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.
Why do animals depend on plants. Plants give animals the food and shelter they need. Herbivores, which are plant eating animals, rely on plants to provide them with a regular source of food. They also provide shelter to may animals, both large and small.
Producers funnel into the ecosystem the energy needed for its biological processes. The carbohydrates and other organic chemicals formed by the producers are consumed and utilized by the heterotrophs, or consumers. First, herbivores -- the primary consumers -- eat the plants. Predators -- the secondary, tertiary consumers -- eat the herbivores. But at each step, much energy is lost. Less than 10 percent of the energy stored in plants is converted to herbivore mass. The loss from herbivore to predator is similar. Thus, energy needs to be added to the ecosystem continuously. This is the producers' role. Shaping the Ecosystem The efficiency of the producers in adding energy to the ecosystem determines how robust that ecosystem will be.