HANKIN: A MULTISTAGE RECRUITMENT PROCESS 



Table 3. — Schedule of daily rations fed to guppy and southern 

 platyfish populations during weeks 0-8. Total is expressed as a 

 wet weight equivalent. 



To determine, multiply dry food ration by 10 and add all food types. 



rations were reduced to equal ration levels in 

 original single species guppy populations. 



WEEKS 8-36. — Neither guppy population bio- 

 mass nor numbers at week 8 differed significantly 

 between original single species populations and 

 mixed species populations so the 10 remaining 

 populations were considered replicates during 

 weeks 8-36. To eventually achieve population age 

 structure which would be finely graded and to 

 achieve equality in numbers of original females in 

 all aquaria, the original females were gradually 

 "phased out" by removal of one adult female from 

 each population at weeks 11, 13, 15, and 17. 

 Original females were easily separated from re- 

 cently matured female progeny by their larger 

 size and were removed by selecting the smallest 

 female first, in each population, to least affect 

 population biomass. Food rations were increased 

 in stepwise increments through week 22 after 

 which time rations were fixed. A slight departure 

 occurred during weeks 28-29 when dried food only 

 was fed twice daily (Table 4). 



Table 4. — Schedule of daily rations fed to guppy popula- 

 tions during weeks 8-36. Total is expressed as a wet weight 

 equivalent.' 



jTo determine, multiply dry food by 10 and add all ration types. 

 0.20 g fed twice daily. Three morning feedings were missed during 

 this period. 



Phase II (Weeks ^6-58) 



Three populations (5, 6, and 12) from the original 

 10 were selected at random to be long-term con- 

 trols. Of the remaining seven populations, two 

 pairs (1 and 2, 4 and 10) were mixed and divided to 

 give three approximately comparable populations 

 (for each mixed pair) of reduced numerical size 

 and biomass. The remaining three populations 

 were simply reduced in size to similar levels. 

 Numbers of individuals in reduced populations 

 ranged from 74 to 81, of which 42-49 were adults in 

 size categories > A55 (the largest adult male and 

 smallest adult female size category, see Table 1). 

 Total reduced population biomass ranged from 12 

 to 14 g, slightly less than one-half of apparent 

 maximum population biomass. 



The nine reduced populations produced in the 

 above manner were assigned to three groups of 

 three each for treatment. Treatment consisted of 

 replacing original 5.0 mm spacing (on centers) 

 refuge fences with refuge fences of 4.5, 5.0, or 5.5 

 mm spacing. Each group contained two popula- 

 tions of mixed population origin and one which 

 had been reduced from a larger single population. 

 Refuge areas were assigned to populations with 

 the restriction that each of the three populations 

 produced from a mixed pair must be assigned a 

 different refuge fence spacing. A summary of 

 manipulations at week 36 is presented in Table 5. 

 Daily rations for Phase II are presented in Table 6. 



RESULTS 

 Phase I 

 Weeks 0-8 



The attempt to examine stock-recruitment rela- 

 tions in mixed species populations failed due to 

 high platy mortality in certain aquaria and an 

 apparent inability of platy fry to successfully 

 compete with guppy fry for food. Relative competi- 

 tive ability of platy and guppy fry was reflected in 

 contrasting mean weights of platy juveniles in 

 mixed and single species populations at the end of 

 week 8. Mean weights of platy juveniles, all born 

 during the first 2 wk of the experiments, were 

 0.0144 g in a mixed species population and 0.1037 

 g in a single species population at week 8. Guppy 

 juveniles, also presumably born within the first 2 

 wk, had reached a mean weight of 0.0979 g by 

 week 8 in the same mixed species population. 



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