System Earth 13a

Mass extinctions

Misha Velthuis

m.velthuis@uva.nl

Tue 26 Nov 2024

Book Brannen

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Content

What is biodiversity

How does it change over time

Mass extinctions

Diversity as a measure
of what is good?

Measuring biodiversity

How to count diversity?

Reproductive isolation?

But what about hybridization?
What about organisms that reproduce asexually?
How to know this with fossils?

Morphology based?

What difference is "different enough"?
At one point does an evolving group of organisms become a new species?

From: Wells, T., Carruthers, T., & Scotland, R. W. (2022). Heuristics, species, and the analysis of systematic data. Trends in Plant Science, 27(6), 524-527. link :

Unlike elements in chemistry, and particles in physics, biology’s best-known unit – the species – remains ill-defined and disputed. Although it continues to be used routinely by researchers from across the field of biology, there are at least 30 competing definitions – termed ‘species concepts’ – in existence. Ongoing discussion about the limitations of one of the most famous species definitions – the biological species concept (BSC) – highlights the continued difficulty of resolving this ‘species problem’. Its emphasis on reproductive isolation (RI) means the BSC remains notoriously difficult to test empirically and cannot be applied to asexual organisms including prokaryotes. Worse, even its proponents admit that notions of RI are undermined by evidence of widespread hybridization between otherwise distinct species, as well as by the protracted and variable nature of speciation itself. Many biologists

herefore choose to use other definitions that emphasise criteria such as mate recognition, ecological niche, or monophyly. But incompatibility among these competing definitions means that this pluralism in relation to species concepts can lead to differing conclusions about species delimitations and counts. This ‘species problem’ has ramifications beyond taxonomy because an indefinable unit is a potentially incomparable one. Knowing which species an organism belongs to is integral to studying and understanding both that organism and the wider world, but if different researchers are using inconsistent definitions of the term species, the comparability of their results might be brought into question [6]. Since species form the basic unit in research as diverse as understanding speciation, estimating biodiversity, modelling species distributions, and conducting conservation assessments, inconsistency in their delimitation impacts biologists from a wide range of disciplines such as systematics, evolutionary biology, ecology, and conservation.

Biased counts?

Also…

… which applies more generally btw

"As Figure 3 illustrates, many of the ground-based weather stations in Africa and Latin America do not report fully into the globally available climate datasets. Data deficiencies are most pronounced in areas of the world where the need is greatest, especially in Africa, where the functioning observation network is less than an eighth of that recommended by WMO [38]. This obviously has implications for the value of using globally available data to try to meet regional or national climate information needs." (Connor et al. 2010).

"A second problem with the temperature data is that the coverage in time and space is much better in some parts of the world than in others. Populated areas of Europe and North America have been monitored most closely and for the longest time, so the coverage is best in these regions. most land areas in the Southern Hemisphere have shorter and less-consistent temperature records." (Kump et al. 2010).

Connor, S. J., Omumbo, J., Green, C., DaSilva, J., Mantilla, G., Delacollette, C., … & Thomson, M. (2010). Health and climate–needs. Procedia Environmental Sciences, 1, 27-36.

Kump, L. R., Kastine, J. F., Crane, R. G. (2010). The Earth System (3rd ed.) Pearson Education, New Jersey

Corrected diversity in genera

Biodiversity as a dynamic equilibrium

Inflow = outflow

"Usually, mutated genes are detrimental to the organism, reducing its prospects for reproduction or survival, but occasionally they are beneficial" (Kump et al. p. 258). (We owe our comfort (the fact that generally things work quite well) to a lot of discomfort).

Origination = if a population of organisms becomes isolated from the rest of the members of its species and acquires characteristics (through natural selection) that make it unable to breed with these other members. (Kump et al. p. 258).

Extinction = loss of all individuals of a species

Estimated origination and extinction rate: 10-25 species originate and go extinct every year (Kump et al., p. 259).

(Although the number of species must have slowly increased over the last 3.5 billion years, which suggests that "origination has slightly exceeded extinction" (Kump et al. p. 260)).

Current estimated total number of species: 8.7 million (= much more than total number of described species).¹

Average "life span" of a species?

Footnotes

Mora, C., Tittensor, D. P., Adl, S., Simpson, A. G., & Worm, B. (2011). How many species are there on Earth and in the ocean?. PLoS biology, 9(8), e1001127.

Origination and extinction

Low diversity: lower origination or higher extinction?

On the long run: equilibrium …

… with catastrophic events

The history of life thus consists of “long periods of boredom interrupted occasionally by panic.”

In times of panic, whole groups of once-dominant organisms can disappear or be relegated to secondary roles, almost as if the globe has undergone a cast change. Such wholesale losses have led paleontologists to surmise that during mass extinction events … the usual rules of survival are suspended. Conditions change so drastically or so suddenly (or so drastically and so suddenly) that evolutionary history counts for little. Indeed, the very traits that have been most useful for dealing with ordinary threats may turn out, under such extraordinary circumstances, to be fatal.

Mass extinction

Most famous: KT-extinction

Most catastrophic: end-Permian

The cast of the biggest horror story ever

Volcanism (of a different kind)

Organic carbon in sedimentary rock

Chemical weathering

… and a "broken" ocean

Ocean acidification

Ocean deoxygenation

Prime suspect: Siberian traps

Siberian traps

Mantle plume below Laacher see

(Siberian traps plume was much more lethal!)

Trappa

Organic carbon making matters worse

Carbonate-silicate weathering to the rescue?

The negative feedback loop of the carbonate-silicate cycle operates on a longer time-scale.

“Adding CO2 increases weathering for two reasons,” Payne said. “One is that it makes rainwater more acidic. But the thing that a lot of geochemists think might actually be more important is that it just warms the planet, which creates more evaporation and more runoff, and the more water you pump through the system the more you can drive chemical weathering.” But rock weathering takes time. Lots of time. Like the proverbial bird-that-sharpens-its-beak-on-the-side-of-a- mountain-eventually-chiseling-it-away-to-nothing sort of time. Jack up carbon dioxide in the atmosphere on timescales faster than the rocks can weather away and you have a recipe for ocean acidification.

Brannen, P. (2017). The Ends of the World: Volcanic Apocalypses, Lethal Oceans and Our Quest to Understand Earth's Past Mass Extinctions. Simon and Schuster.

Carbonate-silicate cycle not to the rescue

Extremely high CO2 concentration:

High acidity rain water
High temperatures
More rainfall
Large inflow of nutrients
Large boost of primary production

When the oxygen that is produced in photosynthesis is exceeded by the oxygen consumed in respiration and decomposition, oxygen levels drop.

In a healthy ecosystem, negative feedback loops maintain a balance.

A sudden increase in biomass, initiated by an influx of normally limiting nutrients, can tip this balance, and the system can end up in a new (dead) equilibrium.

(In geological records, mass extinction events are often characterised by "black shales": lithified marine sediment full of organic material that has not been decomposed.)

Possible extra disaster when oceans are devoid of oxygen:

Add to this whodunit two more suspects—the horrifying specters of ocean anoxia and anoxia’s poisonous bedfellow, hydrogen sulfide, which can be produced by bacteria only in the absence of oxygen.

Ocean acidification

From IPCC AR6 WG1, p. 75 (2021)

Today, in the acidifying waters of the Southern Ocean, the shells of small, translucent, fluttering planktonic snails called pteropods, which form part of the base of the Antarctic food chain, have been found pitted with holes. In 2008, NOAA scientist Nina Bednaršek discovered these corroded creatures during a research cruise around Antarctica. By 2050, ocean acidification will render the entire Southern Ocean uninhabitable by pteropods, an ecological catastrophe. Since her original upsetting discovery around Antarctica, Bednaršek has also found disfigured pteropods off Seattle, where they form up to half the diet for juvenile salmon in the Pacific Northwest. “It’s not a question of if pteropods will be dissolving, or if they will be compromised—it is certain they will be,” Bednaršek told me. It gets little attention now, but the prospect of ocean acidification in the next few decades could be truly world- changing.

Brannen, P. (2017). The Ends of the World: Volcanic Apocalypses, Lethal Oceans and Our Quest to Understand Earth's Past Mass Extinctions. Simon and Schuster.

Analogy

Anthropogenic
perturbation

System Earth 13a

Mass extinctions

Misha Velthuis

m.velthuis@uva.nl

Tue 26 Nov 2024

Book Brannen

Content

Diversity as a measureof what is good?

Measuring biodiversity

How to count diversity?

Biased counts?

Also…

… which applies more generally btw

Corrected diversity in genera

Biodiversity as a dynamic equilibrium

Inflow = outflow

Origination and extinction

Low diversity: lower origination or higher extinction?

On the long run: equilibrium …

… with catastrophic events

Mass extinction

Most famous: KT-extinction

Most catastrophic: end-Permian

The cast of the biggest horror story ever

… and a "broken" ocean

Prime suspect: Siberian traps

Trappa

Organic carbon making matters worse

Carbonate-silicate weathering to the rescue?

Carbonate-silicate cycle not to the rescue

Ocean acidification

Analogy

Anthropogenicperturbation

Diversity as a measure
of what is good?

Anthropogenic
perturbation