Image source: Unsplash
2 billion billion, 20 000 000 000 000 000, 2 followed by 16 zeros: this is the (approximate) number of ants on Earth.
If you were asked the first insect you knew in childhood, most people would probably answer ants. There is no other reason-there are too many ants, and they are found in almost every corner of the land (except Antarctica).
The famous biologist and “father of sociobiology” Edward Wilson (Edward Wilson) was particularly fond of these small creatures. He refers to ants and other invertebrates as “ the little things that run the world”: “They (ants) are in staggering numbers. If Homo sapiens hadn’t happened by chance as a primate on the African savannah , and migrated all over the world, when visitors from other galaxies come to Earth (mark my words, they will come sooner or later), they will certainly be willing to call Earth the ‘Ant Planet’.”
Yet we know next to nothing about these “true masters of the planet.” We can’t even answer the most basic question – how many ants are there on Earth?
“Ants account for two-thirds of the total biomass of all insects. There are millions of species of which we know almost nothing about.” – Edward Wilson (Image source: original paper)
not only curious
This question is not just about human curiosity. We all know that ants play an inescapable role in ecosystems: They disperse seeds, loosen soil, and accelerate the decomposition of organic matter. And the small ants can have such an important ecological status, which is inseparable from their huge number .
Therefore, how many ants are there has become a question that many ecologists have tried to answer. Wilson and the ecologist Bert Hölldobler did some rough calculations: They simply extrapolated global insect populations based on insect densities in south-east England, and assumed ant populations of about Accounted for 1% of all insects, and finally came to 10¹⁶ and another conclusion you may have heard: the biomass of ants (calculated by dry weight, that is, carbon content) is about equal to the biomass of all human beings (at that time the global population of approximately 5 billion).
Image source: Unsplash
Obviously, neither extrapolating the global population of insects from a single region nor estimating that ants account for 1% of the total insect population is inaccurate . We can also think about this problem from another angle: if you want to estimate the number of students in a school, you can of course count the total number of students in the city, and then divide it by the number of schools in the city to get a rough result.
But there is another more accurate method – count how many people are in each class of this school, and then add up the number of people in each class.
2 billion billion
Recently, based on a similar method, a research team at the University of Hong Kong in China obtained a new census number of ants: 2×10¹⁶ individuals .
This number may be difficult to make people feel, but we can look at it from another angle: on average, each person corresponds to 2.6 million ants, and the total biomass (dry weight) of ants is about 12 million tons, accounting for 100% of all human beings. 20% of the volume , approximately equal to the weight of the two Khufu pyramids.
The study, published in the Proceedings of the National Academy of Sciences (PNAS), is the first “bottom-up” method for estimating ant populations. The researchers estimated the average number of ants in different biomes based on ant density surveys in different regions. The biomes here refer to areas with similar climate and geographical conditions, such as tropical rainforests, temperate grasslands, etc., like different classes in a school. Then add the number of ants in each biome to get the total number of ants in the world.
Biomass of different organisms (dry weight, unit: million tons) (Image source: original paper)
Most of these regional data were found from existing literature, and some of them were sampled by the research team themselves. When screening previous literature to calculate the number of ants, the researchers specifically chose the classic Winkler litter extraction method : take away the fallen leaves and topsoil in a specific area, and collect the insects in the litter uniformly by fully drying them. This method can fully collect insects on the ground surface within a certain area, but there are also some problems. Because collections were often performed during a short period of time during the day, changes in insect populations over time were ignored. And in some places where there is a lack of litter, such as open grasslands, this method is not suitable.
Therefore, as a supplement, the research team also chose another method: the trap method . This method only needs to place a trap on the ground to collect the ants that fall into it within a certain period of time. Obviously, this method cannot give the exact number of ants per unit area, but by comparison, the activity intensity of ants in different regions can be judged, and when combined with the Winkler litter extraction method, the number of ants in other regions can be estimated.
Image source: Unsplash
In this way, if it is assumed that the ant species and ecological environment in each biome have negligible influence on the number of ants, the total amount of ants can be extrapolated according to the area of different biomes.
Of course, such a method is only applicable to ground-dwelling ants, and there are a large number of ants living in trees. Therefore, the research team also included data obtained by the aerosol insecticide method . This method uses an atomized insecticide to uniformly kill insects on vegetation in a specific area, and then collects the dead insects together. The ecological cost and labor cost of this method are relatively high, so this kind of data is rare, but it can also be used as a reference to calculate the number of tree-dwelling ants.
Yellow represents the sample data obtained by the litter method, and blue represents the sample data obtained by the trap method (picture source: original paper)
there are more……
Adding ground-dwelling ants and tree-dwelling ants together, we get 2×10¹⁶ this data. This number seems large, but the researchers believe that the actual total number of ants is likely to be much higher than this .
Patrick Schultheiss, corresponding author of the study, is almost certain that the true number of ants is higher than 2×10¹⁶: “We are only scratching the surface.” For one thing, this calculation only covers terrestrial species. Ants and arboreal ants completely exclude underground burrowing ants; in addition, there are fewer related studies in Central Africa, Southeast Asia and other regions, which may cause some ant-dense areas to be missed.
Calculated ant densities for different biomes, yellow for the litter method, blue for the trap method, with darker colors representing higher densities. (Image source: original paper)
Sabine Nooten, one of the authors of the study, also said: “I wouldn’t be surprised if the actual population of ants was an order of magnitude higher than our current estimates.”
However, for researchers, the most important result of this study may not be the number itself, but it shows that there are still a lot of gaps in modern research on biodiversity .
Image source: Unsplash
“Some of the data and results that we see from textbooks and take for granted may not be accurate.” One of the authors of this study, Wang Runxi shared the story behind the research in this article, “Sometimes these data are even just In the early days of research, people made bold speculations based on very limited data. This knowledge provides us with important information for understanding the world, but inadvertently, it also makes us wear a pair of shackles called “classics” and regard them as truth. “
Rather than providing an exact number, this study lays the groundwork for more related research. Over time, perhaps our knowledge of ants and more of biodiversity will grow to fill in these gaps.
How long has it been since you saw ants?
This article comes from the WeChat public account: Universal Science (ID: huanqiukexue) , author: Erqi, reviewer: clefable
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