In the 1930s, william f. whyte moved into a low-income italian neighborhood in boston. for nearly four years, he was a member of the social circle of "corner boys," which he described in street corner society. his goal was to gain greater insight into the community that these men had established. the type of research technique that whyte used is called

I believe the answer is: participant observation

In participant observation  technique, The data collecting process is being done by either observing the event from a close distance or by directly involved within the event. This research technique tend to be favoured if the researchers want to include qualitative data as a factor to create a conclusion.

the invasive species was introduced due to commercial purpouses, as there was a demand for fur clothes and hence, a business opportunity connected to this product. actually, it was when the nutrias scaped, causing harm to the us ecosystems when they acquired the status of invasive species. in this case they have caused an environmental problem, but it could have affected also economic interests or even human health.