5. Ecophysiology of stress

stress

when environmental change results in the decrease in the rate of a physiologically process, which can lead to a decrease in survival, growth, or reproduction deal with stress thru avoidance and tolerance

Stressors that animals and plants face

• Temperatures

• water

• salinity

• pH

• nutrients availability

• presence of toxins

Tolerance

1. confirm: just deal with unstable conditions

2. regulate: change body to deal with unsuitable environment

avoidance

1. migration

2. metabolic shutdown: hibernation/torpor, or resting stages (seeds, spores, cysts)

Temperature

• Thermal tolerance curves

• its effects cascade to higher levels of organization

ii. Effects of temperature on higher levels of organization

Rates of biochem reactions → organization-level performance traits → life history and cycle traits → fitness: reproduction and survival

Ways animals can manage temperature

1. dormacy

2. hiding, burrowing, shelter

3. migrating or moving to better conditions

4. modifying energy balance

5. panting , sweating

6. insulation

7. vasoconstruction, vasodilation

8. behavior (bathing, activity levels, etc)

Ectotherms

animal regulates body temperature thru energyexchange with its external environment 

Ectotherms: cost vs benefits

• Benefits

  • lower cost of doing business

  • larger fraction of energy goes to growth and reproduction 

  • more competitive than endotherms when in optimal conditions 

• Costs:

  • dependence on environmental conditions

  • limited activity in cold temperature  

endotherms

animal that regulates its body temperature thru internal metabolic heat generation 

endotherms: costs vs benefits

• Benefit

  • can be active for longer periods (stamina)

  • gain more access to temporal and geographic niches

  • increase speed with faster metabolism 

  • optimal enzyme activity 

• Cost

  • need more energy to operate 

  • need constant supply of food for energy for constant thermoregulation

Surface area to volume ratios and relationship to heat loss and water loss

• higher ratio= smaller size animal= loses heat more quickly due to all of the S.A.= higher BMR per unit mass= lose water more quickly due to all of the S.A.

• lower ratio= bigger sized animal= retain heat better= lower BMR per unit mass= hold H2O better

Hyperosmotic

more saline than organism’s cells or blood

isoosmotic

similar salinity to organism

hypoosmotic

environment has less salinity than organisms

Water potential and flow of water

• a measure of water’s free energy and its tendency to move from one location to another and water always flows from high to low water potential

Water balance in animals

structure

• fish (gillings)

• humans (kidneys)

• rectal/nasal salt glands

water exchanges: water loss vs water gain

• water loss: respiratory evaporative water loss, cutaneous evaporative water loss, urinary and fecal water loss

• water gain: ingested water, metabolic water production

Solute exchanges

salt and nitrogen wastes; change concentration = change water salt intake, dilute/concentrate urine

Different water balance strategies in freshwater and marine fish

Why do plants need to regulate water potential?

to maintain turgor pressure (avoid wilting), avoid air bubbles in xylem, and maintain stomatal conductance (open stomata) for photosynthesis 

How do plants maintain water balance?

open/close stomata, increase hydraulic resistance in plant tissues (harder for water to flow thru), osmoregulation using solutes, increase amount of roots to take up more water

Strategies for dealing with high temperatures (desert)

1. creating/using microclimates: burrowing

2. locomotion that avoids S.A. contact (fly instead of walking)

3. diel patterns of behavior= be more active at dawn/dusk

4. seasonal patterns of behaviors= balance energy over the course of the week instead of day

5. physiological acclimation= have lowered metabolic rates, have special enzyme isoferms for enhanced heat tolerance

6. color change= light colored surfaces to reduce heat load during the day 

Strategies for dealing with water loss (desert)

• low water permeabilities

• hyperosmotic urine= retain more water

• burrowing=thermal buffering and humidity buffering

• low SA/Vol ratio= lose water less quickly ( be big)

Nasal turbinates

increase S.A. of nasal cavity

drier environment= larger nasal turbinates

Avoidant strategies for extreme cold

• more suitable microclimates locally → burrowing, huddling, bask in sun

• find macroclimate (migrate)

• remain inactive during coldest time of year (hibernate/ torpor)

Tolerating strategies for extreme cold

• overcoming ice crystal formation because can pierce thru cells by

  • freezing point depression= using osmotic solutes to prevent freezing by lowering the temperature at which freezing occurs

  • supercooling= using antifreeze peptides

Regulating strategies for extreme cold

• insulation (fur)

• shunt blood from the surface and extremities

• higher BMR

• shivering thermengenesis

• brown adipose tissue

Marine life challenges

1. food tends to be located in cold water, so avoidance is not an option

2. water has much greater heat capacity and thermal conductivity than air

3. solutions: lower body temperature, decrease SA/Vol ratio (be large), increase metabolism, use insulation (fur or blubber)