Ecosystem Crises Interactions. Merrill Singer
systems an important part of the story of the changing ecology on Earth and the development and interface of ecocrises, including loss of biodiversity and climate impact on health.
2.3.4 Human‐dominated ecosystems
All organisms, past and present, modify their ecosystems, and “studies on lakes, coral reefs, oceans, forests and arid lands have shown that smooth [environmental] change can be interrupted by sudden drastic switches to a contrasting state” (Scheffer et al. 2001). In the case of humans, however, the extent of ecosystem alteration can be both rapid and far‐reaching (Fig. 2.4). At the local or regional scale, human‐dominated ecosystems include agricultural fields, created and maintained pasturelands, planted forests, urban areas, populated islands, and similar settings where the effects of human presence are sweeping. It is even possible to talk of all of Earth as a human‐dominated ecosystem, as there are no terrestrial ecosystems and almost none underwater that are untouched by human activity (Vitousek et al. 1997). When humans clear lands for agriculture, send airplanes across the skies, fish the oceans, operate manufacturing plants, or produce and use cement, we reconfigure the major biogeochemical cycles of Earth, including those of CO2, nitrogen, and sulfur.
The concentration of CO2 in the atmosphere has steadily increased as a result of human activities, especially since the Industrial Revolution, but starting long before that with alterations like clearing and planting. Even indigenous populations cleared forested areas through burning to increase grassy pastures in which to find and hunt grazing wild animals. Human alterations of the hydrological cycle can change regional weather patterns and even longer‐term climate. Implementing irrigation systems raises atmospheric humidity in semiarid locations, which promotes the frequency of rain and thunder storms. Humans have also altered the global nitrogen cycle. A vital biosynthesizing element for living organisms, nitrogen is present in abundance in the atmosphere but must be combined with carbon, hydrogen, or oxygen to form ammonia or other molecules in order to be useable by most lifeforms, a process known as fixation. Human activity has substantially altered the global nitrogen cycle through both fertilizer production and fossil fuel combustion. The global sulfur cycle, meanwhile, has been changed by the acquisition and burning of fossil fuels. Unprecedented increases in the amount of sulfur in both the atmosphere and the oceans is now occurring. Sulfur dioxide emitted by the fossil fuel industry reacts with water vapor in the atmosphere to form acid rain, which is damaging to forests, fish, and other aquatic animals. Oceans, too, feel the impact of acid rain, especially in coastal areas, which are becoming more acidic and being stripped of the carbonate ions needed by shell‐making sea life. The ability of human technologies to change multiple biogeochemical cycles in these ways creates the potential for radical alterations of Earth.
Fig. 2.4 Human alteration of key components of Earth ecosystems.
Source: Modified from Vitousek et al. (1997).
2.3.5 Human ecology
Human ecology is the subfield of ecology that is specifically concerned with understanding relationships between people and their environment, including the built environment of human construction (e.g., an urban neighborhood, a riverine village, or a fishing camp). The presence of humans on Earth is the zig‐zagging, undirected product of evolutionary history, played out under the influence of complex and changing environmental and climatic conditions.
In human ecology, as in the broader field, the environment is conceptualized as an ecosystem. Thus, in human ecology research, a single farm can be studied as an ecosystem, as can New York City. Notably, humans are never the only organisms that inhabit built environments. Some nonhuman species, like dogs and zoo animals, occupy human‐constructed environments because we bring them there. Others, like termites, coyotes, and brown rats, are uninvited but find such settlements contain abundant desirable resources. Of special note to human health in built environments is the role of animal disease vectors like mosquitoes and rats in the spread of infectious pathogens as a result of interacting ecocrises like climate change and flooding.
Some wild species, like the house sparrow (Passer domesticus), are so anthrodependent that if humans abandon a location, the local population goes extinct. The house sparrow is also quite sensitive to changes in human landscapes. In some urban areas, especially in the United Kingdom and Western Europe, their numbers are now declining because of changes in human ecology such as gentrification, which reduces the number of nesting sites and food availability.
Human social systems are a dominant feature of human‐impacted ecosystems. As Marten (2001, p. 1) states:
Although humans are part of the ecosystem, it is useful to think of human–environment interaction as interaction between the human social system and the rest of the ecosystem … The social system is a central concept in human ecology because human activities that impact on ecosystems are strongly influenced by the society in which people live. Values and knowledge … shape the way that we process and interpret information and translate it into action.
Human activities in an environment, such as driving a car, building a new factory, cutting down trees in a rainforest, drilling for oil in a deep‐water site, launching a fleet of factory stern trawler fishing and processing vessels, or planting a field of corn, trigger a chain of effects that reverberate between social systems and ecosystems (Fig. 2.5). Marten (2001, p. 2) cites the following example of this echo process. People in many parts of India traditionally have used wood extracted from the environment for cooking fuel. This was not a great threat to the balance and regenerative capacity of the forest environment until the human population expanded rapidly beginning in the 1950s. As a result:
Fig. 2.5 Feedbacks between human activities and Earth properties leading to global change.
Source: Modified from Hooper et al. (2005).
Many forests have disappeared in recent years because people have cut so many trees and bushes for cooking fuel. Now there are not enough trees and bushes to provide all the fuel that people need. People have responded … by having their children search for anything that can be burned, such as twigs, crop residues … and cow dung. Fuel collection makes children even more valuable to their families, so parents have more children. The resulting increase in population leads to more demand for fuel.
(Marten 2001)
More recently, India’s fertility rate has stabilized, with the average number of children born to a woman during her lifetime dropping from 5.9 in 1951 to 2.3 in 2011 (Nagajan 2016). But India’s population remains quite large and the damage to the environment has been done, not only by small farmers but also by large planation corporations, beginning with colonial British commercial forestry operations. Forest loss has impacted many species and contributed to a growing water crisis in the country’s villages and cities. This poses threats to health, particularly among poorer families.
As this last comment indicates, a central feature in contemporary human societies that shapes the way humans interact with the environment is social inequality. Health anthropologists have developed what they call an ecobiopolitical model for comprehending the complexities of societal–environmental interaction in the production of health and health inequality within society. This approach is informed by a synthetic and holistic exploration of the linkages that connect power and social structures, societal/environmental relations, and health and the environment.