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Species are groups of organisms that can potentially interbreed to produce fertile offspring. If two animals of different species breed with each other, this is called cross-breeding and the result is almost always infertile offspring, consequently preventing the genes of two different species. To avoid this, most species have specific methods, such as courtship rituals, colours, mating calls, etc that ensure they reproduce with members of their species. Very few however, match the elaborate mating dance of the birds of paradise that inhabit the Australasian islands.
There are forty-one different types of these marvellous birds, and each of them only reproduces with others of its same type. During the breeding season, the males perform intricate combinations of movements that display their exotic plumage in order to demonstrate to the females that they are the suitable partner and to prove that they are of the same species. Another entirely different form of a mating ritual is the distinct call of the Indri Lemur, an endemic species, like all lemurs, meaning they can only survive in a particular region-in this case, Madagascar. This can be watched in the video to the left (minute 3:30 to 4:30). While in a natural environment it is fairly rare for cross-breeding to occur, humans have done several experiments to observe the result of two specific species interbreeding, One of the most famous examples is the liger or a tigon, a mix between a lion and a tiger the difference being that when the father is a lion it is a liger and viceversa. While this mix may have happened more often in the past amongst animals that aren't kept in captivity , it is currently extremely rare as the diminishing habitats of both lions and tigers don't overlap. Consequently, when breeders force this to happen in zoos or similar enclosures, the offspring may suffer from birth defects and therefore die young. The cats are usually also grow to be larger than both parents, and thus during the pregnancy their size can cause health issues for the mother and a difficult delivery. In fact, the biggest feline to be alive at this moment is believed to be Hercules, the liger living in the Myrtle Beach Safari wildlife preserve in South Carolina. Within species, organisms are then divided into populations. These are groups of organisms who not only belong to the same species, but also live in the same area at the same moment. This means that while all members of a species can interbreed, it is more likely for this to happen between members of the same population. This is important because if two different populations within one species never interbreed, they can develop different characteristics. However, until members of such two populations don't produce infertile offspring when they reproduce, they are not considered different species. |