What variable did the experimenter change (independent variable), and what variable did the experimenter observe (dependent variable)?

An independent variable can be controlled by the experimenter to observe it's affect on dependent variable which cannot be changed manually. Rather the dependent variable changes due to the effect of independent variable.  

humans are now responsible for causing changes in the environment that hurt animals and plant species. we take up more space on earth for our homes and cities. we pollute habitats. human activity often changes or destroys the habitats that plants and animals need to survive.