Coping with Environmental Variation Flashcards
Temperature and Water
Physical environment influences organisms ecological success on two ways;
1. Extreme conditions can exceed tolerance limits and impact survival
2. Availability of energy and resources impacts growth and reproduction
Temperature of water can affect food sources
Energy supply influences organism’s ability to tolerate extreme environments
Due to plants not moving they are good indicators of physical environment
Example; Aspen distribution predicted based on climate -> low temperatures and drought affect reproduction and survival
Actual geographic distribution of species is related to other factors (disturbance and competition)
Physiological Ecology
- study of interactions between organisms and the physical environments influencing there survival and persistence
- Optimal conditions for functioning
- Deviations from the optimum reduce the rate of the process
- Stress can affect environmental change by;
Decreased rates of physiological processes
Lowering potential for survival
Growth
Or reproduction
Acclimatization
Adjusting to stress through behavior physiology
Organism faces variability within environment
Usually short term and reversible process
In high elevations involves higher breathing rates, greater production of red blood cells, and higher pulmonary blood pressure
Adaptation
The result of natural selection
Populations adapt to environmental stress
Individuals with traits that allow them to deal with stress are favored
Over time genetic traits become more frequent within the population
Ex; bunny in a dessert has larger ears to help dissipate more heat
Acclimatization & Adaptation
Require investments of energy and resources
Represents possible trade-offs (which occur almost always) with other functions that can also affect survival and reproduction
Being good at one environment can cost in another
Ecotypes
Populations with adaptations to unique environments
Eventually become separate species as populations diverge
Become reproductively isolated
Environmental temperatures vary greatly throughout the biosphere
Survival and function of organisms strongly tied to internal temperatures
Lower limits are determined by the temperature at which water freezes in cells (-2 to -5℃)
Some bacteria and archaea can function in hot springs at 90℃
Metabolic reactions are catalyzed by enzymes, and they have narrow temperatures for function
Denaturing can destroy enzymes due to high temperatures
Some species produce different forms of enzymes (isozymes) with different optimum temperatures allowing acclimatization to changing conditions
Temperature affects the properties of cell membranes composed of two layers of lipid membranes
At low temperatures, lipids can solidify, making proteins within not function and leak metabolites
Plants thriving at low temperatures have high proportions of unsaturated lipids
Ectotherms
Regulate body temperature through energy exchange with the external environment
Do not generate heat
The surface area to volume ratio of the body is important in exchanging energy with the environment
The larger area allows greater heat exchange, however, makes it harder to maintain internal temperatures
Small aquatic ectotherms remain same temperature as the water
Some larger ectotherms can maintain higher body temperature (Skipjack tuna)
Terrestrial ectotherms move around to adjust the temperature
Insects and reptiles bask in the sun to warm up after a cold night (increases predation risk increasing benefits of camouflage)
In temperate and polar regions must avoid or tolerate freezing
Avoidance behaviour includes seasonal migration to lower latitudes or to microsites above freezing (burrows in soil)
Tolerance to freezing minimizing damage associated with ice formation in cells
Some insects have high concentrations of glycerol that lower freezing point of body fluids (no heartbeat)
Vertebrates generally don’t tolerate freezing temperatures
Cryonics = preservation of bodies by freezing
Freezing results in tissue damage due to ice crystals puncturing cell membranes and organelles
Animals withstanding freezing water are limited to space outside cells
Ice-nucleating proteins outside cells serve as sites of slow, controlled ice formation
Glucose and glycerol are made inside the cells to lower the freezing point
Endotherms
Rely primarily on internal heat generation-mostly birds and mammals
Can maintain internal temperatures near optimum for metabolic functions
Bees, some fish (tuna), and some plants are endotherms
Skunk cabbage warms its flowers using metabolically generated heat in early spring
Remain active at subfreezing temperatures
Cost is high demand for energy (food) to support metabolic heat production
Metabolic rates are a function of the external temperature and rate of heat loss
The rate of heat loss is related to body size and surface area to volume ratio
Small endotherms with a large surface area to volume ratio have higher metabolic rates
Require more energy and higher feeding rates than large endotherms
The challenge for small organisms
Have to eat more to compensate
Thermoneutral zone
range of environmental temperatures over which a constant basal metabolic rate can be maintained
Lower Critical Temperature
Heat loss is greater than metabolic production; body temperature drops, and metabolic heat generation increases
Arctic mammals have lower critical temperatures than mammals in tropical regions
The rate of metabolic activity increases more rapidly below the lower critical temperature in tropical mammals compared to arctic mammals
Evolution of endothermy required insulation (feathers, fur, and fat)
Insulation limits conductive and convective heat loss
Fur and feathers provide a layer of still air adjacent to the skin
Small mammals have thin fur and not much fat for energy storage
High demand for metabolic energy below the lower critical temperature
Some organisms can survive periods of extreme heat or cold by entering a state of dormancy (little or no metabolic activity occurs)
Surviving in cold climates by entering a dormant state called torpor
Body temperature and basal metabolic rates are low, which conserves energy
Reservation of energy is needed to come out of torpor
Small endotherms may undergo daily torpor to survive a cold night
Longer periods of torpor/hibernation are possible for animals that can store enough energy
Heat stress in animals
Use behavioral changes to control the exchange of energy with the environment
Ex; elephants swim and spray water onto their backs with their trunks to cool their bodies
Moving into shade reduces the amount of solar energy radiation received
Evaporative heat loss in animals includes:
Sweating in humans
Panting in dogs (and other animals)
Licking of the body by some marsupials
Water stress
Arid conditions are a widespread challenge for organisms
Some tolerate dry conditions by going into suspended animation
Many microorganisms do this, and some multicellular organisms
Desiccation-tolerant organisms can lose 80%-90% of their water
Reptiles very successful in dry environments
Thick skin with layers of dead cells
Fatty coatings
Plates or scales
Mammals and birds have thick skin plus fur or feathers to minimize water loss
Sweat glands in mammals are a trade-off between water loss resistance and evaporative cooling
Conduction
Transfer of energy from warmer to cooler molecules
Convection
Heat energy is carried by moving water or air
Energy Exchange in Terrestrial Plants
Plants adjust energy inputs and outputs
Transpiration rates are controlled by specialized guard cells surrounding leaf openings called stomates
Variations in degree of opening and number of stomates control the rate of transpiration and, thus leaf temperature
If soil is limited, transpirational cooling is not a good mechanism
Some plants shed their leaves during the dry season
