Should I Give Gag-Givers Credit?

Cartoonist Jimmy Hatlo in a
Lucky Strike ad

Dear Rich: I write and draw a web comic involving a set of recurring characters. Sometimes I run a joke I'm working on by a couple of my friends, to see if the joke comes through clear, and, if not, how could it be improved. However, now everyone I know is starting to tell me their ideas for gags. Their contributions usually consist of either (a) suggesting a basic concept (man falls off horse) or (b) suggesting a change to my fleshed out joke (farmer falls off COW, dies, etc). In both instances, I am still the one laying out the panels, structuring the joke, coming up with the dialogue, drawing and coloring it. Being friends and all, I want to show my appreciation for their help by giving them credit on the individual strip, but I am worried that by putting his/her tag alongside mine, I am giving up sole control of my copyright on that strip. Is that the case? The Dear Rich Staff is wondering about jokes in which people fall off animals. We suppose that's an interesting niche although the idea of a farmer falling off a cow and dying seems sad to us. Maybe it could be funny if it was a zombie farmer, though frankly, we're not sure about all this "funny" zombie stuff. It must be tragic to be a zombie, worse than having dementia or even worse than being trapped on BART next to a woman iPhoning her friend about wedding invitations. Wait, here's a concept for a web comic strip -- a zombie wedding planner. Or did we see that movie?
Right, you had a question.  We doubt that you would need to share copyright with someone who gives you a gag for a comic strip. We think your contributors are providing concepts that are probably unprotectible under copyright because (1) the concepts are ideas, or, (2) the concepts constitute unprotectible short phrases. As we've written before, it's tough to protect gags and jokes. What's protectible is the manner in which you express your comic strip. If, however you are collaborating with someone and going beyond the basic gag idea -- say for example, discussing what the comic panels would consist of -- then you may be expanding into co-authorship and copyright co-ownership. So avoid going beyond a discussion of the basic gag. If you want to feel more secure, and if you're going to solicit ideas online, provide terms and conditions in which the contributor agrees to give up rights when submitting an idea.
A tip o' the Hatlo hat ... As for providing attribution, that's up to you. It certainly worked for cartoonist Jimmy Hatlo who encouraged readers to send in ideas and then gave the contributor a "tip o' the Hatlo hat" attribution.