Contents
The Biology Topics of ecology involve studying the relationships between living organisms and their environment.
Structural and Functional Concept of Ecology – Levels of Organization, Principles of Ecology
The branch of science which reveals the inter-relationship between living organisms and the environment is called ecology.
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The branch of science which reveals the inter-relationship between vegetative and organic environments is called ecology.
- The science of all the relations of all organisms to all their environments. – Taylor (1936)
- The study of the structure and function of ecosystems or the structure and function of nature. – Eugene Odum (1971)
- Ecology, the science of the environment, is the study of ecosystems, or the totality of the reciprocal interactions between living organisms and their physical surroundings. – M.E. Clark (1973)
- Ecology is the scientific study of the relationship of living organisms with each other and with their environments. – Charles H. Southwick (1976)
Everything that surrounds us may collectively be termed an Environment. It is the environment from where we get food to eat, water to drink, soil on which we stand, air to breathe, and all necessities of day-to-day life. Environment is the sum total of physical and biotic conditions influencing the responses of the organism. The life-supporting environment of planet Earth is called the biosphere, composed of air, water, and soil, which are the components of three major sub-divisions of the environment, atmosphere, hydrosphere, and lithosphere. Environment, environmental studies, and environmental biology are all interconnected with each other. In this chapter, we will discuss the different aspects of the environment.
Concept of Ecology
The term ecology (oekologie) is derived from two Greek words oikos means house or place to live and logos means a discussion or study. Thus, ecology is the study of organisms at home in their native environment. The term was first introduced by Reiter in 1868, but German Biologist Ernest Haeckel (1869) first proposed and defined the term Ecology. According to Haeckel, ecology (Oecologie) is the total relation of the animal to both its organic and inorganic environment, particularly its friendly or hostile relations to those animals or plants with which it interacts.
Aims of Ecology
Ecology is an interdisciplinary field that includes biology and as well as Earth Science. Modern ecology transformed into a more rigorous science in the late 19th Century. Evolutionary concepts on adaptation and natural selection became cornerstones of modern ecological theory. Ecology is not synonymous with environment, environmentalism, natural history, or environmental science. It is closely related to evolutionary biology, genetics, and ethology. An understanding of how biodiversity affects ecological function is an important focus area in ecological studies. Ecologists seek to explain:
- Life processes, interactions, and adaptations.
- The movement of materials and energy through living communities.
- The successional development of ecosystems.
- The abundance and distribution of organisms and biodiversity in the context of the environment.
Ecology is a distinct science because it is a body of knowledge not similarly organized in any other division of biology. It has a unique point of view and the essence of this science entails a comprehensive understanding of the following phenomena:
- The local and geographical distribution and abundance of organisms (habitat, niche, community, biogeography).
- Temporal changes in the occurrence, abundance, and activities of organisms (seasonal, annual, successional, geological).
- The interrelationships between organisms in populations and communities (population ecology).
- The structural adaptations and functional adjustments of organisms to their physical environment (physiological ecology).
- The behaviour of organisms under natural conditions (ethology).
- The evolutionary developments of all these interrelations (evolutionary ecology).
- The biological productivity of nature and how this may best serve mankind (Ecosystem ecology).
- The development of mathematical models to relate the interaction of parameters and predict effects (System analysis).
The Levels of Biological Organization in Ecology
The organization is a systematic arrangement of smaller and simpler components into larger ones in a hierarchy where each level is formed of components of the lower level and itself becomes part of a higher level for achieving a common goal. The various ecological levels of organisation are Organism, Population, Biological Community, Ecology and Ecosystem, Landscape, Biome, and Biosphere.
1. Organism (Individual):
Organisms are the basic units of study of ecology. At the level of the organism, we understand the form, physiology and behaviour, distribution and adaptation in relation to the environmental conditions. Similar organisms having the potential for interbreeding and producing fertile offspring constitute a species.
2. Species:
A species is a group of living organisms consisting of similar individuals capable of exchanging genes or interbreeding and it is the smallest and principal, natural taxonomic unit, ranking below a genus.
3. Population:
A population is a group of organisms of the same species living together in a particular habitat. For example, all the frogs (Rana tigrina) living in a pond form a population. Similarly, all the water hyacinth plants (Eichhornia crassipes) growing in that pond constitute another population. We study how two populations interact, a predator with its prey, or a parasite with its host. Competition, mutualism, and predation are various types of interactions between organisms. The population of an organism living in a specific area is called the local population or deme.
4. Biological Community:
The biological community is the total of all the populations of plants, animals, bacteria, and fungi living in a habitat at any one time. Different populations of a community interact with one another through competition, predation, mutualism, etc. Each biotic community has a specific composition and structure, e.g., Pond Community.
5. Ecology and Ecosystem:
The branch of science which reveals the inter-relationship between living organisms and the environment is called Ecology. Ecology is the scientific study of the relationship of living organisms with each other and with their environment. An ecosystem is composed of a biological community, integrated with its physical environment through the exchange of energy and recycling of nutrients, e.g., the Pond ecosystem. Scientist Tansley, 1935 first used the term ecosystem.
6. Landscape:
A landscape is a unit of land with a natural boundary having a mosaic of patches. These patches generally represent different ecosystems, e.g., the Southern peninsula.
7. Biome:
It is a major category of regional ecological organization which is delimited by a specific climatic zone. Biome is characterized by a major vegetation type with its associated fauna. Each type of biome may possess a patch of a different type of ecosystem, e.g., a lake in a forest. Some examples of terrestrial biomes are tropical rainforests, temperate deciduous forests, and deserts.
Climate | Biome | Important Plants |
1. Equatorial region high temperature and rainfall. | Tropical rain forest. | Broad-leaved evergreen trees, epiphytes, and orchids. |
2. Mediterranean region-rainfall in winter and drought in summer. | Woodland and shrubland. | Evergreen and deciduous forest, drought-resistant trees. |
3. Temperature region. | Deciduous forest. | Mesophyte and deciduous trees. |
4. Polar region. | Polar region tundra alpine tundra. | Herbs, grasses, treeless plants. |
8. Biosphere:
The biosphere is the living mantle of the earth which comprises all the earth’s terrestrial and aquatic biomes. It consists of the lower atmosphere, the land and the oceans, rivers, and lakes, where living beings are found. The biological levels of organization of living things are arranged from the simplest to the most complex. The idea of biological levels can be given through two flow charts:
- Macromolecule → Cell → Tissue → Organ → Organism.
- Individual (Organism) → Population → Biological Community → Ecosystem → Landscape → Biome → Biosphere
Differences between Population and Species:
Population | Species |
1. It is smaller groups of similar organisms. | 1. It is larger groups of similar organisms. |
2. Population occupies a specific area. | 2. Members of species may occur in several localities and belong to more than one population. |
3. Members of a population constitute a single ecotype. | 3. Though the organisms interbreed those of different populations may do so only occasionally. |
4. Polar region. | 4. A species may have several ecotypes. |
5. Population is not reproductively isolated since members of one population can interbreed with the members of other similar populations. | 5. A species is reproductively isolated. |
6. Members of a population do not show morphological, anatomical, and behavioural differences. | 6. Different populations of a species may show minor differences in morphological, anatomical, and behavioral characteristics. |
Differences between Ecosystem and Biome:
Ecosystem | Biome |
1. It is a self-sufficient and self-regulated segment of nature. | 1. It consists of a number of ecosystems. |
2. The size of the ecosystem is comparatively smaller. | 2. The size of the biome is comparatively larger. |
3. An ecosystem may be natural or artificial, temporary or permanent. | 3. A biome is always natural and permanent. |
4. The boundary of an ecosystem is marked by different types of surroundings. | 4. It is delimited by a specific climatic zone. |
Differences between Biome and Biosphere:
Biome | Biosphere |
1. It is a major category of regional ecological organization. | 1. It is the highest category of ecological organization. |
2. It is delimited by a specific climatic zone. | 2. It comprises the whole living mantle of the earth. |
3. Biomes are usually terrestrial and aquatic. | 3. Biosphere exists over the lithosphere, hydrosphere, and atmosphere. |
4. It comprises one or more landscapes each of which has a number of ecosystems. | 4. It comprises all the biomes of the earth. |
Classification of Ecology
According to different aspects, ecology is divided into different ways likes-
A. Based on taxonomic affinities
On the basis of plant or animal ecology, there are two types of ecology as follows: Plant Ecology and Animal Ecology.
B. Based on habitat
On the basis of particular habitats and interactions with their environment, the following types are as follows: Terrestrial Ecology and Marine Ecology.
C. Based on the levels of organization
On the basis of the stages of ecological organization, the following ecological types are as follows: Autecology and Synecology.
(i) Autecology or Species ecology
It is a main branch of ecology. It refers to the study of relationships between individual plants, animals or microbial species throughout their life cycle and environment.
i.e., ecological factors both living and nonliving.
Example: Study of single plant or animal like Cycas or tiger respectively in relation to the environment.
Objectives of Autecology:
- Identification of a species.
- Local and geographical distribution and ecological importance.
- Behaviour of organisms under natural conditions and the physiological, and anatomical differences between the same species living in different habitats.
- Temporal changes in the occurrence, abundance, and activities of organisms.
(ii) Synecology
Synecology is also a main branch of ecology. It refers to the study of relationships between the communities and the environment. It means the study of the structure, nature, organization, and development of plant communities.
Example: Study of Pinus forest in relation to the environment.
Objectives of Synecology:
- Identification of a species and knowing the number of each species.
- Studying the biodiversity of the area and inter-specific relations in a habitat.
- To find out the abiotic factors within the habitat and study succession.
Distinguish between Autecology and Synecology:
Autecology | Synecology |
1. Study of an individual species. | 1. Study of different species. |
2. The relationship between the environment and the individual is simple. | 2. The inter-relationship between species and environment is complex. |
Branches of Ecology
1. Population Ecology
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. Although population ecology is a subfield of biology, it provides interesting problems for mathematicians and statisticians who work in population dynamics.
Fundamentals of Population Ecology:
The first law of population ecology is Thomas Malthus’s “exponential law of population growth”.
Terms used to describe natural groups of individuals in ecological studies:
Term | Definition |
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 (as defined above). |
This principle in population ecology provides the basis for formulating predictive theories and tests that follow. Simplified population models usually start with four key variables including death, birth, immigration, and emigration. Mathematical models used to calculate changes in population demographics and evolution hold the assumption (or null hypothesis) of no external influence. Models can be more mathematically complex where “several competing hypotheses are simultaneously confronted with the data.”
For example, in a closed system where immigration and emigration do not take place, the per capita rates of change in a population can be described as:
\(\frac{dN}{dT}\) = B – D = bN – dN = (b – d)N = rN
Where N is the total number of individuals in the population, B is the number of births, D is the number of deaths, b and d are per capita rates of birth and death respectively, and r is the per capita rate of population change. This formula can be read as the rate of change in the population (\(\frac{dN}{dT}\)) is equal to births minus deaths (B – D).
Using these techniques, Malthus’s population principle of growth was later transformed into a mathematical model known as the logistic equation:
\(\frac{d N}{d T}=a N\left(1-\frac{N}{K}\right)\)
Where N is the biomass density, a is the maximum per capita rate of change and K is the carrying capacity of the population. The formula can be read as the rate of change in the population (dN/dT) is equal to growth (aN) that is limited by carrying capacity (1 – N/K). From these basic mathematical principles, the discipline of population ecology expands into a field of investigation that queries the demographics of real populations and tests these results against the statistical models. The field of population ecology often uses data on life history and matrix algebra to develop projection matrices on fecundity and survivorship. This information is used for managing wildlife stocks and setting harvest quotas.
r/K Selection:
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). 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 favours productivity in r-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 favours efficiency in the conversion of more resources into fewer offspring.
2. Community Ecology
In ecology, a community is an assemblage or association of the populations of two or more different species occupying the same geographical area. The term community has a variety of uses. In its simplest form, it refers to groups of organisms in a specific place or time. Community ecologists study the interactions between the species in communities on many spatial abundance, demography, and interactions between the coexisting populations.
The primary focus of community ecology is on the interactions between populations as determined by specific genotypic and phenotypic characteristics. Community ecology has its origin in European plant sociology. Modern community ecology examines patterns such as variation in species richness, equitability, productivity, and food web structure; it also examines processes such as predator-prey population dynamics, succession, and community assembly.
3. Biome Ecology
Biomes are climatically and geographically defined as contiguous areas with similar climatic conditions on the earth, such as communities of plants, animals, and soil organisms, and are often referred to as ecosystems. Some parts of the earth have more or less the same kind of abiotic and biotic factors spread over a large area, creating a typical ecosystem over that area. Such major ecosystems are termed biomes. Biomes are defined by factors such as plant structures (such as trees, shrubs, and grasses), leaf types (such as broad leaf and needle leaf), plant spacing (forest, woodland, savanna), and climate. Unlike ecozones, biomes are not defined by genetic, taxonomic, or historical similarities.
Ecosystem Ecology:
Ecosystem ecology is the integrated study of biotic and abiotic components of ecosystems and their interactions within an ecosystem framework. This science examines how ecosystems work and relates this to their components such as chemicals, bedrock, soil, plants, and animals.
Ecosystem ecology examines physical and biological structures and examines how these ecosystem characteristics interact with each other. Ultimately, this helps us understand how to maintain high-quality water and economically viable commodity production. A major focus of ecosystem ecology is on functional processes, and ecological mechanisms that maintain the structure and services produced by ecosystems. These include primary productivity (production of biomass), decomposition, and trophic interactions.
4. Evolutionary Ecology
It is concerned with the problems of niche segregation and speciation.
5. Taxonomic Ecology
It is related to the ecology of different taxonomic groups of living organisms.
6. Human Ecology
It is mainly related to population ecology. It studies the inter-relationship between man and man along with the environment. The effects of human beings on the biosphere and the implications of these effects for mankind are the subject matter of human ecology.
7. Eco-system Dynamics
It deals with the ecological study of the process of soil formation, energy flow, productivity, etc.
8. Production Ecology
It examines the gross and net production of different ecosystems like fresh water, seawater, agriculture, horticulture etc. Production ecology attempts for the effective management of the ecosystems so as to maximize production.
9. Ecological Energetics
It deals with energy conservation and its flow in the organisms within the ecosystem.
10. Physiological Ecology (Eco-physiology)
The factors of the environment have a direct relation with the functional aspects of the organism. The eco-physiology deals with the survival of the population as a result of functional adjustment of organisms with different ecological conditions.
11. Habitat Ecology
It deals with the ecological study of different habitats on planet earth and their effects on the organisms living there.
12. Chemical Ecology
It is related to the adaptation of animals to the preferences of particular organisms like insects to particular chemical substances.
13. Ecological Genetics
An ecologist recognized the kind of genetic plasticity in the case of every organism. In any environment, only those organisms that are supported by the environment can survive. Thus, genecology deals with the study of variations of species based on their genetic potentialities.
14. Palaeo Ecology
It is the study of environmental conditions and life of the past ages.
15. Geographic Ecology (Eco-geography)
It focuses light on the study of geographical distribution of animals and plants.
16. Space Ecology
It is concerned with the development of partially or wholly regenerating ecosystems for supporting the life of man during long space flights.
17. Pedology
It deals with the study of soil, especially their acidity, human contents, mineral contents, soil types, etc., and their influence on their organism.
18. Radiation Ecology
It studies the gross effect of radiation and radioactive substances on the environment and living organisms.
19. Ethology
It studies animal behaviour under natural conditions.
20. Sociology
It is the study of ecology and ethology of mankind.
21. System Ecology
It deals with the analysis and understanding of the function and structure of the ecosystem through the use of applied mathematics, advanced statistical techniques, mathematical models, etc.
22. Conservation Ecology
It is the study of land, water, forest conservation, and management. It is also related to the maintenance of biodiversity and the preservation of endangered species.
23. Applied Ecology
In this type of ecological branch, special types of organisms are conserved and economically used. Applied ecology has several more branches are Agronomy, Agriculture, Animal husbandry, Forestry, Wildlife Management, Conservation Ecology, and Pollution Ecology.
24. System Ecology
In this ecological branch, several mathematical models and theories are used for describing the ecological processes.
25. Gene Ecology
In this branch where the changes of genes are discussed for the formation of genetic constituents, new ecads, ecotypes, and new species. Some alternative terms of ecology are Hexicology, Ethology, and Bioecology.
26. Ecotoxicology
It is the study of the fate and action of human-made substances, such as pesticides and detergents in the natural world. Ecotoxicology focuses on the way in which human-made substance affect human health.