There will be far-reaching effects. If for example, the producer is removed, the consequences could be dire. Producers capture sunlight directly and make chemical energy for consumers. If this is the only producer that a particular consumer eats, it may die as well. Pandas eat only bamboo. As bamboo is removed from the habitat, pandas will eventually diminish and possibly die off. If a secondary consumer or tertiary consumer were removed, for example, wolves, the primary consumers overpopulate. This is seen in places where wolves once roamed and no longer do. Deer are overpopulating out of control and they are exceeding the carrying capacity for their range. The deer population can experience an explosion and subsequent die off due to starvation. As you can see, no matter where the food web loses a member, the effects are great.
they would have to find another source of food to it. but it depends where about the organism is on the food chain. if it near the beginning it could wreak the whole food chain up and could kill some animal but if there is another source they would have to adapt to surivie.