The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit. The Rights Holder for media is the person or group credited.
Director
Tyson Brown, National Geographic Society
Author
National Geographic Society
Production Managers
Gina Borgia, National Geographic Society
Jeanna Sullivan, National Geographic Society
Program Specialists
Sarah Appleton, National Geographic Society, National Geographic Society
Margot Willis, National Geographic Society
otherLast Updated
August 9, 2022
As discussed in other units, the Earth contains vastly different specific biomes that are home to many different species of animals. These biomes are determined by a map that takes into account the Sun's energy and earth tilt which disperses heat into different biomes. This range of conditions create specific environments that, depending on the species, are either livable or unlivable. The level of adaptability that a species can utilize to survive in an environment differentiates them to be either a generalist or a specialist. These two categories use a number of factors to divide organisms on their adaptability to different conditions. Some of the factors used to determine this ability are:
Niche/ Adaptability ➢ What niche does the species occupy? How easy would it be for them to adapt to a sudden change?
Diet ➢ What do they eat, how readily is it available, and how much would it impact them to forcibly change their intake?
Location ➢ Where do they inhabit now, and does a change in location or climate directly affect their survival?
Tolerance ➢ How any small or large change would affect their well-being and, if affected, how quickly they would recover?
Characteristics of a Generalist Species
A generalist is a species with a broad niche that is easily adaptable to many environmental conditions. These species are more likely to survive (and in larger numbers) due to the fact that they are able to easily relocate, change food sources, and adapt in other ways to new biomes. Generalists are quickly adaptable to change and are rarely faced with the need to "recover" from any environmental problems. Generalists' diets change in accordance with surroundings and they can even evolve in certain ways to maintain genetic traits specific to their new/recently inhabited biome.
An example of a generalist species would be a raccoon. Found all over the world, whether in trash bins or parks, raccoons can adapt easily to changes in weather or habitat. Their diets are simply consistent with what surrounds them (they are able to forage in trash cans for food if needed) and they don't require any specific or incredibly stable conditions to keep reproducing or maintaining their health.
Characteristics of a Specialist Species
A specialist species, on the other hand, has a narrow niche with incredibly specific needs in order to survive. Specialists require a detailed and consistent climate, diet, and regimen to keep them alive. Specialists are not able to readily move biomes and are more likely to seriously suffer from a natural disaster since their ability to leave or readily adapt to a new environment is massively hindered. Their forms of shelter must remain consistent with equal levels of sunlight and access to water (depending on the species). Specialists reproduce in a way meant to keep all genetic traits needed for survival in their biome present in their offspring.
An example of a specialist species is a panda. Pandas need a certain diet and habitat in order to survive. Pandas are mostly found in Temperate Broadleaf Deciduous Forests, Tropical Broadleaf Evergreen, and Bamboo Forests because of the specific diet they have. Pandas can only survive off eating bamboo and other grasses.
⚡ Checkpoint question
A temperate grassland inhabits a variety of species with plants and animals. A natural disaster destroys their habitat and brings in different species to the habitat. Which organisms are most likely to survive in the new environmental conditions and why?
After the formation of an island, it will be a certain amount of time before it is discovered and subsequently inhabitated by various different organisms. The immigration (arrival) and extinction (death) rate of these organisms help determine how quickly and how efficiently islands are taken over by ecosystems.
As extinction increases, immigration decreases. Larger islands or islands closer to land will have higher rates of immigration due to their proximity to other, larger ecosystems. As more and more species arrive, room runs out, and extinction rates will heighten. Eventually, this duality will balance out, and the point of equilibrium between immigration and extinction rates is ideal for the island.
Size and distance matter greatly when discussing the species richness or accessibility of an island. Larger islands exhibit, on average, many more species than smaller islands. Islands closer to land are also easier to reach than islands too far for certain organisms to travel.
Invasives
Islands are home to many endemic species, or those that occur naturally in only one or certain parts of the world and are confined to that geographical area. Since these species are specialists, they require the specific ecosystem that they live in. This means that their ecological niche (more simply, their survivable environment) is quite narrow (or specialized). These specialists are sensitive to environmental changes as a result of this narrow niche and are often wiped out by invasive species. The invasive species are commonly generalists that have few to no native predators and are able to fill a broad niche. This often leads to the downfall of the endemics. To be clearer, endemic species with fewer livable environments can face extinction if an invasive species with less specific survival guidelines moves nearby.
Effects on Evolution
An excellent example of the IBT’s effects on evolution is Darwin’s Finches found on the Galapagos Islands. A small population was blown over to the island chain from Ecuador by a hurricane. The islands’ distance from the mainland affected the birds’ evolution.
Since there was no further immigration from the mainland, the birds adapted to the islands and evolved away from their mainland cousins. Each island also had its own pressures (food type and habitat) that pushed evolution more. There are now fifteen species living on the Galapagos Islands.