Table 2.

AIC values for the set of logistic models with and without measures of flea abundance. Because the different measures of flea abundance are not available for the same years, the number of years used in the three subsets differs and the AIC values cannot be compared. All data are taken from LSQs 91 and 105.

flea abundance measure	intercepta	+gerbil predictorb	+flea measurec	+gerbil +flead
previous autumn fleas	17.14	14.45	15.77	14.45
spring fleas	17.53	12.75	17.41	12.74
fleas/rodents	18.91	14.99	18.41	15.43

^aLogit(outbreak)=a.

^bLogit(outbreak)=a+b×gerbil occupancy.

^cLogit(outbreak)=a+c×flea measure.

^dLogit(outbreak)=a+b×gerbil occupancy+c×flea measure.