Organismal Biology





Key Concepts




Chapter  17 - Ecology









Ecology is a science of defined boundaries.  Whether looking at a population (collection of all individuals), a community (collection of “all” species), or an ecosystem (collection of “all” factors, biological, chemical, and physical), just the definitions make it clear that boundaries need to be set.  When looking into an ecosystem, how much territory is included – where are the physical boundaries?  How many factors are looked at – as many as you can measure, or just the ones that you believe are relevant to your study?  The same considerations apply to which species get included in the studied community.  Since it isn’t possible to include, or even to know, them all, much will be excluded and parameters must be set.  In many cases, there will be a loosely-established, accepted definition of the various levels.

Physical / chemical factors will include such things as temperature, available water and nutrients, and usable energy.  Ecosystems have tolerance limits – ranges of these factors within which the ecosystem can persist; there are of course optimum levels for each factor, which may or may not be known.  As systems interact with the global rise in greenhouse gases, it has become critical to try to determine how much those effects will perturb their biological aspects.  

Niches are “roles” played by species with an ecosystem. There are often broadly described roles, such as ground-cover plants, canopy-producing plants, browsers, climbers, etc.  Not every niche is available in every ecosystem – niches may have tolerance limits as well. Some ecosystems, especially physically isolated ones, may have available niches with no occupying species.   Ecospecies is a term applied to different species filling the same niche (again, with defined parameters) in different ecosystems.  Some niches are defined as relationships, such as predator and prey, parasite and host.  Symbiosis implies a strong reliance between two species, which may benefit both, mutualism, or just one, commensalism.

Food webs are an attempt to track the flow, usually of energy, through an ecosystem.  At the base of the web is primary production from the synthesizers, usually those that convert frequencies of light to chemical bond energy, through photosynthesis, but in some rare ecosystems such as ocean-floor hydrothermal vents, where chemosynthesis essentially uses heat to help form chemical bonds.  Of course, the available energy is not all converted – in fact, the efficiency of the production level is pretty low.  In an ecosystem, net primary production, where the energy usage of the producers themselves is factored out as not part of the web, is a common calculation.  This first level is the trickiest – for a long time, the need for producers in every known food web stymied the production of theories about the beginnings of Life.  This was known as the plant problem, since only photosynthetic producers were known.  The discovery of primordial soup (“food” established from organic space dust components) and chemosynthesis helped toward working out the first steps.  Consumers depend upon the base – from there up, energy shifts from chemical bond to chemical bond.  At every conversion, however, some if the energy is lost as random particle motion – heat, basically, according with the Second Law of Thermodynamics, also known as the Law of Entropy.  This means that less and less energy is available with every step “up” in the levels. The “leftover” chemical bonds in dead things and incompletely-processed wastes are used by the decomposers, providing the raw materials for the producers to rebuild with.






Types of Ecosystems



On Earth, there are generalized, defined types of ecosystems, called biomes.  Some are on land, the terrestrial biomes, and there are also marine biomes, of the larger contiguous salt-water masses, and freshwater biomes.  Inland salt water and a few others are biomes that don’t easily fit into the larger categories.

The terrestrial biomes include the Tropical Rainforest (also Seasonal Tropical Forest), Temperate Deciduous Forest, Northern Coniferous Forest, Tropical Grassland (Savannah), Temperate Grassland (much of which is today converted to farmland), Desert (which have hot and cool varieties), and Tundra.

The marine biomes include the Open Ocean (also called pelagic), the Upwelling Zones (where nutrients are brought up to the surface by currents), the Continental Shelf, and Estuaries, where the marine water and freshwater mix.

The freshwater biomes include Rivers and Streams, Ponds and Lakes, and Wetlands (which includes Marshes and Bogs).


















Click on term to go to it in the text.
Terms are in the order they appear.



Tolerance Limits
Food Webs
Ecosystem Types





Organismal Biology

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