Why are there different environments?

Answer 1

Because the Earth is not perfectly round, the sun affects it in different ways. In the north the suns rays are less concentrated, and therefore a colder climate exists. On the equator, the sun rays are most concentrated, so an environment suitable to hot, humid weather exists.

Answer 2

As the Earth revolves around the Sun it is slanted on an axis that is about 23 degrees to the plane of it's orbit. That produces variable warming of the Earth's surface. The equator is the warmest because it is the closest to the sun and receives light directly all year round. The poles are cooler during the portion of the year when they are pointed away from the sun because they are further from the sun and because the angle at which the sun's radiation hits the Earth at the poles spreads out the radiation making so the energy is distributed over a larger area - hence lower energy per square meter than at the equator. Similarly, when the pole is pointed towards the sun because of the tilt of the Earth's axis, the poles receive more energy since they are closer to the sun but the incident angle is still such that the energy per unit area of surface is lower than it is at the equator. This differential heating leads to very different climatic conditions and therefore a wide variation in the ecosystems and communities that can be supported on the Earth. In addition, smaller local variations related to proximity to oceans or availability of water, altitude create differing conditions and life has evolved to take advantage of those differences and so can be quite different even at the same latitude.