There is no such thing as a permanent seat on the S&P 500 (^GSPC 0.52%). As 17 companies learned this year (see table below), they must earn their keep or face expulsion. In the following video, Motley Fool contributor John Maxfield discusses why he thinks the next stocks to be expelled could be Cliffs Natural Resources (CLF -0.40%), Newfield Exploration (NFX), and TECO Energy (NYSE: TE).

Date

Removed

Replaced By

Reason for Removal

April 30

MetroPCS Communications

Regeneron Pharmaceuticals

Merged with T-Mobile USA, dropping public float below 50% threshold

May 8

Coventry Health Care

The Macerich Co.

Acquired by Aetna

May 23

Dean Foods

Kansas City Southern

Equity interest in WhiteWave Foods spun off, making Dean Foods "more representative of the midcap market space"

June 6

H. J. Heinz Co.

General Motors

Acquired by Berkshire Hathaway

June 21

First Horizon National

Zoetis

Insufficient market capitalization

June 28

Apollo Education Group

News Corp.

Insufficient market capitalization

July 8

Sprint Nextel

Nielsen Holding

Deal with Japan's SoftBank dropped public float below 50% threshold

Sept. 10

BMC Software

Delta Air Lines

Acquired by private equity firm Bain Capital

Sept. 20

Advanced Micro Devices

Vertex Pharmaceuticals

Insufficient market capitalization

Sept. 20

Science Applications International Corp.

Ametek

Split into two companies: SAIC and Leidos Holdings

Oct. 28

Dell

Transocean

Taken private by founder-led buyout

Nov. 1

NYSE Euronext

Michael Kors

Acquired by Intercontinental Exchange

Nov. 29

J.C. Penney

Allegion

Insufficient market capitalization

Dec. 9

Molex

General Growth Properties

Acquired by privately held Koch Industries

Dec. 20

Abercrombie & Fitch

Alliance Data Systems

Insufficient market capitalization

Dec. 20

JDS Uniphase

Mohawk Industries

Insufficient market capitalization

Dec. 20

Teradyne

Facebook

Insufficient market capitalization

Source: S&P Dow Jones Indices.