Study Questions—Week 6


  1. Contrast major characteristics of organisms that conform to their external environments with those of organisms that regulate their internal "environments".
  2. Conformers allocate low, and relatively constant amounts of energy to maintenance of their bodies. Regulators allocate much more energy to maintain their internal environments at relatively constant conditions, and energy required for regulation increases as external conditions become more extreme. Regulators maintain optimal performance over a wider range of conditions within which they are they are less susceptible to environmental fluctuations.

  3. What differentiates an environmental resource from an environmental condition?
  4. A resource is physical, chemical or biological "material" that is consumed or "used" by the organism. An environmental condition is a physical or chemical property of the environment that affects the organism but is not used.

  5. What is the "fundamental niche" of an organism? How is it determined?
  6. The fundamental niche of an organism is the potential (maximum) array of conditions under which an organism can survive ("place"), the array of resources that it can possibly use, and the maximum potential array of interactions it can participate in with other organisms ("role"). It is usually thought of primarily in terms of conitions and resources, and is measured in laboratory experiments to detrmine tolerance zones and resource spectra.

  7. A) Give an example of an environmental variable; B) draw, partition and label a tolerance response curve; and C) graph the energy a homeostatic organism and a conforming organism will use while responding to this environmental variable.
  8. See graphs in your notes. A) Any resource or condition can be an environmental variable. (ex. Temperature, pH, availability of water, food…etc.). B) The response curve measures a response or some aspect of "performance" of the organism to variation in the environmental variable. An organism within the limits of S will survive. An organism within the limits of M will survive and maintain itself. An organism within the limits of G will survive, maintain itself, and grow. And an organism within the limit of R will survive, maintain itself, grow, and reproduce. C) Regulatory organisms require energy to regulate their internal environment. A is the amount of energy needed to increase the variable internally when the external environment is low in some variable. (ex. Energy needed to shiver when the external temperature is lower than the internal temperature.) B is the amount of energy needed to decrease the variable internally when the external environment is high in some variable. (ex. Energy used in sweating when the external temperature is higher than the internal temperature.) C is the point at which the external environment and internal environment are the same, therefore, no energy is needed in regulating the variable.

  9. What is an ecological "niche"? How do concepts of "tolerance", "resources" and "role" fit into the concept of "niche"? How is niche measured?
  10. Ecological niche is a concept - not a real entity. It describes one or more of:

    a) the environmental conditions within which that organism can survive, maintain itself, grow and/or reproduce (i.e. its ecological "place")

    b) the materials that the organism needs and uses (i.e. "resources")

    c) how that organism interacts with other organisms (i.e. its "role").

    Niche is conceived as a geometric body, a multi-dimensional "hypervolume" in which each axis represents a single environmental factor.

    Niche is measured by determining which parts of each axis describe conditions, resources or roles are actually or potentially available to that organism. Fundamental niche is usually determined from laboratory experiments that measure its limits of tolerance of extreme environmental conditions and limits of possible resources. Realized niche is usually based on field observations and measurements.

  11. What is the difference between a "realized" niche and a "fundamental" niche? How are they usually related?
  12. The fundamental niche describes the potential maximum array of conditions, resources and roles under which it is possible (physiologically, ecologically etc.) for the organism to survive/ grow/reproduce. The fundamental niche describes the conditions, resources and roles that the organism actually experiences and tolerates in the field. The realized niche is usually smaller (a subset of) the fundamental niche.

  13. What are the connections between fundamental and realized niches and "distribution"?
  14. Distribution is a property of a population or species describing the geographic area occupied in the field. The realized niche describes the array of conditions/resources/roles within that area that individuals are actually observed to tolerate/use/or play. The fundamental niche can be used to predict unoccupied geographic areas that it may be possible for the population to occupy.

  15. What is a transplant experiment? Why are they used to study distributions? What are the five types of treatments used in transplant experiments?
  16. A transplant experiment involves moving individuals from one place or habitat to another place or habitat, with or without manipulation of environmental factors. In distribution studies, individuals are normally transplanted to places outside their observed geographic distribution to determine the factors and/or processes that are excluding the species. Ultimately one draws conclusions about whether the unoccupied habitats lie within or outside limits imposed by the fundamental niche, and about what factors cause the observed limits of distribution.

  17. What might allow a realized niche to be larger than the fundamental niche?
  18. Symbioses; habitat modification creating less extreme micro-environments; and relictual distributions in which individuals persist in previously favorable habitats that have changed to exceed some limits of the fundamental niche.

  19. Define "population" for a geneticist/evolutionist and for an ecologist. How and why do they differ?
  20. A geneticist/evolutionist defines a population as a group of interbreeding individuals of the same species that is isolated from similar groups of the same species (i.e. by interruption of gene flow). An ecologist assumes the same basic definition, but often adds that they should live in the same defined area, use the same resources, and be exposed to the same environmental conditions. The differences are usually for practical reasons: it is usually difficult to define genetic populations in the field; ecologists often are interested only in particular places or habitats; or available time and/or effort limit work to part of the population.

  21. Define "dispersion" and "dispersal".
  22. Dispersion is an instantaneous "snapshot" describing the pattern of spatial relationships of individuals within a population (clumped, random, uniform). Dispersal is the process of movement of individuals or groups from one place to another.

  23. What is meant by environmental "grain"? What does it mean to say an environment is "coarse" or "fine" grained?

Environmental grain describes the scale of environmental variation (temporal or spatial), relative to the temporal/spatial scales of activity of the organisms. (i.e. it describes the organism’s "perception" of its own micro-environment.