Biodiversity

Pedro L. Lomas

Biodiversity is defined as the diversity of life on Earth at all levels, from genes to ecosystems.

The concept of biodiversity comes from the contraction of the original term biological diversity, which is generally assumed to have first appeared in the early 20th century in the field of Natural History (Harris, 1916). Originally, the term focused on species richness (the number of species) and their relative abundance within groups of organisms of different species that coexist in a given place and time (biological community). Under this umbrella, just over 10 million species have been described as currently present on the planet (Mora et al., 2011). However, in the 1980s, with increasing awareness of the damage that growing economic activity was causing to biodiversity, the concept was extended by various authors (Thomas E. Lovejoy, Walter G. Rosen, Elliot Norse, Edward O. Wilson, etc.) to encompass all levels of life on Earth (Wilson, 1988). 

The first appearance of the concept in the policy sphere occurred in the context of the 1992 United Nations Conference on Environment and Development in Rio de Janeiro, Brazil, where the Convention on Biological Diversity (CBD) was adopted, providing a framework for the protection of biodiversity. In its Article 2, the CBD defines biological diversity as: 

“…the variability among living organisms from all sources, including, inter alia, terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are part (see ecology); this includes diversity within species, between species and of ecosystems.”

Biodiversity is typically characterized at three levels:

  • Genetic diversity. This consists of the different genetic variants within a single species. Intraspecific variability is vital for a given species to adapt to the characteristics of its environment and, therefore, for its survival.
  • Species diversity. This represents the variety of species found in a given place and time, and it informs the original concept of biological diversity. Different populations and biological communities are adapted to specific environmental conditions. Changes in these conditions or the generation of barriers between individuals within populations, among other phenomena, lead to speciation, a process in which one species evolves into another (anagenesis) or several different species arise from a previous one (cladogenesis).
  • Ecosystem diversity. The variety of ecosystems is the highest level of biodiversity, although, given that the very definition of an ecosystem includes abiotic components, it has been a source of considerable controversy. On one hand, there would be that part of the doctrine that understands ecosystems as a complex system inseparable from the abiotic elements that constitute it and that, therefore, consider it a level of biodiversity; on the other hand, there would be those positions that understand that biodiversity refers only to the biological communities that constitute ecosystems, and not to the ecological system as a whole (see ecosystems and socio-ecosystems).

Within a given evolutionary context, species transform through speciation (transformation into another species or species) or disappear completely through extinction. The fossil record shows that, throughout geological history, most species that have existed have become extinct due to causes that could be called natural or fortuitous (geological and astronomical events, genetic drift, etc.); that is, there is a natural or background extinction rate (De Vos et al., 2015). When there is a substantial increase in the extinction of groups of species (taxa) with a wide geographic distribution over a relatively short period, resulting in a drastic reduction in their diversity, we are talking about a mass extinction (Sepkoski, 1986). Although there is no absolute consensus on the details of this definition, it is generally considered that there have been five major mass extinctions throughout geological history (Raup and Sepkoski, 1982):

  • During the transition between the Ordovician and Silurian periods (445-444 million years ago). Due to a supernova explosion or intense glaciation, it is estimated that 27% of families, 57% of genera, and 85% of existing species disappeared.
  • During the Late Devonian period (between 372 and 359 million years ago). 19% of families, 50% of genera, and at least 70% of existing species disappeared. Several hypotheses have been proposed for their origin, including glaciations and a powerful volcanic eruption.
  • During the transition between the Permian and Triassic periods (252 million years ago). It is estimated that 53% of marine families, 84% of marine genera, and 81% of marine species disappeared, as well as 70% of terrestrial vertebrate species present at that time. The leading hypothesis is a meteorite impact, although significant volcanic activity is also considered.
  • During the transition between the Triassic and Jurassic periods (201.3 million years ago), 23% of families, 48% of genera, and between 70% and 75% of the species that inhabited the planet at that time became extinct. The leading hypothesis is volcanism and major climate change.
  • In the transition between the Cretaceous and Paleogene periods or K-Pg extinction (about 66 million years ago), popularly known as the extinction of the dinosaurs due to a meteorite impact, in which 17% of families, 50% of genera and 75% of species that were part of the planet’s biodiversity disappeared.

Moreover, the phenomenon of Biodiversity Loss as one of the axes of Global Change refers to the Holocene mass extinction event (a period spanning approximately the last 9,000–10,000 years) that is currently underway (also known as the Sixth Great Extinction), and which coincides with key moments of increased intensity in the transformation and appropriation of ecosystems by humans throughout history. According to available data, the current extinction rate is estimated to be between 1,000 and 100,000 times higher than the background extinction rate (Kolbert, 2014). In addition to species extinction itself, two other phenomena characterize the current trend toward biodiversity loss: the geographic homogenization of biodiversity, as a result of the voluntary or involuntary transport of organisms from one area to another by humans (invasive species), and changes in observable (phenotypic) traits resulting from selective pressures exerted by human activities (Díaz and Mali, 2022).

This phenomenon of biodiversity loss could lead to a radical transformation of the world as we know it, with far-reaching social and ecological consequences (Loreau et al., 2022). First, it affects the adaptive capacity and resilience of ecosystems, potentially leading to severe degradation and even ecological collapse of some ecosystems, which would have numerous consequences for life on Earth; It also has a direct impact on the potential for human appropriation of natural resources, affecting various economic activities (agriculture, livestock, etc.), as well as the conditions that constitute our species’ ecological niche (climate, for example). Finally, it also affects human health, either directly (through poor soil, air, or water quality) or indirectly (for example, through the increase in zoonotic diseases). Furthermore, all these impacts can reinforce each other, accelerating the rate of extinction itself, and can also reinforce other phenomena such as climate change, with which biodiversity loss has multiple synergies (Pörtner et al., 2021).

References 

Bambach, R. K. (2006). Phanerozoic biodiversity mass extinctions. Annual Review of Earth and Planetary Sciences, 34, 127-155. https://doi.org/10.1146/annurev.earth.33.092203.122654

Ceballos, G., Ehrlich, P. R., Barnosky, A. D., García, A., Pringle, R. M. & Palmer, T. M. (2015). Accelerated modern human–induced species losses: entering the sixth mass extinction. Science Advances, 1, e1400253. https://doi.org/10.1126/sciadv.1400253  

Convention on Biological Diversity, available in: https://www.cbd.int/convention/text/ 

De Vos, J. M., Joppa, L. N., Gittleman, J. L., Stephens, P. R. & Pimm, S.L. (2015). Estimating the normal background rate of species extinction. Conservation Biology, 29, 452-462. https://doi.org/10.1111/cobi.12380 

Díaz, S. & Malhi, Y. (2022). Biodiversity: Concepts, Patterns, Trends, and Perspectives. Annual Review of Environment and Resources, 47, 31-63. https://doi.org/10.1146/annurev-environ-120120-054300

Harris, J. A. (1916). The Variable Desert. The Scientific Monthly, 3(1), 41–50. http://www.jstor.org/stable/6182 

Kolbert, E. (2014). The Sixth Extinction. An Unnatural History. Henry Holt and Company. 

Louca S., Mazel F., Doebeli M. & Parfrey L. W. (2019). A census-based estimate of Earth’s bacterial and archaeal diversity. PLoS Biol, 17(2), E3000106. https://doi.org/10.1371/journal.pbio.3000106  

Loreau M., Hector A., & Isbell F. (Eds.) (2022). The ecological and societal consequences of biodiversity loss. Wiley-ISTE. 

Mora C, Tittensor D. P., Adl S., Simpson A. G. B. &Worm B. (2011). How Many Species Are There on Earth and in the Ocean? PLoS Biol, 9(8), e1001127. https://doi.org/10.1371/journal.pbio.1001127 

Pörtner, H.O., Scholes, R.J., Agard, J., Archer, E., Arneth, A., Bai, X., Barnes, D., Burrows, M., Chan, L., Cheung, W.L., Diamond, S., Donatti, C., Duarte, C., Eisenhauer, N., Foden, W., Gasalla, M. A., Handa, C., Hickler, T., Hoegh-Guldberg, O., Ichii, K., Jacob, U., Insarov, G., Kiessling, W., Leadley, P., Leemans, R., Levin, L., Lim, M., Maharaj, S., Managi, S., Marquet, P. A., McElwee, P., Midgley, G., Oberdorff, T., Obura, D., Osman, E., Pandit, R., Pascual, U., Pires, A. P. F., Popp, A., Reyes-García, V., Sankaran, M., Settele, J., Shin, Y. J., Sintayehu, D. W., Smith, P., Steiner, N., Strassburg, B., Sukumar, R., Trisos, C., Val, A.L., Wu, J., Aldrian, E., Parmesan, C., Pichs-Madruga, R., Roberts, D.C., Rogers, A.D., Díaz, S., Fischer, M., Hashimoto, S., Lavorel, S., Wu, N., & Ngo, H.T. (2021) Scientific outcome of the IPBES-IPCC co-sponsored workshop on biodiversity and climate change, IPBES secretariat, Bonn, Germany. https://doi.org/10.5281/zenodo.4659158 

Raup, D. M. & Sepkoski, J. J. (1982). Mass extinctions in the marine fossil record. Science, 215(4539), 1501–1503. https://doi.org/10.1126/science.215.4539.1501

Sepkoski, J. J. (1986). Phanerozoic overview of mass extinction. In D. M. Raup & D. Jablonski (Eds.), Patterns and Processes in the History of Life: Report of the Dahlem Workshop on Patterns and Processes in the History of Life (pp. 277-295.). Springer-Verlag Berlin. 

Wilson, E. O. (1988). Biodiversity. National Academy Press.

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