Why do some species only live in one part of the world, even though there are other environments which could be suitable?
The kangaroo question pertains to a species’ ability and/or decision to adapt to a new environment. More specifically, in this particular situation, why do kangaroos only live in Australia? There are plenty places on earth that could comfortably suit their needs, and yet they stay where they have always been. There are many variables that contribute to a species decided habitat, the key issues being dispersal factors, behavioral factors, and more broadly, biotic and abiotic factors.
Biotic factors are physical encounters involving other organisms in the environment, including (but not limited to) parasites, predators, pathogens; any competitors are considered biotic factors. For example, if one were to place a population of kangaroos in a habitat containing large, powerful and carnivorous predators, they most likely will die off from lack of defense mechanisms against these new predators. This would be an impractical biome for kangaroos. This could also go the other way, and kangaroos could over populate, completely removing a species of plant from the area for good. Abiotic factors are characterized by physical attributes pertaining to climate; more specifically, temperature, moisture, oxygen, salinity, sunlight, and the rocks, minerals and soil available in a specific habitat. Obviously, kangaroos couldn’t survive severe cold weather or snow and ice.
Some behavioral factors that inhibit or allow change of habitat could be as simple as a species collectively deciding that they don’t want to be in a certain area; for whatever reason. (For insects) this could be that the blue flowers’ leaves taste better than the purple flowers’, and so as a whole species, the insects won’t survive where there are only purple flowers; simply fact that they don’t want to. This could also be that they enjoy one particular climate more than another, and stay put because they genuinely enjoy their current surroundings. Suitable habitats are sometimes rejected just as how humans decide where they want to live when given more than one option.
Last, but not least of the obstacles, dispersal factors relate more to the movement of organisms/beings. If kangaroos had the option to come to North America, then they would be able to either accept or reject the habitat. Then, biotic and abiotic factors depending, they would survive or die off in their new environment. However, to get to North America, they would have to be introduced to the land against their will, seeing as how kangaroos couldn’t swim the distance of an ocean. An organisms ability to migrate through different terrains certainly limits it’s choices of habitat. Although there may be two nearly identical environments fairly close together, that the kangaroos could thrive in, if there is a mountain between them, it doesn’t matter anyways because they don’t have the necessary abilities to actually get through the mountain to the new area. The same goes for other geographical obstacles such as oceans, deserts, rivers, or any other inhospitable biome.