Springer has released over 400 science books downloadable as pdf for free as part of 'Free Textbooks and Library Link special issue during Covid 19 package'. Lots of stats books and some ecology ones as well You can search and download here: https://link.springer.com/search/page/1?facet-content-type="Book"&package=mat-covid19_textbooks&facet-language="En"&sortOrder=newestFirst&showAll=true