Pernese biomes have been profoundly affected by the cyclical appearance of Thread, a spore which destroys organic material. This has resulted in a relative dearth of terrestrial plants and animals. However, as Thread drowns in water, Pern has a much more populous and thriving aquatic ecology.
Pernese biomes contain both indigenous Pernese flora and fauna and introduced species from other worlds -- primarily Earth. (The original EEC team found that there was very little biodiversity, meaning that the colonists, coming two hundred years later, brought flora and fauna species with them.)
The original Pernese Settlers brought a wide variety of animals and plants with them when they originally settled the planet. However, due to both the disastrous threadfall and the natural Pernese landscape, some animals never adapted at all. Deer and other forest-dwelling animals did not fare well in Pern's warm, tropical climate. Other animals required "genetic adaptation" but survived in some form or another.
The stores of ova and sperm aboard the ships were extensive. Any variety of any species that the biogeneticists had thought would prosper on the new world was included. Animal host mothers, some cows and goats of small but sturdy genotypes, were shipped frozen from Earth to Pern and revived to bear fertilized ova of nearly all the larger animals brought from the Animal Reproduction Banks of Terra.
The bearing techniques had been perfected on First Centauri. A host mother did not need to be of the same species as the fetuses she bore. With help, a goat could carry and bear calves or lambs,and a cow was capable of bringing colts and young llamas to term as easily as it could bear its own calves. The cattle of choice were long-haired Scotch cattle with short, curled horns, a small but very tough breed. Ova implanted in them were every type of cattle suitable for milk, meat or hide. The sheep were of various kinds, both long and short-fleeced. With the exception of the Kashmir, all the goats bred survived.
Permission had been obtained by the bioengineers to use the techniques of the Eridani to adapt animals to Pern. The most important of these methods were gene paring, mentasynth, and chromosome enhancements. Fish and other marine life from Earth were introduced to the waters with minimal adaptations. Horses were improved somewhat by genetic tinkering. The "grubs" whcih rendered a piece of protected ground inimical to Tread, were engineered by a renegade biologist/botanist of the original colony. Unfortunately, he left no records of the research that generated these useful insects. The Southern Continent has unchecked jungle because of the grubs' protection (this jungle is also home to pockets of original Terran trees that were not brought North but have survived on Southern).