Ecology – Level of Organizations
Ecology can be considered on a wide scale, moving from an individual the entire global ecosystem. However, four identifiable sub-divisions of scale are of interest. These are: organisms (individuals), populations, communities and ecosystems. At each level the subject of interest to ecologist’s changes.
Organism refers to any living individual, either unicellular or multicellular. An organism possesses certain characteristics and exhibits individuality, i.e., it is different from other members of the same species in certain respects. At organism level ecologist’s the response of individuals to their environment, -both biotic and abiotic.
The branch of ecology that is concerned with how organisms interact environments by adaptations in their morphology, physiology and behavior is called or species ecology. It involves study of distribution of organisms in relation to environment.
A population is a group of living organisms of same species that occur together one place and at one time. A population is reproductively isolated from other such groups.
It is higher level of organization than an organism. All populations have characteristic features, such as size, density, dispersion (the way the individuals of a population arranged), and demography (statistical study of population). This level has its own attributions such as gene frequency, gene flow, age distribution, population density, population pressure, etc. The branch of ecology concerned with population growth, regulation, intraspecific and interspecific competition is called population ecology. Population ecology concentrates mainly on factors that affect population size and composition.
Populations of different species that live together in the same area (habitat) is a community.
Ecologists are interested in the processes determining their composition structure Interactions within a community include predator-prey Interactions and symbiosis (commensalism, mutualism, parasitism). The ecological study at Community level is known as community ecology.
A community in certain area, together with the non-living factors with which it interacts, is called an ecosystem.
An ecosystem regulates the flow of energy derived from the sun and the cycling of essential elements on which the lives of its constituent plants, animals and other organisms depend. Individual organisms live in a small part of ecosystem known as their habitat. How an organism lives as well as where it lives is its niche.
The study of ecosystem is termed ecosystem ecology.
Biosphere and Biome
The part of the earth containing living organisms is called the biosphere. It is the sum of communities and ecosystems found on the planet Earth. It includes the both Living and non-living components. The biosphere extends from the bottom of the oceans to atmosphere, and amounts to a relatively narrow belt around the Earth.
A major life zone characterized by the dominant plant life, and climatic and soil conditions is called a biome. It is the largest ecological unit. The examples include rain forests, coniferous forests, grasslands, etc. Study of biomes from ecological view is called biome ecology.
Major Biomes of the World
A brief introduction to world’s major terrestrial and aquatic biomes is as follows:
Grasslands occur where rainfall ranges between 250 and 1200 mm (10-60 inches) There are two major types of grassland depending on the temperature: tropical grassland (savannah) and temperate grassland (steppe, prairie and pampas). Grassland soils receive a large amount of organic matter and are very rich. Grassland communities are dominated by grass species but include trees also such as Acacia. In temperate grasslands, the broadleaved flowering perennials are found. The grasslands support large populations of grazing and browsing animals and large mammalian carnivores. Intensive grazing can lead to the destruction of grassland communities, soil erosion and desertification. Grasslands occupy vast areas in North America, northern Europe and Africa.
The arctic tundra forms a circumpolar band between Arctic Ocean and polar ice caps to the north and the coniferous forests to the south but ecologically similar regions found above the tree line on high mountains are called alpine tundra. The temperature is freezing, precipitation is low and occurs mainly as snow, and below a certain depth the ground remains permanently frozen forming permafrost. Tundra has low productivity but is rich in species contents, Animals of tundra include reindeers and other migrants, Tundra vegetation and soils are very slow to recover from disturbance.
Forest type is dependent on rainfall and temperature. It can be divided into:
Boreal Forests: These forests develop in cold climate and high elevation, are characterized by long winters with high precipitation in the winter and more rain in summer. The soils are Podolsk. These are dominated by coniferous tree species. These forest support herbivorous mammals and predatory species.
Temperate Forests: Temperate forests occur at lower latitudes where there is sufficient rainfall. The soils in these forests are well developed and rich. They consist of broad-leaves, deciduous species and their vegetation exhibit layered structure. Birds and small mammals are common animals of these forests.
Tropical Forests: Tropical forests are present near the equator and characterized by heavy rainfall and warm climate. The soils are leached, acidified and poor in nutrients. These forests contain a great diversity of tall trees, canopy forming species, shade-tolerant plants, epiphytes and lianas. They support a great amount of animal diversity as well. The clearing of rains forests result in biodiversity loss, depletes the soil and may lead to erosion.
- Deserts, Semi-deserts and Shrub Lands: Hot deserts are found around latitudes 30 °N and 30 ‘S. The main, desert regions are in northern and south-western Africa (the Sahara and Namib deserts), parts of the Middle East and Asia (Gobi), Australia, the Great Basin and southwestern United States, and northern Mexico. In less arid regions semi-deserts occur while temperate shrub land is found around the shores of Mediterranean Sea, where it is known as marquis and southern California, where it is called chaparral.
Deserts have less than 50 mm of annual rainfall, hot days and cold nights. Soils are poor in nutrients, thin and freely drained. Hot desert vegetation includes thorny shrubs ephemeral annuals, and succulents. Cool deserts have dense shrub Vegetation. Chaparral contains species with small, thick, drought-resistant leaves and the community is maintained and regulated by fire. The most common desert animals are reptiles and insects, however some mammals including rodents and camels are also found.
The primary saltwater biomes are:
Open Oceans: Open oceans cover of the world’s surface. Although these are most extensive biome but are poor in nutrients and unproductive. The surface photic zone where light can penetrate contains phytoplankton and Zooplankton. Below it carnivorous and detritivorous animals occur, feeding on material from the communities above. Light levels and productivity decreases with depth. Bottom or benthic fauna sparse
Continental Shelves: These occur around coasts to a depth of about 200 m and include coral reefs. The continental shelves support some of the most productive marine ecosystems such as kelp forests and fisheries. Coral reef communities occur in warm and very shallow water. Corals are colonial which structurally complex calcareous skeletons on which algae, invertebrates and herbivorous and carnivorous fishes live.
The intertidal Zone: The intertidal zone occurs at land margins and includes sandy beaches and rocky shores. Intertidal rocky shores are dominated by algae. Zonation of algal and animal communities with exposure and distance from the sea occurs. Sandy beaches provide an unstable, abrasive and nutrient-poor substrate colonized by filter-feeding burrowing animals which are themselves food for wading birds.
Salt Marsh, Mudflats and Mangroves: Salt marsh, mudflats and mangroves develop where there is less tidal influence. Salt marsh occurs in sheltered areas protected from wave action and is dominated by salt-tolerant higher plants. Mudflats and estuarine silts are fine substrates rich in organic matter and low in oxygen. Their higher invertebrate’s density supports fish and bird populations. Mangrove forests replace salt marshes in tropical regions and support a rich fauna.
Fresh water biomes include lakes, rivers, bogs, marshes and swamps. These systems are fed by water and nutrient leaching from the surrounding catchment areas.
Streams and Rivers: The physical characteristics of streams and rivers alter along their length. They change from being small near their source to wider and slower at their mouth. Plant and animal diversity and production tends to highest in middle regions where flow rates and substrate allow the growth of macrophytes.
Lakes and Ponds: Lakes have very little or no current, allowing the water body to acquire vertical stratification with illuminated, warm water at the surface and dark, cold water below. Lakes can be nutrient rich (eutrophic) or nutrient poor (oligotrophic).