Ecology and conservation biology are interdisciplinary fields. Here is the UC Davis Libguide to databases in ecology and conservation biology: http://guides.lib.ucdavis.edu/content.php?pid=548218&sid=4512825#16552484.

Perhaps if only one database was searched for a highly interdisciplinary field like ecology/conservation biology the word systematic should be reconsidered as a word in the title and as a description of the scope of the work, even though PRISMA guidelines were followed?