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SPECIES AND COMMUNITIES II : CHEMICAL & CLIMATIC IMPACTS


Click on the links below to view specific sections of the sample material:

OVERVIEW

The increasing reliance on fossil fuels during the twentieth century has led to rising levels of
atmospheric carbon dioxide. Coupled with rising levels of other ‘greenhouse’ gases, the changing
chemistry of the atmosphere has seemingly triggered a warming trend that, unless humans
adopt remedial measures, will continue through the present century and beyond. The climatic
changes stimulated by global warming will affect animal and plant species. Some species appear
able to weather the changes by making small adjustments to their behaviour.

The climatic changes imperil other species, for instance those that live at high altitudes and high latitudes, those that are poor dispersers and those that have a small gene pool. The same climatic changes will force many communities to change. Biomes may expand or contract, or disassemble and reassemble elsewhere, probably with a different set of species. Other human-induced chemical changes in the environment disrupt natural biogeochemical cycles. Humans have boosted the amount of reactive nitrogen in ecosystems, which has both beneficial and
detrimental effects. In industrialized regions, the burning of fossil fuels has produced acid rain, the
effects of which on animals and plants are negative. The release of nitrates and phosphates
from agricultural and domestic sources produces high nutrient levels in lakes, so accelerating the
natural process of eutrophication and harming aquatic wildlife.

Many human-made toxins escape into the environment causing local pollution incidents and, more worryingly, contamination in ecosystems far removed from the source areas. All these human-made drivers of global change, and those discussed in the previous chapter, act together. Their integrated effects are complex, but scientists are beginning to understand them.


LEARNING OUTCOMES

After reading this chapter, you should be able to
understand:

• Which kinds of species are safe in a climatically changed world
• Which kinds of species are at risk in a climatically changed world
• The likely changes in the world’s biomes brought about by the warming trend
• The effects of changing environmental chemistry on the living world, and in particular
  the effects of reactive nitrogen, acid rain, nitrates and phosphates and environmental
  toxins
• How the chief drivers of biodiversity change – land cover, species exploitation and exchange,
  climate and environmental chemistry – act in concert to affect the world’s biomes.
  

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SUMMARY

Global warming, the changing chemical cocktail in the atmosphere and its knock-on effects in soils and water, and environmental toxins threaten biodiversity. Mobile species, such as most birds and butterflies, with broad tolerance of environmental conditions are the least likely to suffer from rising temperatures. Species that live at the margins of a contracting range, species that
live in small areas, species that are highly specialized, species that are disinclined to move and species that have impoverished gene pools are most at risk from rising temperatures and associated changes in weather. This will affect all the world’s biomes, but to varying degrees. The Arctic tundra and Mediterranean-climate biomes are exceptionally vulnerable, tropical forest biomes the least vulnerable. Boreal forest biomes should move northwards but occupy about the
same amount of land. Biomes may move bodily northwards or southwards, creating zones of change where one biome moves into another, as when boreal forests advance into tundra biomes, and zones of no change where, for instance, the southern part of a biome moves into the northern part. Alternatively, biomes may simply disassemble and reassemble elsewhere with a different set of species.

Humans have changed the chemistry of the environment, with some alarming repercussions. They have increased the amount of reactive nitrogen in ecosystems, the results of which are many and varied, some being beneficial and some detrimental. They have created ‘acid rain’, which adversely affects soils, forests, lakes, rivers and their associated wildlife, and accelerates the weathering of buildings. They have encouraged the accelerated build-up of nutrients, mainly nitrogen and phosphorus, in lakes (eutrophication), which has inimical effects on lake ecosystems. They have also released toxins, causing one-off environmental disasters near the site of release. Some toxins spread around the world and accumulate in remote places, such as the Arctic tundra. All the drivers of biodiversity change act together. Land use change is the most potent driver of biodiversity change, but the role of different drivers varies among biomes.

QUESTIONS

1. Why are some animals and plant species    more vulnerable to a warmer climate than    others? 4. Why does ‘acid rain’ pose a threat to    forests and to lakes? 2. How are present biomes likely to respond    to a warming global climate? 5. Examine the causes and effects of    artificial eutrophication. 3. Explain how humans have altered the    nitrogen cycle. What effects have these    alterations had? 6. Why are so many environmental toxins a     cause for concern?

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FURTHER READING

• Hinchliffe, S. (2003) Understanding Environmental Issues. Chichester: John Wiley & Sons.
  A good source of examples.
  
• Lomborg, B. (2001) The Sceptical Environmentalist: Measuring the Real State of the
  World. Cambridge: Cambridge University Press.
  Always worth hearing a good counterargument to the consensus view.
  
• Park, C. C. (2001) The Environment: Principles and Applications. London: Routledge.
  An excellent text, including much material on the topics covered in this chapter.
  
• Sala, O. E., Chapin III, F. S. and Huber-Sannwald, E. (2001) ‘Potential biodiversity change: global patterns and biome comparisons’. In F. S. Chapin III, O. E. Sala and E. Huber-Sannwald (eds) Global Biodiversity in a Changing Environment: Scenarios
  for the 21st Century (Ecological Studies 152), pp. 351–67. Springer: New York.
  A good overview of the changes likely to occur in the world’s chief biomes over the next century, though not an easy read.
  
• Snyder, N. F. R. and Snyder, H. (2000) The California Condor: A Saga of Natural History and Conservation. San Diego: Academic Press.
  An excellent case study of biology and conservation with superb photographs. A pleasure to read.