Keystone species are the species that ''hold the ecosystem together''. They have an important role in the trophic networks (food chains) and often they can even afflict changes in the abiotic part of the ecosystem (change the composition of soil, purify the water, lower the effect of the wind etc) Therefore, when a keystone species is removed it affects greatly the whole ecosystem.
Humans benefit from the domestic dog because they reduce stress, they can prevent depression, and they can improve your health. Dogs benefit from humans because they love the bond they have with their owner.
The Ferris wheel was designed by George Washington Gale Ferris Jr in 1893. It consist of a large rotating wheel with capsules or cars that are used to carry people.
The mechanical advantage is less than one because the input force is greater than the output force.
