At each step, a large part of the energy is lost as heat, and only a small part goes to the eater. For example, some bacteria use the latter as an energy source, and these bacteria are eaten by some nematodes. An ecological rule of thumb is that only 10% of the energy transferred from one trophic level can be accumulated in the next trophic level.
No matter how productive an ecosystem, any food chain rarely exceeds four links because length is limited by the inefficiency of energy transfer. Ecological pyramids are of three categories: a) of numbers, b) of biomass and c) of energy. a) Pyramids of numbers: Pyramids of numbers represent the relationships between the numbers of primary producers and consumers of different orders in an ecosystem. Green plants regulate solar energy through the process of photosynthesis and fixation, and the transfer of energy in an ecosystem is governed by the laws of thermodynamics.
The fixation, loss and storage of energy are governed by two laws of thermodynamics. However, the use of plant biomass by herbivores involves the conversion of energy in the plant to energy in the form of animal biomass.
Energy Flow in an Ecosystem
When energy is transferred from one trophic level to another trophic level, a large part of that energy is lost as heat that is no longer transferable. Certainly, a wide range exists in the efficiency of conversion (assimilation and production efficiency) among different nutritional groups. Production efficiency in photosynthetic organisms (Net production/solar radiation) is low, ranging from 0.34% in some phytoplankton to 0.8 to 0.9% in grassland vegetation.
Due to high maintenance and respiration costs, homeotherms have low production efficiency compared to poikilotherms. The ratio of phytoplankton to zooplankton production in open freshwater ecosystems is about 7.1:1, and the ratio of herbivorous zooplankton production to carnivorous zooplankton production is 2.1:1. The efficiency is lower in the benthic (bottom-dwelling organisms in an aquatic system) community - 2.2 for herbivores and 0.3 for carnivores.
Biogeochemical cycles
State of Dynamic Equilibrium and System Homeostasis
At each level in the trophic structure, any fluctuation in the input rate is counteracted by an equal and opposite attraction of the output rates. Ecotones: The zone of vegetation that separates two different types of communities is called ecotone or tension zone. The development of a community is intimately related to the prevailing environment and as such difference in community structure and physiognomy reflects a difference in their environments such as the moisture condition, biotic influence or any other factors.
Therefore, an ecotone is a region where the influence of two different environmental patterns work together, and therefore the vegetation of ecotones is somewhat specialized. Usually in ecotones the diversity of species is greater than in any of the adjacent communities. The phenomenon of increased variety and of plants at community intersections is called the edge effect and is essentially due to a wide range of suitable environmental conditions.
Ecotypes: The fact that two individuals belong to the same species does not guarantee that they will respond in the same way to certain ecological factors such as temperature or light. Populations with genetically based differences of ecological importance are called ecotypes, although the term now seems to be used mainly to refer to plants that exhibit striking morphological adaptations to habitat. In contrast to such hereditary variants, there are a number of cases where populations exhibit different morphological appearance in different habitats, i.e. the variations are not genetically fixed and these are called ecophenes or ecads.
ECOSYSTEM TYPES
- FOREST ECOSYSTEMS
- GRASSLAND AND SAVANNAH ECOSYSTEMS
- DESERTS, SEMI-DESERTS AND SHRUBLAND ECOSYSTEM
- TUNDRA ECOSYSTEMS
- MAN – MADE ECOSYSTEMS
Temperate forests are mainly composed of broad-leaved, deciduous species, and the complex layered structure of the vegetation leads to high primary production. Grasslands receive a large amount of organic matter and are very rich, making them suitable for growing arable crops such as corn and wheat. Mostly dominated by grass species, but often includes trees, such as Acacia, which are characteristic of the African savanna.
The uniformity of the vegetation structure, the lack of trees and the short growing season limit the diversity of birds and amphibians. The temperate shrub forms around the scrubland of the Mediterranean, where it is known as Maquis, and in Southern California where it is called Chaparral. Hot desert vegetation includes thorny shrubs, ungulates, subterranean fungi, and bulbs and succulents such as cacti.
The vegetation consists of low-growing mats – and hump-forming plants such as e.g. reeds (Carex spp.), lichens, mosses, grasses and dwarf willows (Salix spp.) etc. The long day length in summer, combined with higher temperatures, allows primary productivity at this time of the year to be an order of magnitude higher than in winter. Permanent residents such as reindeer are on the move and span large areas to find enough food.
Migratory birds such as geese, sandpipers, ducks and other waterfowl breed on the tundra in the summer and feed on the vegetation and new insects. Among man-made ecosystems, agroecosystems are widespread in all parts of the world in various forms. The biotic components of such ecosystems vary with agro-climatic conditions and the social makeup of the people who practice it.
Some of the agroecosystems are highly developed; exist by modern scientific input as intensive cultivation practices, while some are still on traditional forms, usually practiced for subsistence needs.
Ecosystem Degradation
Expansion of cultivation on hill slopes: Outside the humid tropical zone, in most third world countries, large forests are common on hill tops and slopes. However, the ever-increasing human population and their growing needs have forced many to move to the mountain slopes to farm. In addition, more and more slopes are cleared of plants and terraces are created, causing the top soil to be washed away into the streams and rivers.
In fact, it is the poor fertility of the soil that has given rise to such an agricultural pattern. The soil is not able to regain its fertility until it is put to use again. As crops fail, more and more land is cleared of forests to be subjected to similar overexploitation.
This practice is prominent in many tropical countries in Asia and Africa, and in India it is widely practiced by the tribal peoples of the northeastern hill-slope region (Ramakrishnan, 1992). Cattle farming has done great damage to the tropical forest in South and Central America. In the case of lightly wooded forests, the pressure is higher compared to the dense forests.
Timber harvesting: Logging and felling of forest trees for obtaining timber is a major cause of the degradation of forest ecosystems in third world countries. In many third world countries, logging has been observed to lead to a permanent loss of forest cover. Pollutants can be added directly to the air (primary pollutants), or they can be created in the air (secondary pollutants) from other pollutants under the influence of electromagnetic radiation from the sun.
Lead, a toxic metal, is added to the atmosphere by car exhausts and exhaust from some industrial facilities.
AQUATIC ECOSYSTEMS
Freshwater ecosystems
They also differ in their height from their height, from their origin in the upper land of the sea. In general, as the mouth of a river is approached: .. i) The speed of water flow decreases, the water becomes less turbulent and oxygen level drops. ii) The volume of water increases as the river moves through its catchment area. iii) The energy of the river decreases, suspended material is deposited and river bed is composed of finer particles and finally silt. iv). The river bed becomes less steep because the greater value of water erodes a wider channel. v) Human influences are increasing.
Streams high up in the catchment that are unpolluted will support caddisfly (Trichoptera) and blackfly (Simulium spp.) larvae that feed on fine organic particles. The water will be too turbulent and nutrient-poor for anything except water mosses, liverworts and algae. Plankton communities consisting of algae, photosynthetic bacteria, crustaceans, and rotifers may develop further downstream where the amount of moving water increases and the current decreases.
WETLAND ECOSYSTEMS
Typically, fens occur at the base of slopes in the path of mineral-charged groundwater, resulting in a nearly neutral to slightly alkaline pH. Marsh milkweed, marsh bellflower, calm's lobelia, grass – or – Parnassus, dwarf birch etc. are common plants. Dogwoods, willows, buttonbushes and birches are the most common shrub species in swamps. e) Swamp.
Forest swamp – with waterlogged soil, often covered by 0.3 meters of water, found along sluggish streams, flat uplands and shallow lake basins.
MARINE or OCEANIC ECOSYSTEMS
Deep marshes are bordered by emergent vegetation such as pond grasses, naiads, wild celery and water lilies. Plants commonly found are tamarisk, arborvitae, spruce, red maple, silver maple, water oak, cup oak, swamp tupelo, black gum, cypress, etc. Below the photic zone, carnivores and herbivores occur, feeding on material from the above communities.
Continental shelves support some of the most productive marine ecosystems, especially in borehole areas where currents bring nutrients from the depths to surface waters. Sandy beaches provide an unstable, abrasive, and nutrient-poor substrate that is home to filter-feeding animals that are themselves food for wading birds. Corals are colonial animals that produce structurally complex calcareous skeletons on which algae, invertebrates and carnivorous fish live.
ESTUARIANE ECOSYSTEM
Three hundred thermal vent species have been described, from sulfur bacteria to limpets, tube worms and fish are unique to this habitat. The dominant plants have shallow, widely spread roots that emerge from the trunk above ground and act as props. Many species have root extensions that take up oxygen to the roots, which are known as pneumatophores.
These are fish that live in burrows in the mud and are able to crawl around on top of it like amphibians.
