02080nas a2200253   4500008004100000020001400041245013900055210006900194260001200263300001400275490000800289520135100297653001601648653001301664653002601677653001701703653001401720653001401734653000901748653001101757100001701768700001701785856002401802       2007                        eng d  a0003-014700aDoes competition between resources change the competition between their consumers to mutualism? Variations on two themes by Vandermeer0 aDoes competition between resources change the competition betwee  c2007///  a744 - 7570 v1703 aHow does competition between resources affect the interaction between consumer species that share those resources? Existing theory suggests that high resource competition can lead to mutualism. However, this is based on an analysis that need only apply near equilibrium, and experimental demonstrations of such mutualism are rare. Two alternative approaches to measuring food web mutualism are examined here. These are based on the population level effects of adding or removing a consumer species or on the amount of additional mortality that can be applied to one consumer without excluding it. Both measures suggest that mutualism is likely to be confined to two situations: when overlap in resource use by the consumers is very low and when the consumers are inefficient users of their resources. Competition between resources is also likely to increase the occurrence and magnitude of "hypercompetition" between consumers, where the reduction in population size caused by the introduced consumer is greater than that caused by a consumer that is identical to the resident species. Competition between resources can also increase the negative interaction between consumers by destabilizing the dynamics of the system. Such destabilization can cause negative indirect interactions between specialist consumers having no overlap in resource use10aCOMPETITION10aDYNAMICS10aindirect interactions10ainteractions10aMORTALITY10aMUTUALISM10aSIZE10atheory1 aAbrams, P.A.1 aNakajima, M.  uISI:000249981500009