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Ecological Issues

Ecological Principles and Issues

Ecology principles

Heterogeneity of resources in ecology

Odumís ideas for the 1990s

First thermodynamical principle of energy conservation

The principle that n species requires n or more limiting resources may apply to ecologically simple systems

An ecosstem is a thermodynamically open, far from equilibrium, system

Second thermodynamical principle of entropy

More than n species may persist on fewer than resources when resources fluctuate and if consumer species differ in their ability to use resources.


The source-sink concept: one aree or poulation (the source) exports to another area of population (the sink).

The most reproductive species have more frequent and more numerous descendancy

The ecological consequences of physical environmental heterogeneity such as disturbance, is dependent on resources levels.


In hierarchical organization, species interactions that tend to be unstable, nonequilibirum, or even chaotic are constrainted by the slower interactions that characterize large system

Law of adaptation to environment (Darwin)

Even when mean resource levels are constant over the long term, short term resources heterogeneity can affect community structure.


The first signs of environmental stress usually occur at the population level, affecting especially sensitive species

Diversity is related to biomass productivity ratio

More than n species may persist on fewer than n resources if consumer species differs in their ability to use the variance of the resource.

Feedback in an ecosystem is internal and has not fixed goal

Law of conservation of matter

The effect of heterogeneity on one resource may be dependent on, or a function of, the level of another resource.

Natural selection may occur at more than one level

Distribution of individual organisms in space partly determine the efficient use of energy by individual and itís population

Ecological consequences of historical factors are dependent on past and current resource levels.

There are 2 kinds of natural selection, or two of the struggle for existence: organism versus organism, which leads to competition, and organism versus environment which leads to mutualism

Principle of saturation of resources use

The effects of resources heterogeneity on the distribution and abundance of species may depend on the ability of colonizing species to select habitat.

Competition may lead to diversity rather than to extinction

Diversity of a stable state is highter in predictable environment

The effects of resource heterogeneity on one trophic level can carry through to another level of food chain.

Evolution of mutualism increases when the ressources become scarce

Optima of adaptation of adaptation of an attribute depends of itís importance in the environment

Heterogeneity of resource level can cause complex indirect as well as direct effect on food webs.

Inderect effects may be as important as direct interactions in food web and may contribute to nwtwork mutualism

trophic levels become saturated according to diversity Z and a rate given by the differenciation of the niche

Effects of resource heterogeneity may vary even for slightly different habitats.

Since the beginning of life on Earth, organisms have not only adapted to physical conditions but have modified the environment in ways that proven to be beneficial to life (e.g., increase O

Use of a ressource is stimulated by increasing disponibility.

Variation in plant nutritive resources for herbivores may be more important than antiherbivores compounds in plants.

Heterotrophs may control energy flow in food webs

Mature systems exploit lesser mature ones.

The effect of variation in resource quality may depend on whether the species are specialists or generalists.

An expanded approach to biodiversity should include genetic and landscape diversity, not just species diversity.

Biomass/productivity grow up in a stable environment

Ecological consequences of resources heterogeneity depend on the life history strategies of the species in assemblage.

Ecosystem development or autogenic ecological succession is 2 phase process

Stable environment allow biodiversity accumulates in mature ecosystems that enforce stability

Heterogeneity of resources or quality may foster coexistence among competing species even if the absolute resource level remains constant.

Carrying capacity is a 2 dimensional involving number of users and intensity of per capita use

An unpredictable variability of major extent of the environment selects prolific species

Resource heterogeneity can affect predator-mediated effects on community structure.

Input management is the only way to deal with nonpoint pollution

Previous generations influence stability or fluctuations of a population

When resources are heterogeneous, competition may be important only at times of low resources.

An expenditure of energy is always requiered to produce or maintain an energy flow or a material cycle.

Different species that coexiste indefinetedly in the same environment must have different niches

Resource heterogeneity can affect local or short-term variation in the distribution and abundance of species while having no effect on regional or long-term variation.

There is an urgen need to bridge the gaps between human-made and natural-life-support goods and services and between no sustainable short-term and sustainable long-term management.

Any specy slightly differe from others in itsí needs from the environment or variations according space, time, that conditioned series of species that can substitute.

Temporal heterogeneity of resources may contribute to cyclic fluctuations in food webs.

transition costs are always associated with major changes in nature and in human affairs.

Spatial distribution of organisms play a role in efficiency with which energy is used by individuals or population


A parasite-host model for man and the biosphere is a basis for turning from exploiting the earth to taking care of it

Source: nfm

Source: nfm

Source: nfm

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