- Introduction To Adaptive Radiation
- Examples of Adaptive Radiation
- Example 1. Australian Marsupials and Placental Mammals
- Example 2. Darwin’s finches in the Galapagos Islands
- Example 3. Adaptations in Human
- Example 4. Malawi cichlids
- Example 5. Hawaiian honeycreepers
- Example 6. Caribbean anoles
- Example 7. Tanganyika cichlids
- Example 8. Victoria cichlids
- Example 9. Species of crickets in Hawaii
Introduction To Adaptive Radiation
Adaptive radiation is an evolutionary process in which an ancestral form gives rise to new species adapted to new habitats and new ways of life.
In adaptive radiation, a population of ancestral species can separate itself into a new habitat, new lifestyle, and new resources to form many separate descendant species populations over the period of millions of years of evolution.
Adaptive radiation usually occurs when the ancestral population of a species gets new exploitable resources.
These new exploitable resources usually occur due to change in the environment, formation of new habitat, destruction of old habitat, change in resource availability, creation of new challenges, or due to the introduction of new environmental niches.
Adaptive radiation is a type of macroevolution because it leads to speciation that is the formation of new species. In such an evolutionary process, the ancestor species shows various small adaptations to its environment and gradually becomes different from the ancestor species after achieving many of such small adaptations altogether.
Adaptive radiation is a type of Natural Selection that causes divergent evolution.
Speciation is one very important result (consequence) of divergent evolution and adaptive radiation is a type of divergent evolution which highly supports it.
Below there are some of the most prominent examples of adaptive radiation that will help you understand the concept of adaptive radiation better and precisely…
Examples of Adaptive Radiation
Example 1. Australian Marsupials and Placental Mammals
Adaptive radiation can also be seen in the placental mammals of Australia. It can be studied by understanding placental mammals and their marsupial counterparts.
It is seen that the placental mammals have evolved in such a way that resembles their similarities to corresponding marsupial mammals of Australia.
Parallel adaptive radiation is shown by Placental mammals as they have evolved from other marsupial mammals and the resemblance of each of them is with a corresponding marsupial.
It is seen that most of the Australian mammal species are marsupials (carry young ones in a pouch), while most mammal species found elsewhere in the world are placental (nourish young ones through a placenta).
This happened because Australia was isolated by water for millions of years, and so these species were able to evolve without competition from (or exchange with) other mammal species elsewhere in the world.
The marsupials of Australia due to their excessive presence have evolved themselves to create a diversity of various marsupial mammal species than the placental ones.
For example: Tasmanian Tiger cat (marsupials) of Australia resembles with Bobcat (placental mammal), Spotted cuscus (marsupials) of Australia resembles with Lemur (placental mammal).
Example 2. Darwin’s finches in the Galapagos Islands
Charles Darwin had observed the finches (small black birds) in the Galapagos Islands. It was seen that many varieties of the same bird were found on the same island that differs from the other island.
The finches (small black birds) in the Galapagos Island shows that those species that eat large seeds tend to have large-tough beaks, while those that eat insects have thin-sharp beaks. All have originated from their ancestral seed-eating finches through large-scale macroevolution.
Darwin observed that the species on these islands appeared to be closely related to the species on the nearest continent.
He concluded that the birds on these isolated islands must have been originated from the nearby continent, due to the formation of these islands during plate tectonics.
As they were separated from the other species on the continent, they gradually evolved into something different over thousands of years.
Darwin’s observation showed that these finches were not found in similar climatic zones elsewhere on Earth but especially in the Galapagos Islands.
This literally proves how island isolation led to the adaptive radiation and speciation of the finches from a common ancestor.
Example 3. Adaptations in Human
Our physical developments like skin color, removal of excess body hairs, etc. are another example of adaptive radiation.
Humans are the most evolved species on the planet, and we also have undergone many changes over time from our ancestors.
Dryopithecus that lived about 15 mya (million years ago) supposed to be the common ancestor of apes and modern man.
Dryopithecus gave rise to Ramapithecus which was the earliest man-like primate.
Ramapithecus gradually gave rise to Australopithecus which were men with an ape-like brain.
Australopithecus gave rise to H. habilis. And then H. erestus, H. sapiens neanderthalensis, H. sapiens fossilis, and then finally the present-day modern-living man H. sapiens sapiens were evolved at the same time at different locations.
This human evolution from Dryopithecus to H. sapiens sapiens have occurred due to adaptive radiation, which took more than 15 million years to complete.
During this evolution, humans became bipedal and our arms and limbs adapted to do various specifically dedicated tasks.
Other adaptations like the occurrence of the amount of melanin in our skin have also occurred. Melanin is representative of the environment we live in, i.e. dark-skinned people occupy hotter climates and show more melanin than people living in cold regions.
Other adaptations like humans who have produced offspring that successfully live in a cold environment tend to be broader and smaller in stature, while hotter environments are occupied by thinner taller humans.
The formation of H. erestus (now extinct), H. sapiens neanderthalensis (now extinct), H. sapiens fossils (now extinct), and H. sapiens sapiens (currently we people) from Australopithecus at different biogeograpghies, is an example of adaptive radiation.
Adaptive radiation is an evolutionary process that produces multiple new species from a single, rapidly diversifying lineage (here Ramapithecus).
Example 4. Malawi cichlids
Adaptive radiation is also seen in the cichlid fishes of Lake Malawi in Tanzania. These Malawi cichlids are descendants of Tanganyikan ancestors that presently live in Lake Tanganyika of East Africa.
It is believed that may be around more than 3.4 billion years ago the Tanganyikan ancestors have somehow reached Lake Malawi in Tanzania.
These have led to adaptive radiation over time to form the present day cichlids fishes of Lake Malawi that constitute a species flock of up to 1000 endemic species.
And, it is seen that only seven cichlid species that belong to genera Astatotilapia, Serranochromis, Oreochromis, and Coptodon in Lake Malawi are not a part of these species flock that include about 1000 endemic species.
This means that about 9993 species out of 1000 species of cichlid had a common Tanganyikan ancestor, whereas the rest of the 7 species had a common ancestor that previously lived in Lake Malawi.
For example, all members of the Malawi species flock are mouth-brooders, and males of most species display predominantly blue coloration when mating.
Example 5. Hawaiian honeycreepers
Another famous example of adaptive radiation is seen in the Hawaii islands. Hawaii honeycreeper birds show adaptive radiations in which they show different morphology in their different types of beaks.
The Hawaiian honeycreepers constitute a large, highly morphologically diverse species group that began radiating in the early days of the Hawaiian archipelago.
The Hawaiian honeycreepers like Hemignathus wilsoni are known for their short-sharp beaks that help them in scraping the bark off of trees and probe the wood underneath to eat insects.
Another Hawaiian honeycreeper species like Drepanis coccinea has a very long curved beak for reaching nectar deep in Lobelia flowers.
An entire clade of Hawaiian honeycreepers, that belong to the tribe Psittirostrini, are thick-billed, mostly seed-eating birds, like the Laysan finch (Telespiza cantans).
It is said that all the Hawaiian honeycreepers in Hawaiian archipelago have evolved from a common ancestor through adaptive radiation some 15 to 20 million years ago.
It is said also that more than 50 Hawaiian honeycreeper species have evolved from one common ancestor, and today only 17 species are known to persist in Hawaii (3 more may or may not be extinct).
Example 6. Caribbean anoles
One of the finest and largest examples of adaptive radiation in lizards can be seen in the Anole lizards with over 400 species (genus Anolis) that are distributed broadly from the Southeastern US regions to South America regions.
Specifically, amongst these 400+ species, anoles that are seen on each of the islands of Cuba, Hispaniola, Puerto Rico, and Jamaica have much more adaptively radiated in separate, convergent ways creating different new species adapted to their way of habitat.
On each of these islands, anoles have evolved with such a consistent set of morphological adaptations that each species can be assigned to one of six “ecomorphs”.
An ecomorph is a local variety of a species whose appearance is determined by its ecological environment and habitat.
The six “ecomorphs” are: trunk-ground anole lizards, trunk-crown anole lizards, grass-bush anole lizards, crown-giant anole lizards, twig anole lizards, and trunk anole lizards.
Each ecomorph shows different types of characteristics that help them better survive and reproduce.
Take, for example, crown-giants anole lizards from each of these islands: the Cuban Anolis luteogularis, Hispaniola’s Anolis ricordii, Puerto Rico’s Anolis cuvieri, and Jamaica’s Anolis garmani (Cuba and Hispaniola are both home to more than one species of crown-giant anoles).
These crown-giants anoles are all large, canopy dwelling species with large heads and large lamellae (scales on the undersides of the fingers and toes that are important for traction in climbing), and yet none of these species are particularly closely related and appear to have evolved these similar traits independently.
The same can be said of the other five ecomorphs across the Caribbean’s four largest islands.
Example 7. Tanganyika cichlids
Tanganyika cichlids are those cichlid fishes that are found in the Lake Tanganyika of East Africa. Lake Tanganyika is the largest rift lake in Africa and the second-largest lake by volume in the world.
Lake Tanganyika being such a large lake, it is obvious that it will have different types of aquatic environments in its different regions.
Due to such a vast variety of aquatic environments, it had caused adaptive radiations in the Tanganyika cichlids species that are thought to have originated from many common ancestors around 9–12 million years ago.
Lake Tanganyika is the site from which nearly all the cichlid lineages of East Africa (including both riverine and lake species) originated. The cichlid species in the lake constitute a single adaptive radiation event.
There are about 250 cichlid species at present in Lake Tanganyika that are more morphologically divergent and ecologically distinct from each other species.
Just, for example, the giant or emperor cichlid (Boulengerochromis microlepis) spawns only a single time, breeding in their third year and defending their young until they reach a large size.
The three species of Altolamprologus are also piscivores, but with laterally compressed bodies and thick scales enabling them to chase prey into thin cracks in rocks without damaging their skin.
Plecodus straeleni has evolved large, strangely curved teeth that are designed to scrape the scales off other fishes as scales are its main source of food.
Another one is the Gnathochromis permaxillaris that possesses a large mouth with a protruding upper lip, and feeds by opening this mouth downward onto the sandy lake bottom, sucking in small invertebrates.
Thus, it can be seen that different species of Tanganyika cichlids show different varieties of lifestyles, way of living, habitat, feeding habits, and spawning procedures to find their kind of aquatic environment in this whole single large Lake Tanganyika.
Thus, this is another fine example of adaptive radiation.
Example 8. Victoria cichlids
Cichlids of Lake Victoria also shows a great variety of adaptive radiation. Lake Victoria is one of the African Great Lakes.
Lake Victoria’s cichlids are also a species flock, once composed of some 500 or more species.
The deliberate introduction of the Nile Perch (Lates niloticus) in Lake Victoria in the 1950s proved disastrous for Victoria cichlids, and as a result, many of the Victoria cichlid species flock has decreased substantially.
Also due to this an unknown number of Victoria cichlid species have become extinct as well.
However, the original range of morphological and behavioral diversity seen in the Victoria cichlids is still mostly present today and explains how adaptive radiation had once occurred to create the present-day large variety of Victoria cichlids species.
These species varieties can be seen as Lake Victoria is famously home to many piscivorous cichlid species, some of which feed by sucking the contents out of mouthbrooding females’ mouths, while other varieties feed on the fish scales and even other aquatic plants.
Victoria’s cichlids constitute far younger radiation than even those of Malawi cichlids, that may have occurred between 200,000 to 14,000 years ago.
Example 9. Species of crickets in Hawaii
Hawaii has served as the site of a number of adaptive radiation events, owing to its isolation, recent origin, and large land area.
Here in this example of adaptive radiation, we’ll talk how the different species of crickets in Hawaii had gradually radiated over time.
It is said that about 240 species of crickets have radiated and evolved from many common ancestors of tree cricket, sword-tail cricket, and ground cricket in the different-different regions of Hawaii archipelago.
Among these 240 species, there are several species that have adapted to subterranean life in the underground environment within underground lava tubes. These can be seen mostly in Maui and the Big Island of the Hawaii archipelago.
Another species of crickets that live underground in Hawaii have reduced eyes and pale color compared to the surface-dwelling species that colonized the islands. These species have reduced coloration, small eyes, and a clear exoskeleton which help them to better adapt to their type of environment.
Presently, it is said that about 240 species are found to be native to the islands before the arrival of humans. Almost all of these are found only in the Hawaiian Islands, and most were new to science.