| The life history traits of copepods in the Georges Bank (GB)/Gulf of Maine (GOM)region are selected by the environment they live in the long history, and the copepodsare adapted to the environment now. The paper discusses the natural selection processto the copepods in the GB/GOM region with Individual Based Model (IBM) in threesections.In the first section, the generalized copepod model is constructed with thegeneralized copepod formulas. Genetic Algorithm (GA) is taken in the model, and thespecific parameters in the generalized copepod formulas are chosen as genes. Thevalue of all genes is picked up randomly in the given range to simulate the initialcopepods with various gene combinations. The climatological averaged surfacetemperature and chlorophyll a time series at a specific location are taken as the modelenvironment every year. The model runs for50years with exact the sameenvironment every year. The top10abundant copepods are analyzed at the end ofmodel run. The results show that some of them correspond well with the realGB/GOM species Calanus finmarchicus, Pseudocalanus, Centropages typicus andCentropages hamatus on the reproduction strategy, peak abundance time, temperaturepreference and adult mass. The Multi-dimensional Scaling (MDS) and ClusterAnalysis (CA) results show that the reproduction strategy is a crucial criterion for thecopepod grouping. For the species taking the egg-carrying strategy, GB and GOMenvironments both selected the small-bodied cold water species represented byPseudocalanus. For the species taking the broadcasting strategy, GB environmenttends to selecte the large-bodied cold water species represented by Calanusfinmarchicus, and GOM environment tends to select the medium-bodied warm waterspecies represented by Centropages (Centropages typicus and Centropages hamatus). It needs to be improved of the gene mutation case for the output copepods with toosimple life history trait combinations.In the second section, two specific species Centropages typicus and Centropageshamatus which both belong to Centropages spp. are researched for the resting eggstrategy selection with the specific species IBM. GA is also taken in the model. Threegenes on the resting egg strategy are set in the model, resting season restsea, restingpropability restpro and resting duration restdur. The model runs for10years to getstable. The results show that both Centropages typicus and Centropages hamatuscould not survive in GOM, no matter if they take resting egg strategy or not. In GB,resting egg strategy is necessary for Centropages hamatus to survive, but Centropagestypicus could still survive without resting egg strategy. If energy loss of the restingegg strategy is included in the IBM, Centropages typicus will not select the restingegg strategy, but Centropages hamatus still selects the strategy to survive. Eggs ofCentropages hamatus enter into resting status almost in spring, and the restingduration could be1or2months, which is the coldest time of year. So it could beguessed that temperature triggers the resting egg strategy for Centropages hamatus.The results also show that the base mortality of Centropages typicus is much higherthan Centropages hamatus, because the reproduction rate of Centropages typicus isalmost2times as high as Centropages hamatus. That’s why the Centropages hamatusselects the resting egg strategy, but Centropages typicus doesn’t.The first and second sections show that mortality plays an important role in thecopepod evolution. In the third section, the influencing effect of environmental factors,including temperature, salinity, chlorophyll a, observed water depth, C5and adulttotal abundance and some possible predator abundance, on the mortality of thespecific species Pseudocalanus, Centropages typicus and Centropages hamatus inGB/GOM region is analyzed. The copepod abundance and environment factors aregot from MARMAP-ECOMON survey data, and C5/Adult mortality forPseudocalanus, Centropages typicus and Centropages hamatus is calculated withVertical Life Table Method (VLT). The relationship between C5/Adult mortality andvarious environmental factors is analyzed with the Generalized Additive Model (GAM). The results show temperature and food are two of the most important factorscontributing to the mortality of the three species in GB/GOM region. In GB and GOM,food is the most important factor for the mortality of Pseudocalanus, and temperatureis the second importamt; for Centropages typicus temperature is the most importantfactor, and food is the second important. For Centropages hamatus, it is quitedifferent in GB and GOM. In GOM, the main mortality contributing factors aretemperature and Euphausiacea predation; and it is a little complicated in GB, themortality contributing factors include C5and adult total abundance, temperature andfood et al. However, it should be more careful for its violation of VLT assumptionbecause of the fluctuation of C5and adult ratio of Centropages hamatus during thefirst half part of year in GB. The results also show that Euphausiacea is a veryimportant predator in GOM for the mortality of the three species, especially forCentropages hamatus. The spatial distribution patterns of the climatological averagedenvironmental factors correspond well with the mortality patterns, which confirms thecorrectness of the GAM analysis.The scientific significances of the study are: research the influence of GB/GOMenvironment factors on the copepod evolution the first time systematically; reveal thenatural selection mechanisms of the GB/GOM environment on the formation of thecopepod life history traits; analyze the trigger of the resting egg strategy forCentropages hamatus and the primary cause for the strategy in GB/GOM; researchthe mortality which is basic in the evolution subjects; analyze the influencing effect ofvarious environmental factors on the specific species mortality rate in GB/GOM. Thiskind of research has never been done in the East China Sea, so the study ismeaningful. |
PDF Full Text Request