HANKIN: A MULTISTAGE RECRUITMENT PROCESS 



A 

 D 

 J 

 U 

 S 

 T 

 E 

 D 



P 

 

 P 

 U 

 L 

 A 

 T 

 I 





 N 



1 

 N 



c 



R 



E 

 M 

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T 



Figure 7. — Adjusted population increment (in t, t + 2) and 

 number of J^ guppy juveniles (at t - 2) plotted against week 

 (at t + 2) in population 3. The plot incorporates a 2-wk time 

 lag. Solid line is adjusted population increment. Dots show 

 juvenile densities. 



born fry and immature juveniles had created a 

 complicated population growth process involving 

 both immature and adult population components 

 as had been briefly mentioned by Ricker (1954). 



A tentative conceptual model of numerical pop- 

 ulation dynamics was proposed and is depicted in 

 Figure 8. Survival of newly born fry in a given 

 experimental interval can be viewed as a two-step 

 process. Fry born must first elude adult predators 

 outside the refuge area. Fry which successfully 

 elude adults and enter the refuge area are faced by 

 predation, competition, or harrassment by large 

 J4 juveniles present in the refuge area. Pulses of 

 numerical increase can easily be created if such a 

 process occurs. Following the initial entrance of 

 fry into the refuge area, growth of fry occurs. Once 

 fry grow to the juvenile size at which interaction 

 with newly born fry occurs, fry survival is inhib- 

 ited so long as juveniles are smaller than the J5 

 size category. Once reaching the J5 size category, 

 juveniles are transferred to the main aquarium 

 environment at enumeration. The refuge area is 

 once more free of juveniles, and fry successfully 

 eluding adult predators and entering the refuge 

 area are once more expected to survive. 



Since the above explanation for the pulsing 

 quality of numerical growth seen in many popula- 

 tions seemed a plausible hypothesis, alteration of 

 the refuge fence design (by either increasing or 

 decreasing spacing between glass rods) would 

 likely increase or decrease the intensity and 

 duration of juvenile-fry interactions within refuge 

 areas. This hypothesis was examined in Phase II. 



Table 9. — Linear correlation coefficients (r) between adjusted 

 population increment (AP/^_ , + 2) and natural logarithm of 

 juvenile numbers [ln(e/4^_2 "'' ^^^ in Phase I guppy populations. 



Population number 



Population number 



Adult 

 Predators 

 at t 



Adult 

 Females 



at t 



Fry Born 

 in t,t+2 



• • •Refuge Fence* • • 



• r 



Fry in 

 Refuge Area 



Growth to 

 J4 



Juveniles 



Predators 

 at t 



Growth to 



Size Category 



• 'Refuge Fence* 



Figure 8. — Diagram depicting the hypothesized numerical 

 dynamics model for guppy populations. Solid lines and arrows 

 indicate path from birth to survival as adult. Small dots and 

 arrows depict paths leading to death through cannibalism by 

 adults or juveniles. 



OTHER OBSERVATIONS. — Additional data 

 collected during Phase I included examination of 

 guppy scales for fluorescent marks and records of 

 disease incidence. Examination of scales removed 

 from fish at week 36 was disappointing. No scales 

 showed more than five to seven marks while the 

 maximum expected number of marks was nine. It 

 is possible that at the final ration level individual 

 fish did not receive sufficient food intake to 

 produce detectable marks. Further research into 

 the matter was not pursued, but marking was 

 continued during Phase II so that experimental 

 manipulations would remain constant. All guppy 

 disease problems were chronic in nature, minor, 

 and were consistently diagnosed as piscine tuber- 



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