EXTERNAL FACTORS ON THE SPAWN DATE 



143 



Let Y = Spawn date in year days, AP = Altitude of Phenological 

 station in feet, AM = Altitude of Meteorological station in feet, 

 RMo = Rainfall in Mo in nun, TMo = Temperature in Mo in °C, 

 RMi = Rainfall in Mi, in mm, TMi =-■ Temperature in Mi, in °C, 

 SMi = Bright simsliine in Mi, in %, RM2 = Rainfall in M2, in 



40 50 6O 

 OBSERVED DATE 



70 80 90 



Fig. 40, An Informal Test of the Regression Equation 



Ten records were taken at random, and the corresponding variables 

 substituted in the equation to give a calculated date. This has been plotted 

 against the actual date. The agreement is good, only one point being far 



wrong. 



mm, TM2 = Temperature in M2, in °C, LT = "Latitude, LG = 

 "Longitude. Then — 



Y = 57-5 + (0-003 5) AP — (0-0031) AM + (o-02)RMo + (o-9i)TMo 

 — (o-0707)RMi + (o-i7)TMi + (o-03o)SMi + (o-oo9)RM2 

 + (3-io)LT-(3-4)LG 



Fig. 40 is an informal illustration of the way in which it fits the facts. 

 Ten dates were chosen at random and the values substituted in the 

 equation, so as to obtain a date by calculation. The actual dates were 

 then plotted against the calculated dates. It can be seen that only one 

 date is much out of line. In the other cases, if the pond had been visited 

 on the calculated date frogs might have been there, just departed or 



