Answer:
Environmental Resistance
Explanation:
Environmental resistance can be defined as all the factors including physical factors, chemical factors and  environmental factors  including biotic and abiotic factors (e.g drought, mineral deficiencies, and competition) limiting the life forms of an organism or kind of organism and impose a restriction on their numerical increase. These factors limit the growth of  species in a population.
 
        
             
        
        
        
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Metaphase is the stage in which the "crossing over" occurs. 
As we know chromosomes carry genetic information. This crossing over process happens in eukaryotic cells and occurs during the mitosis phases of cell division. 
Hopefully this helped.