By 1902, poachers had reduced Yellowstone National Park’s bison herd to about 24 animals. According to the National Park Service, there are 4,680 bison in Yellowstone today. They were last counted in the summer of 2020.

Just exactly how many species are there in our big, diverse world? And where, precisely, do they live? While all of us have probably wondered about such things from time to time, scientists have been grappling with these questions for decades—and trying to ascertain what impacts we humans are having on animal and plant lives and their habitats.

Those are huge goals. We are, however, making progress.

Listing life

As of now, we have no agreed-upon list of all the world’s species. But a paper published on July 7, 2020, in the open access journal PLOS Biology outlines for the first time a road map for creating such a roster, from birds to mammals and from microbes to plants.


How many species of birds are there in the world? It depends on whose count you go by. The number could be as low as 10,000 or as high as 18,000. It’s tough to standardize lists of species because the concept of a “species” itself is a little fuzzy.

Today, iconic groups of animals, such as birds, may have several competing lists, while other, less well-known groups have none. For example, these four lists each purport to include all the known bird species in the world: the BirdLife International Checklist of the Birds of the World (11,126 species), the eBird/Clements Checklist of Birds of the World (10,824 species), the Howard and Moore Checklist of the Birds of the World (10,175 species) and the International Ornithological Community World Bird List (10,896).

This causes problems for governments and organizations that need accurate, reliable and scientifically defensible lists for the purposes of conservation, international treaties and the regulation of trade in endangered species. It also hampers researchers studying Earth’s biodiversity.

The new paper outlines a potential solution: a set of 10 principles for creating and governing such a proposed list, and a suggested governance mechanism for ensuring that the lists are broadly acceptable and well managed. It also clearly defines the roles of taxonomists—the scientists who discover, name and classify species—and stakeholders, such as conservationists and government and international agencies. While taxonomists would have the final say on how to recognize and designate species, the process ensures that stakeholders’ needs are considered when deciding between differing taxonomic opinions.


“Christmas tree worm”—referring to appearance—is the common name for a marine worm native to tropical oceans worldwide. A recent study shows that biodiversity loss in marine ecosystems is outpacing that on land.

We’re all aware that the Earth’s species are facing unprecedented threats, which include climate change, disease, the clearing and overutilization of land, and pollution. It’s driving an accelerating and unprecedented extinction crisis. Developing a single, definitive list of species won’t halt their demise, but it is an important step in managing and conserving the world’s biodiversity—all animals and plants, great and small—for our generation and future ones.

Mapping biodiversity

At the same time that scientists are trying to create a list of all the world’s species, they’re also attempting to map where they live so that the loss of biodiversity can be charted. A change in biodiversity is complex and difficult to understand because it can be measured in different ways, including by the number of unique species or by the population metrics of those species. In addition, biodiversity is affected by various human actions, with different effects and timings. As of now, having a clear understanding of what the net effects of these actions are across the planet is lacking.

A 2019 study, published in the journal Science, focused on mapping biodiversity changes in land and marine ecosystems. It showed that the loss of biodiversity is most prevalent in the tropics, with changes in marine ecosystems outpacing those on land. The research, which involved scientists from leading universities across Canada, Europe and the United States, aimed at reaching a consensus about variations in biodiversity change. It found that there were both negative and positive changes in ecosystems across the world. And although, on average, the numbers of species that live in each place are not changing, many regions were either gaining or losing species.

Pixabay (Created by Candice Gaukel Andrews)

Unfortunately, Amur leopards—such as this one, photographed in a zoo—are one of the world’s most endangered big cats. Between 2014 and 2015, there were only about 92 left within their natural range. That number is now estimated to be less than 70.

To examine geographic changes and variation in species richness and composition, the international team of scientists pieced together and mapped more than 50,000 biodiversity time series from studies throughout the world using the biodiversity database BioTIME. The scientists were then able to identify the places and types of organisms that are changing the most rapidly.

While the researchers concluded that biodiversity is changing everywhere, we’re not losing it everywhere. Some places are recovering and adapting. Usually, say the scientists, when biodiversity is in the news today, it’s because there’s a mass mortality event in coral reefs or another species is on the brink of extinction. However, there’s a lot of recovery also taking place silently in the background, and there are many places where not much is happening. This study puts these things on the map and shows that they are not contradictory.

This research project is an important one because it not only shows that while some locations have experienced decreases in the numbers of species, others have had increases or little change at all. More consistently, however, the identities of species appear to be changing at nearly all sites. Detecting such geographic variation in biodiversity trends will not only improve understanding of how global biodiversity is transforming, but it is critical to planning conservation and management strategies by pinpointing which regions to protect and which regions to help recover, particularly for sites exhibiting rapid turnover.


Due to climate change, the southwest Yukon has seen increasingly warm springs. That encourages white spruce trees to produce more cones, giving female North American red squirrels more to eat and causing them to give birth almost two days earlier per year over the last 10 years. Some of that shift is now attributed to genetic changes inherited over generations.

Changing genetics

While we’re learning how to list and map the world’s species, we are also starting to understand how we’re altering them. Human population density and land use is causing changes in animal genetic diversity, according to researchers.

As reported in the journal Ecology Letters in October 2019, environmental changes caused by humans are leading to changes in genetic variation in thousands of species of birds, fish, insects and mammals. The evidence for human impacts was most clear for insects and fish species.

Because animals depend on genetic variation to adapt and evolve in response to environmental changes, some that we rely on may disappear as their susceptibility to climate change, habitat loss and pollution grows. While the effects of humans on the planet’s biodiversity can be seen through the lens of animal extinctions, it was unclear until now just how much we are eroding the underlying ability of biodiversity to sustain itself.


The American bullfrog is one animal which may find more habitable environments because of global warming. American bullfrog tadpoles show a preference for warmer waters, which allows them to develop more quickly and reduces their exposure to predators.

A team of biologists at McGill University in Montreal, Quebec, Canada, drew upon the largest genetic data repositories available, accumulating more than 175,000 sequences from more than 27,000 populations of 17,082 animal species. Using the year each genetic sequence was collected and its spatial coordinates, the authors were able to assess whether the effect of humans has resulted in temporal trends (increase, decrease, no effect) between 1980 and 2016.

The findings suggest that there is an effect of humans on animal genetic diversity, but it is a matter of which species and spatial scale. They found nearly equal instances of increasing versus decreasing trends. However, the loss of any genetic diversity will hinder the ability of animal and plant populations to adapt to changing environments. We need to monitor the genetic diversity of wildlife so that we can better understand when, where and why it is declining in some places and increasing in others. Without this knowledge, we will have little warning of the losses many species are suffering or the invasive spread of others.

Rolling uphill

Most of us are in the habit of counting; we have a natural affinity for lists and exact tallies. But trying to bring together and categorize all life on Earth may prove to be a Sisyphean task.

If you’d like to help quantify the animal kingdom, one of the best citizen science opportunities is to get involved in a local butterfly monitoring program, such as one for counting monarchs. ©Court Whelan

I say, though, that if by quantifying the biodiversity that we have (listing and mapping) we stop our damaging ways of influencing (changing) nature’s processes, count me in for trying it.

Here’s to finding your true places and natural habitats,