7A – Components constituting the ‘living environment’

Supporting article A: Recapping on the basic components that constitute the living environment as well as new concepts that will be discussed in this issue.


Important words and concepts from Chapter 50, Campbell & Reece, 2002 (3/25/2005):
by Stephen T. Abedon (abedon.1@osu.edu) for Biology 113 at the Ohio State University

(1) Ecology
(a) A few quotes:
(i) “The scientific study of the interactions between organisms and their environments is called ecology.”
(ii) “The trouble with ecology is that you never know where to start because everything affects everything else.” Robert A. Heinlein (from Farmer in the Sky)
(iii) “As an area of scientific study, ecology incorporates the hypothetico-deductive approach, using observations and experiments to test hypothetical explanations of ecological phenomena. . . . ecologists often face extraordinary challenges in their research because of the complexity of their questions, the diversity of their subjects, and the large expanses of time and space over which studies must often be conducted. Ecology is also challenging because of its multidisciplinary nature; ecological questions form a continuum with those from other areas of biology, including genetics, evolution, physiology, and behavior, as well as those from other sciences, such as chemistry, physics, geology, and meteorology.”
(iv) “Ecology concerns itself with the interrelationships of living organisms, plant or animal, and their environments; these are studied with a view to discovering the principles which govern the relationships. That such principles exist is a basic assumption—and an act of faith—of the ecologist. His field of inquiry is no less wide than the totality of the living conditions of plants and animals under observation, their systematic position, their reactions to the environment and to each other, and the physical and chemical nature of their inanimate surroundings . . . It must be admitted that the ecologist is something of a chartered libertine. He roams at will over the legitimate preserves of the plant and animal biologist, the taxonomist, the physiologist, [the microbiologist,] the behaviorist, the meteorologist, the geologist, the physicist, the chemist and even the sociologist; he poaches from all these and from other established and respected disciplines. It is indeed a major problem for the ecologist, in his own interest, to set bounds to his divagations.”

(2) Environment
(a) An organism’s environment may be distinguished into an abiotic component and a biotic component
(b) “Organisms are affected by their environment but, by their very presence and activities, they also change it. Often dramatically.”

(3) Abiotic component
(a) The abiotic component of an environment are all of the non-living components of an organism’s environment
(b) These include such things as
(i) Temperature
(ii) Light
(iii) Water
(iv) Wind
(v) Nutrients
(vi) Substrate (e.g., rock and soil)
(vii) Periodic disturbances
(c) The abiotic component of an environment can and does have a dramatic impact on the ability of organisms to survive and reproduce
(d) Generally, a given organism is capable of surviving over only a limited range of abiotic variables, and the environments in which one (or more) abiotic component ranges outside of an organism’s range of tolerance will not be able to support stable populations of that organism
(e) “The existence of a species in a particular place depends on two factors: The species must reach that location, and it must be able to survive and reproduce in that location once it is there.”

(4) Biotic component
(a) The biotic component of an environment are all of the other organisms found in an environment with which an organism makes contact, directly or indirectly
(b) These organisms may be competing, preying upon, being preyed upon, providing shelter, or in some other way impact on the environment
(c) Generally, organisms, en total, make a significant impact on other organisms within an environment

(5) Evolution in real time
(a) The complexity associated with ecology explains in part why the study of evolution is so intensely difficult: Evolution happens within a context of ecology, i.e., in real ecosystems, one organism at a time
(b) Part of the complexity associated with ecology, however, is a consequence of the impact of evolution on ecosystems: Ecosystems are not only the products of evolution, they also contain populations that are actively evolving, all of the time
(c) In other words, ecology is essentially evolution running in real time, while evolution is essentially the product of enormous numbers of ecological interactions between organisms and their biotic and abiotic environments

(6) Principle of allocation
(a) One way to understand ecology is in terms of flows of energy; organisms take in energy and then use that energy to survive and to reproduce
(b) All adaptations are compromises, no organism is perfectly adapted to everything, and everything costs energy
(c) An organism must balance out its allocation of energy to survival and its need to allocate energy to reproduction
(d) Genotypes that strike a good balance between allocation to survival and to reproduction, such that net reproduction is large compared with other genotypes, are said to have higher relative fit nesses
(e) These ideas form the basis of the principle of allocation
(f) “Each organism has a limited amount of energy that can be allocated for obtaining nutrients, escaping from predators, coping with environmental fluctuations, growth and reproduction.”
(g) Energy allocated to survival is not available for reproduction.
(h) Relatively simple organisms have lower energy needs, but tend also to be more limited in where they live or how much energy they can obtain per unit time

(7) Adaptation
(a) “Organisms can respond to variations in the environment with a variety of adaptations
(i) Behavioral adaptations are almost instantaneous in their effects and easily reversed, whereas
(ii) Physiological adaptations may be implemented and changed over time scales ranging from seconds to weeks.
(iii) Morphological adaptations may develop over the lifetimes of individual organisms or between generations.
(iv) Adaptive genetic changes in populations are slower still, usually evolving over several generations.
(b) The appropriate response to environmental change depends on the duration of that change.”
(c) “The distinction between short-term adjustments on the scale of ecological time and adaptation on the scale of evolutionary time begins to blur when we consider that the range of responses of an individual to changes in the environment is itself the product of evolutionary history.”
(d) “In general, plants are more morphologically plastic than animals; this response helps them compensate for their inability to move from one environmental patch to another.”

(8) Hierarchical study of ecology
(a) The study of ecology is often achieved by concentrating on a certain level of a hierarchy of ecological study, just as more reductionist forms of biology focus on certain levels of organisms ranging from the molecular, through the cellular, through the organismal
(b) “Ecology ultimately deals with the highest levels in the hierarchy of biological organization. The web of interactions at the heart of ecological phenomena is what makes this branch of biology so engaging.”
(c) The hierarchies in ecological study include
(i) Organismal ecology
(ii) Behavioral ecology
(iii) Population ecology
(iv) Community ecology
(v) Ecosystem ecology
(vi) Landscape ecology

(9) Organismal ecology
(a) Organismal ecology is an attempt to understand how the characteristics of individual organisms impact on the ability of those organisms to interact with their environment
(b) Thus, for example, inferring that giraffes use their long necks to reach leaves found high in trees is an example of organismal ecology (though often inferences are just a bit more subtle and difficult than this example)
(c) From an ecological vantage, much of what we study in introductory biology falls under the heading of organismal ecology, i.e., the adaptations individual organisms possess and the impact those adaptations have on the ability of organisms to survive and reproduce
(d) Organismal ecology is concerned with the morphological, physiological, and behavioral ways in which individual organisms meet the challenges posed by their biotic and abiotic environments. The geographic distribution of organisms is often limited by the abiotic conditions they can tolerate.

(10) Behavioral ecology
(a) Essentially a subset of organismal ecology, behavioral ecology studies the non-physiological, non-mophological/anatomical adaptations organisms possess, and the impact those adaptations have on the survival and reproduction of organisms
(b) Behavior, in other words, is how organisms act, and different behaviors can have different impacts on the Darwinian fitness of organisms

(11) Population ecology
(a) Population ecology is the study of the size and composition of populations of organisms
(b) An example of population ecology would be the study of the factors which influence the carrying capacity of a given environment, i.e., the number of individuals an environment can stably sustain

(12) Community ecology
(a) A community is the assemblage of different species of organisms within a given environment
(b) Community ecology is the study of the interactions between these organisms, e.g., predation, parasitism, competition, etc.
(13) Ecosystem ecology
(a) An ecosystem is the assemblage of the biotic and abiotic components of a given environment
(b) Often ecosystems are reasonably unambiguously defined (a lake, a forest, etc.)
(c) Understanding even an approximation of what goes on within an ecosystem, any ecosystem, can be an overwhelming challenge

(14) Landscape ecology
(a) Looking beyond the four basic levels of ecology, we come to landscape ecology, which deals with arrays of ecosytems and how they are arranged in a geographic region. A landscape or seascape consists of several different ecosystems linked by exhanges of energy, materials, and organisms. The landscape level of research focuses on the ways in which interactions among populations, communities, and ecosystems are affected by the juxtaposition of different ecosystems, such as streams, lakes, old-growth forests, and the forest patches that have had their trees removed by clear-cut logging.

(15) Maintaining homeostasis
(a) Part of the energy expended on survival goes toward maintaining the internal environment of an organism
(b) The active maintenance of the internal environment of an organism (by the organism) is termed homeostasis
(c) Some organisms spend considerably more energy on maintaining their internal environment within relatively narrow constraints (regulators)
(d) Other spend less energy on maintaining their internal environment because they do not constrain it narrowly (conformers)
(e) Any energy not spent on homeostasis is potentially available for other needs such as reproduction (principle of allocation)
(f) Note that this principle forms the basis of the conflicting strategies of specialization (e.g., conformers) versus generalization (e.g., regulators)
(g) Specialists potentially have more energy available to reproduce because they very efficiently obtain energy necessary for maintaining homeostasis, though this advantage is maintained only so long as the environment remains amenable to the specialist?s needs (note: try to avoid equating the concept of specialization with the concept of specialization with respect to foraging; the latter, specialization with regard to diet, is essentially a subset of the former)

(16) Conformers
(a) For organisms within relatively stable environments, energy can be made available for other uses if internal environments are allowed to vary as external environments vary
(b) Such organisms may be termed conformers
(c) Note that a conformer may be very successful within its relatively stable environment, but less able to survive outside of this environment
(d) “Conformers that live in very stable environments . . . might be able to channel more energy into growth and reproduction. However, the intolerance of such specialists to environmental change severely restricts their geographical distribution.”
(e) For contrast, see regulators

(17) Regulators
(a) At the opposite end of the spectrum are the regulators (i.e., versus conformers)
(b) These organisms expend a great deal of energy to keep their internal environment constant regardless of the nature of their abiotic environment
(c) Such organisms may be more adaptable, but at the cost of great expenditures of energy that could otherwise be put toward such things as reproduction
(d) “Regulators that allocate a larger fraction of their energy to coping with environmental changes may grow and propagate less efficiently, but such organisms are able to survive and reproduce over a wider range of variable environments.”

(18) Graininess (supplemental discussion, no need to memorize)
(a) Another way of looking at ecology is in terms of environmental and temporal grain
(b) Environmental grain refers to the patchiness of an environment, and the patchiness of an environment is perceived differently by different organisms
(c) A coarsely grained environment has patches which are large enough that they may be distinguished
(d) A finely grained environment has patches which are so small that they may not be readily distinguished, and an “organism may not even behave as though patches exist,” but what is fine-grained to one (typically larger) organism may by coarse-grained to another (typically smaller) organism
(e) Organisms tend to congregate within coarsely grained patches to which they are best adapted
(f) Temporal variation may also be finely or coarsely grained depending, for example, on the life span of the experiencing organism, where short term variations (finely grained) are those which occur over a short span of an organism’s life while long term variation (coarsely grained) occur over a substantial fraction of an organism’s life