In the latter case the resistance is caused by dissipation of mechanical energy when the configuration or the direction of flow is sharply changed, by the formation of vortices and secondary flows as a result of the flow breaking away, by the centrifugal forces, etc.
Animals depend on plants for food as plants produce food and energy which animals can't, so, herbivores eat plants to get energy, carnivores eat herbivores and other carnivores for energy and omnivores eat all four, plants, herbivores, carnivores and also other omnivores for energy.
One of the most important functions of animals is to help disperse seeds and pollinate plants. This provides vital support to a variety of fruit and vegetable crops, many of which would not survive without the help of animals. Primates, for example, help to disperse seeds through the fruits they eat. Bats also help spread seeds and pollinate a variety of plants. Bees are the most important animal to plant ecosystems.