What is keyword cannibalisation?
Keyword cannibalisation occurs when individual pages on the same website begin to compete for the same keyword terms. This can result in both pages losing ranking positions for key terms and can even cause pages to anchor each other down.
Why does it happen?
Each individual page on your website communicates with Google through the title tags, meta descriptions and content you provide. This information is indexed by Google in order to determine what each page is about and how this might be relevant to a search engine user.
If the meta and content on two or more of your web pages have similar or identical information, Google will struggle to differentiate between them and these pages will begin to challenge each other for the same keyword terms.
What can I do?
Define the key terms for the main pages of your website and differentiate the title tags, meta descriptions and content to ensure there is no duplication or conflict. This gives Google a much clearer picture of what each page is about, and the keywords for which you’d like them to compete.
An example
The home page of a website selling cheap DVD players ranks on page one for the keyword term ‘cheap dvd players’. The site also has a page dedicated to selling used DVD players which has similar content and identical title tags and meta descriptions.
Soon the website owner notices that the home page has fallen to page 2, one place above their own ‘used DVD’ page. The website owner acts quickly to differentiate the pages, making sure that the content and meta explains to Google that this second page specialises in ‘used dvd players’.
Gradually, the home page should be restored to its previous first page position as the ‘used DVD players’ page begins to compete for its own specialised key term.
Top tip from BrightonSEO
Speaking on the subject at BrightonSEO, Jon Earnshaw advised that key pages should be made into a ‘Trophy Page’ designated for particular keywords/products. That way individual pages are optimised toward specific web searches and unlikely to conflict with other pages on the same site.