Which of the following organisms does not rely on krill as major food source?
adelie penguins
leopard seal
humpback whale
squid
adelie penguins feed mostly on krill but switch to fish during the breeding season and then to squid during the winter. what is a good explanation for this?
fish and squid are more abundance, and krill is more scarce
fish and squid provide more energy than krill
fish and squid is more abundant, and krill is more available
fish and squid is preferred but is not as available during the other months.

Astudy by solloch and et. al., in 2017, gives the map above which shows the frequency of alleles with a ccr5-delta32 mutations over 87 different countries. this mutation deletes the presence of a co-receptor (ccr5) on the outside of human t-cells (lymphocytes). some viruses, such as the one responsible for the black death and human immunodeficiency virus (hiv), require this receptor for attachment to host cells during the infection process. the black death was an epidemic that passed over northern europe during the 14th century killing nearly 60% of europeans. according to this information, which explanation best explains why northern europeans show a greater immunity for hiv than some other parts of the world?