Adaptations to the Physical Environment Chapter 3 Ecology: Evolution, Application, Integration Ecology: Evolution, Application, Integration                                       David T. Krohne                                Copyright © 2015 Oxford University Press

Concepts 3.1 How Do Environmental Factors Limit Growth and Survival? 3.2 What Adaptations Avoid Harsh Conditions? 3.3 How Do Physiological Adaptations Alter the Organism’s Tolerance Limits? Ecology: Evolution, Application, Integration                                       David T. Krohne                                Copyright © 2015 Oxford University Press

How Do Environmental Factors Limit Growth and Survival? Physical resources The inorganic materials or energy organisms require for existence Physical (abiotic) factors Physical conditions that affect growth and survival Ecology: Evolution, Application, Integration                                       David T. Krohne                                Copyright © 2015 Oxford University Press

How Do Environmental Factors Limit Growth and Survival? Physical resources The inorganic materials or energy organisms require for existence Physical (abiotic) factors Physical conditions that affect growth and survival Ecology: Evolution, Application, Integration                                       David T. Krohne                                Copyright © 2015 Oxford University Press

Shelford’s Law of Tolerance (1913) There are upper and lower limits to the physical factors an organism can tolerate. Ecology: Evolution, Application, Integration                                       David T. Krohne                                Copyright © 2015 Oxford University Press

Shelford’s Law of Tolerance Species differ in the factors that limit their growth and in their ranges of tolerance. Deleterious effects that occur outside the range of tolerance depend on the specific physical factor. Beyond the tolerance limits, organism’s fitness is compromised. Often associated with an organism’s inability to maintain homeostasis Ecology: Evolution, Application, Integration                                       David T. Krohne                                Copyright © 2015 Oxford University Press

Role of Evolution In Shaping The Tolerance Curves This tolerance curve represents the tolerance limit of the entire population. The tolerance curves of individuals vary and some of this variation is genetically determined. What implications does this have for evolution? Ecology: Evolution, Application, Integration                                       David T. Krohne                                Copyright © 2015 Oxford University Press

Role of Evolution In Shaping The Tolerance Curves If the environment changes, some individuals may be better able to tolerate the new range of conditions. If these differences have genetic basis, they will be selected for. Directional selection shifts the population tolerance limit. Ecology: Evolution, Application, Integration                                       David T. Krohne                                Copyright © 2015 Oxford University Press

Environmental Conditions Change in Time Some temporal variability is predictable (blue line) Seasonal Diurnal Tidal Environmental conditions can also change unpredictably (orange line) Temporal variation in the physical environment poses a significant challenge to the organism’s fitness. It is much simpler to adapt to a constant environment than to a variable one. Ecology: Evolution, Application, Integration                                       David T. Krohne                                Copyright © 2015 Oxford University Press

The Principle of Allocation Adaptations to one challenge may preclude or reduce adaptations to others (Levins, 1968) Adaptation involves evolutionary trade-offs There are costs and benefits to every adaptive solution Ecology: Evolution, Application, Integration                                       David T. Krohne                                Copyright © 2015 Oxford University Press

Two Categories Of Adaptive Responses Avoidance Behavioral avoidance Migration Metabolic avoidance Metabolic rate depression Hibernation Estivation Adaptations Traits that match the organism’s tolerance limits to the physical conditions it faces Behavioral Morphological Physiological Biochemical Ecology: Evolution, Application, Integration                                       David T. Krohne                                Copyright © 2015 Oxford University Press

Avoidance Adaptations Metabolic Avoidance Dormancy Seeds Spores In some unpredictable habitats, dormancy can be indeterminate (until the conditions improve). Metabolic arrest For example, brine shrimp, water bears (tardigrades), rotifers Slows down the biological clock Ecology: Evolution, Application, Integration                                       David T. Krohne                                Copyright © 2015 Oxford University Press

Avoidance Adaptations Metabolic Avoidance Torpor Usually in response to cold and food deficiency E.g., hummingbirds Prolonged torpor=Hibernation E.g., bears, ground squirrels Estivation Usually in response to drought and heat E.g., snails Slows down the biological clock Ecology: Evolution, Application, Integration                                       David T. Krohne                                Copyright © 2015 Oxford University Press

Avoidance Adaptations Metabolic Avoidance Obligate hibernators Facultative hibernators Quickly enter a torpid state Quickly aroused by external stimuli. Drop in the metabolic rate and body temperature not as deep as in the obligate hibernators Must enter hibernation each year Accumulate significant fat reserves Metabolic rate and body temperature drop Heart rate and respiration slow down Kidney function often ceases Ecology: Evolution, Application, Integration                                       David T. Krohne                                Copyright © 2015 Oxford University Press

Benefits of Hibernation Avoidance of harsh conditions Protection against predators Survival of hibernators (orange) is higher than in physically and ecologically similar non-hibernators (blue) What may be the costs of hibernation? Bats Other mammals Ecology: Evolution, Application, Integration                                       David T. Krohne                                Copyright © 2015 Oxford University Press

Avoidance Adaptations Behavioral Avoidance Migration—the seasonal movement from one region to another and back May be obligate or facultative Advantageous when the abiotic challenges are seasonal and predictable External stimuli serve as cues for migration Ecology: Evolution, Application, Integration                                       David T. Krohne                                Copyright © 2015 Oxford University Press

Avoidance Adaptations Behavioral Avoidance: Large Scale Migration—the seasonal movement from one region to another and back May be obligate or facultative Advantageous when the abiotic challenges are seasonal and predictable External stimuli serve as cues for migration Ecology: Evolution, Application, Integration                                       David T. Krohne                                Copyright © 2015 Oxford University Press

Benefits and Costs Of Migration Avoid harsh environmental conditions Expand resource base by separating breeding and overwintering grounds Costs Considerable energy cost High risk of mortality Ecology: Evolution, Application, Integration                                       David T. Krohne                                Copyright © 2015 Oxford University Press

Avoidance Adaptations Behavioral Avoidance: Small Scale Behavioral thermoregulation Moving to spots with more favorable temperatures Basking Modifying posture Contact with the substrate Affects heat exchange by conductance and convection Local stress and predator avoidance Burrowing Nocturnal behavior Ecology: Evolution, Application, Integration                                       David T. Krohne                                Copyright © 2015 Oxford University Press