Introduction To Organisms And Its Environment
* Ecology is a subject which studies the interactions among organisms and between the organism and its abiotic environment.
* Ecology deals with four levels of biological organisation-organisms, populations, communities and biomes.
* Each organism is surrounded by a host of abiotic and biotic components of the environment with which it continuously interacts.
* Abiotic components of the environment are temperature, water, light, soil, humidity and wind.
* Biotic components of the environment are pathogens, parasites, predators and competitors.
* Annual variations in temperature and precipitation are responsible for the formation of major biomes such as deserts, rainforests and tundra.
* Each biome is affected by local and regional variations, which has resulted in the formation of a wide range of habitats.
Major Abiotic Factors
* Some major abiotic factors of the environment are temperature , light, water and soil.
* Organisms that tolerate a wide range of temperatures are called eurythermal, while organisms that tolerate a narrow range of temperatures are called stenothermal.
* The levels of thermal tolerance of different species greatly influence their geographical distribution.
* Organisms that tolerate a wide range of salinities are known as euryhaline, while organism that tolerate a narrow range of salinities are known as stenohaline.
* In forests, many small shrubs and herbs are able to survive as they are adapted to synthesise their food in low sunlight conditions.
* The nature and properties of soil vary in different regions of our planet.
Responses to Abiotic Factors
* A change in abiotic conditions also affects the organisms living in that habitat.
* To respond to stressful conditions, various organisms regulate, conform, migrate , hibernate, aestivate or suspend themselves.
* Homeostasis is defined as a physiological process by which an organism regulates its internal environment in response to the fluctuating external environment.
* Organisms that are capable of maintaining homeostasis by physiological or behavioural means are called regulators.
* Organisms that partially regulate their internal environment or conform to external conditions are known as conformers.
* Migration is seen in animals that are capable of moving from stressful environmental conditions to a place that offers a favourable climate.
* Plants usually suspend themselves in unfavourable conditions.
* During unfavourable conditions, bacteria , fungi and lower plants produce thickwalled spores, while higher plants produce seeds and other vegetative reproductive structures.
Adaptations by Organisms
* To adapt to unfavourable conditions, organisms undergo morphological, physiological and behavioural changes.
* Adaptation is any attribute of the organism that enables it to survive and reproduce in its habitat.
* Plants in the tropical rainforests have drip tips and thick, waxy surfaces which allow water to run off.
* Desert plants have spongy stems, which store water and leaves that are reduced to tiny pointed spines, while desert animals have adapted themselves to survive without water for days.
* Mammals from colder climates generally have shorter tails, limbs and ears, which help reduce the loss of heat.
* Some marine invertebrates and fish thrive in deep, ocean waters and exhibit a fascinating array of biochemical adaptations.
* Some organisms such as earthworms, frogs, moles and snakes burrow into the soil to escape the above-ground heat.
Population Attributes
* Population is a group of individuals belonging to the same species living in a given geographical area that share or compete for similar resources and interbreed only among themselves.
* A population has certain characteristics or attributes such as birth rates and death rates, sex ration, age distribution and population density.
* Birth and death rates are expressed in terms of per capita, that is , by dividing the total number of births or deaths y the total populations that exists in a given time period.
* At any point in time, a population consists if individuals of different ages, who belong to pre-reproductive, reproductive and post-reproductive age groups.
* The shape of the age pyramid reflects the growth status of a population and indicates whether the population is growing, stable or declining.
* Population size, also known as population density, is denoted by the letter ‘N’ , which can be a numerical density or biomass density.
Population Growth
* Populations are dynamic. They are constantly changing due to their interactions with various biotic and abiotic factors.
* Natality is the number of births in a population that are added to the initial density during a given period.
* Mortality is the number of deaths in a population during a given period.
* Immigration is the number of deaths in a population during a given period.
* Emigration is the number of individuals of a population who leave the habitat and go elsewhere during a given period.
* In a population, natality and immigration result in an increase in population density while mortality and emigration result in a decrease in population density.
* When resources are unlimited, population growth is exponential but when resources are limited, the growth pattern is logistic.
* The intrinsic rate of natural increase(r) is a measure of the inherent potential of a population to grow.
* The maximum number of individuals that can be supported in a habitat is called the carrying capacity (K) of the species.
Mutualism, Commensalism and Amensalism
* When populations of two different species interact, it leads to interspecific interactions.
* Interspecific interactions may benefit, harm or have a neutral effect on one or both species.
* In commensalism, the interaction is beneficial to one species and neutral to the other.
* In mutualism, both species benefit from the interaction.
* In amensalism, one species is harmed and the other remains unaffected.
* Some of the most fascinating examples of mutualism are seen in plant-pollinator interactions.
* Mutualists, especially in plant-animal interaction, exhibit the phenomenon of coevolution.
Population Interactions- Competition and Parasitism
* When populations of two different species interact, it leads to interspecific interactions, which may benefit, harm or have a neutral effect on one or both species.
* During competition, both species lose out during interaction while in parasitism, the interspecific interaction benefits one species and harms the other.
* Competition is defined as a process in which the fitness of one species, measured in terms of its intrinsic rate of natural increase (r), is significantly lowered in the presence of another species.
* Competition may occur between closely related species as well as unrelated species for the same limiting resources.
* When the feeding efficiency of one species is reduced in the presence of another species, it is known as interference competition.
* By the mechanism of resource partitioning , species could avoid competition by choosing different developing or foraging patterns.
* Parasites that feed on the surface of a host are called ectoparasites while those that live inside a host are called endoparasites.
* Some birds show brood parasitism, in which the parasitic bird lays its eggs in a host’s nest for incubation.
Population Interactions- Predation
* All species belonging to the plant or animal kingdom not only co-exist but also depend on each other for their survival.
When populations of two different species interact, it leads to interspecific interactions, which may benefit, harm or have a neutral effect on one or both species.
* When both species benefit from interaction, it results in mutualism.
* When both species lose during interaction, it results in competition.
* In both parasitism and predation, the interspecific interaction benefits one species while it harms the other species.
* When interspecific interaction is beneficial to one species and neutral to another, the
* interaction is known as commensalism.
*During interaction, if one species is harmed and the other is unaffected, the interaction is known as amensalism.
* Predation helps in the transfer of energy from one trophic level to another.
* Predation keep prey populations under control and help maintain species diversity.