Ecology is an important subject. It tells us what we need to understand if we want to survive and thrive. It tells us what a species-appropriate lifestyle in a species-appropriate environment is. We need this for our own lives, for the lives of humans in general, for the lives of our pet cats, dogs, horses, and more, for the lives of farm animals and plants, and for the lives of the wildlife we care about and depend upon.

Ecology is “the branch of biology that deals with the relations of organisms to one another and to their physical surroundings.” –Oxford English Dictionary

“The original definition [of ecology] is from Ernst Haeckel, who defined ecology as the study of the relationship of organisms with their environment.” –the Cary Institute of Ecosystem Studies, “Definition of Ecology

“All zoology is really ecology. We cannot fully understand the lives of animals without understanding our microbes and our symbioses with them.” –Ed Yong, I Contain Multitudes: The Microbes Within Us and a Grander View of Life

What ecology is and why it’s important is discussed in some episodes of the CCERP Podcast.

1. Episode 2 UT Professor Jim Fordyce on Ecology and Its Importance
2. Episode 33 Teri MacArthur of the Woodlands Township on Ecosystems, Invasive Species, and Why They Matter
3. Episode 32 Teri MacArthur of The Woodlands Township On Water Quality, Why It Matters To You, and What You Can Do
4. Episode 6 Kelly Norrid of Texas Parks and Wildlife Department: All About Our Local Plants, Parks, and Wildlife

“Careful observations of the natural world can lead to an understanding of relationships at several levels of complexity. Similarly, we can examine the science of ecology at several levels. To know the ecology of an individual organism is to know its natural history. … A second level of understanding is to know the ecology of a population, all of the organisms of a certain kind living in a specified area. … [The] community, a third level of organization, [is defined by ecologists] as all the populations in a specified area. A fourth level consists of the community and its physical environment, the soil, air, nutrients, climate, and other nonliving components. This is single, interesting unit is called an ecosystem.” –John Tester, Minnesota’s Natural Heritage: an Ecological Perspective, page 44.

“The variety and number of organisms in the soil, including algae, fungi, bacteria, and nematodes, are astonishingly high. These organisms play a vital role in maintaining soil texture and fertility through their role in decomposition in nutrient cycling.” –John R. Tester in Minnesota’s Natural Heritage: an Ecological Perspective p. 25

A multi-episode series on ecology by The Wild Report, having videos ranging from 4:41 to 11: 51 long:

“Here is a lesson that we’re going to be taught again and again in the coming years: Most animals are not just animals. They’re also collections of microbes. If you really want to understand animals, you’ll also have to understand the world of microbes inside them. In other words, zoology is ecology.” –Ed Yong, “Gut Bacteria Allows Insect Pest to Foil Farmers.” ©2013 by National Geographic Society (as used on a Fall 2020 PSAT test)


Fundamentals of Ecology by Eugene P. Odum, University of Georgia

Minnesota’s Natural Heritage: an Ecological Perspective by John Tester (See also Minnesota’s Natural Heritage: Second Edition (12Jan2021) by John R. Tester, Susan M. Galatowitsch, Rebecca A. Montgomery, John J. Moriarty.)

Fundamentals of Ecology is an icon among biology textbooks — the most influential such work as measured by the number of students recruited into the field as researchers and teachers. The rebirth here of this classic, in a much modified fifth edition, but under the original title, is welcome. –EO Wilson, in the Foreword to the Fifth Edition

In Fundamentals of Ecology (second edition, (c) 1959 by W.B. Saunders Company, ISBN: B0018QZMS0; third edition ISBN-13: 978-0721669410, ISBN-10: 0721669417), Eugene P. Odum wrote (pp. 3-7):

Man has been interested in ecology in a practical sort of way since early in his history. In primitive society every individual, to survive, needed to have definite knowledge of his environment, i.e., of the forces of nature and of the plants and animals around him. Civilization, in fact, began when man learned to use fire and other tools to modify his environment. It is still necessary, or perhaps even more necessary than ever, for mankind as a whole to have an intelligent knowledge of the environment if our complex civilization is to survive, since the basic “laws of nature” have not been repealed; only their complexion and quantitative relations have changed, as the world’s human population has increased.

Like all phases of learning, the science of ecology has had a gradual, if spasmodic, development during recorded history. The writings of Hippocrates, Aristotle, and other philosophers of the Greek period contain material which is clearly ecological in nature. However, the Greeks literally did not have a word for it. The word “ecology” is of recent coinage, having been first proposed by the German biologist, Ernst Haeckel, in 1869. As a recognized distinct field of biology, the science of ecology is still younger, dating from about 1900, and only in the past few years has the word become part of the general vocabulary to the extent that one may find it in popular magazine articles.

The word ecology is derived from the Greek oikos, meaning house” or “place to live.” Literally, ecology is the study of organisms “at home.” Usually ecology is defined as the study of the relation of organisms or groups of organisms to their environment, or the science of the interrelations between living organisms and their environment. Because ecology is concerned especially with the biology of groups of organisms and with functional processes on the lands, in the oceans and in fresh waters, it is more in keeping with the modern emphasis, to define ecology as the study of the structure and function of nature (it being understood that mankind is a part of nature). In the long run the best definition for a broad subject field is probably the shortest and least technical one, as, for example, “the science of the living environment’ or simply “environmental biology.”

So much for definitions. To understand the scope of ecology, the subject must be considered in relation to other branches of biology and to “ologies” in general. In the present age of specialization in human endeavors, the inevitable connections between different fields are often obscured by the large masses of knowledge within the fields (and sometimes also, it must be admitted, by stereo- typed college courses). At the other extreme, almost any field of learning may be so broadly defined as to take in an enormous range of subject material. Therefore, recognized “fields” must have bounds, even if these bounds are somewhat arbitrary and subject to shifting from time to time.

For the moment, let us look at the divisions of biology, “the science of life.” When knowledge was limited, few subdivisions were needed, but now, to facilitate mental digestion, we cut the biology “layer cake,” as it were, into small pieces in two distinct ways, as shown in Figure 1. We may divide it “horizontally” into what are usually called “basic” divisions, because they are concerned with fundamentals common to all life or at least are not restricted to particular organisms. Morphology, physiology, genetics, ecology, and embryology are examples of such divisions. We may also divide the cake “vertically” into what may be called “taxonomic” divisions, which deal with the morphology, physiology, ecology, etc., of specific kinds of organisms. Zoology, botany, and bacteriology are large divisions of this type, and phycology, protozoology, mycology, entomology, ornithology, etc., are divisions dealing with more limited groups of organisms. Thus ecology is a basic division of biology and, as such, is also an integral part of any and all of the taxonomic divisions. Both approaches are profitable. It is often very productive to restrict work to certain taxonomic groups, because different kinds of organisms require different methods of study (one cannot study eagles by the same methods used to study earthworms or oak trees) and because some groups of organisms are economically or otherwise much more important or interesting to man than others. Ultimately, however, unifying principles must be delimited and tested if the subject field is to qualify as “basic.” It is the purpose of Part I of this book to outline briefly this aspect of ecology.

Perhaps the best way to delimit modern ecology is to consider it in terms of the concept of levels of organization. Although the number is arbitrary it is convenient to recognize ten levels of organization which are best visualized as a sort of “biological spectrum” as follows:
organ systems

Ecology is concerned largely with the right-hand end [or bottom end, as I wrote it here —MG] of this spectrum, that is, the levels beyond that of the organism. In ecology the term population, originally coined to denote a group of people, is broadened to include groups of individuals of any one kind of organism. Likewise, community in the ecological sense (sometimes designated as “biotic community”) includes all of the populations occupying a given area. The community and the nonliving environment function together as an ecological system or ecosystem. The portion of the earth in which ecosystems operate is conveniently designated as the biosphere, which is as far as we need go at the moment. It is important to note that no sharp lines or breaks were indicated in the above “spectrum,” not even between the organism and the population. Since introductory biology courses usually stop abruptly with the organism, and since in dealing with man and higher animals we are accustomed to think of the individual as the ultimate unit, the idea of a continuous spectrum may seem strange at first. However, from the standpoint of interdependence, interrelations and survival, there can be no sharp break anywhere along the line. The individual organism, for example, can not survive for long without its population any more than the organ would be able to survive for long without its organism. Similarly, the community can not exist without the cycling of materials and the flow of energy in the ecosystem.

One reason for listing the levels of organization horizontally instead of vertically [I wrote them vertically here because it was easier; call me lazy.—MG] is to emphasize that, in the long run, no one level is any more or less important, or any more or less deserving of scientific study than any other level. Some attributes, obviously, become more complex and variable as we proceed from the left to the right [or top to bottom, as I wrote it here —MG], but it is an often overlooked fact that other attributes become less complex and less variable as we go from the small to the large unit. Because homeostatic mechanisms, that is, checks and balances, forces and counter forces, operate all along the line, a certain amount of integration occurs as smaller units function within larger units. For example, the rate of photosynthesis of a whole community may be less variable than that of individuals or species within the community, because when one individual or species slows down another may speed up in a compensatory manner. When we consider the unique characteristics which develop at each level, there is no reason to suppose that any level is any more difficult or any easier to study quantitatively. The enumeration and study of the units of an organism (i.e., the cells and tissues) is not inherently easier nor more difficult than the enumeration and study of the units of a community (i.e., the organisms). Likewise, growth and metabolism may be effectively studied at the cellular level or at the ecosystem level by using units of measurement of a different order of magnitude. Furthermore, the findings at any one level aid in the study of another level, but never completely explain the phenomena occurring at that level. This is an important point because persons sometimes contend that it is useless to try to work on complex populations and communities when the smaller units are not yet fully understood. If this idea was pursued to its logical conclusion, all biologists would concentrate on one level, the cellular, for example, until they solved the problems of this level; then they would study tissues and organs. Actually, this philosophy was widely held until biologists discovered that each level had characteristics which knowledge of the next lower level explained only in part. It is now evident that science must advance along a broad front. This situation is analogous to the advance of an army; a breakthrough may occur anywhere, and when one does, the thrust will not penetrate far until the whole front moves up.

Anyone with a deep affection for Minnesota’s natural resources, highly seasonal and variable climate, diverse ecosystems, and beautiful landscapes [or ecology in general.–MG] should read the second edition of Minnesota’s Natural Heritage. This book chronicles the evolution of our state’s natural systems and the challenges of sustainably managing them in the context of climate change. It should be part of every home reference library.

Mark Seeley, author of Minnesota Weather Almanac

In Minnesota’s Natural Heritage: an Ecological Perspective (first edition, University of Minnesota Press, (c) 1995 by the Regents of the University of Minnesota, ISBN 0-8166-2133-0), John Tester wrote (pp. 43-45):

The web of life that surrounds us is complex and interconnected (figure 3.1). Ecology is the study of the relationships and connections between the living things that constitute this web and their environment. In this chapter I will present some of the principles of ecology, which will provide a basis for understanding the structure of the many kinds of ecosystems in Minnesota and how they function.

To introduce the field of ecology, I will describe the relationships discovered by an ecologist between black cherry trees, tent caterpillars, and ants. Black cherry trees are common around the Twin Cities and in many deciduous forests in Minnesota. In early spring the buds open, producing leaves with tiny, glandlike nectaries along the edges. The nectaries on a single leaf last for only a few days, but the buds continue to produce new leaves for several weeks. Thus, the tree has nectaries for several weeks in the spring.

Thatching ants form colonies in open fields and in clearings in forests. The colony lives in a mound of dirt, grass, leaves, and twigs, and the ants prey on many kinds of insects, obtain nectar from plants and aphids, and also scavenge. They feed intensively from the nectaries on black cherry leaves for about three weeks in spring. David Tilman (1978) observed in a study conducted in Michigan that other insects that approach a feeding thatching ant are quickly attacked and if captured, are carried back to the ant colony.

Tent caterpillars often cause severe damage to the leaves of black cherry trees. Eggs laid on the tree in the previous year hatch in spring, and the caterpillar larvae develop through five or six stages. Larvae in the tent caterpillar colony (figure 3.2) feed on the margins of leaves and are thus likely to come in contact with the nectar-feeding ants. Tilman watched the ants grasp young larvae in their jaws and carry them back to the ant colony. When he returned to the same tree one or two days later all of the tent caterpillar larvae were missing. No mature tent caterpillar colonies were found in small black cherry trees located within I0 yards of an ant colony. It is likely that the thatching ants killed all of the tent caterpillar larvae.

Tilman’s observations led him to suggest that the nectaries may result in less damage to the leaves by attracting ants that prey on tent caterpillars. This suggestion is supported by the findings that the nectaries are present when the tent caterpillar larvae are small, and that the nectaries are positoned on the margins of leaves, where the larvae feed.

This example illustrates how careful observations of the natural world can lead to an understanding of relationships at several levels of complexity. Similarily, we can examine the science of ecology at several levels. To know the ecology of an individual organism is to know its natural history. The description of the thatching ant illustrates this level. A second level of understanding is to know the ecology of a population, all of the organisms of a certain kind living in a specified area. All of the thatching ants in a colony represent a population. Some ecologists study the growth and regulation of populations. But the thatching ants do not live in isolation. They feed on insects and plants and interact with tent caterpillars and other organisms and are eaten by predators. They are part of a community, a third level of organization, which ecologists define as all the populations in a specified area. A fourth level consists of the community and its physical environment, the soil, air, nutrients, climate, and other nonliving components. This single, interacting unit is called an ecosystem.

When our observations enable us to determine how organisms are linked in food chains and food webs, we can begin to understand the structure and functioning of ecosystems. The cherry trees, the ants, and the caterpillars are part of a food web. Sunlight, water, and nutrients are used by the cherry trees to produce nectar and leaves. The flow of energy and the transfer of nutrients continue when the tent caterpillar larvae feed on the leaves and the ants feed on the nectar and caterpillars. Competition may occur between ants and caterpillars for parts of the cherry trees. Predation occurs when ants kill and eat the larvae.

These and other aspects of the structure and functioning of ecosystems will be explained in this chapter. From this base we can build an understanding of the interactions of populations. Finally we can examine the process of succession, by which communities and ecosystems change over time.


Two terms are used to describe the place where an organism lives: environment and habitat. Environment encompasses everything, whether living or nonliving, that has an effect on an organism. Habitat generally refers to the place where we would go to find an organism and is analogous to an address. For example, the habitat of a white pine is a forest in northern Minnesota. The environment of a white pine, however, is much broader and includes physical factors, such as soil, water, nutrients, heat and light, and biological factors.

The most complete treatment of Minnesota’s natural environment, compiled and accessibly written by scientists whose collective knowledge spans the book’s expansive content, Minnesota’s Natural Heritage is the one indispensable companion for both visitors and inhabitants, as enlightening to page through as it is valuable to study.

(Book description on Amazon.)