Response to Environmental Variation

Chapter 4 Coping with Environmental Variation

Response to Environmental Variation

The Liebig law of minimum - under stable conditions, the essential constituent available in amounts most closely approaching the minimum need tends to be the limiting one. a.k.a. - a limiting factor / condition

* Can be a single factor or multiple (combinations)

* factor substitutions / modifications can offset minor deficiencies

Shelford law of tolerance - Not only too little but too much of a limiting factor may be harmful; thus a range of tolerance exists.

* More tolerate organisms generally more widely distributed

* unfavorable effects from one factor may reduce other factors tolerances

* a factors net effect may be a combination of factors

* life stage changes can change factor tolerances

Organisms are able to adapt to their physical environment to make it less of a limiting situation

* as a result of this, ecotypes (genetically different subspecies populations adapted to specific environment) are able to develop and exist in diverse environments

* adaptations can occur at a genetic level, a physiological level of adjustment or even a morphological change

Each species has a range of environmental tolerances that determines its potential geographic distribution.

* Organisms have two options for dealing with environmental variation: Tolerance and avoidance

* Example: Spruce trees in the boreal forest must be able to tolerate temperatures from -50oC to 30oC.

* Physiological ecology is the study of interactions between organisms and the physical environments that influence their survival and persistence.

* The physical environment influences an organism's ecological success:

* Availability of energy and resources-- impacts growth and reproduction

* Extreme conditions 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.

Because plants don't move, they are good indicators of the physical environment.

* Example: Low temperatures and drought affect reproduction and survival of Aspen distribution.

* A species' climate envelope is the range of conditions over which it occurs and is a useful tool for predicting its response to climate change

Physiological processes have optimal conditions for functioning.

* Deviations from the optimum reduce the rate of the process.

* Stress (environmental change) results in decreased rates of physiological processes, decreasing survival potential, growth, or reproduction

* Example: At high altitudes, lower partial pressure of oxygen in the atmosphere results in hypoxia which causes "altitude sickness," which is physiological stress.

Acclimatization: Adjusting 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 population adaptation to environmental stress.

* Individuals with traits that enable them to cope with stress are favored and in time these genetic traits become more frequent in the population.

* Ecotypes: Populations with adaptations to unique environments can eventually become separate species as populations diverge and become reproductively isolated

* Example: Humans living in Andes Mountains have adapted to the low-oxygen conditions by having higher red blood cell production and greater lung capacity.

* Adaptations can vary among populations:

* Populations in the Andean and Tibetan highlands have different adaptations.

* Andean populations have high red blood cell concentrations and large lung capacity and faster breathing rates.

* Acclimatization and adaptation require investments of energy and resources, representing possible trade-offs with other functions that can also affect survival and reproduction.

Variation in Soil Quality

Soil - weathered layer of Earth's crust with living organisms intermingled with products of their decay (depends largely on climate).

* Important to overall system since generally decomposition occurs in the soil and subsequently the liberated chemicals are then available to be used by primary producers

* All soil is not the same

* For example - rhizospheres which are aggregations of microbes around pellets, patches of organic matter, and mucus secretions (hot spots for primary productivity) account for 90% of metabolic activity in soil but account for only 10% of soil volume.

* Inorganic component is product of weathering process - the mechanical and chemical breakdown of rocks and sediments on or near the Earth's surface due to a change in the physical environment the rmaterial experiences

Within a soil structure there are several layers (horizons) of these components as well as regional and lateral differences.

Typical Soil Profile: A Horizon - (topsoil) - organic rich layer

AO - detrital layer