Tag Archives: Critique 1

Ecology of Some Warblers of Northeastern Coniferous Forests. Robert H. MacArthur (1958)

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Ecology of Some Warblers of Northeastern Coniferous Forests asks one central question, how is it that five species of warblers with similar needs and similar capabilities are able to live in the same region without one species out-competing the others and all but the dominant one being eliminated. MacArthur hypothesized that the species were in balance with one another because the factor limiting each species growth was intraspecific competition rather than interspecific competition.

To determine which factors governed the competition among species and among individuals of a single species, MacArthur observed the behavior of the species to discover their feeding habits and zones, nesting, and territoriality.

Observations showed each of the five species had preferences in their feeding habits and nesting locations. The species-wide preference in feeding locations largely meant that when a particular species was hunting for food, it was more likely that another individual from its own species had been there than an individual of any other species. The preference in feeding zone directly correlated to preference in nesting zone and territoriality as well, given that each warbler tended to build their nest in their preferred feeding ground and defend just enough space as they needed to eat and provide for young.

Further evidence that most competition was intraspecific is that each species nested as slightly different times of the year, meaning that the need for food was greatest among a single species at a time rather than among all species at once. When considered along with the preference for a single feeding area, the likelihood of a particular zone being over-hunted, thereby leading to the mortality of fledglings, was due to the behavior of others of the same species. There were several times when new parents of fledglings would feed only one or two of their young.  This was shown to be the most common cause of mortality among fledglings.

To close the essay, MacArthur succinctly states that differences in feeding position, behavior, and nesting date reduce competition among species and instead focuses competition among individuals of each species.

The Use and Abuse of Vegetational Concepts and Terms. Arthur Tansley (1935)

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Throughout this essay, Tansley argues for the standardization of the definition of several temrs commonly used in the discussion of vegetation and ecology. I will herein define in my own words what those terms are as well as discuss several of Tansleys arguments for them and some of my own thoughts on the essay.

Succession: A series of changes in the life cycle of a plant, quasi-organism, or eco-system. Each change leading to the next. The change is continuous, but can be categorized into successional phases.
Autogenic Succession: A succession primarily brought on by the actions of the plant life on their environment. E.g. A reduction in soil quality due to leeching leading to less growth.
Allogenic Succession: A succession primarily brought on by factors other than those actions of the plant life on their environment. E.g. A forest fire.
Anthrogenic Succession: A succession primarily brought on by the actions of humans on the plant life and its environment. E.g. The clearing of forest for grazing land.
Retrogressive Succession: Tansley argues that retrogressive succession is an ill-suited, though others ( use it to mean “regression” from a “higher” to “lower” form of vegetation (No clarification is given as to what higher and lower here mean) Tansley seems to say that retrogressive isn’t the correct term because the plant life is still adapting in a forward direction given the conditions of its environment at any given time.
Quasi-Organism: A mature, well-integrated plant community having enough of the characteristics of an organism. A community of plants that reaches a dynamic balance. Others use the term “complex organism”, which Tansley objects to on the grounds that an individual plant or animal is a complex organism and a network of complex organisms ought to have another name. (I initially took quasi-organism to mean the same as my understanding of an eco-system until eco-system was defined later in the text)
Climax: Permanent of apparently permanent condition reached when vegetation is in equilibrium with all Incidental factors. (There are arguably many sub-types of climax e.g. “mowing climax” a climax wherein the plant life is in a state of balance with its frequent mowing, where it doesn’t over-grow, or die off as a result of this action)
Ecosystem: The exchange among a quasi-organism and its environment. Components of which are both organic (plants, animals) and inorganic (soil, climate).
Two terms which were not defined in the text but which I found useful to look up are
Edaphic: of or relating to soil
Sere: A series of ecological communities formed in succession

My first impression of Tansley is that a contemporary reader likely would have either found him very funny or very annoying. He refers to himself twice as someone who was a heretic or who did not keep the “faith” of popular belief among ecologists of the day, instead challenging their ideas and definitions. I was intrigued by his thought on “retrogressive succession” and whether all change was necessarily “forward”, as well as the times he referred to minute and constant change in an ecosystem or quasi-organism and whether those two beliefs are related. In my notes, I likened the constant minute changes to the movement by the driver of a steering wheel on a straight road; the direction of the vehicle is always forward but the steering wheel is always being slightly turned to maintain that status. There is also the question as to whether human action can be considered part of nature, Tansley doesn’t clearly give his opinion, though through the addition of the definition of anthrogenic succession, seems to imply that humans are too great a variable to count among allogenic successions. I agree with this descision, because unlike all other animals and plants, humans don’t have to be at balance with their local environment to survive. Humans are at liberty to radically change their environment because of their ability to transport resources from afar.

Overall, I found the reading itself interesting, though, as it was my first reading of this kind, it will take me some time to be able to more fully digest its meaning and implication.