I don't understand my biology homework on natural selection. here's the question it would be great if you helped, you don't have to answer maybe give a clue.
"Scientists have been collecting evidence about the size of animals living on islands. Islands often have a shortage of food and other resources. They are often exposed to wind and have little shelter.
Some Scientists report that animals living on the islands are bigger than similar animals on the mainland.
Other scientists report that the animals on islands are smaller than similar animals on the mainland.
Show how Charles Darwin's theory of natural selection can explain BOTH sets of evidence."
thanks
"Scientists have been collecting evidence about the size of animals living on islands. Islands often have a shortage of food and other resources. They are often exposed to wind and have little shelter.
Some Scientists report that animals living on the islands are bigger than similar animals on the mainland.
Other scientists report that the animals on islands are smaller than similar animals on the mainland.
Show how Charles Darwin's theory of natural selection can explain BOTH sets of evidence."
thanks
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Some animals, such as mice, are small for security reasons. If confronted by a nasty, mean-minded pussy cat, a mouse can take evasive action by disappearing into a small opening. Being small helps with not being eaten by a largish mammalian predator.
Often, islands don't have any largish mammalian predators, and especially so if the nearest mainland is a boat voyage away. Small fry such as mice, on the other hand, can sometimes accidentally raft in on suitable debris. And should a pair of the complementary sexes arrive on the same natural raft, then they can found a dynasty together; one free from annoyances such as cats.
Given the shortage of predators, disappearing down small openings is no longer a survival advantage. The limit on size is loosened and larger mice can survive to breed as well. That's liable to lead to an average increase in size. And, still being reasonably small, the somewhat restricted availability of food is less of a problem. They don't need that much.
Now consider a population of elephants on Malta. There might not being any there now, but Malta used to have elephants. Their ancestors wandered in when the Mediterranean was on holiday. When the sea returned, the now resident elephants were stranded and food was restricted. That made being large disadvantageous due to food shortage. This was less of a problem for elephants that happened to be smaller.
Malta, and other local islands, ended up with elephants of a large-dog sort of size. The selective pressures of a low food supply meant small is goodiful while elephant big elephants starved. And starving to death plays havoc with your breeding prospects.
Often, islands don't have any largish mammalian predators, and especially so if the nearest mainland is a boat voyage away. Small fry such as mice, on the other hand, can sometimes accidentally raft in on suitable debris. And should a pair of the complementary sexes arrive on the same natural raft, then they can found a dynasty together; one free from annoyances such as cats.
Given the shortage of predators, disappearing down small openings is no longer a survival advantage. The limit on size is loosened and larger mice can survive to breed as well. That's liable to lead to an average increase in size. And, still being reasonably small, the somewhat restricted availability of food is less of a problem. They don't need that much.
Now consider a population of elephants on Malta. There might not being any there now, but Malta used to have elephants. Their ancestors wandered in when the Mediterranean was on holiday. When the sea returned, the now resident elephants were stranded and food was restricted. That made being large disadvantageous due to food shortage. This was less of a problem for elephants that happened to be smaller.
Malta, and other local islands, ended up with elephants of a large-dog sort of size. The selective pressures of a low food supply meant small is goodiful while elephant big elephants starved. And starving to death plays havoc with your breeding prospects.
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Being bigger (on the island) would mean that it is easier to reach high foods and it may be easier to resist harsh wind, but smaller animals on the island would find it easier to find shelter and would not need as much food.