Behavior

The behavior of an organisms may affect its dispersal. Many animals actively choose the environment they will occupy. This behavior is known as "habitat selection". As an example, pillbugs (Porcellio scaber) in a humidity gradient move at random with respect to the gradient (see movies below). However, they move more quickly in dry areas which causes them to move out of the unsuitable environment. Once they find themselves in a high humidity environment they slow down and become motionless. This type of orientation is known as a kinesis (orientation without respect to the direction of the stimulus). In particular, this is an orthokinesis (a change in the rate of movement) versus a klinokinesis (a change in the rate of turning). Convince yourself that both an orthokinesis and a klinokinesis can lead to habitat selection (scribble lines on paper as a proof).

Response of Pill Bugs to High and Low Humidity Environments

The top half of the container is a high humidity environment. The Bottom is a low humidity environment.
Note that animals stay in the high humidity environment. (Original: 1 frame/60 seconds)

One animal was placed in a moist habitat, the other in a dry environment. Note the obvious
differences in their rate of movement (Original: 1 frame/5 sec)

A taxis, on the other hand, is a directed response. Examples of taxes are shown below: