Basics of Ecology and Environment:

Chapter 1: Basic Concepts of Ecology:

Concept of Ecosystem

Principles of Ecosystem

Types of Ecosystem

Concept of Biome

Hierarchy

1. Population Ecology

Density and Patterns of Age Structure.

Survivorship curve

Growth Pattern

a) Sigmoid curve

b) J-curve

2. Community Ecology

Niche

Guild

Ecotone and Edge effect

Shannon Index

Keystone Species

3. Ecosystem Ecology

Energy Flow

Ecological Succession

Climax

Edge Effect

Ecological Pyramid

The Law of 10%

Biogeochemical Cycles

Ecology.

Ecology is the scientific study of the relationships that living organisms have with each other and with their natural environment.

Therefore, Ecology becomes an interdisciplinary field that includes biology and Earth science. The word ecology was coined in 1866

by the German scientist Ernst Haeckel.

Ecology as a science seeks to explain:

Life processes and adaptations

Distribution and abundance of organisms

The movement of materials and energy through living communities

The successional development of ecosystems, and

The abundance and distribution of biodiversity in the context of the environment.

Besides , there are many practical applications of ecology in natural resource management , city planning , community health,

economics, basic and applied science, and human social interaction .

Ecosystem: An ecosystem is a fundamental functional unit occupying spatial dimension of earth space ship characterised by total assemblage of

biotic community and abiotic components and their mutual interactions within a given time unit. The term Ecosystem was first

coined by A.G. Tansley in 1935 and according to him, the ecosystem is comprised of two major parts i.e. biome( the whole complex

of plants and animals of a particular spatial unit) and habitat( physical environment) .

In fact the concept of ecosystem can be realised more precisely in terms of the basic properties of ecosystem. These are:

An ecosystem is composed of three basic components such as: energy, biotic components and abiotic

components.

It occupies certain well defined area on the earth-space ship i.e. ecosystem is having a spatial dimension.

It is also viewed in terms of time unit i.e. the concept of ecosystem is associated with temporal dimension.

An ecosystem is an open system which is characterised by continuous input and output of matter and energy.

The solar energy is the prime source of energy for an ecosystem.

It is a functional unit wherein the biotic components ( plants, animals including man and micro-organisms) and

abiotic ( physical environment ) components ( including energy component ) are intimately related to each

other through a series of large scale cyclic mechanisms such as energy flow, water cycle, biogeochemical cycles

, mineral cycles etc.

Ecosystems sustain life-supporting functions and produce natural capital through the regulation of continental

climates, global biogeochemical cycles, water filtration, soils, food, fibres, medicines, erosion control, and many

other natural features of scientific, historical, economic, or intrinsic value.

There is inbuilt self regulatory mechanism known as homeostatic mechanism in nature ecosystem. Any change

brought in the natural ecosystem is counter balanced by this mechanism and ecosystem and ecological stability

is re-established.

Types of Ecosystem: There are basically two types of ecosystems; Terrestrial and Aquatic. All other sub-ecosystems fall under these two.

 Terrestrial ecosystems

Terrestrial ecosystems are found everywhere apart from water bodies. They are broadly classified into:

 The Forest Ecosystem

These are the ecosystems where abundance of flora (plants) is seen and they have a large number of organisms living in relatively

small areas. Therefore, the density of life in forest ecosystems is very high. Any small change in the ecosystem can affect the whole

balance and collapse the ecosystem. You can see wonderful diversity in the fauna of these ecosystems too. They are again divided

into few types.

Tropical evergreen forest: Tropical forests which receive an average rainfall of 80 to 400 inches in a year. These forests

are marked by dense vegetation comprising of tall trees with different levels. Each level gives shelter to different kinds of

animals.

Tropical deciduous forest: Dense bushes and shrubs rule here along with broad levels of trees. This type of forests is

found in many parts of the world and large variety of flora and fauna are found here.

Temperate evergreen forest: These have very few number of trees but ferns and mosses make up for them. Trees have

spiked leaves to minimize transpiration.

Temperate deciduous forest: This forest is found in the moist temperate regions with sufficient rainfall. Winters and

summers are well defined and with trees shedding their leaves during winter.

Taiga: Situated just south of the arctic regions, Taiga is distinguished by evergreen conifers. While the temperature is

subzero for almost six months, the rest of the year it is buzzing with insects and migratory birds. 

The Desert Ecosystem

Desert ecosystems are found in regions receiving an annual rainfall of less than 25cm. They occupy around 17 percent of all land on

the planet. Due to very high temperature, intense sunlight and low water availability, flora and fauna are very poorly developed and

scarce. Vegetation is mainly bushes, shrubs, few grasses and rarely trees. Leaves and stems of these plants are modified to conserve

water. The best known desert plants are the succulents like spiny leaved cacti. Animal life includes insects, reptiles, birds, camels all

of whom are adapted to the xeric (desert) conditions.

The Grassland Ecosystem

Grasslands are found in both temperate and tropical regions of the world but the ecosystems are slightly varying. This area mainly

comprises of grasses with very little amount of shrubs and trees. Main vegetation is grasses, legumes and plants belonging to

composite family. Many grazing animals, herbivores and insectivores are found in grasslands. Two main types of grasslands

ecosystems are:

1. Savanna:  These tropical grasslands are seasonally dry with few individual trees. They support large number of grazers and

predators.

2. Prairies: This is temperate grassland. It is completely devoid of trees and large shrubs. Prairies can be categorized as tall grass,

mixed grass and short grass prairie.

 

The Mountain Ecosystem

Mountain lands provide a scattered but diverse array of habitats in which a large range of plants and animals are found. At higher

altitudes harsh environmental conditions generally prevail, and only treeless alpine vegetation is found. The animals living here

have thick fur coats prevention from cold and hibernate in winter months. Lower slopes commonly are covered by coniferous

forests.

Aquatic Ecosystems

An aquatic ecosystem is an ecosystem located in a body of water. It comprises aquatic fauna, flora and the properties of water too.

There are two types of aquatic ecosystems, Marine and freshwater.

 

The Marine Ecosystem

Marine ecosystems are the largest ecosystems with coverage of nearly 71% of the Earth's surface and containing 97% of the planet's

water. The water in Marine ecosystems has salts and minerals dissolved in them in high amounts. Different divisions of marine

ecosystems are:

Oceanic: The relatively shallow part of the ocean that lies over the continental shelf.

Profundal: Bottom or deep water.

Benthic Bottom substrates.

Inter-tidal: The area between high and low tides.

Estuaries

Salt marshes

Coral reefs

Hydrothermal vents-where chemosynthetic bacteria form the food base.

 

Many types of organisms are found in marine ecosystems including brown algae, dinoflagellates, corals, cephalopods, echinoderms,

and sharks.

 

The Freshwater Ecosystem

In contrast to the Marine ecosystem, freshwater ecosystems only cover 0.8% of the Earth's surface and contain 0.009% of its total

water. There are three basic types of freshwater ecosystems:

 

Lentic: Still or slow-moving water like pools, ponds, and lakes.

Lotic: Fast-moving water like streams and rivers.

Wetlands: Places where the soil is saturated or inundated for at least some time. 

These ecosystems are home to amphibians, reptiles and almost 41% of world’s fish species. Faster moving turbulent water typically

contains greater concentrations of dissolved oxygen, which supports greater biodiversity than the slow moving water of pools.

The hierarchy of ecological studies: The Ecological study can be carried out at various levels and the study of the ecosystem at each level is associated with various

peculiarities. The various levels of ecological studies are given below:

Biosphere : It is the highest level of the ecological study. In biosphere the sum of all living things taken in conjunction

with their environment is taken into account. In essence, where life occurs, from the upper reaches of the atmosphere to

the top few meters of soil, to the bottoms of the oceans. The earth is divided into atmosphere (air), lithosphere (earth),

hydrosphere (water), and biosphere (life).

Ecosystem : It is the next level of ecological study and is associated with the relationships of smaller groups of

organisms with each other and their environment. Since, according to Darwin's theory, organisms adapt to their

environment, they must also adapt to other organisms in that environment. We can discuss the flow of energy through an

ecosystem from photosynthetic autotrophs to herbivores to carnivores.

Community : A the community level of the ecological study the focus is upon the relationships between groups of

different species. For example, the desert communities consist of rabbits, coyotes, snakes, birds, mice and such plants as

sahuaro cactus, Ocotillo, creosote bush, etc. Community structure can be disturbed by such things as fire, human activity,

and over-population.

Populations : Ecological study at the population level focuses upon the groups of similar individuals who tend to mate

with each other in a limited geographic area. This can be as simple as a field of flowers, which is separated from another

field by a hill or other area where none of these flowers occur.

Individuals : One or more cells characterized by a unique arrangement of DNA "information". These can be unicellular or

multicellular. The multicellular individual exhibits specialization of cell types and division of labor into tissues, organs,

and organ systems.

Organ System : (in multicellular organisms). A group of cells, tissues, and organs that perform a specific major function.

For example: the cardiovascular system functions in circulation of blood.

Organ : (in multicellular organisms). A group of cells or tissues performing an overall function. For example: the heart is

an organ that pumps blood within the cardiovascular system.

Tissue : (in multicellular organisms). A group of cells performing a specific function. For example heart muscle tissue is

found in the heart and its unique contraction properties aid the heart's functioning as a pump.

Cell : The fundamental unit of living things. Each cell has some sort of hereditary material (either DNA or more rarely

RNA), energy acquiring chemicals, structures, etc. Living things, by definition, must have the metabolic chemicals plus a

nucleic acid hereditary information molecule.

Organelle : A subunit of a cell, an organelle is involved in a specific subcellular function, for example the ribosome (the

site of protein synthesis) or mitochondrion (the site of ATP generation in eukaryotes).

The Study of Ecology can be done in the following levels 1. Population Ecology

2. Community Ecology

3. Ecosystem Ecology

Population ecologyPopulation ecology studies the dynamics of species populations and how these populations interact with the environment. A

population consists of individuals of the same species that live, interact and migrate through the same niche and habitat.

Population ecology is a sub-field of ecology that deals with the dynamics of species populations and how these populations interact

with the environment. It is the study of how the population sizes of species living together in groups change over time and space.

Some of the terms associated with Population Ecology:

Term Description

Species

population

All individuals of a species.

Metapopulation A set of spatially disjunct populations, among which there is some immigration.

Population A group of conspecific individuals that is demographically, genetically, or spatially disjunct from other groups of

individuals

Aggregation A spatially clustered group of individuals

Deme A group of individuals more genetically similar to each other than to other individuals, usually with some

degree of spatial isolation as well.

Local population A group of individuals within an investigator-delimited area smaller than the geographic range of the species

and often within a population (as defined above). A local population could be a disjunct population as well.

Subpopulation An arbitrary spatially delimited subset of individuals from within a population.

Population GrowthA population is a group of individuals of the same species living in the same geographic area. The study of factors that affect growth,

stability, and decline of populations is population dynamics. All populations undergo three distinct phases of their life cycle:

1. growth

2. stability

3. decline

Population growth occurs when available resources exceed the number of individuals able to exploit them. Reproduction is rapid,

and death rates are low, producing a net increase in the population size.

Population stability is often proceeded by a "crash" since the growing population eventually outstrips its available resources.

Stability is usually the longest phase of a population's life cycle.

Decline is the decrease in the number of individuals in a population, and eventually leads to population extinction.

Factors Influencing Population Growth

Nearly all populations will tend to grow exponentially as long as there are resources available. Most populations have the potential

to expand at an exponential rate, since reproduction is generally a multiplicative process. Two of the most basic factors that affect

the rate of population growth are the birth rate, and the death rate. The intrinsic rate of increase is the birth rate minus the death

rate.

Survivorship Curve: A survivorship curve is a graph showing the number or proportion of individuals surviving at each age for a given species or group

(e.g. males/females). There are three generalized types of survivorship curve, which are simply referred to as Type I, Type

II and Type III curves.

Type I survivorship curves are characterized by high survival in early and middle life, followed by a rapid decline in

survivorship in later life. Humans are one of the species that show this pattern of survivorship.

Type II curves are an intermediate between Type I and III, where roughly constant mortality rate is experienced regardless of

age. Some birds follow this pattern of survival.

In Type III curves, the greatest mortality is experienced early on in life, with relatively low rates of death for those surviving

this bottleneck. This type of curve is characteristic of species that produce a large number of offspring. One example of a

species that follows this type of survivorship curve is the Octopus.

Population Growth Pattern: Two modes of population growth.

The Exponential curve (also known as a J-curve) occurs when there is no limit to population size.

The Logistic curve (also known as an S-curve) shows the effect of a limiting factor (in this case the carrying capacity of the

environment).

r/K selection Theory: An important concept in population ecology is the r/K selection theory. The first variable is r (the intrinsic rate of natural increase in

population size, density independent) and the second variable is K (the carrying capacity of a population, density dependent).

r-selected species : An r-selected species (e.g., many kinds of insects, such as aphids) is one that has high rates of

fecundity, low levels of parental investment in the young and high rates of mortality before individuals reach maturity.

Evolution favors productivity in r-selected species.

K-selected species: In contrast, a K-selected species (such as humans) has low rates of fecundity, high levels of parental

investment in the young and low rates of mortality as individuals mature. Evolution in K-selected species favors efficiency

in the conversion of more resources into fewer offspring.

The age within it's individual life cycle at which an organism reproduces affects the rate of population increase. Life history refers to

the age of sexual maturity, age of death, and other events in that individual's lifetime that influence reproductive traits. Some

organisms grow fast, reproduce quickly, and have abundant offspring each reproductive cycle. Other organisms grow slowly,

reproduce at a late age, and have few offspring per cycle. Most organisms are intermediate to these two extremes.

Populations Transition between Growth and Stability:

Limits on population growth can include food supply, space, and complex interactions with other physical and biological factors

(including other species). After an initial period of exponential growth, a population will encounter a limiting factor that will cause

the exponential growth to stop. The population enters a slower growth phase and may eventually stabilize at a fairly constant

population size within some range of fluctuation. This model fits the logistic growth model. The carrying capacity is the point where

population size levels off.

Population Decline and ExtinctionExtinction is the elimination of all individuals in a group. Local extinction is the loss of all individuals in a population. Species

extinction occurs when all members of a species and its component populations go extinct. Scientists estimate that 99% of all

species that ever existed are now extinct. The ultimate cause of decline and extinction is environmental change. Changes in one of

the physical factors of the environment may cause the decline and extinction; likewise the fossil record indicates that some

extinctions are caused by migration of a competitor.

Dramatic declines in human population happen periodically in response to an infectious disease. Bubonic plague infections killed

half of Europe's population between 1346 and 1350, later plagues until 1700 killed one quarter of the European populace. Smallpox

and other diseases decimated indigenous populations in North and South America.

Human Impact

Human populations have continued to increase, due to use of technology that has disrupted natural populations. Destabilization of

populations leads to possible outcomes:

population growth as previous limits are removed

population decline as new limits are imposed

Agriculture and animal domestication are examples of population increase of favoured organisms. In England alone more than

300,000 cats are put to sleep per year, yet before their domestication, the wild cat ancestors were rare and probably occupied only a

small area in the Middle East.

Pollution

Pollutants generally are releases of substances into the air and water. Many lakes often have nitrogen and phosphorous as limiting

nutrients for aquatic and terrestrial plants. Runoff from agricultural fertilizers increases these nutrients, leading to runaway plant

growth, or eutrophication. Increased plant populations eventually lead to increased bacterial populations that reduce oxygen levels

in the water, causing fish and other organisms to suffocate.

Pesticides and Competition

Removal of a competing species can cause the ecological release of a population explosion in that species competitor. Pesticides

sprayed on wheat fields often result in a secondary pest outbreak as more-tolerant-to-pesticide species expand once less tolerant

competitors are removed.

Removal of Predators

Predator release is common where humans hunt, trap, or otherwise reduce predator populations, allowing the prey population to

increase. Elimination of wolves and panthers have led to increase in their natural prey: deer. There are more deer estimated in the

United States than there were when Europeans arrived. Large deer populations often cause over grazing that in turn leads to

starvation of the deer.

Introduction of New Species

Introduction of exotic or alien non-native species into new areas is perhaps the greatest single factor to affect natural populations.

More than 1500 exotic insect species and more than 25 families of alien fish have been introduced into North America; in excess of

3000 plant species have also been introduced. The majority of accidental introductions may fail, however, once an introduced

species becomes established, its population growth is explosive. Kudzu, a plant introduced to the American south from Japan, has

taken over large areas of the countryside.

Community ecology: Community ecology is the study of the interactions among a collection of species that inhabit the same geographic area. This

requires an understanding of the community connections between plants (i.e., primary producers) and the decomposers (e.g., fungi

and bacteria), or the analysis of predator-prey dynamics affecting amphibian biomass. Food webs and trophic levels are two widely

employed conceptual models used to explain the linkages among species.

Interspecific interactions in Community Ecology:

Species interact in various ways: competition, predation, parasitism, mutualism, commensalism, etc. The organization of a biological

community with respect to ecological interactions is referred to as community structure.

CompetitionSpecies can compete with each other for finite resources. It is considered to be an important limiting factor of population size,

biomass and species richness. Many types of competition have been described, but proving the existence of these interactions is a

matter of debate. Direct competition has been observed between individuals, populations and species, but there is little evidence

that competition has been the driving force in the evolution of large groups.[4]

1. Interference competition: occurs when one population attacks, or consumes the resources, of another. Examples

include a lion chasing a hyena from a kill, or a plant releasing allelopathic chemicals to impede the growth of a competing

species.

2. Exploitative competition: occurs via the consumption of resources. When an individual of one species consumes a

resource (e.g., food, shelter, sunlight, etc.), that resource is no longer available to be consumed by a member of a second

species. Exploitative competition is thought to be more common in nature, but care must be taken to distinguish it from

apparent competition.

3. Apparent competition: occurs when two species share a predator. The populations of both species can be depressed by

predation without direct exploitative competition.[5]

PredationPredation is hunting another species for food. This is a positive-negative (+ -) interaction in that the predator species benefits while

the prey species is harmed. Some predators kill their prey before eating them (e.g., a hawk killing a mouse). Other predators are

parasites that feed on prey while alive (e.g., a vampire bat feeding on a cow). Herbivores feed on plants (e.g., a cow grazing).

Predation may affect the population size of predators and prey and the number of species coexisting in a community.

MutualismMutualism is a symbiotic interaction between species in which both benefit. Examples include Rhizobium bacteria growing in

nodules on the roots of legumes. Pollination is a common mutualistic interaction. The plant gains gamete transfer, the animal gets

nectar (and also pollen). 

Some other examples of Mutualism are :

Gut symbionts in herbivores: mammals can't digest cellulose 

endosymbiosis and the origin of eukaryotic cells: mitochondria, flagella, chloroplasts are thought to be derived from free-

living bacteria 

pollination systems 

the coral polyp and its endosymbiont "alga" (actually a dinoflagellate) 

CommensalismCommensalism is a type of relationship among organisms in which one organism gets the benefit where as the other organism is

neither benefited nor harmed. The organism that benefited is called the commensal while the other organism that is neither

benefited nor harmed is called the host. For example, an epiphytic orchid attached to the tree for support benefits the orchid but

neither harms nor benefits the tree. When one species benefits, and the other species is neither benefited nor harmed, the

interaction is "+/0". In the southeastern US and in South America, it is common to see egrets in cattle pastures. They follow the

cattle, eating insects that are dislodged or forced to fly as cattle graze in the field. One might suppose that egrets benefit cattle, by

consuming insects that might compete with cows for food. The interaction would be a mutualism if this was demonstrated (but it

seems a bit far-fetched). Assuming no benefit to the cattle, this is a commensalism. It often is the case, as this example illustrates,

that we aren't sure if the interaction is "+/O" or "+/+". 

The clown fish and anemone also illustrates this point. The clown fish hides from enemies within the stinging tentacles of a sea

anemone, to which the clown fish is immune. Some report this interaction as a mutualism, arguing that the clownfish drops scraps of

food into the mouth of the anemone. Careful studies have failed to find much support for any benefit to the anemone, so this appears

to be a commensalism. 

Name Description Species 1 Species 2

Indifferent No interaction 0 0

Commensalism One benefited , other not affected + 0

Ammensalism One is harmed , other not affected - 0

Parasitism One species feeds on the other species by nutrient adsorption + -

Predation One species feed by killing the other + -

Mutualism Benefit each other + +

Concept of Keystone Species:

The keystone species concept is one of the best-known ideas in community ecology. A keystone species is a species that is connected

to a disproportionately large number of other species in the food-web. Keystone species have lower levels of biomass in the trophic

pyramid, but plays a critical role in the survival of the community.

Some points to be noted regarding Keystone Species are:

The loss of a keystone species results in a range of dramatic cascading effects that alters trophic dynamics, other food web

connections, and can cause the extinction of other species.

  Although it is true that many species potentially interact with one another in a food web , in nature there are big players

and little players.  The biggest players of all are referred to as keystone species. 

This is a species whose presence or absence, or substantial increase or decrease in abundance, profoundly affects other

species in the community. 

Sea otters are commonly cited as an example of a keystone species because they limit the density of sea urchins that feed

on kelp. If sea otters are removed from the system, the urchins graze until the kelp beds disappear and this has a dramatic

effect on community structure. Hunting of sea otters, for example, is thought to have indirectly led to the extinction of the

Steller's Sea Cow .

While the keystone species concept has been used extensively as a conservation tool, it has been criticized for being

poorly defined from an operational stance. It is difficult to experimentally determine what species may hold a keystone

role in each ecosystem. Furthermore, food web theory suggests that keystone species may not be common, so it is unclear

how generally the keystone species model can be applied.

Habitat and Niche: Ecological niche

The habitat of a species describes the environment over which a species is known to occur and the type of community that is formed

as a result. More specifically, "habitats can be defined as regions in environmental space that are composed of multiple dimensions,

each representing a biotic or abiotic environmental variable; that is, any component or characteristic of the environment related

directly (e.g. forage biomass and quality) or indirectly (e.g. elevation) to the use of a location by the animal.

For example, a habitat might be an aquatic or terrestrial environment that can be further categorized as a montane or alpine

ecosystem. The ecological niche is a central concept in the ecology of organisms and is sub-divided into the fundamental and the

realized niche.

Fundamental niche: The fundamental niche is the set of environmental conditions under which a species is able to persist.

Realised niche: The realized niche is the set of environmental plus ecological conditions under which a species persists.

The habitat plus the niche is called the ecotope, which is defined as the full range of environmental and biological variables affecting

an entire species.

Ecosystem ecology

Ecosystem ecology is associated with the study of the interaction of the biotic components with the abiotic components (i.e. environment) and the continous flow of energy and matter between various components. The most important aspects of the Ecosystem Ecology are: Trophic levels and Food chains and Food webs.

The solar energy or the sunlight is received and trapped by the green plants in the biosphere. The green plants contain pigment chlorophyll through which they convert the solar energy into organic molecule ( green plants use light energy to convert carbon dioxide and water into carbohydrates) . This process of conversion of light energy into food or chemical energy is called photosynthesis. The organisms which produce their own food are called primary producers. They are also known as autotrophs.

The productivity of an ecosystem refers to the rate of growth of energy or organic matter per unit time by autotrophic primary producers through the process of photosynthesis with the help of solar energy. Thus the productivity of the ecosystem depends upon mainly two factors such as:

1. The availability of the amount of solar radiation to the autotrophic primary producers.2. The efficiency of the plants to convert solar energy ( light energy) into chemical energy ( food energy)

True production of organic matter takes place only in the chlorophyll possessing plants and certain synthetic bacteria, and this has been referred to as the primary production. Only a very small portion of the light energy absorbed by green plants that is transformed into food energy (gross production) because most of it is dispersed as heat. Furthermore, some of the synthesized gross production is used by the plants in their own respiratory processes (respiratory losses, leaving a still smaller amount of potential energy (net production) available for transfer to the next trophic level.

The transfer and assimilation of food energy takes place in hierarchical order in the ecosystem through various levels. Thus the levels through which food energy passes from one group of organism to the other group are called trophic level. The chain of transformation and transfer of food energy in the ecosystem from one group of organism to the other group through a series steps or levels is called food chain.

In other words, the chain of transfer of food energy in the ecosystem from one group of organism to the other group in the biosphere, is called food chain and the point where food energy is transferred from one group of organism to the other group is called trophic level. On an average four trophic levels of a food chain are identified. These are:

First trophic level: It  is represented by Producer. They are organisms like plants that produces food from carbon dioxide and water using photosynthesis. Producers can be plant, algae, plankton or bacteria. Primary producers in an aquatic ecosystem are various species like phytoplankton, algae and higher plants.Primary producers in an terrestrial ecosystem are various species like green plants.

Second trophic level: Second trophic level is represented by primary consumers. The primary consumers are herbivores that feeds on plants. Eg insects, birds and mammals in terrestrial ecosystem and mollusc's in aquatic ecosystem.

Third trophic level: This level is represented by secondary consumers. These are Primary carnivores .The consumers that feed on herbivores are carnivores, are called primary carnivores

Fourth trophic level: It is represented by tertiary consumers. They are usually  top carnivore,a consumer at the top of a food chain with no predators

Some of the terms associated with Ecosystem Ecology: Ecologists use the following terms to describe various categories of the effects of a change (in abundance, or presence vs absence) of one species on another. 

Direct effects refer to the impact of the presence (or change in abundance) of species A on species B in a two-species interaction.

Indirect effects refer to the impact of the presence (or change in abundance) of species A on species C via an intermediary species (A --> B --> C)

Cascading effects are those which extend across three or more trophic levels, and can be top-down (predator --> herbivore --> plant) or bottom-up (plant --> herbivore --> predator).

Keystone species are those which produce strong indirect effects.

Ecological succession:

"Ecological succession" is the process of change in the species structure of an ecological community over time. Within any

community some species may become less abundant over some time interval, or they may even vanish from the ecosystem

altogether. Similarly, over some time interval, other species within the community may become more abundant, or new species may

even invade into the community from adjacent ecosystems. This observed change over time in what is living in a particular

ecosystem is "ecological succession".

In other words, ecological succession is a phenomenon or process by which an ecological community undergoes more or less

orderly and predictable changes following disturbance or initial colonization of new habitat.

Succession may be initiated either by formation of new, unoccupied habitat such as a lava flow or a severe landslide or by some form

of disturbance such as fire, severe windthrow, logging of an existing community.

Succession that begins in new habitats, uninfluenced by pre-existing communities is called primary succession, whereas succession

that follows disruption of a pre-existing community is called secondary succession

Every species has a set of environmental conditions under which it will grow and reproduce most optimally. In a given ecosystem,

and under that ecosystem's set of environmental conditions, those species that can grow the most efficiently and produce the most

viable offspring will become the most abundant organisms. As long as the ecosystem's set of environmental conditions remains

constant, those species optimally adapted to those conditions will flourish. Under the changed conditions of the environment, the

previously dominant species may fail and another species may become ascendant.

Ecological succession may also occur when the conditions of an environment suddenly and drastically change. A forest fires, wind

storms, and human activities like agriculture all greatly alter the conditions of an environment. These massive forces may also

destroy species and thus alter the dynamics of the ecological community triggering a scramble for dominance among the species still

present.

Principles of Ecological Succession:

Ecological Succession is an orderly sequence of different communities over a period of time in a particular area. Important General

Principles Associated with Ecological Succession

o The physical environment determines which communities can exist in a particular place.

o Succession is community controlled, i.e., succession is caused by modification of the surrounding physical environment by

the existing community, i.e., a successional community will alter the environment so that the environment is then more

favorable for a different community than the existing one.

o Ecological succession is directional - and therefore predictable

o Succession ends in a stabilized community and ecosystem called the ecological climax. It is in equilibrium with the

physical environment of that particular area and perpetuates itself. Usually an external disturbance to the area, e.g., fire,

puts the area back into an earlier successional stage. This tendency for the ecosystem to reach a stage where it stays in

equilibrium is an example of Homeostasis – developing and maintaining stability.

o High diversity produces stability.

Types of Ecological Succession

(Diagram)

1. Primary Succession: begins on an area that has not been previously occupied by a community, e.g., newly exposed

rock. There is no soil. Soil is a combination of broken down rock plus organic matter (humus and small, living

organisms). Humus is accumulated, decomposed plant and animal material. Primary succession takes place very slowly

with a low rate of production of biological material.

2. Secondary Succession: begins on an area where a community has previously existed. Secondary succession usually

begins on an already established soil. Secondary succession has a higher level of production of biological material at a

faster rate than primary succession.

3. Cyclic Succession: Unlike secondary succession, these types of vegetation change are not dependent on disturbance

but are periodic changes arising from fluctuating species interactions or recurring events. These models propose a

modification to the climax concept towards one of dynamic states.

Causes of Succession:

On the basis of the forces responsible for the changes, the successions are divided into two types. These are:

Autogenic secession, where the succession is the product of the organisms themselves or succession is brought about by

naturally by the living inhabitants.

Allogenic succession, where the succession occurs due to the outside forces particularly the physical factors.

Autogenic succession can be brought by changes in the soil caused by the organisms there. These changes include accumulation of

organic matter in litter or humic layer, alteration of soil nutrients, change in pH of soil by plants growing there. The structure of the

plants themselves can also alter the community. For example, when larger species like trees mature, they produce shade on to the

developing forest floor that tends to exclude light-requiring species. Shade-tolerant species will invade the area.

Allogenic succession is caused by external environmental influences and not by the vegetation. For example soil changes due to

erosion, leaching or the deposition of silt and clays can alter the nutrient content and water relationships in the ecosystems. Animals

also play an important role in allogenic changes as they are pollinators, seed dispersers and herbivores. They can also increase

nutrient content of the soil in certain areas, or shift soil about (as termites, ants, and moles do) creating patches in the habitat. This

may create regeneration sites that favour certain species.

Climatic factors may be very important, but on a much longer time-scale than any other. Changes in temperature and rainfall

patterns will promote changes in communities. As the climate warmed at the end of each ice age, great successional changes took

place. The tundra vegetation and bare glacial till deposits underwent succession to mixed deciduous forest. The greenhouse effect

resulting in increase in temperature is likely to bring profound Allogenic changes in the next century. Geological and climatic

catastrophes such as volcanic eruptions, earthquakes, avalanches, meteors, floods, fires, and high wind also bring allogenic changes.

Concept of Sere in Succession:

A seral community is an intermediate stage found in an ecosystem advancing towards its climax community. In many cases more

than one seral stage evolves until climax conditions are attained. A prisere is a collection of seres making up the development of an

area from non-vegetated surfaces to a climax community. Depending on the substratum and climate, a seral community can be one

of the following:

Types Explanation Hydrosere Community in freshwater

Lithosere Community on rock

Psammosere Community on sand

Xerosere Community in dry area

Halosere Community in saline body (e.g. a marsh

The Concept of Climax: According to classical ecological theory, succession stops when the sere has arrived at an equilibrium or steady state with the

physical and biotic environment. Barring major disturbances, it will persist indefinitely. This end point of succession is called climax.

Climax community

The final or stable community in a sere is the climax community or climatic vegetation . It is self-perpetuating and in equilibrium

with the physical habitat. There is no net annual accumulation of organic matter in a climax community mostly. The annual

production and use of energy is balanced in such a community.

Characteristics of climax The vegetation is tolerant of environmental conditions.

It has a wide diversity of species, a well-drained spatial structure, and complex food chains.

The climax ecosystem is balanced. There is equilibrium between gross primary production and total respiration, between

energy used from sunlight and energy released by decomposition, between uptake of nutrients from the soil and the

return of nutrient by litter fall to the soil.

Individuals in the climax stage are replaced by others of the same kind. Thus the species composition maintains

equilibrium.

It is an index of the climate of the area. The life or growth forms indicate the climatic type.

Types of climax

Types of Climax Explanation

Climatic Climax If there is only a single climax and the development of climax community is controlled by the climate of the

region, it is termed as Climatic climax

Edaphic Climax When there are more than one climax communities in the region, modified by local conditions of the substrate

such as soil moisture, soil nutrients, topography, slope exposure, fire, and animal activity, it is called Edaphic

climax.

Catastrophic

Climax

Climax vegetation vulnerable to a catastrophic event such as a wildfire.

Disclimax When a stable community, which is not the climatic or edaphic climax for the given site, is maintained by man or

his domestic animals, it is designated as Disclimax (disturbance climax) or anthropogenic subclimax (man-

generated).

Edge Effect: Edge effect refers to the influence that two ecological communities have on each other along the boundary that separates them.

Because such an area contains habitats common to both communities as well as others unique to the transition zone itself, the edge

effect is typically characterized by greater species diversity and population density than occur in either of the individual

communities.

Some of the aspects of Edge effect1. The occurrence of greater species diversity and biological density in an ecotone than in any of the adjacent ecological

communities.

2. Environmental conditions enable certain species of plants and animals to colonize on the borders. Plants that colonize

tend to be shade-intolerant and tolerable of dry conditions, such as shrubs and vines. Animals that colonize tend to be

those that require two or more habitats such as, white-tailed and mule deer, elk, cottontail rabbits, blue jays, and robins.

3. Some animals may travel between habitats, while those that are restricted only to the edge are known as edge species.

Larger patches include more individuals and therefore have increased biodiversity. The wideness of the patch influences

diversity, a patch must be deeper than its border in order to develop interior conditions.

Concept of Ecological Pyramids:

The trophic relationships of an ecosystem can be represented graphically in the form of ecological pyramid. The base of the pyramid

represents the producers and the successive tiers represent the subsequent higher levels. The ecological pyramids are of three

types:

Pyramid of energy

Pyramid of Biomass

Pyramid of number

(Diagram)

The Pyramid of Energy The energy pyramids give the best picture of the overall nature of the ecosystem.Here there will be gradual decrease in the

availability of energy from the autotrophs higher trophic levels. In other words, there is decrease in energy flow from autotrophs

on\ at successive trophic levels. In the course of energy flow from one organism to the other, is considerable loss of energy in the

form of heat. More energy is available in the autotrophs t in the primary consumers. The least amount of available energy will be in

the tertiary consumer. Therefore, shorter the food chain, greater is the amount of energy available at the top.

The important aspects are:

The energy pyramid always upright and erect.

It shows the rate of energy flows at different trophic levels.

It shows that energy is maximum at producer level and minimum at the carnivores' level.

At every successive trophic level there is a loss of energy in the form of heat, respiration etc.

The Pyramid of Biomass There will be gradual decrease in the biomass from the autotrophs to the higher trophic levels. This may be illustrated by studying

the trophic levels in a pond. The biomass in autotrophs like algae, green flagellates, green plants etc. is the maximum. The biomass is

considerably less in the next trophic level occupied by secondary consumers like small fishes. The least amount of biomass is

present in the last trophic level.

The important aspects are :

This pyramid shows the total biomass at each trophic level in a food chain

Pyramid in erect.

It indicates a decrease in the biomass at each trophic level from the base to apex of pyramid.

Example: Total biomass than herbivores, which is again more than carnivorous.

The Pyramid of Numbers They show the relationship between producers, herbivores and carnivores at successive trophic levels in terms of their number.

Here there will be a gradual decrease in the number of individuals from the lower to the higher trophic levels. This may be studied

by taking the example of trophic levels in grassland.

The grasses occupy the lowest trophic level and they are abundantly present in the grassland ecosystem. The deers occupy the

second level; their number is less than compared to the grasses. The wolves, which feed upon the deers, are far less in number when

compared to the number of deers. The lions, which occupy the next trophic level, feed upon wolves, and the number of individuals in

the last trophic level is greatly reduced. In the parasitic food chain, the pyramid of numbers is founds to be inverted. Here, a single

plant or tree might support varieties of herbivore. These herbivores like birds in turn, support varieties of parasites like lice, bugs

that outnumber the herbivores. Subsequently each parasite might support a number of hyperparasites like bacteria and fungi, which

will outnumber the parasites. Thus from the producer level onwards, towards the consumers, in the parasitic food chain there is a

gradual increase in the number of organisms, instead of the usual decrease. As a result of this, the pyramid becomes inverted in the

parasitic food chain. There is a gradual increase in the numbers of individuals from autotrophs to the higher trophic levels.

The important aspects are :

It shows the number of organism at different levels.

The pyramid can be either erect or inverted.

The smaller animals are preyed upon larger animals and smaller animals increase faster in number of organism at each

stage of food chain, makes a triangular figure that is known as pyramid of number

The Law Of 10 Percent:

The law of 10% is associated with the transfer of energy from one trophic level to the next trophic level. The ten percent law implies

that exactly 90% of the energy is lost in the transfer at each trophic level, and that only 10% is passed on as useable biological

energy. Thus at each transfer of energy through a trophic structure, only a small percent of the energy remains available for use by

the organism in the next level up in the system. The majority of the energy is lost to the surroundings in forms such as waste heat.

Lindemann (1942) put forth ten percent law for the transfer of energy from one trophic level to the next. According to the law,

during the transfer of organic food from one trophic level to the next, only about ten percent of the organic matter is stored as flesh.

The remaining is lost during transfer or broken down in respiration. Plants utilise sun energy for primary production and can store

only 10% of the utilised energy as net production available for the herbivores. When the plants are consumed by animal, about 10%

of the energy in the food is fixed into animal flesh which is available for next trophic level (carnivores). When a carnivore consumes

that animal, only about 10% of energy is fixed in its flesh for the higher level. So at each transfer 80 - 90% of potential energy is

dissipated as heat where only 10 - 20% of energy is available to the next trophic level.

Energy lost at each level result in a pyramid of biomass: less energy available at the level of carnivores, for example, means less

biomass at that level than at the level of herbivores. The growth and numbers of organisms in an ecosystem are closely (if not

always directly) related to, and limited by, the amount of energy available, and that decreases markedly at each level of the

food/energy system.

Diagram)

Bio Geo Chemical Cycles or Movement of matter in Ecosystem:

The functioning of the biotic world largely depends upon the flow of energy and the flow of nutrients through the ecosystem. This

flow of energy and the nutrients affects various aspects of the ecosystem such as:

Abundance of the organism

The metabolic rate at which they live

The complexity of the ecosystem

Thus there are two aspects associated with the functional aspect of the Ecosystem :

1. Flow of energy

2. Flow of nutrients

Here we are to emphasis upon the flow of the nutrients in ecosystem through various biogeochemical cycles.

The nutrients are further divided into two parts: Micro nutrients and macro nutrients. Micro nutrients are the nutrients which are

needed by the organisms in traces where as macro nutrients are the nutrients which are needed by the organisms in large amounts.

Groups Elements Main Reservoir

Micro Nutrients: They present in traces.

1. Aluminium Lithosphere

2. Boron Lithosphere

3. Bromine Lithosphere

4. Zinc Lithosphere

5. Cobalt Lithosphere

6. Iodine Lithosphere

7. Chromium Lithosphere

Macro Nutrients

Group I : They constitute

more than 1% each of dry

organic weight.

1. Carbon Atmosphere

2. Hydrogen Hydrosphere

3. Oxygen Atmosphere

4. Nitrogen Atmosphere and soil

5. Phosphorous Lithosphere

Group II: They constitute

0.2 to 1% each of dry

organic weight.

1. Calcium Lithosphere

2. Chlorine Lithosphere

3. Copper Lithosphere

4. Iron Lithosphere

5. Magnesium Lithosphere

6. Sulphur Lithosphere and Atmosphere

7. Sodium Lithosphere

8. Potassium Lithosphere

Biogeochemical cycle refers to any of the natural circulation pathways of the essential elements of living matter. These elements in

various forms flow from the nonliving (abiotic) to the living (biotic) components of the biosphere and back to the nonliving again. In

order for the living components of a major ecosystem (e.g., a lake or forest) to survive, all the chemical elements that make up living

cells must be recycled continuously . In other words , biogeochemical cycle or substance turnover or cycling of substances is a

pathway by which a chemical element or molecule moves through both biotic (biosphere) and abiotic (lithosphere, atmosphere, and

hydrosphere) compartments of Earth. A cycle is a series of change which comes back to the starting point and which can be

repeated.

The term “biogeochemical” tell us that biological, geological and chemical factors are all involved. The circulation of chemical

nutrients like carbon, oxygen, nitrogen, phosphorus, calcium, and water etc. through the biological and physical world are known as

biogeochemical cycles. In effect, the element is recycled, although in some cycles there may be places (called reservoirs) where the

element is accumulated or held for a long period of time (such as an ocean or lake for water).

Water, for example, is always recycled through the water cycle, as shown in the diagram. The water undergoes evaporation,

condensation, and precipitation, falling back to Earth clean and fresh. Elements, chemical compounds, and other forms of matter are

passed from one organism to another and from one part of the biosphere to another through the biogeochemical cycle.

Chloroplasts conduct photosynthesis and are found in plant cells and other eukaryotic organisms. These are Chloroplasts visible in

the cells of Plagiomnium affine — Many-fruited Thyme-moss.

Ecological systems (ecosystems) have many biogeochemical cycles operating as a part of the system, for example the water cycle,

the carbon cycle, the nitrogen cycle, etc. All chemical elements occurring in organisms are part of biogeochemical cycles. In addition

to being a part of living organisms, these chemical elements also cycle through abiotic factors of ecosystems such as water

(hydrosphere), land (lithosphere), and/or the air (atmosphere)

The living factors of the planet can be referred to collectively as the biosphere. All the nutrients—such as carbon, nitrogen, oxygen,

phosphorus, and sulfur—used in ecosystems by living organisms are a part of a closed system; therefore, these chemicals are

recycled instead of being lost and replenished constantly such as in an open system.

The flow of energy in an ecosystem is an open system; the sun constantly gives the planet energy in the form of light while it is

eventually used and lost in the form of heat throughout the trophic levels of a food web. Carbon is used to make carbohydrates, fats,

and proteins, the major sources of food energy. These compounds are oxidized to release carbon dioxide, which can be captured by

plants to make organic compounds. The chemical reaction is powered by the light energy of the sun.

It is possible for an ecosystem to obtain energy without sunlight. Carbon must be combined with hydrogen and oxygen in order to

be utilized as an energy source, and this process depends on sunlight. Ecosystems in the deep sea, where no sunlight can penetrate,

use sulfur. Hydrogen sulfide near hydrothermal vents can be utilized by organisms such as the giant tube worm. In the sulfur cycle,

sulfur can be forever recycled as a source of energy. Energy can be released through the oxidation and reduction of sulfur

compounds (e.g., oxidizing elemental sulfur to sulfite and then to sulfate).

Although the Earth constantly receives energy from the sun, its chemical composition is essentially fixed, as additional matter is only

occasionally added by meteorites. Because this chemical composition is not replenished like energy, all processes that depend on

these chemicals must be recycled. These cycles include the living biosphere and the nonliving lithosphere, atmosphere, and

hydrosphere.

Each cycle can be considered as having a reservoir (nutrient) pool—a larger, slow-moving, usually abiotic portion—and an

exchange (cycling) pool—a smaller but more active portion concerned with the rapid exchange between the biotic and abiotic

aspects of an ecosystem.

Biogeochemical cycles can be classed as gaseous, in which the reservoir is the air or the oceans (via evaporation), and sedimentary,

in which the reservoir is the Earth’s crust. Gaseous cycles include those of nitrogen, oxygen, carbon, and water; sedimentary cycles

include those of iron, calcium, phosphorus, and other more earthbound elements.

Gaseous cycles tend to move more rapidly than do the sedimentary ones and to adjust more readily to changes in the biosphere

because of the large atmospheric reservoir. Local accumulations of carbon dioxide, for example, are soon dissipated by winds or

taken up by plants. Extraordinary and more frequent local disturbances can, however, seriously affect the capacity for self-

adjustment.

Sedimentary cycles vary from one element to another, but each cycle consists fundamentally of a solution phase and a rock (or

sediment) phase. Weathering releases minerals from the Earth’s crust in the form of salts, some of which dissolve in water, pass

through a series of organisms, and ultimately reach the deep seas, where they settle out of circulation indefinitely. Other salts

deposit out as sediment and rock in shallow seas, eventually to be weathered and recycled.

Plants and some animals obtain their nutrient needs from solutions in the environment. Other animals acquire the bulk of their

needs from the plants and animals that they consume. After the death of an organism, the elements fixed in its body are returned to

the environment through the action of decay organisms and become available to other living organisms again.

.

The hydrologic (water) cycle

Plants absorb water from soil, and animals drink water or eat animals, which are made mostly of water. When plants go through the

process of transpiration (that's when water evaporates from a leaf and more water is pulled up from the roots of the plant and out

through the cells on the surface of the leaf), they give off water. When animals create perspiration, they release water, which is

evaporated into the atmosphere. Water also is released from plants and animals as they decompose. Decomposing tissue becomes

dehydrated, which is what causes the dried-out tissues to break down and fall off into the soil.

As water evaporates into the air, wind moves air over bodies of water, and precipitation (rain, snow, sleet, hail) releases water into

larger bodies of water such as lakes, rivers, oceans, and even glaciers. Water from precipitation and decomposing tissue also gets

into groundwater, which ultimately supplies larger bodies of water.

The carbon cycle

Plants take in carbon dioxide for photosynthesis. Animals consume plants or other animals, and all living things contain carbon.

Carbon is what makes organic molecules organic (living). Carbon is necessary for the creation of molecules such as carbohydrates,

proteins, and fats. Plants release carbon dioxide when they decompose. Animals release carbon dioxide when they decompose or

respire. (Animals take in oxygen and release carbon dioxide when they breathe.) Carbon dioxide also is released when organic

matter such as wood, leaves, coal, or oil are burned. The carbon dioxide returns to the atmosphere, where it can be taken in by more

plants that are then consumed by animals. Decomposing animals and plants leach carbon into the ground, forming fossil fuels such

as coal or oil. Peat also forms from the decomposition of organic matter. Some carbon is stored in the form of cellulose in the wood

of trees and bushes.

The phosphorus cycle

ATP, that ubiquitous energy molecule created by every living thing, needs phosphorus.

You can tell that by its name; triphosphate indicates that it contains three molecules of phosphate, which requires phosphorus.

DNA and RNA, the genetic molecules present in every living thing, have phosphate bonds holding them together, so they require

phosphorus, too, as does bone tissue. Plants absorb inorganic phosphate from the soil. When animals consume plants or other

animals, they acquire the phosphorus that was present in their meal. Phosphorus is excreted through the waste products created by

animals, and it is released by decomposing plants and animals. When phosphorus gets returned to the soil, it can be absorbed again

by plants, or it becomes part of the sediment layers that eventually form rocks. As rocks erode by the action of water, phosphorus is

returned to water and soil.

The nitrogen cycle

Because amino acids build proteins, nitrogen is pretty important. Nitrogen also is present in the nucleic acids DNA and RNA. Life

could not go on without nitrogen.

The nitrogen cycle (Figure 1) is the most complex biogeochemical cycle because nitrogen can exist in several different forms.

Nitrogen fixation, nitrification, denitrification, and ammonification are all parts of the nitrogen cycle.

Figure 1: The nitrogen cycle.

Nitrogen fixation: In the soil, as well as in the root nodules of certain plants, nitrogen is "fixed" by bacteria, lightning, and

ultraviolet radiation. The "fixing of nitrogen" does not mean nitrogen was broken; a better term might be "fixated,"

because the bacteria put elemental nitrogen into a form that can be used by living organisms and do not allow it to leave

that form and revert to elemental nitrogen.

Nitrification: Certain bacteria take the forms into which nitrogen was fixated and further process it (oxidization).

Oxidation provides energy for the nitrogen cycle to take place — the bacteria that live in soil cannot harness energy from

the sun. The energy they use during their work in the nitrogen cycle comes from this process.

Denitrification and ammonification. Plants absorb nitrates or ammonium ions from the soil and turn them into organic

compounds. Animals obtain nitrogen by consuming plants or other animals. Therefore, the waste products of animals

contain nitrogen. Ammonium ions, ammonia, urea, and uric acid all contain nitrogen. So regardless of what form of

excretion an animal has, some nitrogen is released back into the ecosystem through excrement. Dead plants and animals

are food for decomposing bacteria.

The flow of chemical elements and compounds between living organisms and the physical environment. Chemicals absorbed or

ingested by organisms are passed through the food chain and returned to the soil, air, and water by such mechanisms as respiration,

excretion, and decomposition. As an element moves through this cycle, it often forms compounds with other elements as a result of

metabolic processes in living tissues and of natural reactions in the atmosphere, hydrosphere, or lithosphere