As the most intelligent and technologically advanced species on Earth, we humans like to think that we own the place. But evolutionary success can be measured any number of ways. As evolutionary biologist Stephen G. Gould once noted, complexity, intelligence, and ferocity don't count for much in the long run — adaptability and reproductive success matter more. With that in mind, here are the eight most prolific and versatile organisms that rule our planet.
Photo by Alex Wild.
There's no question that bacteria is the killer app of nature. In fact, a number of biologists have suggested that we actually live in the Age of Bacteria. And indeed, bacteria can be found virtually everywhere, including soil, acidic hot springs, radioactive waste, water, and deep within the Earth's crust. A large prokaryotic microorganism, bacteria is best understood as a domain of organisms rather than a distinct species, so it's worth breaking them down into smaller groups. Take, E. coli for example. Over the course of life, there will be more E. coli living in the gut of each human being than the total number of people who have ever lived. And according to Lynn Margulis, "Fully 10 percent of our own dry body weight consists of bacteria, some of which, although they are not a congenital part of our bodies, we can't live without." Another particularly prolific type of bacteria is cyanobacteria, also known as blue-green algae. It's been known to dwell in a diverse range of habitats and take on extremophile characteristics. But no classification of bacteria compares to the SAR11 clade, a bacteria that that lives on the surface of oceans. Its population has been estimated at an unfathomable 2.4 x 1028 individuals, making it the most successful organism on the planet.
Phytoplankton are microscopic organisms that blanket the surface of most oceans and bodies of fresh water. A subset of the larger plankton community, they cannot be seen with the unaided eye, but because they exist in such large numbers they can actually discolor large expanses of water. These tiny autotrophic critters account for half of all photosynthetic activity on Earth — which, when considering how many plants exist on the planet, is nothing short of astounding. As a result, they are integral to the planet's oxygen supply. They also drive the 'biological pump' that converts 100 million tonnes of atmospheric carbon dioxide a day into organic material. Phytoplankton also serve as the base for the aquatic food web, offering themselves a readily available meal for baleen whales. In terms of numbers, there are over 5,000 known species — but because new ones keep getting discovered, it's difficult to put an exact number on them. And disturbingly, their numbers are decreasing at a rate of 10% a year, likely on account of climate change.
Emerging from wasp-like ancestors over 130 million years ago, ants have become the most successful terrestrial macro-scale species this planet has ever seen. Often considered a superorganism on account of their hive-mind composition, their evolutionary success has been attributed to their highly coordinated social organization, an ability to modify habitats, exploit resources, and defend themselves. Nearly 12,500 species have been identified, but it's thought that as many as 22,000 species may actually exist. Ants have also colonized virtually every landmass on Earth, and may comprise anywhere from 15 to 25% of the total terrestrial animal biomass. Put another way, there are more ants on this planet by weight than all humans combined. In terms of numbers, E. O. Wilson has estimated that there are 10,000 trillion individual ants alive at any given moment.
Coleoptera, what are commonly called beetles, includes more species than any other insect order, constituting almost 25% of all known life-forms. They make up about 40% of all known insect species (about 400,000 in total) and comprise about 500 recognized families and subfamilies. Actually, it's probably even more than that; it has been estimated that there may be as many as one million different beetle species. Highly adaptable, beetles can be found in all major habitats (except marine and polar regions), and are non-specialist detritus feeders — a generalized adaptation that allows them to break down animal and plant debris — including waste and fungi.
Another social insect, termites are members of the Isoptera order, and contrary to belief are only distantly related to ants (they're actually more closely related to beetles). Like ants, they are eusocial insects that divide their labor among castes and take care of their young collectively. There are an estimated 4,000 species of termites, and colonies can contain anywhere from hundreds to millions of individuals. And as many of us tragically know, they are insatiable devours of wood — but their ability to recycle wood and other plant matter has made them an indelible component of the biosphere. It has been estimated that termites cause around $22 billion in structural damage annually around the world. Termites are so prolific that they're actually being considered as a potential renewable fuel source by the U.S. Department of Energy on account of their ability to produce copious amounts of hydrogen.
Simply put, grass is the most dominant form of vegetation on the planet. Among the most versatile life forms on Earth, grasses have adapted to conditions in rain forests, deserts, mountains and even intertidal habitats. They are now the most widespread plant on the planet, and as a consequence, have become a primary food source for all sorts of wildlife. Also known as graminoids, there may be as many as 3,500 different species. Grass has also benefited from humans, owing to our love for lush lawns, parks, and playing fields.
Originally a tropical insect, cockroaches have adapted disturbingly well to human civilization. Though not as prolific as some of the other creatures on this list, cockroaches are incredibly hardy and resilient. Some species are capable of remaining active for months without food and are able to survive on limited resources — including glue from the back of postage stamps. Some cockroaches can even go without air for up to 45 minutes. And as for the old adage that cockroaches can survive a nuclear holocaust, there may be some truth to it. Because their cells divide only once each time it molts, it has a higher radiation resistance than most vertebrates, capable of withstanding a dose six to 15 times that which a human could endure.
Rats are probably the most resilient mammal on the planet — and like the cockroach, they have benefited from human activity. Known as commensals (opportunistic survivors that have taken full advantage of urban environments), rats, or more accurately the brown rat, will eat almost anything. They can live in a wide variety of habitats, and are expert jumpers, climbers, and swimmers. They can produce up to five litters per year, each one containing anywhere from six to 22 young. In fact, a single pair of rats can multiply to 200 in just one year. It's thought that there are billions of rats on this planet, making them the most successful mammal (excepting humans). They're also hard to kill — and are becoming increasingly immune to poisons. In fact, genetic mutations are so pronounced in some populations that their DNA has become irrevocably altered.
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