Ecology Lecture No. 4: Coping With Environmental Variation (Temperature & Water)
Thursday September 20 , 2012
Availability Of Energy & Resources:
-The physical environment influences an organism’s ecological success in two ways: the availability of
energy and resources (which impacts growth and reproduction) and extreme conditions (which can
exceed tolerance limits and impact survival). Energy supply can influence an organism’s ability to
tolerate environmental extremes. The actual geographic distribution of a species is also related to other
factors, such as disturbance and competition.
Abundance & Distribution Of Species:
-Because plants don’t move, they are good indicators of the physical environment. For example, aspen
distribution can be predicted based on climate (like pollen records from 10,000 years ago). Low
temperatures and drought affect their reproduction and survival. A species’ climate envelope is the
range of conditions over which it occurs.
-Physiological ecology is the study of interactions between organisms and the physical environments
that influence their survival and persistence. Physiological processes have optimal conditions for
functioning. Deviations from the optimum reduce the rate of the process. Stress is environmental
change that results in decreased rates of physiological processes, lowering the potential for survival,
growth, or reproduction.
Acclimatization & Adaptation:
-Acclimatization describes the adjustment to stress through behavior or physiology. It is usually a short-
term, reversible process. Acclimatization to high elevations involves higher breathing rates, greater
production of red blood cells, and higher pulmonary blood pressure.
-Over time, natural selection can result in adaptation of a population to environmental stress.
Individuals with traits that enable them to cope with stress are favored. Over time, these favourable
genetic traits become more frequent in the population.
-Acclimatization and adaptation require investments of energy and resources, representing possible
trade-offs with other functions that can also affect survival and reproduction. Ecotypes are populations
with adaptations to unique environments. Ecotypes can eventually become separate species as
populations diverge and become reproductively isolated. Temperature:
-Environmental temperatures vary greatly throughout the biosphere. Survival and functioning of
organisms is strongly tied to their internal temperature. Some Archaea and bacteria in hot springs can
function at 90°C. Lower limits are determined by temperature at which water freezes in cells (-2 to -5°C).
-Metabolic reactions are catalyzed by enzymes, which have narrow temperature ranges for optimal
function. High temperature destroys enzymes function through the process of denaturation. Some
species produce different forms of enzymes called isozymes with different temperature optima that
allow acclimatization to changing conditions.
-Temperature also affects the properties of cell membranes, which are composed of two layers of lipid
molecules. At low temperatures, these lipids can solidify, embedded proteins can’t function, and the
cells leak metabolites. Plants that thrive at low temperatures have higher proportions of unsaturated
lipids (with double bonds) in their cell membranes.
Ectotherms & Endotherms:
- Endotherms, mostly birds and mammals, rely primarily on internal heat generation. They can also
maintain internal temperatures near optimum for metabolic functions as well as extend their native
geographic range. Some other organisms that generate heat internally include bees, some fish, such as
tuna, and even some plants. Skunk cabbage warms its flowers using metabolically generated heat in
early spring. Ectotherms regulate body temperature through energy exchange with the external
Factors Affecting Body Temperature:
- An ectotherm’s surface area-to-volume ratio of the body is an important factor in exchanging energy
with the environment. A larger surface area allows greater heat exchange, but makes it harder to
maintain internal temperature.
- Small aquatic ectotherms remain the same temperature as the water. Some large ectotherms can
maintain higher body temperature. The Skipjack tuna, for instance, use muscle activity and heat
exchange (counter current exchange) between blood vessels to maintain a body temperature 14°C
warmer than the surrounding seawater.
- Many terrestrial ectotherms can move around to adjust temperature. Many insects and reptiles bask in
the sun to warm up after a cold night. Because this increases risk from predators, many are camouflaged
and can change coloration to match the backgrounds of their native environment.
- A smaller surface area relative to volume decreases the animal’s ability to gain or lose heat. As body
size increases, the surface area-to-volume ratio decreases, and large ectotherms are thus improbable.
This led to speculation that large dinosaurs may have had some degree of endothermy. Ectothermic Freezing Tolerance:
- Ectotherms in temperate and polar regions must avoid or tolerate freezing. Avoidance behavior
includes seasonal migration to lower latitudes or to microsites that are above freezing (e.g., burrows in
soil). Tolerance to freezing involves minimizing damage associated with ice formation in cells. Some
insects have high concentrations of glycerol, a chemical that lowers the fr