Chapter 4 – Adaptations to Variable Environments:

  • Variable environments favour evolution of variable phenotypes
  • Many organisms have evolved adaptation to variation in many aspects of life

Ecological systems and processes vary in time and space:

  • Two main focuses:
  • Temporal variation in the environment
  • Spatial variation in the environment
  • Temporal variation:
  • How environmental conditions change over time
  • Some are predictable and other are not
  • Weather: Variation in temperature and precipitation over periods of hours or days
  • Is an unpredictable variation
  • Can only be predictable in short intervals
  • Use of warm and cold air mass information
  • Climate: Typical atmospheric conditions that occur throughout the year
  • Measured over many years
  • Population response from organism will vary depending on how frequent and impactful the changes occur
  • Extreme events tend to be less frequent
  • Looks on severity and frequency of events
  • Spatial variation:Environmental variation
  • Variation in the following is included in this category
  • Climate
  • Topography
  • Soil type
  • Moving individual’s individual perceives spatial variation as temporal variation
  • Increasing one’s speed will increase the exposure of encountering new environmental conditions, thus shortening the temporal scale of variation
  • Both plants and animals are affected by this variation

Environmental variation favours the evolution of variable phenotypes:

  • Producing different phenotypes can be an effective strategy in changing environments
  • Phenotypic trade-off: Situation in which a given phenotype experiences higher fitness in one environment whereas other phenotypes experience higher fitness in other environments
  • In short: A certain phenotype will experience higher fitness in one area in which another won't
  • Phenotypic plasticity: Ability of a single genotype to produce multiple phenotypes
  • Nearly all of life possess this
  • Changes occur at different rates as do the environments that surround the organism
  • High levels of performance tend to be present with changing environments
  • Like a mechanism for homeostasis, but for variable environments
  • Many traits are influenced by phenotypic plasticity
  • Behaviour, growth, development, and reproduction
  • Fitness advantages are at its peak for both temporal and spatial variation that occur frequently
  • Acclimation: An environmentally induced change in an individual’s physiology
  • Example: Human adaptation to low-oxygen conditions
  • Takes a few days for our physiological mechanisms to adapt
  • Behavioural responses tend to be reversible at fast rates
  • Morphological responses tend to be slow and irreversible
  • Example: Daphnia that has morph “caps” on their head when predation is high vs no “caps” when predation is low

Many organisms have evolved adaptations to variation in enemies, competitors, and mates:

  • Enemies:
  • Adaptations to predators, herbivores, parasites, and pathogens
  • Threat to well-being of an organism
  • Adaptations may include: Increased resistance, better methods of escape, changes in morphology, a counter trait to difficult obstacles
  • Predators also have plastic abilities
  • They too will adapt and change accordingly to their prey
  • Cycle of “cat and mouse”
  • Other adaptations organisms will make is behavioural
  • Example: Some species of birds will forage in low exposure, low-risk areas for food
  • Competition for scarce resources:
  • Competition varies from high to low
  • Organisms adapt accordingly
  • Can be morphological, behavioural, or other changes
  • Exploitation of niches for resource in both plants and animals
  • Example: Digestive tract of Burmese python
  • Changes in intestine and manipulation of stomach for hunting prey
  • Captured prey can make up 25% of its body mass
  • Low mobility
  • Becomes more vulnerable
  • Reduction of weight in stomach and intestine to reduce carrying cost
  • Can double surface area of intestine in 24 hours once meal is completed
  • 10x more blood is sent to intestine to maximize absorption
  • Mates:
  • Hermaphrodite: An individual that produces both male and female gametes
  • Occurs when reproduction is a challenge
  • Mate scarcity
  • Can fertilize eggs with own sperm
  • Gives rise to inbreeding depression
  • Inbreeding depression: Decrease fitness caused by matings between close relatives due to offspring inheriting deleterious alleles from both the egg and the sperm
  • Invertebrates, vertebrates, and plants all have some species that is hermaphroditic

Many organisms have evolved adaptations to variable abiotic conditions:

  • Biotic: competitors, and mates
  • Abiotic: Temperature, water availability, salinity, and oxygen
  • Varies just as much as biotic conditions
  • Evolution of phenotypically plastic traits that allow increased/ improved fitness of an organism
  • Temperature:Many variable adaptations to changes in temperatures
  • Many animals respond by moving to more favourable environments
  • Example: Migrating birds
  • Microhabitat: Specific location within a habitat that typically differs in environmental conditions from other parts of the habitat
  • Example: Desert iguana
  • Dependent on environment for heat
  • Moves to more shaded areas in the desert
  • Finds hotspots to bath for heat
  • Water availability: Most can move to microhabitats that have availability
  • Plants are more complex in combating this issue
  • They are root, therefore have adapted a variety of traits to solve this issue
  • Many phenotypically plastic adaptions
  • Closing of stomata is a common adaptation
  • Reduces water loss
  • Reduction of transpiration through stomata
  • Salinity:Freshwater and saltwater organisms
  • Fluctuation in solute concentrations
  • Adaptations for rapid physiological adjustments
  • Refer to chapter 2 notes for osmotic changes/ differences
  • Hypo and hypertonic conditions
  • Oxygen: Adjustments to low-oxygen atmospheres
  • Example: Human populations that have adapted to high altitude environments
  • Physiological adaptations that occur through time and space
  • Requires a few days to months to fully adapt to such intense environments

Migration, storage, and dormancy are strategies to survive extreme environmental variation:

  • Migration:seasonal movement of animals from one region to another
  • Phenotype is behaviour of living in a particular location
  • Plasticity is displayed in the act of migrating
  • May occur in response in scarcity in food resources
  • Storage:variation in shifts of food supplies
  • Food supply can change between feast into famine
  • Storage of resource can be an adaptive strategy
  • Hibernation
  • Increase in fat reserves
  • Can make an individual more vulnerable as they are less agile
  • Dormancy: A condition in which organisms dramatically reduce their metabolic processes
  • Species that do not migrate
  • Occurs when environments become so cold, dry, or depleted in nutrients
  • Diapause: Type of dormancy in insects that is associated with a period of unfavourable environmental conditions
  • Hibernation: Type of dormancy that occurs in mammals
  • Reduction in energetic cost of being active by lowering their heart rate and decreasing their body temperature
  • Can be short or long-termed depending on the varying environmental changes
  • Torpor: A brief period of dormancy that occurs in birds and mammals in which individuals reduce their activity and their body temperature
  • Aestivation:Shutting down of metabolic processes during the summer in response to hot or dry conditions
  • Allows for survivability in unfavourable environments
  • Reduction in exchange of an organism and its environment

Variation in food quality and quantity is the basis of optimal foraging theory:

  • Are representative of phenotypically plastic behaviour
  • Allows for different feeding strategy
  • Determination of where to forage, how long to forage, and which types of food to eat
  • Cost and benefit consideration
  • Optimal foraging theory: A model describing foraging behaviour that provides the best balance between the costs and benefits of different foraging strategies
  • There are four responses to food variation in space and time
  • Central place foraging
  • Risk-sensitive foraging
  • Optimal diet composition
  • Diet mixing
  1. Central place foraging:
  2. Foraging behaviour in which acquired food is brought to a central place – such as a nest with young
  3. Increase distance travelled away from the nest/ home results in an increase in potential food source
  4. Increase in time, exposure to risk, and energy cost
  5. Animal must choose time spent gathering food before returning to the nest – as well as how much food to bring
  6. Relationship of how much food is obtained vs how much time it takes to obtain
  7. Refer to figure 4.18 and 4.19 (Page 104 and 105 of the textfor a detailed graph representing the relationship between length of time foraging vs number of prey caught)
  8. Risk-sensitive foraging:
  9. A Foraging behaviour that is influenced by the presence of predators
  10. Risk vs reward
  11. Example was young creek chub (fish)
  12. Foraging favoured vs 2 predators when the density of food was high or very high
  13. Optimal diet composition:
  14. Handling time: The amount of time that a predator takes to consume a captured prey
  15. Animals have a variety of food choices
  16. Relation between amount of energy spent to capture prey and how much energy is returned from consuming it
  17. Also considered is the abundance of a prey
  18. Energy gained per unit of time
  19. Dividing energy benefit of a prey item by its handling time
  20. Predator should always eat the prey species that provides highest energy benefit
  21. Must be abundant
  22. Maximizes animal’s energy gain
  23. Diet mixing:
  24. Animals that consume a variety of food because all the nutrients aren’t obtainable through one option
  25. Can accelerate growth and development
  26. Example: nymphs of American grasshopper