Adaptations to the Physical Environment

Adaptations to the Physical Environment

Chapter Overview

  • Title: Ecology: Evolution, Application, Integration

  • Author: David T. Krohne

  • Copyright: © 2018 Oxford University Press

How Do Environmental Factors Limit Growth and Survival?

  • Physical Resources:

    • Food

    • Physical (abiotic) Factors:

    • Water

    • Temperature

  • Growth and survival is optimal in a specific range: referred to as "the sweet spot." Under certain conditions, growth is favored.

Shelford’s Law of Tolerance (1913)

  • Definition: There are upper and lower limits to the physical factors that an organism can tolerate.

  • Key Points:

    • Different species experience different limiting factors and have unique ranges of tolerance.

    • Tolerance limits visualized through Venn diagrams for various species.

    • Deleterious effects occur when any physical factor lies outside the tolerance range. Does this mean species like become deleted

    • Example: Drought, flood, hurricane.

    • Fitness compromises result if an organism cannot maintain internal homeostasis in suboptimal conditions.

    • Homeostasis Definition: The ability to maintain physiological systems within certain limits across a range of external conditions. The ability to maintain your physiological systems in the midst of your changing environment.

Role of Evolution in Shaping the Tolerance Curves

How does evolution affect an organism’s tolerance in its environment?

  • Tolerance Curve Representation:

    • Graphically represents the tolerance limits of an entire population.

    • This curve is the summation of the tolerances of individual organisms within the population. It showcases the range of conditions under which the population can thrive, displaying the minimum and maximum thresholds for factors such as temperature, moisture, and nutrient availability.

  • Genetic Variation in Tolerance:

    • Individual tolerances may vary based on genetic predispositions.

  • Evolutionary Implications:

    • Environmental changes affect individuals' ability to tolerate new conditions.

    • Genetically advantageous traits are selected for, shifting the population’s tolerance limits. (Traits that are able to survive in the new conditions)

    • Directional Selection: Natural selection that drives a shift in population tolerance based on environmental changes. (ex?)

Environmental Conditions Change Over Time

  • Predictable Temporal Variability:

    • Events that follow cyclical patterns:

    • Seasonal changes

    • Diurnal patterns

    • Tidal movements

  • Unpredictable Environmental Changes:

    • Variability in conditions poses significant challenges to an organism's fitness.

    • Adaptation is easier in stable environments compared to variable ones.

Upland Habitats Patterns

  • Description: Upland habitats tend to be cooler and wetter compared to adjacent lowlands.

  • Species Adaptations:

    • Upland species exhibit specific physiological adaptations to endure cooler temperatures.

    • Examples of Upland Habitats:

    • Upland coniferous forests in Southern California

    • Upland tropical rainforest in Peninsular Malaysia

Historical Climate Cycles

  • Glacial Cycles Impact:

    • Glacial maximum: Cold temperatures permit the expansion of cool-weather-adapted forests into lowlands.

    • Glacial minimum: Warmer temperatures cause these forests to retreat upslope.

  • Climatic Cycling:

    • Occurred 50 times over the last 2.5 million years.

    • Upland regions have been fragmented into "islands" for only 3.5% of this time.

Case Studies of Tolerance and Adaptation

  • Ovophis convictus (Egg-laying pitviper):

    • Maintained genetic identity across disjunct populations despite 100 km separation.

  • Pseudocalotes Dragon Lizards:

    • Adapt to cooler temperatures on mountain tops, evolve into new species in isolated conditions.

Pleistocene Drying Trends

  • Impact on Species:

    • Species were confined to upland habitats due to evaporating water resources following drying trends.

    • Those unable to adapt went extinct.

  • Examples:

    • Large-blotched Salamanders: Different species on various mountain tops.

    • Mountain Kingsnakes: Potentially different species across San Jacinto Mountain and Laguna Mountain.

The Principle of Allocation

  • Definition: Adaptations to address one challenge can limit adaptations to others (Levins, 1968).

  • Trade-offs in Adaptation:

    • Every adaptive solution has associated costs and benefits, influenced by historical constraints.

NATURE’S TRADE-OFFS - Historical Constraints

  • Cheetahs:

    • Adapted for speed; lack strength and endurance.

  • Turtles:

    • Morphologically constrained, unable to adapt significantly beyond their shell design.

  • Sea turtles:

    • Adaptations include a hydrodynamically-shaped shell for swimming and beak-like jaws for feeding.

Categories of Adaptive Responses to Environmental Changes

  • Avoidance Responses:

    • Behavioral Avoidance: Migration, seasonal movement based on environmental cues.

    • Metabolic Avoidance: Includes metabolic rate depression, hibernation, estivation, and torpor.

  • Adaptations:

    • Traits matching organisms’ tolerance limits through various mechanisms:

    • Morphological adaptations

    • Physiological adaptations

    • Biochemical adaptations

Specific Examples of Avoidance Adaptations

  • Metabolic Avoidance Techniques:

    • Dormancy: Seen in seeds and spores, with certain species capable of indefinite dormancy until conditions improve.

    • Examples:

    • Southern Pacific Rattlesnake (Crotalus helleri) uses hibernation for survival in cold.

  • Physiological Changes:

    • Populations change their hibernation behaviors based on climatic variations.

Hibernation - Benefits and Costs

  • Benefits:

    • Avoids harsh environmental conditions and improves predator avoidance.

    • Generally, higher survival rates than non-hibernators.

  • Costs:

    • Energy expenditures and risks of mortality while migrating or interacting with ecological pressures.

Behavioral Avoidance Adaptations - Migration

  • Types of Migration:

    • Obligate Migration: Species that migrate without choice.

    • Facultative Migration: Migration that may not occur every year.

  • Advantages of Migration:

    • Avoids harsh conditions and provides access to varied resources (breeding/overwintering locations).

  • Costs of Migration:

    • Significant energy costs and potential for increased mortality.

Benefits and Costs of Migration

  • Specific Examples:

    • Bar-tailed Godwit:

    • Migrates approximately 11,000 km non-stop from Alaska to New Zealand, demonstrating extreme migratory capability.

Behavioral Thermoregulation in Lizards

  • Adapting to Environmental Conditions:

    • Ectotherms exhibit diverse behavioral thermoregulatory strategies, such as basking and changing posture.

    • Zebra-tailed Lizards (Callisaurus draconoides):

    • Hypothesis: Use of thermal microhabitats for thermoregulation supported by experimental predictions.

Physiological Adaptations to Adaptations' Impact on Tolerance Limits

  • Overview of Physiological Responses:

    • Physiological adaptations, biochemical characteristics, and morphology determine organism's tolerance limits.

  • Responses to Environmental Changes:

    • Species can develop tolerance for varying internal conditions or mechanisms to counteract external challenges, often at an energetic cost

Temperature and Water Availability

  • Temperature: Essential to physiological and biochemical reactions.

    • Extreme temperatures can lead to protein denaturation or freezing of intracellular water.

  • Water: Crucial for life and biochemical reactions; optimal conditions must be maintained within narrow limits.

Temperature Adaptations: Selective Pressures and Responses

  • Responses to High Temperatures:

    • Production of heat shock proteins, heat-stable proteins, and increases in G-C content of DNA.

  • Responses to Low Temperatures:

    • Production of low molecular weight cryoprotectants and antifreeze glycoproteins.

Physical Mechanisms of Heat Transfer

  • Mechanisms influencing temperature adaptations: conduction, radiation, convection, evaporation, and metabolic heat regulation.

  • Thermoregulation can involve:

    • Homeotherms: Maintain constant body temperatures with varying external environments, utilizing mechanisms like sweating and panting.

Water Conservation in Desert Mammals

  • Unique adaptations enable desert mammals to mitigate water loss and manage temperature, e.g., eland and oryx have specialized thermoregulatory and metabolic strategies for conserving water.

Water Conservation and Thermoregulation in Desert Birds

  • Birds exhibit behavioral adaptation by seeking shade and utilizing food sources with high moisture content to conserve water.

  • Efficient kidneys minimize liquid excretion, aiding survival without drinking water for prolonged periods.

Species Differ in Degree of Water Homeostasis

  • Two Categories:

    • Osmoconformers: Their osmotic concentrations fluctuate with the environment, e.g., marine invertebrates.

    • Osmoregulators: Maintain constant internal osmotic concentration despite environmental changes, e.g., various saltwater and freshwater animals.

Case Study: Crab-eating Frog (Fejervarya cancrivora)

  • This species serves as an osmoregulator with adaptations for surviving in saline environments, regulating its internal composition through various physiological means.

Excretion of Nitrogenous Waste Entails Water Loss

  • Different organisms process nitrogenous waste differently, affecting water conservation in various environments, from ammonia in aquatic to uric acid in terrestrial species.

Thermal Adaptations in Plants

  • Morphological Features: Leaf structure and orientation impact temperature regulation and overall plant health in regard to thermal conditions.

  • Water Challenges on Land: Waxy cuticles and effective stomata function allow roots' moisture transport, enabling survival in various terrestrial habitats.

The Photosynthesis Dilemma

  • Plants face a challenge between gas exchange for CO2 and the risk of water loss. In arid conditions, adaptations such as C4 photosynthesis promote efficient carbon fixation while minimizing moisture loss.