The element calcium has the atomic number of 20 and the mass number of 40, how many neutrons dose it have

The mass number is the sum of the number of protons and number of neutrons the atom has.

So, we can write the equation as:

x + 20 = 40

x = 20 neutrons.

if the type of the food available changes, then the frequency of beak types will change, because birds with beaks more suited to the available food will be more successful over time.

primary succession occurs in essentially lifeless areas regions in which the soil is incapable of sustaining life as a result of such factors as lava flows, newly formed sand dunes, or rocks left from a retreating glacier. secondary succession occurs