Introduction to Ecology

DEFINITION AND SCOPE

The term ecology is derived from the Greek "oikos " meaning 'habitation' or 'house'. It refers to the living place of life.  Ecology is the study of organisms at home which is called as the environment. The terms life and environment are inseparable. The Science of Ecology involves: The study of the relation of organisms or a group of organisms to their environment and the study of the totality of man and his environment. Ecology is Environmental Biology. It is well known that Biology is the science of life. Since ecology also deals with the life and its surrounding conditions, it is also called as “ Environmental biology”. 

Ecology deals with:

1. the spatial distribution of an abundance of organisms

2. the temporal changes in the occurrence, abundance and activities of organisms

 3. the interrelations between organisms, communities and populations

4. the structural adaptation and functional adjustments of organisms to the change in environment,

5. the behaviour of organisms under natural environment, the productivity of organisms

6. energy and other natural resources to mankind and

7. the development of interactive models for analytical or predictive purposes.

ENVIRONMENTAL INTERACTIONS

 Ecology deals with organisms, populations, communities, ecosystems and the biosphere. A lot of interactions between the life and the surrounding conditions and among the organic world are expected to happen at all time. Several types of interactions may happen between 

a. an organism & its place of living,

b. an organism & its neighbor

c. an organism & its own community,

d. an organism & other communities,

e. a group of organisms & an organism and

f. a community to a community.

 MAJOR SUB-DIVISIONS

In general, ecology is classified into two major divisions:

Animal ecology : This branch deals with the animal population, its changes, their bahaviour, and their relationships with the environment.

Plant ecology : This branch deals with the relationships of plants to other plants and their environment.  It is known that all animals mostly depend on plants for both food and shelter. Hence, animal ecology deals with both animal and plant communities.

Due to these, the science of ecology is divided into

a) synecology 

b) autecology, based on the organism and habitats.

SYNECOLOGY:

This branch deals with the study of groups of organisms or the community. This is a habitat based study. A habitat is a place where an organism or species population or a community thrives. There are two major habitats as 1. terrestrial habitats and 2. aquatic habitats.

Examples:  Aquatic habitats( water related) - Marine, Fresh water, Estuarine life.

The branches related are: Marine ecology, Estuarine ecology, Limnology, etc

Terrestrial habitats(land based) - life in Forests, Grasslands, Deserts.

The branches related are: Forest ecology, Grassland ecology, etc.

The Synecology includes the study of 1. population characteristics, 2. position of an individual in a population and its relationship (intraspecific), 3. regulation of population, 4. impact of population on the environment, 5. community characteristics and their interrelationships (interspecific), 6. successional changes and 7. the impact of communities over an environment.

AUTECOLOGY

This branch deals with the study of species or the relationship of an organism to one or more environmental conditions. This is also called as species ecology.  It deals with the nutrition, growth, reproduction, development and life history of individual species in an environment.

OTHER BRANCHES OF ECOLOGY

1. Population Ecology : Study of a population, its growth, competition, means of dispersal etc.

2. Community Ecology : Study of distribution of animals in various environments.

3. Ecosystem Ecology : Relation and interaction of plant and animal communities with their total environment. It deals with the formation of soil, chemical cycles, food and feeding relationship, exchange of energy and productivity.

4. Evolution Ecology : Concerned with the manner in which all ecological structure and functions have evolved.

5. Geographical Ecology : Deals with the distribution of organisms over the world and the factors and forces brought out this distribution.

6. Palaeoecology : Deals with the organisms and their environment existed in the distant geological past.

7. Applied Ecology : Deals with wild life management, forest conservation, biological control, animal husbandary and pollution control.

8. Oceanography : Study of marine habitat and organisms.

9. Limnology : Study of life in freshwater bodies.

10. Terrestrial Ecology : This is a major field including a. Forest Ecology, b. Cropland Ecology and c. Grassland Ecology.

Biological levels of organization-genes to biosphere

The biological levels of organization represent the hierarchical structure of life, ranging from individual molecules to entire ecosystems. Each level builds upon the previous one, with increasing complexity and emergent properties.  Overview of the biological levels of organization, from genes to the biosphere:

GENES

Genes are the basic units of heredity and genetic information encoded in DNA molecules. Genes contain instructions for building proteins and controlling cellular processes, such as growth, development, and metabolism.

CELLS

 Cells are the fundamental units of life, consisting of various organelles and structures enclosed within a membrane. Cells carry out essential functions such as metabolism, reproduction, and response to stimuli. Different types of cells specialize in specific tasks within multicellular organisms.

TISSUES

Tissues are groups of similar cells that work together to perform a specific function. Examples include epithelial tissue, connective tissue, muscle tissue, and nervous tissue, which combine to form organs.

ORGANS

 Organs are structures composed of two or more types of tissues that work together to carry out specific functions within an organism. Examples include the heart, lungs, liver, brain, and kidneys.

ORGAN SYSTEMS

 Organ systems are groups of organs that work together to perform integrated functions and maintain homeostasis within an organism. Examples include the digestive system, respiratory system, circulatory system, nervous system, and endocrine system.

ORGANISMS

Organisms are individual living entities capable of carrying out life processes such as growth, reproduction, metabolism, and response to stimuli. Organisms can be unicellular (e.g., bacteria, protists) or multicellular (e.g., plants, animals, fungi).

POPULATION

 Populations consist of groups of individuals of the same species living in the same geographic area and capable of interbreeding. Populations are characterized by factors such as population size, density, distribution, and genetic diversity.

COMMUNITY

 Communities are assemblages of populations of different species that interact and coexist within a particular ecosystem. Communities exhibit species diversity, species interactions (e.g., competition, predation, mutualism), and community structure (e.g., species richness, evenness).

ECOSYSTEM

 Ecosystems are dynamic systems composed of biotic (living) and abiotic (non-living) components interacting with each other within a defined area. Ecosystems include terrestrial ecosystems (e.g., forests, grasslands) and aquatic ecosystems (e.g., lakes, rivers, oceans) and exhibit energy flow, nutrient cycling, and ecological processes.

BIOMES

Biomes are large-scale ecological regions characterized by distinctive climates, vegetation types, and ecological communities. Examples include tropical rainforests, deserts, grasslands, temperate forests, tundras, and aquatic biomes.

BIOSPHERE

The biosphere encompasses all of Earth's ecosystems, biomes, and living organisms, as well as the physical environments in which they exist. The biosphere includes the atmosphere, lithosphere (Earth's crust), and hydrosphere (water bodies), and it represents the interconnected web of life on our planet.

Population Characteristics

Population characteristics refer to the various attributes and features of a population, which are used to describe and understand its composition, dynamics, and behavior. These characteristics provide insights into the size, structure, distribution, growth, and other demographic aspects of populations. 

POPULATION SIZE

 Population size refers to the total number of individuals in a population at a given time. It is a fundamental measure of population abundance and can vary greatly among different species and populations.

POPULATION DENSITY

 Population density is the number of individuals per unit area or volume of habitat. It provides information about the spatial distribution and crowding of individuals within a population.

POPULATION DISTRIBUTION

 Population distribution refers to the spatial arrangement of individuals within a population across a given area or habitat. It can be clumped, uniform, or random, depending on factors such as resource availability, social interactions, and environmental conditions.

AGE STRUCTURE

 Age structure describes the distribution of individuals in different age groups within a population, typically classified as pre-reproductive (juveniles), reproductive (adults), and post-reproductive (seniors). Age structure influences population growth rates, reproductive strategies, and demographic trends.

SEX RATIO

 Sex ratio is the proportion of males to females in a population. It can affect reproductive success, mating behavior, and population dynamics, particularly in sexually reproducing species.

POPULATION GROWTH RATE

Population growth rate is the rate at which a population increases or decreases in size over time, usually expressed as a percentage per unit time. It is influenced by factors such as birth rates, death rates, immigration, and emigration.

NATALITY

Birth rate, also known as natality, is the number of births per unit time per 1,000 individuals in a population. It reflects the reproductive capacity and fertility of a population.

MORTALITY

 Death rate, also known as mortality rate, is the number of deaths per unit time per 1,000 individuals in a population. It indicates the level of mortality and survival within a population.

LIFE EXPECTANCY

 Life expectancy is the average age to which individuals in a population are expected to live. It is influenced by factors such as genetics, healthcare, nutrition, disease prevalence, and environmental conditions.

POPULATION GROWTH PATTERN

Population growth pattern describes the trajectory of population growth over time, which can be exponential (rapid growth), logistic (s-shaped curve with slowing growth), or cyclic (fluctuating over time).

POPULATION DYNAMICS

Population dynamics refer to the changes in population size, structure, and composition over time, resulting from interactions between birth, death, immigration, and emigration processes.

POPULATION HEALTH

Population health encompasses the overall well-being and health status of individuals within a population, including factors such as disease prevalence, nutritional status, access to healthcare, and environmental quality.

Understanding population characteristics is essential for ecological research, wildlife management, conservation planning, public health, urban planning, and policy development. By analyzing population data and trends, researchers and policymakers can assess population health, demographic patterns, and ecosystem dynamics, and develop strategies to address population-related challenges and promote sustainable management of natural resources.

Biotic Interaction

Biotic interactions, also known as biological interactions, are the relationships between living organisms within ecosystems. These interactions can be classified based on the effects they have on the participating organisms, ranging from beneficial to detrimental. Biotic interactions play a crucial role in shaping ecological communities, influencing population dynamics, species distribution, and ecosystem functioning. Biotic interactions can be categorized into positive and negative interactions based on the effects they have on the participating organisms. Positive interactions benefit one or both of the interacting species, while negative interactions harm one or more of the organisms involved.

POSITIVE BIOTIC INTERACTIONS

1. MUTUALISM

Mutualism also called as symbiosis, is a positive interaction where both participating species benefit from the association. Each species provides resources, services, or protection that enhance the fitness and survival of the other.

Examples include pollination by insects and plants, nitrogen-fixing bacteria and leguminous plants, and cleaner fish and their hosts.

Lichens: lichens are symbiotic association between algae and fungi. the body of lichen composed of fungal matrix in which the algal cells are embedded. The fungi provide protection to algal components and also provide moisture and nutrients to them. The algal components in turn will supply carbohydrates for fungus.

Mycorrhizae: They are the symbiotic association between fungi and the roots of some trees. Fungal components help in the absorption of water and minerals by the plants. The plant in turn supplies foot to fungal components.

2. COMMENSALISM

Commensalism is a positive interaction where one species benefits, and the other is unaffected. The commensal species exploits resources or habitat modifications created by the other species without providing any benefit or harm in return.

Examples include epiphytic plants growing on trees, barnacles attaching to whales, and birds nesting in tree hollows.

Climbers and Lianas such as Bauhinia, Tinospora etc. which are rooted in the soil but climb over large trees. These climbers use other trees as support to get enough sunlight, more than that, the supporting plants do not have any positive or negative effect.

3. PROTO- COOPERATION

In proto-cooperation, organisms engage in interactions that provide some benefit to one or both parties involved. The benefits may include access to resources, increased fitness, reduced predation risk, or enhanced reproductive success. Unlike mutualism, proto-cooperation does not involve a high level of specialization or dependency between the interacting species. Proto-cooperation interactions may vary in intensity and duration, and they can be context-dependent, influenced by environmental conditions, resource availability, and the behavior of the interacting organisms.

Examples

Seed dispersal by animals: Some plants produce fruits with nutritious pulp or seeds that are dispersed by animals. While the plants benefit from the dispersal of their seeds to new locations, the animals may obtain food from the fruits. This interaction provides a benefit to both the plant and the animal, but it does not involve the level of coevolution or mutual dependency seen in more specialized seed dispersal mutualisms.

NEGATIVE BIOTIC INTERACTIONS

1. COMPETITION

Competition is a negative interaction where individuals or species vie for limited resources such as food, water, shelter, or territory. It can occur within or between species. Competition can lead to resource partitioning, niche differentiation, and competitive exclusion, where one species outcompetes another, leading to local extinction or niche restriction. The competition in the ecosystem may be of two types:

a. Intraspecific Competition(within population)

b. Interspecific Competition(between population)

2. PREDATION

Predation is a negative interaction where one organism (predator) captures, kills, and consumes another organism (prey) for food. Predation influences population dynamics, prey behavior, and predator-prey coevolution.

Examples include carnivores hunting herbivores, herbivores consuming plants, and parasitoids attacking insect hosts.

3. PARASITISM

Parasitism is a negative interaction where one organism (parasite) benefits at the expense of another organism (host), which is harmed but usually not killed. Parasites obtain nutrients or resources from the host, often causing damage, disease, or reduced fitness.

Examples include ticks feeding on mammals, tapeworms infecting the digestive tracts of vertebrates, and mistletoe plants parasitizing trees.

4. AMMENSALISM

Amensalism is a negative interaction where one organism is negatively affected, while the other organism is unaffected. The negatively affected organism may experience inhibition, suppression, or reduced fitness due to the presence of the other organism.

Examples include allelopathy, where plants release chemicals that inhibit the growth of nearby plants, and the production of antibiotics by microorganisms.

Chlorella vulgaris produces a toxin(chlorellin, an antibiotic) which is harmful to other algae.

5. CAANIBALISM

Cannibalism is a negative type of interaction of individuals in the same population. In cannibalism, bigger individual of a species kill and feeds on smaller individual of same species. Cannibalism is a natural method of population control in the ecosystem.

Community Dynamics

COMMUNITY DYNAMICS

Community dynamics refers to the changes in the structure, composition, and interactions among species within ecological communities over time. These changes result from various ecological processes, including species interactions, population dynamics, environmental factors, disturbances, and evolutionary processes. Community dynamics play a crucial role in shaping the diversity, stability, and functioning of ecological communities. 

SPECIES INTERACTIONS

 Species interactions, such as competition, predation, mutualism, and parasitism, are fundamental drivers of community dynamics. These interactions influence the distribution, abundance, and behavior of species within communities and can lead to changes in community structure and composition over time.

POPULATION DYNAMICS

 Population dynamics, including birth rates, death rates, immigration, and emigration, determine the size and density of populations within communities. Changes in population size and demographic characteristics can affect species interactions, resource availability, and community composition.

SUCCESSION

Succession is the process by which ecological communities undergo predictable and sequential changes in species composition and community structure over time. Primary succession occurs in newly formed habitats with no previous biological community, while secondary succession occurs following disturbances that disrupt existing communities.

DISTURBANCE

Disturbances such as fires, floods, storms, and human activities can disrupt ecological communities, alter species interactions, and create opportunities for colonization and succession. Disturbance regimes influence community composition, diversity, and resilience to environmental changes.

ENVIRONMENTAL FACTORS

 Environmental factors, including climate, topography, soil properties, and resource availability, shape the distribution and abundance of species within communities. Environmental gradients and heterogeneity create niche opportunities and influence species distributions along ecological gradients.

BIOLOGICAL INVASIONS

 Biological invasions by non-native species can impact community dynamics by outcompeting native species, altering species interactions, and disrupting ecosystem processes. Invasive species can become dominant members of communities, leading to changes in community structure and function.

EVOLUTIONARY PROCESSES

 Evolutionary processes, including adaptation, speciation, and genetic drift, influence community dynamics by shaping the traits and interactions of species within communities. Coevolutionary interactions between species can lead to reciprocal adaptations and the diversification of species over time.

ECOSYSTEM FUNCTIONING

 Community dynamics affect ecosystem functioning, including nutrient cycling, primary production, decomposition, and energy flow. Changes in community composition and structure can alter ecosystem processes and services, impacting the resilience and stability of ecosystems.