Introduction to Autecology

Part I. Physiological ecology: functional responses to environment

Definition of Physiological Ecology: The study of physiological characteristics and responses of organisms with respect to a specific set of environmental factors acting as selective agents.

Terms that are frequently used with respect to maintenance of homeostasis in plants and animals

Physiological and behavioral ecology are central to the study of Life History and Allocation Theory: The study of how organisms acquire and allocate scarce resources (mainly carbon) to the competing functions of maintenance, growth and reproduction.

Goals of Study

Introduction to Environmental Heterogeneity

I. Space and Time

A. Spatial

B. Temporal

II. Graininess

A. Coarse-grained environment: patches are relatively so large that the individual can choose among them in time or space

B. Fine-grained: patches are so small that the individual cannot usefully distinguish among them in time or space - the environment appears essentially uniform.

    Examples:

III. Activity Space

    • Cactus Wren:
    • Lizard: mallee dragon
    • Desert Iguana (Dipsosaurus dorsalis)

Homeostasis and Acclimation

I. Homeostasis: maintenance of the internal conditions of an organism at some optimum level for its functioning.

II. Ultimate vs. Proximate Causes Revisited What determines the best internal condition?

    Ultimate causation is fitness
    Path of causation
    Cost vs. benefit analysis, an optimization function.

III. Concept of Optimality

A. Examples

Point: When conditions in the surrounding environment differ from the optimum for cellular performance, organisms face a choice of impairment or investment in the metabolic and carbon costs to maintain proper cellular function.

B. Assessment of cost, measuring the cost of maintenance

1. Energetic cost
2. In terms of constraints on organism function (opportunity cost)

IV. Feedback Responses

A. Regulation of body temperature in endotherms (homeotherms).

1. Maintenance of 37o C for endothermic organisms.

Negative Feedback Loop:

Stimulus--> sensor---> effector---> response

Point: All organisms engage in homeostasis in some fashion.

2. Behavioral regulation is also used by many different organisms, endotherms and ectotherms (e.g.,birds fluff up feathers in cold). Note that behavior is part of the concept of a "functional response" to variation in the environment.

B. Regulation in ectotherms (Poikilotherms).

V. Proximate Costs of Homeostasis.

    To maintain a constant body temperature, an organism must replace heat that is lost by releasing heat energy metabolically. Thus the rate of metabolism required to maintain body temperature increases in direct proportion to the difference between body and ambient temperature.

A. Definitions

    1. Basal metabolism
    2. Lower Critical Temperature (Tlc)
    3. Lower Lethal Temperature (c)
    4. Critical Ecological Temperature (b)

B. Cheap tricks: methods of conserving energy

    1. Counter-current heat exchange
    2. Torpor

VI. Regulators and Conformers

 Compare and contrast endotherms and ectotherms: few organism do each strategy perfectly. Extremities are cooler in homeotherms. Many ectotherms do generate metabolic heat.

A. Examples

    1. Temperature
    2. Ionic: osmotic stress

B. Surface area-to-volume considerations

1. As body size increases, volume increases as a power of 3, whereas surface area increases as a power of 2.
2. In general, for endotherms the lower the SA / V (e.g., big mammals), the more comprehensive and precise regulation can be

C. Thermal inertia

1. Thermal inertia of the environmental medium can greatly alter the expense of regulation vs. conformation.
2. Body size vs. thermal interia.

D. Oxygen consumption and metabolism in endotherms and ectotherms.

  • Different classes of organisms are part of different regression between total metabolic rate and body mass. The larger and more endothermic organisms tend to have higher total metabolic costs.
  • There is an inverse relationship between O2 consumption per g body mass and total body mass during activity, such as locomotion shown in the figure below. (figures above and below from Schmidt-Nielsen, How Animals Work)

E. Other benefits of thermoregulation -> locomotion and maximizing performance

Water Balance in Hot Deserts

I. Relationship between water balance and heat:

Hot environments tend to be dry envronments (but not always so)
Evaporative cooling is necessary but costly for most organisms

II. Examples:

    A. Kangaroo Rat
    B. Cactus Wren
    C. Camel
    D. Nocturnal activity
    E. C4 and CAM physiology in plants.

Adaptative Variations of Photosynthesis: C3, C4 & CAM

I. Evolution of C4 Metabolism 

II. C4

C4 plants have spatial separation of the C4 and C3 pathways of carbon fixation.

III. CAM

Crassulacean acid metabolism plants have a temporal separation of C4 and C3 pathways of carbon fixation.