Week 6.1
Module 3: Interactions between Animals and the Environment
Lecture 3.1: Thermal Biology
Abiotic Processes Affecting Animals
Key Points:
Biomes are shaped by mean and seasonal variations in temperature and rainfall.
Traits defining animals in each biome are largely shaped by abiotic factors (e.g., temperature, rainfall).
Local diversity relates to temperature on land and in the sea, as well as rainfall on land.
Life histories, reproductive strategies, and movement are strongly influenced by abiotic seasonality.
Duration of benign conditions for breeding.
Harshness of non-breeding times influences animals' life histories.
Abiotic factors influence energy allocation in endotherms, impacting metabolic costs related to temperature regulation.
Major Aspects of Animal Ecology Affected by Abiotic Conditions
Factors Influencing Ecology:
Temperature
Moisture
Humidity
Nutrient concentrations
Wind
Light
Currents
Salinity
pH
Minerals
Radiation
Pollutants
Structural components of the landscape
Acoustic landscape
Influence of Animals on Abiotic Environment
Some animals can influence the abiotic environment, shaping factors such as temperature and moisture.
ambient temperature = outside
internal temp = inside animal body
endotherms maintain very stable temperatures
while ectotherms rely on external sources to regulate their body heat. This distinction is crucial for understanding how different species adapt to their environments and manage energy efficiently.
internal temp affects the amount of energy output and metabolic processes in both endotherms and ectotherms, influencing their behavior, habitat choices, and overall survival strategies in varying climates.
ectotherms have much broader range of energy output and endotherms have much smaller range in their metabolic rates, allowing them to remain active across diverse environmental conditions. This variance showcases how each group has evolved distinct adaptations to cope with temperature fluctuations, ultimately impacting their ecological niches.
Related Lectures:
Lecture 3.5: Ecosystem Engineers
Lecture 3.6: Case Study
The Experience of Temperature in Ectotherms and Endotherms
Distinction between energy output and core temperature, and internal and external temperatures.
Thermal Biology: Ectotherms
Importance of Temperature for Ectotherms:
Ectotherms rely on environmental heat and do not maintain a constant high body temperature.
Higher temperatures result in:
Increased metabolic rates—"biochemical modification of chemical compounds."
Enhanced gas exchange, neuron transmission, enzymatic activity, muscle contraction.
Consequences:
Faster locomotion, digestion, and perceptual abilities.
chem reactions speed up in warmer environments so when temps are higher in ectotherm they can respond to things more quickly and have processes happen faster
allows them to find and digest pray faster and move faster
this puts pressure on ectotherms to keep their internal temp within a certain range to optimize their physiological processes, ensuring they remain agile and efficient in their hunt for food.
ex basking in sun
sitting in warm road during dusk
modulate not getting too hot by getting in shade
Ectotherm Body Temperature Modulation
Behavioral Modulation Techniques:
E.g., lizards moving to and from sun/shade.
E.g., fish having species-specific preferred water temperatures; ambient temperature (Ta) is sensed via skin sensors, guiding swimming behavior to optimal thermal environments.
heated outflow = warmer water that come from a different source than the main source of water (small river flowing into ocean
swimming conditions seek out best environment most likely due to sensors on their body
Heat Generation in Ectotherms
Through catabolism, ectotherms can convert complex molecules into energy, releasing metabolic heat.
Example: Glanville Fritillary Butterfly:
Basks in the sun to quickly gain heat through wings, transferring heat to thorax to power flight.
do this before they go on flights…. hemolent flowing through wings…. wings are thin and absorb heat quickly warming up hemolint quickly
muscles that power the flight are in the core of body…. take heat from wings and transfer to thorax…
Cool during flight; flight duration relates to how quickly they cool.
longer the flight the more they cool
Risk of Overheating in Ectotherms
Biological processes have specific temperature ranges for functionality:
Arrhenius Activation Energy:
Long-term survival limit.
7–12% rate increase in processes per degree Celsius.
Acute heat injury and mortality risks arise above specific temperature thresholds.
these animals arent as passive in what they require
actively avoid situations of over heating and want to maintain temperatures in optimal rance of life…. aren’t doing this through their own metabolism
Ectotherms display high sensitivity to slight temperature increases (>LTC).
Adaptation of Ectotherms to Cold Environments
Options Available:
Living in ocean (thermally buffered environment).
don’t vary ias much as terrestrial environment
Cold hardy through life-stage adaptations (e.g., holometabolous insects overwintering in a cold-tolerant stage).
cold hardy - avoid coping with cold by going through different times in life cycle…. moth are in pupus stage in cacoon during winter cuz they don’t have to do anything
microhabitat - choosing locations that help them aboid really bad temps such as burrows…. need to protect themselves so need a good hole can’t be just any
freexe aboidance - tolerate cold temps through physiological properties that avoid ice crystals forming in their body….
freeze tolerance - freeze some of their body water…. can’t freeze cells bcs this leads to death…. can only happen in intracellular space
Using buffered microhabitat (e.g., underground overwintering sites for frogs, turtles, and salamanders).
Freeze Avoidance:
Eliminating ice-nucleating agents, utilizing anti-freeze proteins, and partial dehydration.
Freeze Tolerance:
Only a few taxa can keep ice outside cells.
Examples include Cecropia moths and Discus snails.
The Impact of Temperature on Ectotherms
Effects occur over multiple time scales:
Short-term: Slower locomotion, less frequent reproduction, slower foraging.
short term reduction in optimal performance for that animal
reversible
Medium-term: Longer developmental rates and reduced reproductive activity (changes in pheromone signaling).
slower responses to signals
tend to be reversible but life stage specific
Long-term: Effects on body sizes, life span, and egg number/size (life history trade-offs).
evolutionary changes towards larger body sizes
not reversible
Thermal Biology: Endotherms
Significance of Temperature for Endotherms:
Endotherms maintain relatively constant high body temperatures mainly through endogenous heat production propelled by catabolism.
This process leads to tolerance levels for both hot and cold climates.
converting complex molecules into energy relases metabolic hear
Key Elements of Endothermic Thermal Biology
Metrics of Interest:
Ambient temperature (Ta): especially the difference from internal body temperature.
Internal body temperature (Tb): typically needs to remain stable for proper physiological functioning.
heterothermy in endo thermic animals is why typically not always… gen happens in very specific reasons …such as during periods of extreme environmental stress or when resources are scarce, leading to adaptations that allow them to maintain internal temperature despite external fluctuations.
Scholander Curves in Endotherms
Illustrate the relationship between ambient temperature and energy use in endotherms.
x axis we have ambient temp
y axis is how much energy they are expending based on the temperature
Thermal Neutral Zone (TNZ):
Temperature range where energy expenditure for maintaining Tb is minimal; no active regulation needed.
range of outdoor temp where animal is not too hot not too cold
Critical Temperatures:
Upper and lower critical temperatures (UCT & LCT) signify thresholds where active cooling or warming is required.
if we go above or below critical temps we have to expend energy
muscles contractions like shivering to generate heat
evaporative cooling like through sweating or panting
Endothermic Responses to Cold Conditions
Short-term Strategies:
Behavioral modifications (avoiding cold, fluffing for insulation)… goose bumps in humans…. humans don’t do a good job with this, as our body relies heavily on other mechanisms for thermoregulation rather than just behavioral adaptations.
mecock monkey in japan sit in hotsprings
some birds pull their legs into feather one at a time
Increasing internal heat generation (shivering).
avoidance
Seasonal Adaptations:
Adjustments in insulative layers;
Hibernation, heterothermy, and migration as long-term responses.
black dots and cblack line is under summer conditions for amount of energy by temp…. acclimate to colder temps and don’t need as much energy to get through colder temps…. turn down internal thermostat
Example: Willow Ptarmigans lower their thermostat in winter.
Long term:
body increases
aboidance strategis
deep heterothermy like torpor
Cost Implications of Temperature Variance
Sub-lethal Costs:
Common and vary in severity, frequency, and duration.
Cumulative effects manifest as energetic and opportunity costs.
can be cumulative
opportunity cost = time spent doing one thing that takes away from another
cuddling in penguins takes away from time foraging
Lethal Costs:
Occur during extreme cold.
can die
Endothermic Responses to Excessive Heat
Short-term Avoidance Strategies:
Behavior changes to evade heat.
Actively losing heat through evaporation (sweating in mammals, birds over moist surfaces like the mouth/throat).
Redirecting blood flow for maximum cooling.
sweating , panting, gular flutter (pouch in birds that expands and contracts to aid in cooling) are all effective physiological responses to manage body temperature during extreme heat conditions.
vultures pee on themselves to cool
Seasonal Changes:
Adjustment in color and insulation through moulting.
Example: Vultures urinate on their legs to cool.
sub lethal
bats will fan their wing
they cluster might have to do with shading
the y salivate to increase evaporation from mouth
a panting bat is in great distress anything past that can kill tem
Data on Heat Effects in Endotherms
Study by Australian Bureau of Meteorology:
Illustrates immense heat stress during significant temperature peaks (e.g., on February 7, 2009).
Visual Data:
Metabolic costs at various ambient temperatures and measures of temperature stress seen in subtropical animals.
Acute versus Chronic Heat Stress
Lethal Costs:
Extreme heat has led to significant population losses, demonstrated by the loss of around one-third of Australia’s spectacled flying fox population during severe temperature events.
These significant losses underscore the vulnerability of these species to heat stress and highlight the need for effective conservation strategies to mitigate further impacts.
Comparative Insight on Temperature Impacts
Heat constitutes a more acute problem than cold due to:
Internal temperatures conducive to life being closer to lethal ambient heat thresholds (especially in birds).
Different death mechanisms in heat (protein denaturation) versus cold.
lethal temps for endotherm are very close to lethal temp
mechanism of death differ
under extreme hear protein denature → cooking egg… enzymes change chape when cooking
Body Size and Thermal Biology
Metabolic Rates and Size Relation:
Smaller animals exhibit higher mass-specific metabolic rates.
on a gram per gram basis a little animal is doing more per unit time
Higher metabolic rates lead to increased heat generation.
smaller animals have higher internal temps bcs they gen more heat per unit body mass
Result: Smaller animals tend to achieve higher internal temperatures.
Conductance and Heat Exchange
Conductance:
Defined as the rate of heat exchange with the environment.
Influenced by insulation type (fur or feathers) and surface area to volume ratio.
Smaller animals possess a greater surface area relative to volume, allowing for increased heat loss.
affected by ratio between animal volum and surface area, smaller animals have more surface area to volume ratio, which contributes to their higher rates of heat exchange and susceptibility to temperature changes in their environment.
Body Size Consequence for Heat Loss
Bergmann’s Rule:
Body mass tends to increase with higher latitudes as an adaptation to conserve heat.
higher latitudes = larger body mass
bohemian waxwing have counterparts cedar waxwing… bohemians are more up north and they are also larger that cedars
Example: Cedar Waxwing (33.1g) vs. Bohemian Waxwing (56.4g).
Endotherm Size Constraints and Heat Relationships
At the smaller end (2g), animals exhibit:
Fastest heat loss due to high conductance requiring elevated mass-specific metabolic rate.
High metabolic rates correspond to substantial heat generation, pushing internal temperatures near critical limits.
limits to how much energy they can take in at once
Examples include Cuban Bee Hummingbird, Thai Bumblebee bat, and Etruscan shrew (2.3g). → smaller than a penny
Interconnectedness of Thermal Tolerance, Body Size, and Water Balance
Endotherms avoid overheating through evaporation which necessitates water loss.
Smaller animals face higher internal temperatures and faster metabolic responses, complicating water conservation.
endotherms cool themselves by evaporation and tho avoid overheating they must loose water, small animals loowse and gain water faster
psmall animal have smaller range at basal level and steep metabolic rate to water loss rate
Influence of Wind on Heat Exchange
Wind significantly enhances heat exchange rates between birds and their environment, increasing overall conductance.
Example Data:
Heat loss under different wind conditions, revealing temperature effects at 15 °C with/without wind.
Thermal Niches: Linking Physiology to Ecology
Individual performance varies with ambient temperature extremes, affecting population growth and distributions.
Long-term consequences of changing temperatures influence offspring numbers and survival rates.
Physiological limits determine geographical distribution, with energetic costs related to temperature extremes.
Variability of Thermal Tolerance Ranges
Thermal tolerance ranges exhibit variability depending on the ecological context, with temperate animals enduring more substantial seasonal temperature shifts than tropical species.
Comparative Analysis of Thermal Niches
Tropical vs. Temperate Animals:
Tropical endotherms likely experience narrower thermal niches due to lower seasonal variation in comparison to temperate counterparts.
Take-home Points
Multiple abiotic factors deeply influence animal habitation, while sometimes animals regulate those abiotic conditions.
Endotherms and ectotherms distinctly respond to temperature variations due to differing temperature stability characteristics.
Ectotherms can generate internal heat and perform best within specific temperature ranges but face risks of overheating and performance decline in cold conditions.
Cold survival mechanisms include behavioral avoidance, cold hardiness, and adaptive life stages.
Temperature-related responses span various time scales—physiological and behavioral to evolutionary adaptations.
Endotherms maintain stable temperatures through metabolism, requiring active regulation outside the TNZ.
Understanding lethal and sub-lethal costs is crucial in assessing responses to thermal extremes.
Heat presents a greater challenge than cold for endotherms, particularly regarding internal temperature proximity to lethal thresholds.
Body size implications on thermal biology relate to metabolic rates and surface area dynamics, influencing heat retention and loss across populations.
Water evaporation links with thermal tolerance and requires careful management in energetic processes, especially for small endotherms.
Wind notably mediates heat exchange rates and must be considered in habitat utilization strategies.
Understanding thermal niches links physiological processes with population dynamics, encompassing a broader ecological framework for animals, focusing on temperate and tropical distinctions as they adapt to environmental pressures.