can physically support, it is likely that some of the offspring will not be born, but may be resorbed by the mother's body or born dead along with the rest of the litter alive and healthy. This study found that litter size was influenced by breed size, mating method, and dog age. Differential size at birth is largely a function of placental placement and other uterine factors, while final size is almost entirely a genetic function: a “dwarf” often traps or outperforms the rest of the litter, and the largest puppy may end up being the smallest adult.
Humans have control over certain aspects of when and how a dog is raised that can affect litter size, but there are limits. Large dogs tend to have larger litters, while small dogs tend to have smaller litters, most obviously because the size allows larger dogs to have more puppies safely. Secondly, knowing the number of litters beforehand can help reputable breeders determine how many puppies will go to their new homes. There are a number of different factors that contribute to the eventual number of pups in a given litter, and this is something that both veterinary professionals and dog owners discuss extensively.
