Ecology is possibly one of the most ancient disciplines. Its evolution has been gradual, and it will continue to evolve with humankind's ability to comprehend and understand his own surroundings and the interaction of its components. Rooted in the Greek word oikos, which means home, the subject shares its origin with the study of economics. The term ecology is fairly recent, coined by German biologist Ernst Haeckel in 1869. It is pertinent for students of ecology to deeply appreciate its fundamental principles, subdivisions, constraints, and challenges and some of the recent breakthroughs ecologists have made in advancing the subject.
Engagements with the basic tenets of ecology have a long history, with some of the earliest written reflections of the natural world in the writings of Greek philosophers like Hippocrates and Aristotle. In the early 1700s, Anton van Leeuwenhoek, the philosopher and scientist, initiated the study of living beings and their linkages through the food chain and population regulation. There have been several efforts to define “ecology”; possibly the simplest definition offered by E. P. Odum was “the study of the structure and function of nature.” Hanns Reiter was probably the first to combine the words oikos (house) and logis (study of) to form the term ecology. French zoologist Isodore Geoffroy St. Hilaire proposed the term ethology for the study of the relations of the organisms within the family and society in the aggregate and in the community. Today ethology has become synonymous with animal behavior. St. George Jackson Mivart coined the term hexicology in 1894 to describe the study of relations between organisms and their environment as regards the nature of the locality they frequent, the temperatures that suit them, and their relations to other organisms as enemies, rivals, or accidental and involuntary benefactors. Concerned with the sociology and economics of animals, Charles Elton, a British ecologist, defined ecology as “scientific natural history.”
The domain and scope of ecology is vast and cuts across many other disciplines that entail human endeavors and nature. Broadly, the subject has two divisions: autecology, which involves study of one organism or an individual species, and synecology, which deals with a group of organisms that are associated together as a unit. A very commonly used term in the science of ecology is ecosystem, which is a community of interacting organisms together with the physical environment within which it exists, and with which the species in the community also interact. Ecosystems can be natural, such as terrestrial, including forests and deserts; aquatic (freshwater and marine); or man-made, such as an agricultural, rural, or urban landscape. The boundaries of ecosystems are not very rigid—an ecosystem can be anything from a small pond, to an ocean or a small aquarium, to a vast rain forest; thus, a hierarchy exists from very local to global.
The subject of ecology has gained tremendous relevance in light of the present global efforts to retain healthy ecosystems. Ecosystems are dynamic, but are not randomly moved by uncontrollable forces. Healthy ecosystems maintain certain trajectories that are strongly influenced by species composition, species groups, landscape patterns, soil and atmospheric chemistry, and various other factors. Balances are dynamic rather than static. Understanding the interrelationship between balance and the flux—or between the structure and processes of nature—is the essence of modern ecology. Efforts to understand the ecology of a system are a prerequisite because it is not possible to manipulate an ecosystem without disturbing its elements and constituents. It is the degree of disturbance and the nature and intensity of the effects that ecologists are most often concerned with in the event of manipulation.
Ecology has various subdisciplines: physiological ecology is the study of how environmental factors influence the physiology of organisms; population ecology, the study of dynamics, structure, and distribution of populations; community ecology, the study of interactions among individuals and populations of different species; evolutionary ecology, the study of the physical and biological environment and processes that act as a filter and allow some individuals within a population to reproduce and pass the genetic materials to the next generation and screen others; and ecosystem ecology, the study of the patterns and interactions in an ecosystem. Finally, landscape and global ecology is the study of interactions among different ecosystems. Students of ecology learn about the flow of the energy in the ecosystems from plants (producers), which transform solar energy and carbon dioxide through the process of photosynthesis, through consumers (herbivores), then to carnivores, and finally to decomposers, which are microbes. This happens as a continuous cycle in nature. A very significant aspect of ecology are biogeochemical cycles—the cycling of water—the hydrological cycle, the gaseous nutrient cycle of carbon and nitrogen, and the sedimentary nutrient cycle of sulfur and phosphorus.
The domain of ecology is in spatial (space) and temporal (time) patterns of distributions, and in the abundance of organisms, including their causes and consequences. Several principles operate within this domain, with which ecologists widely agree. Samuel Scheiner and Michael Willig have summarized the principles of ecology.
Organisms are distributed in space in heterogeneous distributions.
Organisms interact with their abiotic (the nonliving) and biotic (living) environment.
The distribution of organisms and their interactions depend on contingencies.
Environmental conditions are heterogeneous in space and time.
Resources are finite and heterogeneous in space and time.
All organisms are mortal.
The ecological properties of species are the result of evolution.
Many of the tools and techniques needed for the science of ecology are interdisciplinary in nature. Ecological studies draw and integrate knowledge systems from other disciplines like geography, mathematics, hydrology, physics, chemistry, biology management, social sciences, economics, among others.
Ecology and ecologists are facing constraints and challenges on a global scale. In the face of global changes like deforestation, rapid urbanization, a rise in levels of pollution, climate change, and global warming, the world is experiencing multiple stresses. Central to everyday life is the need to meet the developmental challenge of alleviating poverty for the more than 1.3 billion people who still live on earnings of less than $1 a day; trying to meet the everyday basic needs of food, energy, and water; and the rapid loss of the world's biological diversity. There has been an increase in demand per capita in food and resources (40 percent in grains, 100 percent in fish, and 33 percent in wood). The International Union for Conservation of Nature-The World Conservation Union has reported on the rapid loss of the world's biological diversity. In Europe and Russia, 16 million square kilometers of forests have been reduced to 3.5 million square kilometers. Similarly, only 1 square kilometer of the Asian forests remains of every original 15. Markets have failed to recognize the true value of biodiversity, and institutions have failed to regulate biological resources. In a classic 1997 paper, Robert Costanza valued the world's ecosystem resources at $33 trillion a year. Rise in population, inappropriate use of technology, and inequitable distribution of costs and benefits have exacerbated the problem.
More and more ecologists are involved in managing complex ecological issues; however, their task is made more daunting because they often have to cope with uncertainties. Strong sets of databases often needed to make management decisions are lacking; however, newer tools and techniques in ecology offer many concepts that can be used to address the many issues and to minimize vulnerabilities to natural disasters. Knowledge of a species' functional traits and ecosystem processes can be used to design more productive agroforestry systems and productive ecosystems, and can be applied to improve the lives of millions of people suffering from hunger, lacking clean drinking water and reliable, efficient energy sources, dying from preventable diseases, and suffering disproportionately from natural disasters. Robert Costanza, director of the Gund Institute of Ecological Economics at the University of Vermont, recognizing the coevolution of humans, their culture, and their interaction with the larger ecological system, has emphasized the need for robust analytical and modeling tools. Studying ecology at the landscape level has emerged as a new and effective tool. A landscape is viewed as a mosaic of different land uses, and a holistic view is taken to understand threats and pressures before developing conservation action plans.
As a part of the ecological implications of human impacts of development, Paul Ehrlich and John Holdren developed an IPAT model (Impact = Population × Affluence × Technology), in which the human impact equals the product of population, affluence (quality and quantity of consumption), and technology (efficiency of production and waste assimilation). A very recent approach to assess humankind's impact on the Earth's resources is using an ecological footprint analysis, designed by J. Loh and M. Wackernagel. An ecological footprint could be used to measure, monitor, and manage consumption of natural resources in pursuit of sustainable development. Ecological footprint analysis seeks to provide a unified comparable measure of human ecological impact.
The World Wide Fund for Nature (known in North America as the World Wildlife Fund) released two Living Planet Indexes, one in 2004, and one in 2008. The indexes showed that the natural ecosystems across all biomes and regions of the world are under severe pressure. The anthropocentric threats identified included habitat loss, fragmentation, expansion of agriculture, overexploitation of species (particularly as a result of fishing and hunting), pollution, and the spread of invasive species. The indicator has been designed to monitor the state of the world's biodiversity. The ecological footprint measures humanity's demand on the biosphere in terms of area of biologically productive land and sea needed to provide the resources we use and to absorb our waste. The Living Planet Index tracked the number of key threatened species of the world using a method similar to the way a stock market is monitored. In 2005, the global ecological footprint was 17.5 billion globe hectares (gha) or 2.7 gha per person. (A global hectare is a hectare with world-average ability to produce resources and absorb wastes.) On the supply side, the total productive area or biocapacity was 13.6 bha, or 2.1 gha per person. Humanity's footprint first exceeded the Earth's total biocapacity in the 1980s, and this excess has been increasing ever since. In 2005, demand was 30 percent greater than the supply.
Ecosystems have evolved over large time scales, and even the simplest of ecosystems is highly complex in nature is still not completely understood. We have been through several ecological crises—the widening hole in the ozone layer, acid rain, Minamata disease—caused by severe mercury poisoning, desertification, and global warming, to name a few. The challenge that lies ahead for economists and scientists is immense. The Eco Summit 2007, held in Beijing by the Chinese Academy of Sciences, the International Council for Scientific Union, and Elsevier publications, called for humankind to work together to prevent further ecological deterioration of the Earth. This will require collaboration between civil society, governments, and scientists to apply the goals of ecology to everyday life.
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