([SHULPHQWDO=RRJHRJUDSK\RI,VODQGV7KH&RORQL]DWLRQRI(PSW\,VODQGV $XWKRUV’DQLHO66LPEHUORIIDQG(GZDUG2:LOVRQ 6RXUFH (FRORJ\ 9RO1R0DUSS 3XEOLVKHGE\(FRORJLFDO6RFLHW\RI$PHULFD 6WDEOH85/http://www.jstor.org/stable/1934856 $FFHVVHG YouruseoftheJSTORarchiveindicatesyouracceptanceofJSTOR’sTermsandConditionsofUse,availableat http://www.jstor.org/page/info/about/policies/terms.jsp.JSTOR’sTermsandConditionsofUseprovides,inpart,thatunless youhaveobtainedpriorpermission,youmaynotdownloadanentireissueofajournalormultiplecopiesofarticles,andyou mayusecontentintheJSTORarchiveonlyforyourpersonal,non-commercialuse. Pleasecontactthepublisherregardinganyfurtheruseofthiswork.Publishercontactinformationmaybeobtainedat http://www.jstor.org/action/showPublisher?publisherCode=esa. EachcopyofanypartofaJSTORtransmissionmustcontainthesamecopyrightnoticethatappearsonthescreenorprinted pageofsuchtransmission. JSTORisanot-for-profitorganizationfoundedin1995tobuildtrusteddigitalarchivesforscholarship.Weworkwiththe scholarlycommunitytopreservetheirworkandthematerialstheyrelyupon,andtobuildacommonresearchplatformthat promotesthediscoveryanduseoftheseresources.FormoreinformationaboutJSTOR,pleasecontactsupport@jstor.org. EcologicalSocietyofAmericaiscollaboratingwithJSTORtodigitize,preserveandextendaccesstoEcology. http://www.jstor.org