So the original form is somewhat wrong on a substantive point or two, which weakens my original point. Series is clearly singular possessive, so it is not quite as bad as I originally supposed, mostly because the consensus is not as strong as that. As a result, this question may be askable. This warrants a reassessment of the issue on my part. After doing so, I still suspect it should be closed, but perhaps it may be salvageable.
Many of the points remain the same. To reitterate and clarify:
The edit's usefulness in excluding general reference answers is still not apparent, because it addresses a rule written specifically for personal names specifically, rather than common nouns, or even proper nouns generally.
Commonly available resources that should have been checked have not been factored into the question, permitting them to be used as the sole basis of an answer.
I think the scope of the question is narrower than proposed. Although they can be closely related and complimentary, what should be done, and why it is done are two different subjects. I only saw a question asking what should be done, and answers addressing what should be done. Editing guidelines suggest we should not change the intention of a post, and I suspect that is what is being attempted.
The propensity of this being a duplicate is high, also due to the commodity of the subject matter of using apostrophes with a noun ending in terminal s.
What may be at issue is that because I misparsed a couple of things, my proposed general references referencing the most basic orthographic do not adequately address the matter. That might be true.
However in consideration of that possibility, that does not necessarily mean that the research is good enough in its present form. The standard for general reference is to perform research regarding the question per step 1 of the flowchart.
What I was proposing before was rather substandard research, to emphasize the hopelessness of the matter if a basic orthographic rule applied. This is something that shows that perhaps the question can be salvaged, but not necessarily that it is good enough in its present form.
Before I perform a reassessment based upon that though, I would like to suggest that the research standard for editors should be higher than for original posters, because getting information from the original posters benefits us in ways that editing it in does not:
A. It helps us to understand, and address any misapprehensions made apparent by the inadequate research efforts. When we add research on their behalf.
B. It helps us to understand what type of explanations and evidence fail to satisfy the questioner. This way, we do not end up repeating what they already saw, or merely use evidence of the same quality. This also promotes further explanation of the issue, beyond what references can provide.
Without some indication from the questioner, an editor can only speculate as to what type of answer can satisfy somebody else, so they should assume that any reasonably adequate answer that might be readily found could suffice, and must perform a research effort to see if one exists. You say that this question has its basis in pronunciation, which is possible.
Your concerns regarding why we spell species' the way we do (assuming that is a uniform rule, which I have reason to doubt) are not the same as O.P's. concerns regarding how he should spell it. These are admittedly complimentary subjects, but the requisite for an adequate answer to the question as it is asked is lower for this one, we need to keep in mind what was actually asked:
Any authoritative suggestion regarding how to spell the singular possessive form of the word suffices to answer this question, regardless of whether or not what causes us to spell the word that way is the same.
With these factors in mind this respect, we need to consider the question as it was actually asked: A research effort was disclosed, but not included, the intended, adequate context was given, and finally the question was asked:
Would it be species' or species's ?
No reason for suspecting one way or the other is better was indicated by the questioner. I see no reason anybody should have to explain the phonological aspects that may underlie the orthography, or even much effort to address them in any existing answer. Any relatively authoritative suggestion may suffice.
I have devised a basic few searches to see if I could find one, and perhaps not for the reason you might suspect. What I am trying to determine is what answers they share in common, so I can know what any one person might have found if they had only used one of the searches. I want to avoid treating google itself as general reference, because it is not and if it was, that could put us out of a job. I want to see if a general reference result can be easily found using google, qualifying it as a commonly available resource and hence off-topic.
First, to avoid setting my own potentially biased standards, I interpreted the flowchart given in Are Some Questions Too Basic most literally, and did a word for word search for the question as it was asked. I used series in both of the other searches, to see what the specific rules regarding that word may be. I used apostrophe in one of the searches, since that is the name of the mark in question, and hence reasonably derived from the sentence/question as possible (since the actual mark in isolation doesn't bear much upon google search results). I used possessive instead in the other, since this regards the possessive form.
My three searches bear three interesting results in common:
An older potential duplicate question, with an existing answer. The duplicate guidelines suggest that preference should be given to this newer question, since it is in an overall better state, but I think this should have been considered before reopening.
A couple of grammarbook entries, from the the website of The Blue Book of Punctuation and Grammar's (by Jane Straus [deceased]). One is just a gloss over in a pop quiz format, so I shall omit it for brevity, but the more interesting of which is Apostrophes: Dueling Rules, which states the following:
• CMOS adds just an apostrophe when a noun ending in s is the same whether singular or plural. The guidebook offers three examples: politics’ true meaning, economics’ forerunners, and this species’ first record. The GrammarBook.com staff agrees with politics’ and economics’, but prefers this species’s, because in normal English usage, species is just as likely to be singular as it is to be plural—one often hears “a species,” but who says “a politics” or “an economics”?
These results suggest that the question is not quite up to standards, since the grammarbook website was a professionally endeavor, designed to address these issues, and makes mention of the Chicago Manual of Style rule considered to be the authoritative answer. The difference of opinion leaves a little room for doubt, but not much if this is a presumably reliable report, given how much more respected the Chicago Manual of Style itself is.
Now perhaps I am mistaken, but I suspect anybody perhaps research for this question in earnest could have at least found these results. Editing this information into the question would most certainly be barred, as an attempt to reply (as it is meant to answer the question)
My most preferred result would be for the original poster to include their own research, for the reasons aforementioned in points A. and B. Failing that, especially since it may be harder to coax that information out of a question with an accepted answer, I would really appreciate information regarding what research methodologies went into determining that the question should be reopened. Perhaps that can give some perspective on whether or not the answer is really as readily answerable as I presently surmise, and meritorious enough to merit remaining open.
Otherwise, I still recommend closure of the question in its current state.