How many animals are there in the world?

How many animals are there in the world can be expressed as number of individuals, number of species and biomassThe weight of living organisms. Biomass can be measured in relation to the amount of carbon, the dry weight (with all moisture removed) or living weight. In general it can be used to describe the volume of energy that is contained inside systems, as the size of animals relates to their metabolism and therefore, how much energy they contain and More. Until 2017, the best estimates for the total number of species in the animal Kingdom were between 1.5 and 11 million. New studies have smashed this assumption as now we believe there may be 164 million and if you throw in everything else, plants, fungi, microbes, the lot, maybe up to six billion (Table 1) [1].

But number of species is only one dimension in the story of how many animals there are on Earth.

Brian Tomasik has estimated the number of individual animals as approximately 20,000,121,091,000,000,000. This is 20 quintillion, or 20 billion billion. In Table 1, I’ve summarised the number of species and the biomass [4] as a percentage of all animals. Biomass is a measure of the weight of carbon in

Table 1. How many animals are there in the world (numbers and biomass)?

What is the diversity of animals compared to plants?

Animal impactWhat is Animal Impact? Without wildlife, Earth would not be habitable for humans, because it's animals that stabilise ecosystems. It’s a fundamental law of nature that animals (and humans) exist because we are the most likely lifeforms to minimise environmental chaos. Animal impact, therefore, is a measure of how much all wildlife is collectively responsible for creating a habitable Earth. The More derives from the abundance of species and their interaction. There are in fact, about 500 species of animal for every type of tree, shrub or flower that we know about in the world. Without this diversity of animals working together, the ecosystemsHow ecosystems function An ecosystem is a community of lifeforms that interact in such an optimal way that how ecosystems function best, is when all components (including humans and other animals) can persist and live alongside each other for the longest time possible. Ecosystems are fuelled by the energy created by plants (primary producers) that convert the Sun's heat energy More we know, the ones that cradle animals like us, would fall apart. Studies on mangroves have found between 66 – 128 leaf-eating species and in one study, from the Andaman Islands and Nicobar, an overall total of 276 insects [2].

What are the most animal-rich habitats?

Ten years ago, ecologist Rob Wolton started recording all the animals he could see, with the naked eye, living in a 85m-long hedge next his house in Devon, England [3]. In the first two years, he recorded 2,000 species. As the number of new species he can find has declined, it’s led Wolton to conclude the total might end up at about 3,000. Each of these species is interacting with the chemistry and thermodynamicsThermodynamics are at the heart of our understanding of ecosystems and not an altogether difficult concept to grasp but one that isn't widely taught to ecologists. Basically, all life on Earth, is derived from the Sun's heat. This renewable energy source constantly bombards ecosystems with energy but they would overheat, if it wasn't for the absorptive capacity of food webs. More of the ecosystem, because they are mobile. If only 50 animals are interacting with each other, the number of permutations would be more than the number of atoms on Earth. That’s the level of complexity we are dealing with, once we introduce animals. And it’s that complexity that enables ecosystems to stabilise and is what we mean when we say “biodiversity” –which is very different to species richnessThe number of species within a given area. Note, this is often confused with biodiversity but is very different. Species richness is not equal in all areas. Desert species richness is lower but the scale and intensity of species function can still be significant as biodiversity is not about number of species, it's about ecosystem processes. More.

Grasslands are thousands of times more species-rich on a small scale, than rainforests. A hectare of the Ecuadorian rainforest has about 950 species but grasslands in the Czech Republic can have 44 species for every 25 x 25 cm – that’s 7,500 times more species-rich. We have a habit of thinking on one scale … the scale at which we live: things that are about the same size, or bigger than us. Grasslands are microscopic habitatsWhat is habitat for animals and people? Habitat, hence the word "habitable" describes the natural surroundings in which any animal (or human) lives, that houses basic needs, such as food and shelter. Vegetation, for example, is habitat for animals. On its own, habitat is not necessarily stable or sustainable, which is why it differs from an ecosystem. Habitat in disrepair More but the biodiversityWhat is the definition of biodiversity? When we ask, what is the definition of biodiversity? It depends on what we want to do with it. The term is widely and commonly misused, leading to significant misinterpretation of the importance of how animals function on Earth and why they matter a great deal, to human survival. Here I will try to More processes they contain, are off-the-scale intense, due to the huge animal impact that occurs over every square centimetre.

Think about it – this is why our prime agricultural land is mostly built on historic grasslands. It wasn’t the presence of grass that created the soil fertility, it was the thousands of animals that tilled the soil for millennia.

When you next look at a tree in your local park, think about how many animals are residing among its branches and leaves. Because it is the downward pressure on plants, that creates diverse forests and grasslands, while maximising the amount of carbon absorbed, and helping cool the Earth.

Then think about how much better it would be for you and the human race, if there was a more natural abundance of wildlife.

Table 2. How many animals are there in the world (different species)?

1. Larsen, B., E. Miller, and M. Rhodes, Inordinate Fondness Multiplied and Redistributed: the Number of Species on Earth and the New Pie of Life. Quarterly Review of Biology, 2017. 92.
2. Burrows, D., The role of insect leaf herbivory on the mangroves Avicennia marina and Rhizophora stylosa. 2003.
3. Wolton, Robert. (2015). Life in a hedge. British Wildlife. 26. 306-316.
4. Bar-On, Yinon & Phillips, Rob & Milo, Ron. (2018). The biomass distribution on Earth. Proceedings of the National Academy of Sciences. 115. 201711842. 10.1073/pnas.1711842115.