What is biodiversity, and why is it important?
Biodiversity is a term that encompasses the diversity of life at different levels, and is almost synonymous with nature or wildlife in common usage, but the important hope is that this synonymy is not perfect. Biodiversity has been shown to be a crucial factor in maintaining the well-being of humans, as well as that of nature and all its interconnected components. This chapter answers the questions: “What is biodiversity? And why does it matter?” by exploring how biodiversity is a living cog in nature’s machinery. The second chapter, “What’s the problem?”, addresses the questions of what determines whether biodiversity is resilient, where it is vulnerable, and what threatens it (and by extension all of us). The next question is: What should be done? Or, as expressed in Chapter 3: What is the purpose of conserving biodiversity? This is not as easy a question as it once seemed. Building on these basic points, the remainder of this very short introduction will analyze some of these risks in more detail, consider what can be done about them, why it matters, and what comes next.
The amazing diversity of life on Earth
You are a eukaryote; that is, an organism made up of cells that have a membrane-bound nucleus, which contains genetic material and membrane-bound organelles. Prokaryotes are organisms whose cells do not have a nucleus or membrane-bound organelles. In the 250+ years since Swedish scientist Carl Linnaeus began taxonomy, 1.2 million eukaryotic species (animals, plants, fungi, and protists) have been identified and classified.
Conserving biodiversity
That is, less than 15 percent of the estimated 8.7 million eukaryotic species that exist. On average, 50 new species are discovered, mostly insects, but even among mammals, a new species is documented every three years: the most recent were the Risers whale (in 2021) and the Pupa langur monkey (in 2020) (Figure 1-1). A new vertebrate is discovered in the open ocean every five years. If the world’s biodiversity were a library, how would it be catalogued? Peter Holland’s book The Animal Kingdom: A Very Short Introduction offers an answer that is as comprehensive as the diversity of the plant kingdom (in Tim Walker’s Plants: A Very Short Introduction). Among the competing definitions of biodiversity, the Oxford Dictionary starts with a simplified definition, which defines it as “the presence of a large number of different species of animals and plants that are in balance.” The American Museum of Natural History elaborates on the definition by saying that biological diversity “refers to the variety of life on Earth at all levels, from genes to ecosystems, and can include the evolutionary, ecological, and cultural processes that sustain life.” Today, genetic diversity can be measured: I just received the complete genome of one of the badgers I study from the Sanger Institute. Not long ago, this would have seemed like science fiction, but now you can buy the genome of a species for the price of a meal at a restaurant. Diversity and abundance at the population level can also be measured.
In taxonomy, individuals are grouped into categories, each of which goes back to increasingly distant common evolutionary ancestors. These categories are called kingdom, phylum, class, order, family, genus, and species (and there are many subcategories as well). For example, a chimpanzee would be classified as: Kingdom: Animalia; Phylum: Chordata; Class: Mammalia; Order: Primates; Family: Hominidae; Genus: Pan; Species: Pantroglodytes. By the way, you and chimpanzees are only different at the genus (Homo) level. If you search the library archives, you will find that there were nine species of humans that lived on Earth 300,000 years ago, all of them were humans (Homo but not Homo sapiens), and our ancestors likely drove many of them to extinction through competition (with a bit of genetic blurring of the boundaries between species through interbreeding).
How is biodiversity regulated?
Coexistence patterns may reflect shared habitat requirements, whether driven by interactions between organisms or by human-induced pressures, such as changes in land use. The two coexisting species may be prey and predator, whose fates overlap according to the relationship between one’s quest for survival and the other’s quest for food, or they may be competitors. When two seemingly similar species live side by side in the same habitat—“coexisting”—they may avoid each other in their use of space and time. Species’ niches collide with each other in highly dynamic ways. For example, from the perspective of spotted hyenas, their encounters with lions go from positive during the wet season, when they encounter lions while they scavenge their prey, to negative during the dry season, when lions often chase them away from the remaining water-filled pits where scarce prey is concentrated. Among mammals, we have an example of the determinants of community structure in carnivore communities that consume the same resources: trait substitution, for example, where the evolution of different forms indicates different functions that allow for cohabitation. Ecological partitioning occurs when species are sufficiently different to cohabit; for example, weasels, stoats, skunks, minks, martens, and beavers. Competing species face intense intra-group conflict, often in the form of a larger species, such as a tiger, bullying a smaller species, such as a leopard. Many carnivores are apex predators—that is, they sit at the top of the food chain—and as such play important roles in ecosystem management, providing ecological stability by acting as a negative feedback loop on prey numbers.
Members of the cat family, the felines, provide a useful model for understanding spatial separation, competition, and the drivers of biodiversity. A recent study in the Boreal Forest Complex in Myanmar used camera traps to explore how leopards, clouded leopards, and jaguars all coexist. Leopards, Asian golden cats, spotted cats, and jaguars were nocturnal, while clouded leopards and jaguars were primarily diurnal, and golden cats were active throughout the day.
Among the three medium-sized species (clouded leopards, golden cats, and spotted cats), the more similar their body sizes were, the less they used the same space at the same time. The differences in space and time use were most pronounced.
Among the three smaller species. These small cats have adapted their lives to the gregarious lives of their larger relatives; the spotted cat (3 kg) in particular avoided the tigress (4 kg).
The Asian golden cat (8 kg), which in turn avoided the lion cat (8 kg).
These manifestations of the formation of a carnivorous group, in microcosm, reflect the principles of competition and coexistence that resonate throughout the animal and plant kingdoms, albeit through complex processes that are much broader than habitat variation.
One mechanism by which species evolve to coexist is adaptive divergence; that is, one species produces many species occupying different ecological niches, often rapidly.
We have the classic example, always clearly expressed, of adaptive divergence in the 14 species of finches that have divided the Galapagos Archipelago between them over the past two to three million years. As Darwin wrote in 1842:
The most curious thing is the complete gradation in the size of the beaks of the different species of Geospiza
(ground sparrows) … When one sees this gradation and structural diversity in a small, closely related group of birds, one might imagine that a single species has been adapted for different purposes from a limited number of native birds of this archipelago.
He was quite right. The competition and coexistence within this group is shown by the relationship between beak size and structure, and diet, which is most evident when comparing the small insectivorous song sparrows (weighing about eight grams) with the large grain-eating ground sparrows (weighing 30 grams).
On a smaller scale, the four species of ants associated with a single species of acacia, the whistling thorn acacia (Acacia drippanulopium), form a class of invertebrates.
Near the nutrient-rich soil in and around which termites build their nests, more fresh acacia shoots emerge and densities of invertebrates living in the droppings (an important food source for acacia ants) are higher than farther from their nests. This spatial variation in resource availability is associated with competition among termites for host trees; near the nests, dominant species are more likely to displace subordinate species, while subordinate species displace dominant species on host trees to a greater extent the further away from the ant nests.
White. Thus, the variation in habitat caused by termites affects the dynamics of the ant community living on acacia trees, contributing to the coexistence of species in a highly competitive community.
How large numbers of competing plant species can coexist remains a mystery;
The classical explanation, that each species occupies its own ecological niche, seems to collapse in the face of the large amount of observations that most plants require the same set of resources and have a limited number of ways to obtain them. However, diving into the finer details reveals that plant communities are divided along the axes of these ecological niches, such as gradients in light, soil moisture, and root depth, as well as sharing nutrients in the soil with the beneficial mediation of soil microbes. In fact, recent research reveals that plants are able to actively promote microbial communities and also coordinate their interactions with microbes to improve nitrogen and phosphorus uptake.
From species and groups we move to the next level of organization, assemblages, such as the 51 different species of insect-eating bats observed in nearly 3 square kilometers of pristine rainforest in Malaysia, or the entire range of more than 300 species of fish found in coastal waters around the British Isles. The adaptability is astonishing, and the relationships that link biodiversity are almost infinite in their complexity. Consider, for example, the strange alliance that allows the spotted hummingbird to hide safely from predators among the hairy limbs of a burrowing tarantula (the frog eats the ants that threaten the spider’s eggs); or the hornbill and dwarf mongoose that share the benefits of foraging and alerting when danger is detected; or how the extraction of clams by sea otters increases genetic diversity in fields of eelgrass disturbed by their digging. John Vucetich’s book Restoring the Balance focuses on the complex and wide-ranging relationships of biodiversity and the complexity they pose to its conservation; massive infestations of microscopic ticks negatively impact moose survival, which in turn impacts forest structure and wolf population dynamics. These relationships are links in ecosystem processes, leading to ecosystem services, both large and small, on which human activity depends, and occurring at different stages of ecological biomes.
