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A Cross-Cultural Introduction to Bioethics
36
B2. Biodiversity and Extinction
Chapter objectives
Biodiversity is genetic, taxonomic and ecosystem variety.
What is the significance of species extinction?
This chapter aims to:
1. Highlight the importance of biodiversity & its loss.
2. Discuss extinction & past/present mass extinctions.
B2.1. Biodiversity.
Biodiversity is the variety and richness of life on earth, measured at different levels such as the
diversity of genes, species, higher taxonomic groups, and ecosystems. Genetic diversity
increases reproductive fitness, allowing outbreeding and adaptation to environmental change.
Species diversity is required for the effective functioning of ecological communities. Ecosystem
diversity provides habitat and the highest-level richness of the world. In simple terms,
biodiversity makes life more interesting.
Attempts to resurrect extinct species (popularised by 'Jurassic Park') have not yet been
successful. A project of the Australian Museum to resurrect the thylacine, or Tasmanian tiger, has
recently been cancelled. Another project unable yet to be completed was to resurrect the
mammoth from tissue samples preserved in permafrost. Mixing of genetic material with that of a
host egg cell does not reproduce the pure original form.
Cloning research and cryopreservation (preservation by freezing) of DNA, cells, gametes and
embryos in genome resource banks, despite limited current applications, are potential
investments in the future of conservation. The first successful natural breeding of cloned male
and cloned female American wildcats was reported in August 2005, which offers proof of
principle for efforts to clone extinct species. It will need to be tested over further generations
however.
Seed banks and captive breeding programmes in zoos are also very important for endangered
species. However, technological breeding methods must not also breed complacency. After all, it
will be technically impossible to replicate or replace the most important unit of biodiversity viable whole ecosystems.
Q1. Discuss differences between prevention and cure. Can extinction be
‘cured’?
Q2.
.
How are seed banks useful for conservation and agriculture?
Collaborating author: Morgan Pollard, Australia
© Eubios Ethics Institute
Bioethics for Informed Citizens across Cultures
< http://www2.unescobkk.org/eubios/betext.htm
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A Cross-Cultural Introduction to Bioethics
B2.2. Biodiversity - the drama
Extinction is the death, and loss for ever from the Earth, of a
genetic lineage of a species. Extinction can be viewed as a
tragedy, although it has happened throughout biological history.
Even from a purely human centered view, ignoring any intrinsic
moral value of life, extinction means we lose essential ecosystem
support services, potential new information, ideas, patterns,
processes, foods, chemicals, products and may impact on other
economic, aesthetic and spiritual values.
Threatened species are those at risk of extinction, indicated by
rapid decline of population, limited extent of occurrence, models
of ecological disturbance or fluctuation, projected habitat loss or
fragmentation, and/or low absolute number of remaining
individuals. Along the descending journey, threatened species
pass through the categories of 'vulnerable', 'endangered',
'critically endangered' and 'extinct in the wild'. A 'ghost species'
is a non-viable population, or the ‘living dead’ with negligible
chance of escaping extinction.
What happens to an ecosystem when some of its inhabitants go
extinct? Feedback interactions occur, and the fluctuations of the adjusting system put further
species at risk. If a keystone species is affected, the repercussions may include rapid and
dramatic unravelling of the whole community. As a well-known example, hunting of the
north-eastern Pacific sea-otter for its fur allowed its sea-urchin prey to grow to excessive
population size, resulting in the decline of beautiful kelp forests in favour of an exposed-seabed
community with reduced biota. Similarly, if a seemingly-successful population expands beyond
the limits of its food or resource-base, loss of equilibrium and catastrophic population decline
typically follow, unleashing the 'Four Horsemen': conflict, famine, pestilence and death.
Risk factors which make a group more susceptible to extinction include some of the following
characteristics: small population size (rarity is the predominant risk factor), narrow geographic
distribution, niche or habitat specificity, large body size, symbiotic dependence on other species
(e.g. for pollination), narrow diet, low dispersal ability, slow reproduction, morphological
ornateness, susceptibility to stress, and stenotypy (or specialised lifestyle with limited
adaptability). Bad luck can perhaps also be mentioned, as there seems to be a random component
to the fossil record of mass extinctions. Furthermore, weird and wonderful adaptations,
seemingly beneficial over the short term, such as over-reliance on symbiosis or strange features
resulting from evolutionary arms races, may in fact be detrimental to survival over the longer
term, leading unwitting species down a potentially dead-end path known as an evolutionary
cul-de-sac.
Q3.
Is it possible that the human species is in an evolutionary cul-de-sac (dead
end street)? Which behaviours, seemingly adaptive over the short term,
may be disadvantageous to our survival over the longer term?
© Eubios Ethics Institute
Bioethics for Informed Citizens across Cultures
< http://www2.unescobkk.org/eubios/betext.htm
A Cross-Cultural Introduction to Bioethics
38
B2.3. Extinction
Five mass extinction events of the geological record are flagged and graphed by loss of whole
families in Figure 2. The big five should act as warnings. They marked the end of the
Ordovician, Devonian, Permian, Triassic and Cretaceous (extinction of the dinosaurs) geological
periods, and seem to have been caused at different times by combinations of climate change,
comet or meteorite impact, super-volcanism, marine regression and/or broad ecological
restructuring or collapse. A case in point is death by suffocation, such as when the evolutionary
blossoming of photosynthesis created a (then) toxic oxygen-rich atmosphere, or during the
Permian extinction with up to fifty percent less oxygen postulated for a temporary period. Mass
extinctions may occur over millions of years, or may take only a few decades depending on
whether the cause is gradual (uniformitarianism) or suddenly nonlinear (catastrophism).
Researchers have differing opinions on the causes and history of extinction as interpreted from
the fossil record. Despite vigorous debate about the past, most experts in evolution or ecology
display uncanny agreement about the present. As an example in the following quote, from within
a minority view - uniformitarian argument - for gradual change during past eras, we nevertheless
see emerge the majority-view which is warning of catastrophism for the present era.
"Although the fossil evidence does not support the concept of historical mass extinctions
or mass killings, there is a catastrophic extinction event occurring in contemporary time.
Raven (1990) has estimated that, by the first quarter of the 21st century, the world will
have lost 2 million out of a minimal world total of 10 million animal species and about
65,000 out of 300,000 species of vascular plants. These losses, due to habitat
destruction by humans, are occurring with a rapidity that is unprecedented in
Phanerozoic time. Historic extinction episodes were so gradual that many lineages were
able to accommodate in an evolutionary and ecological sense. The tempo of the current
extinctions precludes any such adjustments."
John Briggs (1994) 'Mass Extinctions: Fact or Fallacy?' p.235-6
Figure 2: History of Biodiversity Illustrating Mass Extinction Events
Q4.
Do you agree it is likely we have now entered the sixth great mass
extinction?
© Eubios Ethics Institute
Bioethics for Informed Citizens across Cultures
< http://www2.unescobkk.org/eubios/betext.htm
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A Cross-Cultural Introduction to Bioethics
"I will consider only species being lost by reduction in forest area … I will not
include overharvesting or invasion by alien organisms. I will assume a number of
species living in the rain forests, 10 million (on the low side), and I will further
suppose that many of the species enjoy wide geographical ranges. Even with these
cautious parameters, selected in a biased manner to draw a maximally optimistic
conclusion, the number of species doomed each year is 27,000. Each day it is 74,
and each hour 3."
E.O. Wilson (1992) 'The Diversity of Life' p. 268
Change in global biodiversity is measured by a simple equation - number of speciations
(evolutions of new species) minus number of extinctions. The average longevity of a species is 1
to 10 million years, only about half that for mammals. Estimated normal 'background' extinction
has been estimated at less than one species per million per year. How are we managing the
living world at this moment? As usual estimates vary, but the important thing is that detailed
scientific studies agree the current extinction rate is very large. The above quote is based on
decades of study and satellite imagery observations of habitat destruction and fragmentation
in tropical rainforests (the most biodiverse terrestrial ecosystem) by Thomas Lovejoy and E.O.
Wilson. Empirical biogeography theory indicates that a tenfold decrease in habitat area removes
approximately half of existing species. The quote below reflects scientific predictions for tropical
coral reefs (the most biodiverse marine ecosystem) in a world of global warming, susceptible to
widespread death by coral bleaching, where essential symbionts of coral polyps (tiny
dinoflagellates called zooxanthellae) are lost and the reef dies a barren white.
Nevertheless, average biodiversity has increased over the long-term history of life (Figure 2), the
rebounds partly explained by species selected for extinction resistance taking advantage of
vacated niches. Unfortunately however, recovery of biodiversity is slow enough to ensure that
even if Homo sapiens were to survive a mass extinction event, we would live in an impoverished
world for longer than our expected natural lifespan.
"Even under the best case scenario, losses of at least 50% of the [Great Barrier] Reef's
living coral cover are likely to occur by 2050. How humans will be affected by these
changes is still uncharted yet is enormously important." (p.1), "Projections of changes
in water temperature do not bode well for coral and the reefs that they help build.
Already increases in water temperature of only 0.6°C since 1880 have increased the
bleaching and mortality of reef-building corals across the planet … These levels of
change in sea temperature are unsustainable by corals growing where they are today,
even under the milder scenarios in which seas only warm by 2°C." (p.54), and "these
temperatures will exceed the local thermal tolerances of reef-building corals on annual
basis by 2030-2060. The calculated thermal stress levels rise to several-fold higher than
those seen in 2002 and lead to the highly probable conclusion that reefs dominated by
coral will be rare in the Great Barrier Reef region by 2050." (p.84)
Hans & Ove Hoegh-Guldberg (2004) 'The Implications of Climate Change
for Australia's Great Barrier Reef'
Q5.
Everyone dies. But can Homo sapiens, the human species, go extinct?
How likely do you think it might be over short, medium and long
time-scales? What are the alternatives to extinction?
© Eubios Ethics Institute
Bioethics for Informed Citizens across Cultures
< http://www2.unescobkk.org/eubios/betext.htm