Ecosystems

A community and its physical environment is called its Ecosystem. An ecosystem is a biological environment consisting of all the organisms living in a particular area, as well as all the non-living (abiotic), physical components of the environment with which the organisms interact, such as air, soil, water and sunlight.

What is an eco system?

Ecosystem is an open system with inputs, internal transfers and outputs of energy and nutrients. Sunlight is the initial energy source for nearly all ecosystems. 

Types of Ecosystem

The different types of ecosystems are

(i) Natural Ecosystem

(a) Terrestrial ecosystem

(b) Aquatic ecosystem

(c) Lentic (lake, pond or swamp)

(d) Lotic (river, stream or spring)

(ii) Artificial Ecosystems

ecological community

The species that live and interact in an area constitute an ecological community. Ecological communities are loose assemblages of organisms.

The organisms in a community can be divided into trophic levels (the position of an organism in food chain) based on the source of their energy.

Primary producers get their energy from sunlight. Herbivores that get their energy by eating primary producers are primary consumers; organisms that get their energy by eating herbivores are secondary consumers; and so on.

 A sequence of interactions in which a plant is eaten by a herbivore, which in turn eaten by a secondary consumer, and so on, is known as food chain. Food chains are usually interconnected to make a food web because most species  in a community eat and are eaten by more than one species. Most communities have three to five trophic levels. 

Energy and biomass decreases as it flows from lower to higher trophic levels and thus can be represented in the form of pyramid. Most of the energy ingested by organisms that is converted to biomass is eventually consumed by decomposers.

Ecological pyramids An important feature of energy flow is that most of the energy going from one trophic level to the next, in a food chain and food web, dissipates into the environment as a result of the second law of thermodynamics. Ecological pyramids often graphically represent the relative energy values of each trophic level. There are three main types of pyramids— a pyramid of numbers, a pyramid of biomass and a pyramid of energy.

Ecosystem productivity The gross primary productivity (GPP) of an ecosystem is the rate at which energy is captured during photosynthesis in a given period of time. In addition, a plant respires to provide energy for its own use; this acts as a drain on photosynthesis. Energy in plant tissues after cellular respiration has occurred is net primary productivity (NPP). 

Both GPP and NPP are expressed as energy per unit area per unit time. Humans consume (32%) far more of earth’s resources than any other of animal species. If we want our planet to operate sustainably, we must share terrestrial photosynthetic product with other organisms.

In environments that show variations in salinity, temperature and other environmental conditions, food webs tend to have short chains. In stable environments, such as parts of the deep ocean, food chains are longer. In addition to energy inputs, primary productivity and ecosystem structure require a cycling of nutrients. Water and minerals move slowly through the physical environment, rapidly through organisms, and back to the environment in biogeochemical cycles. 

Water moves through a hydrological cycle. In land ecosystems, plants stabilise soil and minimise nutrient loss during the cycle as runoff. In atmospheric cycles, a nutrient prevails mainly in gaseous form (such as carbon, in carbon dioxide). 

In the carbon cycle, carbon dioxide is the main gas in the atmosphere. The ocean is carbon’s main reservoir. Burning of fossil fuels, logging and conversion of natural ecosystems for farming disrupt the global carbon budget and may be responsible for global warming.

Nitrogen is a limiting factor in the total net productivity of ecosystem on land. Gaseous nitrogen is abundant in the atmosphere. Nitrogen–fixing bacteria convert N2 to ammonia and nitrates, which producers take up.

Mycorrhizae and root nodules, two symbiotic interactions, enhance the nitrogen uptake. Sedimentary cycles interact with the hydrological cycle to move mineral nutrients to and from ecosystems.

Certain human activities are depleting minerals from ecosystems, as when weathered soil of tropical forests is cleared for agriculture.

Some human activities are accelerating the process of eutrophication. They are adding nutrients such as nitrates and phosphates to aquatic ecosystems.

This promotes growth and decay of destructive algal blooms. The decomposition of these plants leads to the depletion of oxygen in the water, which threatens fish and other animal populations.

ECOLOGY

Ecology is the scientific study of the rich and varied interactions between organisms and their abiotic environment. In ecological studies, the environment encompasses both abiotic (such as water, mineral nutrients,light, temperature) and biotic factors (living organism).  

Interactions between organisms and their environment is a two way process in which organisms influence and are influenced by their environment. There are many reasons to care about ecology. Our lives are enriched by the fascinating interactions between the organisms. 

Watching a butterfly visiting a flower and bringing about pollination is worth seeing. Beyond simple curiosity, information from ecological sciences is needed to solve many practical problems. An understanding of ecology allows us to grow food, control pests and diseases and deal with natural disasters such as flood, drought and earthquake.

BRANCHES OF ECOLOGY

Ecology and Evolution

1. Ecology and Evolution

Ecology and evolution are considered sister disciplines of the life sciences.Natural selection, life history, development, adaptation, populations and inheritance are examples of concepts that correlate equally in to ecological and evolutionary theory.

(a) Behavioural Ecology 

This is the study of animal behavior in the natural environment, also known as ethology. Behavioural ecology also deals with ecological and evolutionary changes, because of the interactions among the organisms. 

Adaptation is the central unifying concept in behavioural ecology.The behaviours evolve and become adapted to the ecosystem because they are subject to the forces of natural selection. 

Consider the edible beetles that direct sprays of poisonous chemicals at their attacker. Predator-prey interactions are an introductory concept in behavioral ecology.

(b) Social Ecology 

This is concerned with the relationships between organisms and their environment. Social ecological behaviours are notable in the social insects, slime molds, social spiders and human society. Individuals that belong to a social group have to face competition for food, mates and other limited resources. They face diseases and parasitic infections. 

A special kind of behavior exists between many groups known as altruism (Behavior that harms the individual who performs it but benefits other individuals).Parenting is also altruism, where the children are benefited. Altruism is extreme among some insect societies, such as honeybee and termite colonies.Groups that are predominantly altruists beat groups that are predominantly selfish.

(c) Co-evolution 

Populations of the other species are part of any organism’s environment. The population having prey-predator interactions exert pressure on each other. If prey evolves, the predator counter develops mechanisms to catch the prey. 

This is the basis of co-evolution in populations. There are many examples where interacting organisms evolve together e.g., Lithops (flowering stone) growing in the open area develop stone like pattern and color to hide from herbivores.

(d) Bio-geography 

This is the comparative study of the geographic distribution of organisms and the corresponding evolution of their traits in space and time. Bio-geographical processes that result in the natural splittingof species explain modern distribution of the earth’s biota (flora and fauna).

2. Molecular Ecology

Molecular ecology is a relatively new field where the important relationship between ecology and genetic inheritance is analysed using modern techniques of molecular analysis. 

Molecular ecological research became more feasible with the development of rapid and accessible genetic technologies, such as the polymerase chain reaction (PCR). The DNA of different organisms is compared and their evolutionary relationships are analysed.

3. Human Ecology

Human ecology is the interdisciplinary investigation into the ecology of our species. It is the discipline that inquires into the patterns and process of interaction of humans with their environment. It studies human values, life styles, resource use, waste etc. The human species is not an external disturbance. It is the keystone species within the system.

4. Landscape Ecology

Landscape ecology is a sub discipline of ecology that studies ecological  processes that operate over large areas. A landscape ecologist examines the connections among ecosystem found in a particular region.

THE HIERARCHICAL STRUCTURE OF ECOLOGICAL SYSTEM

The different levels of biological organisation include:

The characteristics of molecules and their organization in a cell up to speciation are discussed in the biology section. This chapter includes interaction at population and the levels above it.

Population Ecology

Population is a group of organisms of the same species that live in the same area at the same time. Certain principles govern the growth and sustainability of populations over time. Ecological interactions start within and between populations.

Each population has its own gene pool and range of traits. It also has a characteristic size, density, distribution pattern and age structure.Environmental conditions and species interactions influence thesecharacteristics. Population size is generally an outcome of births, deaths, immigration and emigration. As long as the per capita birth rate remains evenslightly above per capita death rate, a population can grow exponentially.

Resources in short supply put limits on the growth of population. The maximum number of individuals of a population that can be sustained indefinitely by the resources in a given environment is referred as carrying capacity. The number may rise or fall with changes in resource availability.

The size of a low-density population may increase gradually; go through a rapid growth phase, then levels off once the carrying capacity for the population is reached. The limiting factors vary in their relative effects and vary over time, so, population size also changes over time. Limiting factor such as competition for resources, disease and predation are densitydependent.

Density-independent factors, such as weather on the rampage,tend to increase the death rate or decrease the birth rate more or less independently of population density.

Community Ecology

Community is a natural association that consists of all populations of different species that live and interact within an area at the same time. These interactions in turn influence the structure of communities.The many ways in which organisms interact with one another are as following:

Symbiosis 

Any intimate relationship or association between members of two or more species. Symbiosis is the result of co-evolution. Flowering plants and their pollinators have a symbiotic relationship.

Parasitism: 

Interactions in which one organism is harmed, but the other is benefited. A parasite may weaken its host; it rarely kills its host. More than 100 parasites live in or on the human species. When it causes a disease and sometimes the death of host, it is known as pathogen.Crown gall disease, caused by a bacterium, occurs in many plants.

Mutualism: 

Interactions in which both participants are benefited. The interdependent association between nitrogen fixing bacteria of the genus Rhizobium and legume, is an example. Another example is the association between reef building coral animals and microscopic algae.The symbiotic alga is called zooxanthellae. Mycorrhizae is such an association between fungi and roots of 80% plants.

Commensalism: 

Interactions in which one participant benefits but the other is unaffected, e.g., relationship between two insects; silverfish and army ants, relationship between a tropical tree and many epiphytes, smaller plants, such as mosses, orchids and ferns that live attached to the bark of the tree’s branches. The epiphytes anchor itself to the tree to obtain adequate light and water and not for obtaining nutrients from the tree.