In the survival series “Alone,” the tension ratchets higher whenever participants encounter bears. Some participants live warily alongside bears, while others tap out. A similar thing happens among investors when they encounter a bear market. What is a bear market? People define bear markets in different ways. Some people say a share price decline of 20 percent is bear market territory. Last week, the Standard & Poor’s (S&P) 500 Index was down 19.6 percent before Friday’s rally, according to Ben Levisohn of Barron’s, and the Nasdaq Composite was already down more than 20 percent. Other people say a bear market occurs when more investors are bearish than bullish. That’s certainly the case today. The Association of Independent Investors’ Consumer Sentiment Index found 49 percent of investors were bearish and 24 percent were bullish last week. Other sentiment indicators, including the Consensus Bullish Sentiment Index cited by Barron’s, also show that investors and investment professionals are feeling more bearish than bullish.