A Haven For Endangered Species?

The Norfolk Broads is a unique managed environment, providing a shelter for a number of endangered British species, including Cetti’s Warbler and the Norfolk Hawker Dragonfly.

A recent press release highlights the value of such protected regions; however, the Norfolk Broads is by no means safe. 

Climate change is accelerating rates of sea level rise, placing the Broads at risk of flooding. Seawater intrusion is likely to result in salinisation, and subsequent ecological damage (Broads Authority).

Research has found that beyond a critical threshold, habitat fragmentation, a likely effect of sea level rise in the Norfolk Broads area, results in loss of genetic diversity, population decline and extinction. Shallow lakes are prone to dramatic state shifts following excessive nutrient loading, leading to eutrophication and species loss (Scheffer et al 2001). Worryingly, Thomas et al (2004) and Walther et al (2002) also note that shifts in timing of seasonal activities of plants and animals due to climate change, combined with habitat fragmentation, can result in large scale species loss.

Although undoubtedly valuable, protected areas such as the Norfolk Broads are still susceptible to the repercussions of climate change. With this in mind, is there any hope of preventing a mass extinction?

References

Opdam P. and Wascher D. (2004) ‘Climate change meets habitat fragmentation: linking landscape and biogeographical scale levels in research and conservation’, Biological Conservation, 117, 285-297.

Scheffer M., Carpenter S., Foley J.A., Folke C. and Walker B. (2001) ‘Catastrophic shifts in ecosystems’, Nature, 413, 591-596.

Thomas C.D., Cameron A., Green R.E., Bakkenes M., Beaumont L.J., Collingham Y.C., Erasmus B.F.N., Ferreira de Siqueira M., Grainger A., Hannah L., Hughes L., Huntley B., van Jaarsveld A.S., Midgley G.F., Miles L., Ortega-Huerta M.A., Townsend Peterson A., Phillips O.L. and Williams S.E. (2004) ‘Exctinction risk from climate change’, Nature, 427, 145-148.

Walther G.R., Post E., Convery P., Menzel A., Parmesan C., Beebee T.J.C., Fromentin J.-M., Hoegh-Guldberg O. and Bairlein F. 2002. Ecological responses to recent climate change. Nature 416, 389–95

Case study: The Honey Bee

Bees are an integral component of both agricultural and wild species pollination, widely acknowledged as being economically indispensable. It has been estimated (vanEngelsdorp et al. 2008) that up to a third of the food we consume is pollinated by bees.

Increasingly, however, honeybee populations have been declining, leading to a pollination crisis, in which reductions in pollinators results in the loss of plant species (Ghazoul 2005), Klein et al. 2007).

Honey bees require a diverse community of flowering plants that bloom throughout the spring and summer. Climate change induced shifts in floral density and distribution can lead to alterations in species interactions. In particular, dry regions are predicted to become drier, which will deprive honeybees of necessary moisture, rendering them unable to cope. Yields of pollinator dependent crops have declined, perhaps due to expansion and simplification of agricultural areas on such a scale that numbers of bees simply cannot meet the demand placed upon them. Despite these negative anthropogenic effects, new research suggests that the introduction of new plant species, whose pollen is rich in protein, can be beneficial to bees.

Honeybee mortalities cannot be attributed purely to common diseases and pests, such as the mite Varroa destructor (Sammataro et al. 2000). A recent paper points out that Apis mellifera, the Western honeybee, is under increasing threat from anthropogenically induced habitat fragmentation. In addition to this, the introduction of non-native species, such as the Italian Bee Apis mellifera carnica, and the aggressive African honeybee Apis mellifera scutellata, has resulted in reductions in A. mellifera populations (Ghazoul 2005).

CCD, Colony Collapse Disorder, has been blamed for widespread reductions in honeybee numbers. The disorder is characterised by fewer adult bees within hives, accompanied often by disease pathogens (Olroyd 2007). This phenomenon is not yet fully understood, but it is thought to be multifactoral, a combination of attack from viruses and fungi, depleted immunity, and the narrow genetic base of colonies (Ghazoul 2005). Colony loss is so severe that in the USA, colony numbers have fallen from 5.9 million in 1947 to 2.44 million in 2008.

Colony Collapse Disorder is explained in this clip:

For beekeepers, colony loss is upsetting. But from a large-scale environmental perspective, the repercussions of permanently losing these industrious creatures could be devastating. Indeed the reproductive decline of wild plants has been attributed to pollination failure (Ghazoul 2005).

Le Conte (2008) notes that although A. mellifera has shown remarkable resilience to past changes in climate, there is doubt as to whether it will be able to adapt to the level of environmental change that Earth is currently undergoing.


References

Ghazoul J. (2005) ‘Buzziness as usual? Questioning the global pollination crisis’, Trends in Ecology and Evolution, 20, 7, 367-373.

Klein A.-M., Vassiere B.E., Cane J.H., Steffan-Dewenter I., Cunningham S.A., Kremen C. and Tscharntke T. (2007) ‘Importance of pollinators in changing landscapes for world crops’, Proceedings of The Royal Society Biological Science, 274, 303-313.

Le Conte Y. and Navajas M. (2008) ‘Climate change: impact on honey bee populations and diseases’, Revue Scientifique et Technique Office, 27, 2, 499-510.

Levy S. (2011) ‘The Pollinator Crisis: What’s best for bees’, Nature, 479, 164-165.

Olroyd B. (2007) ‘What’s killing American Honey Bees’, Public Library of Science Biology, 5, 6, 1195-1199.

Ratnieks F.L.W. and Carreck N.L. (2010) ‘Clarity on honey bee collapse’, Science, 327, 152-153.

Sammataro D., Gerson U. and Needham G. (2000) ‘Parasitic Mites of Honey Bees: Life, History, Implications, and Impact’, Annual Review of Entomology, 45, 519-548.

Soland-Reckeweg G.S., Heckel G, Neumann P, Fluri P and Excoffier L. (2009) ‘Gene flow in admixed populations and implications for the conservation of the Western honeybee, Apis mellifera’, Journal of Insect Conservation, 13, 317-328.

vanEngelsdorp D., Hayes J., Underwood R.M. and Pettis J. (2008) ‘A survey of honey bee colony losses in the US, Fall 2007 to Spring 2008’, Public Library of Science, 3, 12, 1-6.

A sixth mass extinction; are humans to blame?

Arguments that we are now entering a sixth mass extinction event have been discussed in the previous post, but are humans actually responsible for this dramatic loss of biodiversity?

Generally, the Holocene has been a time of regularity in terms of temperature and freshwater supply; hence current Earth systems are now very sensitive to small changes in climatic variables. Synergy hypotheses, those that link mass extinction events to the changes in climate, atmosphere and ecological conditions, can be used to explain or predict a potential move towards a sixth mass extinction. Investigations using DNA and phylochronology have demonstrated that modern interpretations of species richness and evenness are low relative to conditions considered to be normal a few thousand years ago.

Rokstrom et al (2009) and Barnosky et al (2011) are agreed that human behaviour is the main cause of global environmental change during the turbulent end-Holocene period, the Anthropocene. The species extinction rate has accelerated considerably during this time, and is currently estimated to be between 100 and 1,000 times greater than what is considered to be natural, suggesting that we are indeed in the midst of a sixth mass extinction.

 The Sixth Mass Extinction is quite distinct from previous events, the primary difference being that it has been initiated by humans, a biotic factor, rather than by a physical cause. Humans are now a geophysical force, with a destructive impact capable of changing the atmosphere and climate as well as global flora and fauna. The global population has doubled in the past 60 years, oriented by selfish sexual and reproductive drives facilitated by the technical advances of agriculture, and has now exceeded the environment’s natural carrying capacity (Wilson 2005, Eldredge 2011).

The human population places huge demands on the environment. The ecosystems existing today began to evolve at the end of the last glacial period, at a time in which Homo sapiens had relatively little impact on the Earth. Human activity has since led to habitat fragmentation through changing land use, the introduction of non-native species and pathogens, removal of species, and changing global climate. These factors combine to cause regional level biodiversity loss, which influences the functioning of the earth system as a whole.

It is evident from comparisons with previous mass extinctions, such as that of the late-Pleistocene, that human influence has had a significant impact on loss of biodiversity. Whilst the late Triassic event is thought to have been caused by substantial disturbance to the global carbon cycle, sea level change and possibly bolide impact the late-Pleistocene, or K-T, event, can be explained using the Overkill and Infectious Diseases hypotheses (Tanner et al 2004). The Overkill Hypothesis is based on the observation that large-scale human hunting in newly discovered North America resulted in severe species losses.

Evidence for The Overkill Hypothesis

1) Climate change is not indicated in palaeoclimatological records.  Extinctions were very sudden and appear to follow the spread of humans, and the main species targeted during this time were large mammals, which would suggest that hunting was to blame.

2) In Africa where humans and animals coevolved, fauna became adapted to survive human presence. Conversely, when Native American ancestors entered North America 14,000 years ago, the large creatures already living there had no inherent fear of humans, could be hunted with ease, and so became extinct very quickly, resulting in large-scale ecological disruption.

3) There is no evidence of competition from exotic species on a sufficient level to cause extinctions.

4) Arguments that fossil evidence is insufficient to indicate large-scale hunting have been countered by the suggestion that there was insufficient time to preserve all fossils during the time in which extinctions took place.

5) There is little evidence of small animals, which would not be of interest to humans, also dying during this time. Equally, occurrence of extinctions before human arrival in North America seems unlikely based on palaeo data.

6) The Overkill Hypothesis is supported by the Keystone Herbivore Hypothesis. This states that large animals are ecosystem engineers, and that without them, habitats would be sufficiently altered to result in the demise of other smaller creatures (American Museum of Natural History). 

IPCC reports confirm that climate change is occurring, and albeit by small increments, this could lead to dramatic species disturbances. Amphibians have historically managed to escape extinction events relatively unscathed, but now, due to changing environmental conditions, up to a third of the 6,300 amphibian species are threatened with extinction. This trend is likely to accelerate because most amphibians live in small habitat ranges, aren’t capable of moving far or adapting quickly to habitat pressures imposed by humans, and their moist skin is vulnerable to changes in humidity and temperature (Pounds 2006, Wake and Vredenberg 2008). 

These chilling statistics suggest that humanity needs to change its ways, and fast, but have we already passed the point of no return? Is there anything that can be done to reverse the trend of large-scale species loss? Await the next post for further discussion.

References

American Museum of Natural History, What is the Overkill Hypothesis?, [www] Available from http://www.amnh.org/science/biodiversity/extinction/Day1/overkill/Bit1.html, [Acessed 10 November 2011]

Barnosky A.D., Matzke N., Tomiya S., Wogan G.O.U., Swartz B., Quentel T.B., Marshall C., McGuire J.L., Lindsey E.L., Maguire K.C., Mersey B., Ferrer E.A. (2011), ‘Has the Earth’s sixth mass extinction already arrived?’, Nature, 471, 51-57

Eldredge, N. (2001) The Sixth Extinction. Retrieved [www] Available from http:/ /www.actionbioscience.

org/newfrontiers/eldredge2.html [Accessed 10 November 2011].

Pounds J.A., Bustamante M.R., Coloma L.A., Consuegra J.A., Fogden M.P.L., Foster P.N., La Marca E., Masters K.L., Merino-Viteri A., Puschendorf R., Ron S.R, Sa´nchez-Azofeifa G.A., Still C.J. and Young B.E. (2006) ‘Widespread amphibian extinctions from epidemic disease driven by global warming’, Nature, 439, 12, 161-167.

Rockstrom et al (2009) ‘A safe operating space for humanity’, Nature, 461, 472-475.

Tanner L.H., Lucas S.G. and Chapman M.G. (2004) 'Assessing the record and causes of Late Triassic extinctions', Earth Science Reviews, 65, 103-139.

Wake D.B. and Vredenberg V.T. (2008) ‘Are we in the midst of the sixth mass extinction? A view from the world of amphibians’.

Wilson E.O. (1993) 'Is humanity suicidal?', Biosystems, 31, 2-3, 235-242. 

A Sixth Mass Extinction?

There is much debate as to whether a sixth mass extinction event is currently underway. A recent paper by Barnosky et al (2011) argues we are now irrevocably in the midst of species loss which could rival that of the ‘big 5’. Papers by Rockstrom et al (2009), Raup and Sepkoski (1986) and Wakeand Vredenberg (2008) also discuss this issue, and will be used to detail some of the complexities of the ‘sixth’ mass extinction.

·       Comparison with ‘normal’ extinctions. Under normal background extinction conditions, those taxa that go extinct tend to be from small populations in restricted geographic ranges. Hence if certain species can be seen to decline rapidly in number, large creatures in particular, then extinction selectivity may be changing to enter a mass extinction state. Although 99% of all species that have ever lived on earth are now extinct, this species loss is usually balanced by speciation. Given the current rates of species loss, however, teamed with the fact that evolution of new species takes many thousands of years and revival from mass extinction spans millions of years, no meaningful biodiversity recovery is likely to take place in our lifetime (Barnosky et al 2011).

·       Estimations of species loss. Species-area relationships can be used to relate species losses to habitat area losses, these suggest that future species extinctions will be between 21 and 52% of all current species. Major problems can arise because most species have not yet been formally described; fossil remains are biased and incomplete, not all species fossilize well, if at all, and fossil analysis is often carried out at genus rather than species level which can lead to species being lumped together. Thus, estimations are likely to be under-representative as if one species in a genus becomes extinct, the genus as a whole will remain relatively untouched.

·  Approaches to reconstructions. Using an E/MSY, extinctions per million species years, approach, Barnosky et al (2011) observe that current extinction rates are notably higher than both background rates and those of the previous half-millennia. Alarmingly, comparison of historical and recent extinction rates using a 500-year rate approach has shown that if all threatened species went extinct within the next hundred years, bird and mammal extinction would take somewhere between 240 and 500 years to match the level of the big five extinctions, and in 2,265 years 75% of species would be lost. Hitherto, there have been discrepancies in the assessment of species loss through the use of rate and magnitude, and questions have been raised as to effectiveness of extrapolation of extinction rates of well-studied taxa. These rates are highly dependent on the length of time for which they are measured, so current short-term extinction measurements are not accurately comparable with long-term data. A solution to this is the estimation of species extinction rates by maximising fossil background rates and minimising current extinction rates, and the use of combined rate-magnitude comparisons.

Figure 1. Current extinction magnitudes, expressed as percentage of species. This illustrates the severity of extinctions within taxonomic classes, and suggests that extinction levels comparable to those of the big 5 are not far off. Source: Barnosky et al (2011).

·       Climate models. Climate change has progressed to the extent that some Earth systems have now exceeded their stable Holocene state. This has resulted in retreat of summer sea ice in the Arctic Ocean, retreat of mountain glaciers, loss of mass from Greenland and Antarctic ice sheets and rapid rates of sea level rise. Climate models don’t take long-term feedbacks into account, however, so may underestimate the severity of long-term climate change by ignoring considerable threats to ecological life support systems.

Conclusion

Although extinction is a necessary part of evolution, species losses are occurring at a much higher rate than is considered normal. This topic requires further discussion, and the focus of the next post will be the extent to which humans are to blame for the species loss that is arguably underway.

References

Rockstrom et al (2009) ‘A safe operating space for humanity’, Nature, 461, 472-475.

Barnosky A.D., Matzke N., Tomiya S., Wogan G.O.U., Swartz B., Quentel T.B., Marshall C., McGuire J.L., Lindsey E.L.,    Maguire K.C., Mersey B., Ferrer E.A. (2011), ‘Has the Earth’s sixth mass      extinction already arrived?’, Nature, 471, 51-57

Wake D.B. and Vredenberg V.T. (2008) ‘Are we in the midst of the sixth mass extinction? A view from the world of amphibians’, Proceedings of the National Academy of Science of the United States of America, 105, 1, 11466-11473.

Raup D.M. and Sepkoski J.J. (1986) ‘Periodic extinction of families and genera’, Science, 231, 4740, 833-836.