Fish farm nets on the East coast. Shaunl | E+ | Getty Images A version of this article first appeared in CNBC's Inside Wealth newsletter with Robert Frank, a weekly guide to the high net worth investor and consumer.  Sign up  to receive future editions, straight to your inbox. Equity Group Investments, backed by the family of late billionaire Sam Zell, owns a John Deere dealership, a bluefin tuna fishery and a pedestrian bridge that connects San Diego to Tijuana International Airport. While those holdings sound entirely unrelated, what unites the private investment firm's wide-ranging portfolio is a focus on old-economy businesses that are less susceptible to disruption from artificial intelligence and other technologies, according to EGI's president, Mark Sotir. "We tend to put our capital to work for a longer duration than most [private equity] firms. If you're thinking out 10 years, 12 years, you have to start with picking a company in an industry that you know will be around," he said.…