CHAPTER 11 ECOSYSTEM
LEVELS OF ORGANISATION
The biosphere is where all life occurs on Earth. The biosphere is made of three parts, called the lithosphere, atmosphere, and hydrosphere. The atmosphere is the air that living organisms use for respiration, and which supports life up to 2,000 meters above the planet’s surface. The hydrosphere is the aquatic portion of the planet, all of which supports life. The lithosphere is the landmass, excluding Earth’s mantle and core, which do not support life.
APPROACHES TO ECOLOGY
1-Autoecology
a is the study of an individual organism and its relationship with the environment. It may be called the ecology of individuals. In autecology, individuals are the units of study. Individuals are studied for details of their distribution, morphology, the pattern of the life cycle, and the environmental factors which influence these.
2-Synecology
is the study of groups of organisms together regarding their environment. Here, groups of organisms rather than the individual constitute the units of study. Since organisms live in nature as groups and not as isolated individuals, synecology is believed to reflect the natural conditions better than autecology. Synecology also takes into consideration the interactions between organisms.
Succession is a series of progressive changes in the composition of an ecological community over time.
The climax of succession is a relatively stable community that is in equilibrium with environmental conditions.
3- Ecosystem Approach
In this approach, we study the living organisms and their non-living environment in terms of their interaction, flow of energy, and cycling of matters.
4- Habitat Approach
An estuary is a partially enclosed, coastal water body where freshwater from rivers and streams mixes with saltwater from the ocean. Estuaries, and their surrounding lands, are places of transition from land to sea.
Microhabitats are the small-scale physical requirements of a particular organism or a community of organisms. For example, a decomposing log in a forest supports a distinct population of decomposers, plants, and invertebrates, but the forest houses the log itself.
5- Evolutionary Approach
Evolutionary ecology lies at the intersection of ecology and evolutionary biology. It approaches the study of ecology in a way that explicitly considers the evolutionary histories of species and the interactions between them.
6- Historical Approach
Ecological succession
Ecological succession is the gradual process by which ecosystems change and develop over time. Nothing remains the same and habitats are constantly changing.
Climax
A climax community is the final stage of succession, remaining relatively unchanged until destroyed by an event such as fire or human interference.
11.3 The Ecosystem
An ecosystem consists of a community of organisms together with their physical environment. ·
11.3.1 Components of an Ecosystem
1- Abiotic Components (material & energy)
a- Climatic
(i) Light
Light intensity refers to the strength or amount of light produced by a specific source.
Light intensity influences the manufacture of plant food, stem length, leaf color and flowering. Generally speaking, plants grown in low light tend to be spindly with light green leaves.
Light duration is the photoperiod, or the number of continuous hours of light in each 24-hour period. Photoperiod regulates flowering in many greenhouse crops, and that is why we have photoperiodic response categories such as short-day plants and long-day plants.
Biological rhythm, periodic biological fluctuation in an organism that corresponds to, and is in response to, periodic environmental change.
The generalized cycle of annual life-history stages of New Zealand bar-tailed godwits. A typical adult male routine is shown below. Large arrows indicate major migratory flights.
Light quality, also called spectral composition and spectral energy distribution (SED), refers to the composition of light as to wavelengths that are effective in photosynthesis and other plant growth and development processes.
(ii) Temperature
Temperature has the single most important influence on the distribution of organisms because it determines the physical state of water. Most organisms cannot live in conditions in which the temperature remains below 0 °C or above 45 °C for any length of time.
(iii) Water
Living organisms need water to survive. Many scientists even believe that if any extra-terrestrial exists, water must be present in their environments. All oxygen-dependent organisms need water to aid in the respiration process. Some organisms, such as fish, can only breathe in water. Other organisms require water to break down food molecules or generate energy during the respiration process. Water also helps many organisms regulate metabolism and dissolves compounds going into or out of the body.
(iv) Atmosphere and wind
Wind affects plant growth, reproduction, distribution, death, and ultimately plant evolution. Some of the effects depend on the air boundary layers next to the aerial parts of a plant, across which gas and heat exchanges with the environment occur. Others relate to the mechanical deformation of the plant by the frictional drag of the moving air. Wind also disperses many types of particles (pollen, plant propagules, disease organisms) as well as moving gas molecules (CO2, pollutants). Because of the many effects of wind, ranging from obvious crop or forest destruction during gales to subtle effects on a leaf boundary layer, the literature available is vast and covers many disciplines.
(v) Fire
Fire can lead to changes in ecosystem processes at landscape scales. The reduction in biomass caused by burning and changes in soil properties lead to temporary hydrological changes in patterns of stream flow. Severe fires can lead to increased soil erosion.
Some fungi are found only in burnt areas, or at least have strong preferences for burnt areas. One effect of fire (or heat in general) is that it stimulates the germination of the spores of a number of fungi, including species in the genus Anthracobia. Interestingly, the heat of a fire may also induce the germination of the spores of various dung fungi that are lying dormant in the soil.
b- Topographic Factors
(i) Altitude
Elevation may affect the type and amount of sunlight that plants receive, the amount of water that plants can absorb and the nutrients that are available in the soil. As a result, certain plants grow very well in high elevations, whereas others can only grow in middle or lower elevations.
(ii) Slope
slope also brings about variations in soil water contents. The steepness of the slope determines the rapidity with which water flows away from the surface, the degree of wetness of the soil surface, the intensity with which the sun rays can heat the soil surface, and the denseness and height up to which vegetation can occur. The steepness of the slope also affects the amount of humus and other degenerating organic matter in the soil. On very steep slopes most of the humus is carried away along with rainwater
(iii) Exposure
Exposure to the light and wind also effects the vegetation.
c- Edaphic Factors (influenced by soil)
Weathering is the breaking down or dissolving of rocks and minerals on Earths surface. Once a rock has been broken down, a process called erosion transports the bits of rock and minerals away. Water, acids, salt, plants, animals, and changes in temperature are all agents of weathering and erosion.
2- Biotic Components
(i) Producer
(ii) Consumer
(iii) Decomposer
Saprotroph, also called saprophyte or saprobe, organism that feeds on nonliving organic matter known as detritus at a microscopic level.
11.4 Biogeochemical Cycles
The ways in which an element—or compound such as water—moves between its various living and nonliving forms and locations in the biosphere is called a biogeochemical cycle. Biogeochemical cycles important to living organisms include the water, carbon, nitrogen, phosphorus, and sulfur cycles.
11.4.1 Nitrogen Cycle
Nitrogen Cycle is a biogeochemical process through which nitrogen is converted into many forms, consecutively passing from the atmosphere to the soil to the organism and back into the atmosphere. It involves several processes such as nitrogen fixation, nitrification, denitrification, decay and putrefaction.
Ammonification.
When an organism excretes waste or dies, the nitrogen in its tissues is in the form of organic nitrogen (e.g. amino acids, DNA). Various fungi and prokaryotes then decompose the tissue and release inorganic nitrogen back into the ecosystem as ammonia in the process known as ammonification.
Positive Interaction
Lichen
A lichen is an organism that results from a mutualistic relationship between a fungus and a photosynthetic organism. The other organism is usually a cyanobacterium or green alga. The fungus grows around the bacterial or algal cells.
The lichen fungus provides its partner(s) a benefit (protection) and gains nutrients in return.
Negative Interaction
When two organisms compete or fight for the same limited resource such as food, shelter, a mate, or sunlight, there is usually a winner and a loser (+ -), but if the competitors fight literally to the death and kill each other, the interaction has become negative for both (- -).
An intraspecific interaction/ association occurs within a species (e.g., two bull elephant seals competing for a harem of females or two English ivy plants competing for space and sunlight), and an interspecific interaction/ association occurs between members of different species (e.g., when two different species of corals compete for space and sunlight on a coral reef by trying to outgrow each other).
1- Parasitism
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