Human Dependence on Nature

How to Help Solve the Environmental Crisis

Haydn Washington

• Publisher: Routledge
• Year: 2013
• Print ISBN: 9780415632577
• eBook ISBN: 9781136214592
• Edition: 1
• Topic: Economics
• Subtopic: Sustainability in Business
• Index: Economics

Humanity is dependent on Nature to survive, yet our society largely acts as if this is not the case. The energy that powers our very cells, the nutrients that make up our bodies, the ecosystem services that clean our water and air; these are all provided by the Nature from which we have evolved and of which we are a part. This book examines why we deny or ignore this dependence and what we can do differently to help solve the environmental crisis.

Written in an accessible and engaging style, Haydn Washington provides an excellent overview of humanity's relationship with Nature. The book looks at energy flow, nutrient cycling, ecosystem services, ecosystem collapse as well as exploring our psychological and spiritual dependency on nature. It also examines anthropocentrism and denial as causes of our unwillingness to respect our inherent dependence on the natural environment. The book concludes by bringing these issues together and providing a framework for solutions to the environmental crisis.

1 Energy is life

The gathered power

Of a yellow star,

Slowly garnered

By the growing green …

Fire-friend,

We see within you

The endless years

Of our long journey.

Living starlight

You, the man-maker,

Will we pass the test,

Our time of growing?

Or will we fail the flame,

Your trust in man?

(‘Fire’, Washington 2010)

Energy is life, or at least the prerequisite for life. We depend on Nature for the energy that powers the crops in our fields, the animals on our farms and the pets in our homes. We depend on it even for the energy that powers our own bodies. All the fossil fuels that power our civilization are carbon compounds trapped by photosynthesis in past ecosystems and preserved (fossilized) as fossil fuels millions of years ago. The petrol and diesel that power our cars and the coal that is burnt to make electricity makes use of an energy preserved from hundreds of millions of years ago, where the energy-rich long chain organic compounds created by photosynthesis survive in a condensed and fossilized form today as oil and coal. Our planet is bathed in a life-giving stream of energy flowing from the Sun. Through the wonder of photosynthesis, plants trap 1–2 per cent of the sunlight that falls on them (Hall and Rao 1999). This powers almost all of the Earth’s ecosystems, the only exceptions being bacteria known as chemo-autotrophs that derive their energy from converting energy-rich chemicals in rocks (such as sulphur). So the ancient Egyptians had it right – the Sun is the font of life. Its light drives almost all the living world.

The second law of thermodynamics tells us that in Nature, energy goes from a useable form to an unusable form as ‘entropy’ (disorder) increases. Energy passes from a high energy state to a low energy state. It goes in one direction. As comic songwriters Flanders and Swann (1963) quipped, ‘Heat won’t pass from a cooler to a hotter …You can try it if you like but you far better notter’. So unlike nutrients, you cannot ‘recycle’ energy, it moves in one direction, from the high-energy sunlight to low-energy heat. The direction can be reversed by human actions, but this takes energy to do this. Thus, ultimately, the amount of life the Earth can support is determined by the fixed amount of sunlight falling on the Earth, an amount that varies only slightly with solar cycles. Unlike our society’s energy consumption, solar energy is not increasing exponentially. There is a fixed amount of life-giving energy that falls upon the Earth.

Productivity and food webs

We need to discuss a few ecological terms to get a grasp on energy flow in ecosystems. The first of these is Gross Primary Productivity (GPP), which is the total amount of carbon fixed by plants (‘autotrophs’ or ‘producers’) through photosynthesis. Incoming solar energy is trapped in sugars, which can then be used to make other compounds. However, plants use some of the energy fixed as sugars to run their own cells, and this is called ‘respiration’ (in this case it does not mean breathing). Respiration uses roughly half of the energy fixed in sugars by photosynthesis (Cain et al. 2008). The balance of the fixed carbon, once we subtract respiration, is called Net Primary Productivity (NPP). NPP represents the energy (fixed and stored as sugars) left over for plant growth and for consumption by herbivores (and ‘detritivores’ that break down plant matter in the soil). It is NPP then that is the basis of all the food chains and food webs that make up the Earth’s web of life. More NPP means more opportunities for life, less NPP means fewer opportunities. NPP (the Sun’s energy trapped as organic matter) is thus the fundamental foundation on which the rest of the living world is built. It is, however, a foundation of fixed size. We can degrade ecosystems (e.g. by land-clearing) so that we have less of this foundation, but we cannot build more of this foundation than the sunlight will allow.

The sugars produced in photosynthesis can be converted into starch for storage (for times of need), or can be converted to cellulose to build cell walls. They can be converted to ‘lignin’ also, the cement that makes cell walls rigid and ‘woody’. They can have nitrogen added to make amino acids that link to form proteins. In forest ecosystems, over time the NPP tends to decrease as the forest matures, because leaf area and photosynthesis rates are lower. However, this should not be construed as a ‘bad’ thing (as some loggers tend to claim) where the forest is ‘over-mature’ or senescent. The decline in NPP over time in a forest is a natural function of ecological succession, and the older or ‘climax’ forest is better at nutrient recycling, water management and other ecosystem services (MEA 2005).

NPP is constrained by both physical and biological environmental factors. Sunlight is one. Climate is also clearly a key controller of NPP, especially rainfall. NPP increases with rainfall up to a figure of 2,400 mm a year (Cain et al. 2008), after which it decreases (owing to cloudy conditions, waterlogged soils, etc.). NPP also tends to increase with annual average temperature (provided there is enough water). Nutrient availability and the plant species present will also affect NPP, and in aquatic ecosystems, nutrient availability (e.g. phosphorus) controls NPP.

Energy is continually being added to ecosystems from the Sun, being trapped by plants (producers) and these plants are eaten by herbivores (known as ‘first order consumers’) that may be eaten by carnivores (‘second order consumers’). This flow of energy in an ecosystem is called a food or ‘trophic’ chain (trophic is Greek for ‘feeding’) and the flow of energy through different species along such chains is called a food web. At each step in the chain usable energy is lost. This has led to what has been called ‘Lindeman’s Law’, where the next step in the food chain has only about 10 per cent of the biomass of the step before it. This is why most food (trophic) chains have only 4 or 5 steps, as the amount of energy remaining after this becomes too small to support a viable population of animals.

Figure 1.1 shows a simple food web for the Australian platypus. Of course, most food webs are much more complex and interwoven, and can be said to resemble a ‘spaghetti diagram’ (Cain et al. 2008). Carnivores can of course eat at several levels in the food web. For example, a predator may eat fruits or nuts, as well as the insects that eat these, and the animals that eat those insects. So food webs are complex.

Figure 1.1 Simple food web for the Australian platypus.

Source: adapted from www.mghs.sa.edu.au/Internet/Faculties/Science/Year9/livingTogether.htm.

Keystone species

There is another side to this complexity, as each species in a food web may not have equal importance or impact on other species. Not all members of the web affect each other evenly. Ecologists speak of ‘interaction strength’ as the measure of the effect of the population of one species on the size of another species population. Another way to look at it is that some species have more effect on how energy moves through a food web, and even on what species are present in an ecosystem. These are known as keystone species, and are important, little known, parts of ecosystems.

The classic example of a keystone species was identified in an experiment in the rocky intertidal zones in the Pacific Northwest of the US, where ecologist Robert Paine (1966) removed the sea star Pisaster to see what happened. Barnacles initially became more abundant, but were then crowded out by mussels and goose-neck barnacles. After two and a half years the number of species had dropped from 15 to 8, and even after the sea star was reintroduced, mussel dominance remained, as they had grown to sizes that prevented predation by the sea stars (Paine 1966). The sea star Pisaster was thus a keystone species that determined what the species mix ended up being in that ecosystem. It also actually maintained high species diversity in that ecosystem. Keystone species are found all around the world and include organisms from almost all ecosystem types.

There are three types of keystone species – ‘predators’, ‘mutualists’ and ‘ecosystem engineers’. Keystone predators are often found at high levels in the food web, but are not necessarily the top predator. Some are in fact top predators, such as wolves and jaguars (Nowell and Jackson 1996) and dingos (Purcell 2010). However, the sea otter is one keystone species not found at the top of the food chain, for it is preyed on by killer whales (Orcas). Similarly, the sea star Pisaster is also preyed on by several other predators. Keystone mutualists are organisms that participate in mutually beneficial interactions with other organisms, and the loss of keystone mutualists would have a profound impact upon the ecosystem as a whole. For example, in the Avon wheat belt region of Western Australia, there is a period of each year when Banksia prionotes (Acorn Banksia) is the sole source of nectar for honeyeaters, which play an important role in pollination of numerous plant species. Therefore the loss of this one species of tree would probably cause the honeyeater population to collapse, with profound implications for the entire ecosystem. Other examples of mutualist keystone species are fruit eaters (frugivores) such as the cassowary, which spreads the seeds of many different trees around the rainforest. Some trees will not grow unless they have been through the digestive tract of the cassowary (Walker 1995).

In North America, the grizzly bear is a keystone species, not as a predator but as an ecosystem engineer. They transfer nutrients from the oceanic ecosystem to the forest ecosystem. The first stage of the transfer is performed by salmon (rich in inorganic nutrients) that swim up rivers, sometimes for hundreds of miles. The bears then capture the salmon and carry them onto dry land, dispersing partially eaten carcasses and nutrient-rich faeces. Bears leave up to half of the salmon they harvest on the forest floor (Reimchen 2001). The prairie dog is also an ecosystem engineer. Its burrows provide the nesting areas for mountain plovers and burrowing owls (NGP 2011). Prairie dog tunnel systems also help channel rainwater into the water table to prevent runoff and erosion (Outwater 1996; Miller et al. 2000). Another ecosystem engineer is the beaver, which transforms its territory from a stream to a pond or swamp (Wright et al. 2002). In the African savannah, the larger herbivores, especially the elephants, are ecosystem engineers that strongly influence their environment. The elephants destroy trees, making room for the grass species. Without these animals, much of the savannah would turn into woodland (Leakey and Lewin 1999). The caiman is an ecosystem engineer, and its removal from areas in the Amazon has led to a decline in fish populations (and hence fish catch), because of reduced nutrient cycling in the food chain which the Caiman made possible (Williams and Dodd 1980). The alligator is similarly a keystone species in the Everglades (Amsel 2007). The impacts of herbivores on savannah are altered in major ways by Tsetse flies, as only certain herbivores survive. The Tsetse fly may be small, but is also a keystone species (Elmqvist et al. 2010).

Overall then, keystone species are of great importance to keeping ecosystems healthy. Sadly, we don’t know all the keystone species present on Earth, and we may in fact never know them all. We often only learn what species are keystone once they are lost or in major decline. We often fail to learn of the benefits provided by a species until it is gone. The Passenger Pigeon used to darken the skies with its huge flocks, and was deemed inexhaustible. However, it was sent extinct at the start of the twentieth century as a consequence of over-hunting. It was later realized that the pigeon had been eating huge amounts of acorns, and after its disappearance these were then eaten by deer and mice. This led to a boom in these mammals and thus in the ticks that lived on them, and in the spirochaete bacteria that lived in those ticks. This boom in spirochaetes caused an unexpected epidemic of Lyme’s disease in humans several decades after the loss of the pigeons themselves (Pascual et al. 2010). We thus do not often know which species is a keystone species until long after we have sent them extinct. It is clear that many top carnivores are keystone species. The removal of the wolf from areas has led to an explosion in herbivores that overgrazed ecosystems (causing erosion and nutrient loss). The removal of the dingo, the top land predator in Australia, is implicated in the extinction of native animal species as a result of increased cat and fox predation (which the dingo had been controlling) (Purcell 2010).

One other term we should discuss is the ‘trophic cascade’. This is about indirect effects within food webs. For example, when a carnivore eats a herbivore there is often a direct positive effect on the plant (primary producer). One key example is the sea otter eating the sea urchins that eat the kelp on the west coast of America. The sea otter was discovered to be a keystone species, but only when it was hunted for its fur almost to extinction. The sea urchin populations exploded and the kelp forest went into decline. So it is often through ‘trophic cascades’ that keystone species affect ecosystems. Trophic cascades are thus a series of changes in energy and species composition in an ecosystem. They are best known from aquatic systems, often through unintended releases of non-native (feral) species. The introduction of brown trout into New Zealand led to the decline of native fish, with some local extinctions. This happened through a trophic cascade where the trout reduced invertebrate (water creepy-crawlies) density and increased algae growth (Cain et al. 2008).

Diversity, stability, resilience and ecosystem services

Biologists speak of ‘biodiversity’, which is another name for plants and animals and the ecosystems they form. Biodiversity is made of three parts: the genetic diversity within a species, the species themselves, and the ecosystems that are made up of species (Cain et al. 2008). All three components are important. In regard to food webs and biodiversity, there has been much debate among ecologists on whether complex food webs (high biodiversity) are more stable than simpler food webs that are less diverse. ‘Stability’ is a term with many meanings, but is usually defined as the tendency of the community to remain the same in structure and function (Cain et al. 2008). The term is now avoided by some ecologists. For example, the UNEP project ‘The Economics of Ecosystems and Biodiversity’ or TEEB (Kumar 2010) talks about high biodiversity leading to ‘less variability in functioning’ rather than the term ‘stability’ as such. Stability is usually gauged by the size of the changes in organism populations over time. A less stable food web means greater potential for extinction. The question of greater diversity leading to stability has been hotly contested within ecology, with Odum (1953) and Elton (1958) believing this was the case, while May (1973) used food web models to suggest that food webs with high diversity are less stable.

However, rainforests and coral reefs do have high biodiversity and do indeed persist over time. The relationship of biodiversity and stability is still...

Table of contents

• Cover 
• Title
• Copyright
• Dedication
• Contents 
• List of figures
• Foreword by Professor Paul R. Ehrlich
• Acknowledgements
• Introduction
• 1. Energy is life
• 2. The great cycles
• 3. Ecosystem services – essential but overlooked
• 4. Collapse
• 5. Psychological, cultural and spiritual dependence on Nature
• 6. The great divide – anthropocentrism vs ecocentrism
• 7. Dealing with denial
• 8. Do we have a problem?
• 9. Solutions to keep our roots in the Earth
• References
• Index