Most people who have participated in group projects will recognize that maintaining clear channels of communication among team members can be a big challenge. We at NCEAS encourage scientists to discuss authorship and data sharing early and often. Many publications resulting from NCEAS work are authored by large groups of individuals. These individuals may not know each other well at the beginning of the project, and they may represent fields which have diverse views on authorship and data sharing.
Check the "Publication" section of the Ecological Society of America's Code of Ethics  as a starting point for discussions about co-authorship. NCEAS endorses these principles in establishing authorship. You might also wish to check guidelines published by the journal(s) to which you anticipate submitting your work.
The NCEAS Data and Information Policy  outlines our requirements for making data public when your work is supported by NCEAS.