In recent years the slight balance of ecosystems has suffered deep alterations due primarily to the drastic increase in human activities, on a global, regional and local geographical scale. The great development experienced since the post-war period in fact has brought, in addition to countless benefits, also many consequences on the environment, including the reduction of the ozone layer and the release of numerous pollutants.
The definition of ecosystem asks for important conceptual elements: energy, the biotic community, trophic chains, the exchange of matter and energy, the extension and balance of the ecosystem. These elements help to develop a model that allows us to understand the complex structure of an ecosystem and, in addition, to analyse its main alterations.
During this lesson we will try to answer the following questions: what is an ecosystem? What are its main elements? How have human activities altered ecosystems? How is reported this complex field of natural sciences by mass media and perceived by the audience?
1. Ecosystem: suggestions for a definition
Exercise: Identify the main elements of an ecosystem. Why are we using the word system? Give me an example of a simple system and a complex system.
The concept of ecosystem has various definitions. Some focuses exclusively on biotic components, assimilating the ecosystem to a series of food chains. Other definitions focus on trophic networks, but take also in count abiotic components such as physical conditions of the environment. To better depict the complexity of an ecosystem it is useful to adopt a definition that considers all the different components, biotic and abiotic. In this context we can represent the ecosystem as a system extended over a certain portion of territory, consisting of a set of living communities that interact with each other and with the physical environment.
EP Odum (Fundamentals of ecology, 1971) defined the ecosystem as a unit that includes all the organisms of a given area interacting with physical environment in such a way that the flow of energy leads to a well-defined trophic structure, a biotic diversity and a cyclization of matter within the system.
Solar energy is at the basis of the biotic component. This, as a whole, works like an organism in which all life forms are linked together. If one element were missing, the physiognomy of the community would adapt accordingly, assuming a new organization (biocenosis).
The biotic community build up a set of trophic networks that are interconnected. We can decompose this network into three main categories of elements:
- The producers, such as vegetables that process organic substances from minerals.
- The consumers, which directly or indirectly feed on organic substances provided by producers.
The decomposers, which decompose dead organisms and organic substances, bringing them back to mineral state.
In an ecosystem we have different flows of matter and energy. Vegetable kingdom receive solar energy; a part of this is not used, the other part supports the synthesis of organic matter. Only a portion of this mass is assimilated by herbivores. The other portion is decomposed by decomposers. A part of the matter integrated by herbivores (the rest is lost with excrement or through breathing) can later be used by carnivores. As we can see, energy transfers take place at every stage; and at each stage there are also important energy losses.
This circular relationship simplifies the organization of trophic networks. Biocenosis can be analysed considering plant and animal elements that make up the trophic network, their relationships and the ability to use physical components of the ecosystem. It is characterised by two principles:
- Numerous and rich abiotic components correspond to numerous biotic communities.
- If living conditions become more difficult, the number of species decreases, but each species records a population increase.
The ecosystem has the following properties (Vallega, 1995, p. 66):
- It is a real system: its elements have closer relationships than those related to external environment (interconnective capacity).
- It is composed of organic elements (trophic networks) and inorganic elements:
- Hydrosphere : Water-climate system.
- Lithosphere : Earth-atmosphere interface.
- Atmosphere : Energy-atmosphere system.
- It has its own organization (biocenosis).
- It is a dynamic system in continuous evolution.
- It is able to continue to complete its functions even in presence of external impulses (resilience).
Each ecosystem has one or more habitats on which the survival of a species depends. The biotic community is made up of a variable number of species, animals and plants. We can distinguish two main groups: The first is characterized by few species, each of which has a large number of individuals, to the point of becoming dominant species. The second is characterized by a high number of species, each of which has a reduced number of individuals. These are rare species.
Example of species diversity. Diagram shows marine ecosystems: In y-axis is represented the number of species, in the x-axis the population for each category of species. Tropical Low Waters (ABT), Deep Waters (AP), waters above the Continental Platform (PC), Low Boreal Waters (ABB), Boreal Estuaries (EB).
Factors influencing the dynamics of the ecosystem are numerous, such as the presence or absence of water resources, food, wind, location, temperature, exposure, pedology, or man.
4. Geographical scale
Ecosystems can be defined at various geographical scales. For example, a rainforest is a global ecosystem stretched over the equator. In its turn, it is composed by smaller ecosystems where biotic and abiotic aspects take on different characteristics. We refer to the ecosystem in both cases: the entire extension of the rainforest and the parts in which it breaks down.
Gerarchia spaziale dei sistemi ecologici (Massa, 1999)
Classification of large ecosystems based on the identification of biomes (Vallega, 1995):
- Rainforest (Southeast Asia, Africa, Northeast Australia)
- Rainforest with dry season, monsoon forest (Southeast Asia)
- Temperate forest in regions with heavy rains (Eastern Australia)
- Rainforest mountain forest
- Deciduous temperate forest (Eastern United States, Western Europe)
- Evergreen temperate forest
- Taiga (North America, Eurasia)
- Dwarf forests
- Acacia forests
- Shrub formations in arid climate
- Temperate forest
- Shrub coverings
- Savannah (Africa, South America)
- Prairie and steppe (Eurasia, New Zealand)
- Alpine forest
- Arctic tundra (Asia, North America)
- Tropical desert (North Africa, Asia Minor, western South America)
- Warm temperate desert (South and Central Asia, Australia, Argentina)
- Desert with scrub (western United States, inner Asia)
- Mountain desert
- Forest in continental wetlands (Amazon basin)
- Forest in areas of contact between fresh and salt waters (south-eastern United States)
- Mangrove forest (intertropical coasts and estuaries)
- Coastal wetland
- Pelagic marine environment
- Benthic marine environment
- Rocky coast
- Sandy coast
Creating classifications and types of large ecosystems does not present big difficulties. The operation may be harder at local level.
5. How to define an ecosystem?
Geography is a discipline that is often concerned with defining a phenomenon on the territory. The problem to limit an ecosystem is particularly complex. If we assume a basic definition of ecosystem, such as a series of food chains, the boundaries are relatively simple to define. The difficulties increase if we include other components and relationships that characterize them.
Exercise : Put down on a piece of paper the limits of a natural park or reserve in your region: 1 - define main elements of the ecosystem. 2 - what kind of relationships can you see between those elements? 3 - how to delimitate the ecosystem? 4 - what are anthropic elements that characterize the park or its borders?
6. Alterations of the ecosystem: an evolutionary system
When ecosystems register external inputs, they adjust in different ways. Most oh them would modify part of their organization, using their autopoietic abilities (ability to react to inputs).
However, external forces can be so intense that they challenge the entire ecosystem organization, transforming or destroying parts of the trophic networks. The result is a new ecosystem that takes place of the modified one. In this case autopoietic abilities are not enough and morphogenesis, structural change, arises.
The climax is the final equilibrium situation achieved after a long process of ecological succession.
We can identify two main categories of external impulses: alterations caused by human activities and alterations inside or outside components of the system.
6.1. Ecosystem alterations: internal and external alterations to the system
Numerous external natural factors can alter significantly the state of the ecosystem: climatic factors such as a modified energy supply, presence or absence of water, temperature, light, wind, soil pedology, ...
In general, these changes are slow and constant, especially those related to topography and pedology. But natural phenomena can also involve instantaneous and brutal changes: floods, landslides, volcanic eruptions, droughts, hurricanes.
- The woods devastated by storms Viviane and Lothar in Europe.
- The eruption of Raung volcano in Indonesia.
- The tsunami that devastated Southeast Asia.
Disruptive processes and effects for biotopes and species (Massa, 1999)
6.2. Ecosystem alterations: human activity
Human activity represents an important source of ecosystem alterations at different scales, from global to local. Anthropic impacts are not only impoverishing and weakening the Planet, but have also encouraged the birth of new ecosystems, for example agrarian and urban’ one.
6.2.1. Alterations on a global scale
Overall, human society plays an increasing role not only in ecosystems dynamics on a local scale, but also in biogeochemical cycles on a planetary scale. On global level we can define three main types of alteration (Primack R.B., Carotenuto L., 2003):
- Land surface: Land use and resource extraction have transformed a growing part of land surface. Interventions can be of different nature: destruction, fragmentation, pollution, exploitation, manipulation, transformation.
- Nitrogen cycle: Every year activities such as cultivation of nitrogen-fixing plants, use of nitrogen fertilizers or fossil fuels release more nitrogen composites in terrestrial systems than those released by natural processes.
- Atmospheric carbon cycle: According to some authors, within the middle of the XXI century the use of fossil fuels will double the amount of carbon dioxide present in atmosphere.
These interventions are affecting the balance of the habitats of numerous species.
6.2.2. Population growth
Human population growth and consequent increase in natural resources consumption is one of the major causes to ecosystem alteration. Until a few centuries ago, population evolution has been measured and marked by Malthusian cycle. Industrial Revolution is a point of rupture and has determined an acceleration in its growth.
Population went from one billion people in 1850 to two billion in 1930 and 6 billion in 1998. Reasons for this growth are the decrease in mortality and a birth rate that remained almost constant during the XX. century. In the early 2000s a slowdown in growth has been recorder for the first time: according to UN experts we are moving towards a new phase of balance that will bring the world population to stabilize at around 11 billion by 2100 ( https://www.un.org /en/development/desa/population/publications/trends/population-prospects.asp ).
Demographic increase has important consequences on natural resources consumption and on alterations of the ecosystems. Large industrial and commercial activities are responsible for impacts that affect local and global environments. Mines, industrial fishing, deforestation, intensive agriculture, wetland recuperation, construction of dams, are just a few examples of human activities related to this trend.
Even when an ecosystem is not directly affected by destruction or fragmentation, human activities can play an important role in its specific structure. The cenoses are often damaged by external factors, which in the early stages of alteration process do not affect dominant species and therefore the impact is not immediately evident. Over time, the composition and structure of the system tends to adapt to new conditions determined by the degradation of the ecosystem.
The most frequent form of degradation is pollution, mainly caused by pesticides, synthetic fertilizers, chemicals, sewage, industrial sewage, urban settlements, intensive agriculture, toxic gases. Their presence is not always perceptible. Pollution can affect the climate, the quality of water, air and soil, posing a threat to biodiversity and finally it is a potential danger to human health.
6.2.4. Local scale alterations
At the local level alterations affect well-defined ecosystems: a forest, a swamp, a meadow. Actions that could compromise the stability of an ecosystem are different: deforestation, land reclamation, agriculture, tourism infrastructure or settlements development. In this case, the importance of anthropic impacts has led to the birth of a particular ecosystem: urban ecosystem . The biotope is composed of natural and artificial physical elements such as constructions, communication networks, sewer systems, ... The urban biocoenosis is the association of all organisms living in urban biotope: plant population (phytocoenoses), animal (zoocenosis) and human (anthropocenosis).
The main characteristic of this system is the strong demand for resources and energy from outside. This generates several problems:
- Strong ecological footprint of urban system: strong incidence of this spatial set on other local, regional and continental ecosystems. Internal processes of the city require a lot of energy and matter.
- Poor autonomy: anthropocenosis fails to continue without continuous external contributions to urban system.
- Imperfect metabolism: the system produces a large amount of waste and emissions.
We can highlight how global and local alterations are interconnected, shaping immediate changes (or not) in different ecosystems.
Exercise: take a postcard of your city dating from the beginning of twentieth century: what considerations can you depict from it compared to the present? Take a piece of paper and try to schematize urban development on a spatial level. In another scheme, try to imagine how your city will be set up in 50 years from now.
To sum up, ecosystems are composed of two fundamental elements: biocenosis and one or more biotopes. Relationships are constituted by trophic chains and ecological cycles (circulation of matter and energy). It is an open system: system’s input is solar energy, its output are biomass and thermal energy.
As we have seen, ecosystem and its alterations can involve a great number of difficulties. Applying the concept of ecosystems it is important to focus on some fundamental aspects: the definition of the main constituent elements and the analysis of their behaviour in relation to the solicitations they receive. In fact, it is impossible to know everything about the trophic chains, the abiotic aspects or the relationships between different elements.
Men (individual, group, society) have developed functions that require a significant use of resources: to live, work, study, have fun or communicate. Ecosystems, territories, spaces take in different roles that evolve over time.
“I would like there to exist places that are stable, unmoving, intangible, untouched and almost untouchable, unchanging, deep rooted; places that might be points of reference, of departure, of origin: My birthplace, the cradle of my family, the house where I may have been born, the tree I may have seen grow (that my father may have planted the day I was born), the attic of my childhood filled with intact memories . ..
Such places don't exist, and it's because they don't exist that space becomes a question, ceases to be self-evident, ceases to be incorporated, ceases to be appropriated. Space is a doubt: I have constantly to mark it, to designate it. It's never mine, never given to me, I have to conquer it.
My spaces are fragile: time is going to wear them away, to destroy them. Nothing will any longer resemble what was, my memories will betray me, oblivion will infiltrate my memory, I shall look at a few old yellowing photographs with broken edges without recognizing them.”
(Perec, Georges, and John Sturrock. 2008. Species of spaces and other pieces. London: Penguin Books)
Human society modifies structures and potentials of ecosystems: alterations have impacts that can be positive and negative, important or less significant. Global impact analysis of human activities is a difficult subject to deal with and requires notions coming from various academic disciplines. As a general rule, it is better to be wary of simplistic statements reported on media and to keep in mind that this is a politicized issue. We already have numerous examples of how catastrophic visions are not useful or opportune: it is better to focus on a documented and solid approach, aimed primarily at intelligent management of resources and sustainable exploitation of ecosystems, which allows a uniform progress of human communities.
In this sense, selecting the best sources is fundamental, both in terms of research quality and in its update: using the latest data in this context is absolutely relevant.
A problem of definition: nature and Anthropocene
Right now, humans can make their crops and their timber, to pasture their animals. If you added up to the human beings, we would weigh 10 times as much as the wild mammals put together. We cut roads through the forest. We have added little plastic particles to the sand on ocean beaches. We have changed the chemistry of the soil with our artificial fertilizers. And of course, we've changed the chemistry of the air. I know when you take your next breath, you will be breathing in 42 percent more carbon dioxide than you were breathing in 1750. I know all of these changes, and many others, how to kind of lumped together under this rubric of the "Anthropocene." This is a term that some geologists are suggesting we should give to our current epoch, given how pervasive human influence has been over it. Now, it's still just a proposed epoch, but I think it's helpful to think about the magnitude of human influence on the planet.
So where does this put nature? What counts as nature in the world where everything is influenced by humans?
I know 25 years ago, environmental writer Bill McKibben said that because of the climate change. In fact, he called his book "The End of Nature."
I disagree with this. I just disagree with this. I disagree with this definition of nature, because, fundamentally, we are animals. Right? Like, we evolved this planet in the context of all the other animals with which we share a planet, and all the other plants, and all the other microbes. And so I think that nature is not that which is untouched by humanity, man or woman. I think that nature is everywhere where there are multiple species together, anywhere that's green and blue and filled with life and growing. And under that definition, things look a little bit different.
Now, I understand that there are certain parts of this nature that speak to us in a special way. Places like Yellowstone, or the Mongolian steppes, or the Great Barrier Reef or the Serengeti. Places that we think of kind of representations of nature before we screwed everything up. They are less impacted by our day to day activities. Many of these places have no roads or few roads, so on, like such. But ultimately, even these Edens are deeply influenced by humans.
Now, let's just take North America, for example, since that's where we're meeting. So between about 15,000 years ago, when people first came here, they started a process of interacting with nature that led to extinction of large, large animals, from the mastodon to the giant ground, saber-toothed cats, all of these cool animals that unfortunately are no longer with us. And when those animals went extinct, you know, the ecosystems didn't stand still. Massive ripple effects changed grasslands into forests, So even in these Edens, in these perfect-looking places that seem to remind us of humans, we're essentially looking at a humanized landscape. Not just these prehistoric humans, but historical humans, indigenous people all the way up until the moment when the first colonizers showed up. And the case is the same for the other continents as well. Humans have just been involved in nature in a very influential way for a very long time.
Now, just recently, someone told me, "Oh, but there are still wild places."
And I said, "Where? Where? I want to go."
And he said, "The Amazon."
And I was like, "Oh, the Amazon. I was just there. It's awesome. National Geographic sent me to Manú National Park, which is in the Peruvian Amazon, but it's a big chunk of rainforest, uncleared, no roads, protected as a national park, one of the most, in fact, biodiverse parks in the world. And when I got there with my canoe, what I did, but people. People have been living there for hundreds and thousands of years. They just do not float over the jungle, they grow crops, they grow domestic crops, they are their houses. make pets out of animals That we consider to be wild animals. These people are there and they're interacting with the environment in a way that's really meaningful and That you can see in the environment.
Now, I was with an anthropologist on this trip , and he told me, as we were floating down the river, he said, "There are no demographic voids in the Amazon." This statement has really stuck with me, because it is that the whole Amazon is like this. There's people everywhere. And many other tropical forests are the same, and not just tropical forests. People have influenced ecosystems in the past, and they continue to influence them in the present, even in places where they're harder to notice.
So, if all of the definitions of nature that we might want to use that involve it being untouched by humanity or not having people in it, if all of those actually give us a result where we don't have any nature, then maybe they're the wrong definitions. Maybe we should define it by the presence of multiple species, by the presence of a thriving life.
Source: Emma Marris: Nature is everywhere - we just need to learn to see it , TED Talk. https://www.ted.com/talks/emma_marris_nature_is_everywhere_we_just_need_to_learn_to_see_it/transcript?language=en
Balance and perception
Have you heard people say that humans used to live in balance with nature?
Well, yes, there was a balance. But let’s avoid the rose-tinted glasses. Until 1800, women gave birth to six children on average. So the population should have increased with each generation. Instead, it stayed more or less stable. Remember the child skeletons in the graveyards of the past? On average four out of six children died before becoming parents themselves, leaving just two surviving children to parent the next generation. There was a balance. It wasn’t because humans lived in balance with nature. Humans died in balance with nature. It was utterly brutal and tragic.
Today, humanity is once again reaching a balance. The number of parents is no longer increasing. But this balance is dramatically different from the old balance. The new balance is nice: the typical parents have two children, and neither of them dies. For the first time in human history, we live in balance.
Source: Rosling, 2018
In Rosling's text, a recurring theme is introduced: perception and the role of mass media. To stay on the theme of alterations of ecosystems, one of the most common chapters in world media is global warming. If on the one hand the media report a scientific datum, on the other they do it with a particular emphasis.
Look at the first graph (source: NASA) and comment on it in class. If you were a journalist, what title would you give to the article accompanying this image? Have you ever found similar titles or graphics in the media?
Now look at the second graph and repeat the activities proposed for the first graph. Remember that the two graphs are both correct, only the scale changes.
Maps that show us who we are (not just where we are)
There are a huge number of good news stories in the world. Infant mortality is falling and has been falling at an incredible rate. A few years ago, the number of babies dying in their first year of life in the world fell by five percent in just one year. More children are going to school and learning to read and write and getting connected to the Internet and going on to go to university than ever before at an incredible rate, and the highest number of young people going to university in the world are women, not men. I can give you good news story after good news story about what is getting better in the planet, but we tend to concentrate on the bad news that is immediate. Rebecca Solnit, I think, put it brilliantly, when she explained: "The accretion of incremental, imperceptible changes which can constitute progress and which render our era dramatically different from the past" — the past was much more stable — "a contrast obscured by the undramatic nature of gradual transformation, punctuated by occasional tumult." Occasionally, terrible things happen. You are shown those terrible things on the news every night of the week. You are not told about the population slowing down. You are not told about the world becoming more connected. You are not told about the incredible improvements in understanding. You are not told about how we are learning to begin to waste less and consume less.
Source: Dorling, Danny. Maps that show us who we are (not just where we are). https://www.ted.com/talks/danny_dorling_maps_that_show_us_who_we_are_not_just_where_we_are
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Roland Hochstrasser, geographer
Comments, corrections and suggestions are welcome and will get serious attention. Italian version: http://rhpositive.net/index.php/23-territorio-e-sviluppo-sostenibile/33-le-alterazioni-dell-ecosistema
Licenza Creative Commons Attribuzione 3.0 Unported.
Citazione della fonte: "Roland Hochstrasser, www.rhpositive.net".