Plant Ecology II Notes 2023 MSc Botany 3rd Semester.More than a century ago, in 1958, Charles Darwin (1809-1882) and Alfred Russel Wallace (1823-1913) combinedly credited the theory of evolution by natural selection and published the book “Origin of species”.
Plant Ecology II Notes MSc Botany 3rd Semester
In 1859, Darwin separately published the book called “On the origin of species by means of natural selection”. After the death of Darwin, Neo-Darwinism theory was develope base on genetic character whe the gene was discovere in 1901 by American scientists Margon, Shutton, etc.
Plant Ecology II Notes 2023 MSc Botany 3th Semester
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Facts that influenced Darwin’s thought or Development of the theory of natural selection
- In 1831, Darwin was the naturalist on the Voyage when he was just 22 years old. As a naturalist, he observed, collected, and analyzed specimens of plants, animals, rocks, and fossils. He spent more than three years exploring nature on the island and distant continents.
- Darwin made many observations during the long Voyage, which helped him develop the theory of evolution.
- Darwin follows the idea of Lamarck and assumes that species can change over time. Fossils he found helped conveniently follow Lamarck’s theory.
- From Charles Lyell’s book “Principles of Geology”, Darwin concluded that there had been enough time for evolution to cause the great diversity of life because he saw the earth and its life were very old.
- In late 1830, Darwin attended a meeting of animal breeders and intently read their publications. He was aware that humans could bread animals and plants to have valuable traits by selecting plants or animals which are allowe to reproduce over time to time. They could change an organism’s traits. He called this type of change variation in an organism; artificial selection.
- The term fitness was coine by Darwin and referred to an organism’s relative ability to survive and produce offspring. Variation occurs naturally, So he called this type of selection natural selection.
- Darwin spent several years thinking about the work of Lamarck, Lyell, and Malthus, what he knew about artificial selection and observation, and the results he had made his Voyage. Collecting all ideas, and all together, helped formulate his theory.
- Wallace also traveled to different Places to study nature, and he also developed the same theory of evolution as Darwin. Wallace sent a paper he had written explaining his evolutionary theory to Darwin. Wallace’s idea helped to confirm Darwin’s theory.
- At the time of controversy about the theory of natural selection, Wallace was in Indonesia, and he could not champion Darwin’s defense by adding his point of view. Thus, the theory is calle the Darwinian rather than the Darwin-Wallace theory of evolution.
Plant Ecology II Notes 2023 MSc Botany 3rd Semester
The natural selection process is a continuous process of trial and error on an enormous scale for all living matter.
Natural selection includes the following five elements (factors or causes of natural selection).
- The universal occurrence of variation:
- Every group of organisms (animal and plant) may differ in many ways, known as variation. The Darwin and Wallace period did not know the source of variation and assumed it might be one of the innate properties of the organism. Still, now we know that inherite variations are caused by mutation.
- An excessive natural rate of multiplication:
- Without environmental checks, every species has great reproductive potential (reproductive rate tends to increase geometrically). If all the species remained alive and reproduced, it would soon be challenging to survive, obtain food, and crowd all other species from earth.
- Struggle for existence:
- There is an interspecific or intraspecific, or environmental struggle for survival (competition for food, mates, space, and as well as survival in drought or cold).
- The consequent elimination of the unfit and the survival of only those that are satisfactory adaption:
- Some of the variations shown by living things make it better adaption for them to survive; others are handicaps that bring about the elimination of the possessors. The core of the natural selection theory is the idea of the survival of the fittest.
- The inheritance of mutations or recombination that make for success in the struggle for existence:
- The individual who survives will give rise to the next generation, and with this method, the successful variations are transmitte to the succeeding generation.
- A less fit individual is eliminate before being reproduce.
- Successive generation becomes better adapted to their environment. If the environmental condition changes, further adaption occurs.
- The operation of natural selection over time in many generations may produce descendants (different from their ancestors). This way, two or many more species may arise or produce from a single ancestral stock.
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Criticisms of Darwinism or natural selection theory
- Darwin did not mention vestigial organs, which are in animals.
- The role of mutation in the origin of new species is not include. Without mutation, new species never evolved by natural selection.
- Variation, whether genetic or somatic, because only genetic variations are heredity.
- Darwin’s theory became a failure in Human being due to these reasons; the human population never becomes constant, not only struggling for existence other also continuing life cycles like beggars, and instead of survival, the fitness in man only arrival become most fitted.
Types of natural selection
Population geneticists have categorized three types of natural selection that can occur in nature. These are as follows:
1. Directional selection
- The variation that can occur when a population shows a particular trend through time is referre to as directional selection. It happens when the environment changes constantly. The directional selection process favors individuals that are better adapte to a new environment or situation or new ecological situation.
- The directional selection also transforms the gene pool of a species toward the highest level of adaptedness that can be reached in the new environment.
- A very simple example of directional selection is the neck of a giraffe. Each giraffe has a different neck length. This variation in the trait gives each giraffe various advantages like a giraffe with a longer neck is easy to reach the food source, so better able to survive and reproduce. Over time, long-neck giraffes will reproduce more offspring and pass on their gene to the next generation. Thus, the future generation of giraffes has longer necks. If directional selection remains, this new population can eventually become a new species.
2. Stabilizing selection
- In this type of selection, average values for the given trait are favored eliminating extreme value in a population. It is the most common type of selection occurring in the population and is homeostatic that maintains the status quo. This selection reduces the variability in the population.
- For example: In a plant, plants that are a more height are exposed to more wind and are at risk of being blown over, whereas a short-height plant fails to get an abundant amount of sunlight to prosper. Thus, the plants are average height between the two get both enough sunlight and protection from wind.
3. Disruptive selection
- In this selection, two adaptive traits are selected when the population exists in a heterogeneous environment. It favors the extreme if they have better traits or fitness and intermediates are disadvantageous. This selection results in diversification concerning traits.
- For example, an area that has black, grey, and white bunnies contains both white and black rocks. Natural selection will favor both the traits of white and black since they both prove useful for camouflage. The intermediate trait of grey does not prove useful so selective pressure act against the trait.
The evolutionary biologist also recognized sexual selection and group and kin selection.
- Sexual selection
- Most species of animals are dimorphic (male and female). Males and females are different in terms of color, specialized song patterns, behaviors, sex organs, capability, etc.
- Sexual selection is directly related to differential reproduction, including finding and acquiring a mate, copulation, fertilization, and parental care.
- Those organisms whose more capable of securing mates and is more fitted to the environment. Sexual selection aims to reproduce in which an individual needs to be able to find and protect a mate and produce viable offspring.
- In 1938, Huxley recognized two types of sexual selection; Epigamic selection (based on the choice made between male and female) and Intrasexual selection (this selection is based on the interaction between animals of the same sex, generally between males).
- Group and kin selection
- Group selection is a selection of a group of individuals, favoring one group over the other, leading to the evolution of a trait that is group advantageous.
- The altruistic behavior of an individual involved in kin selection occurs when natural selection favors a trait that benefits related group members.
Importance of natural selection
- Natural selection drives the evolution and diversity of life on earth.
- Favorable traits are transmitted through generations.
- Natural selection can lead to specification, where one ancestor species gives rise to a new and distinctly different species.
Example of natural selection
- Galapagos Finches: Galapagos finches have larger and small beaks. During drought time, the finches with long beaks survived better than those with smaller beaks however, in rainy times, more small seeds were produced, and finches with smaller beaks survived better. Thus, the environment supports both types of beaks.
- The tail of peacock: Peacock females choose their mate according to the male tail. Peacocks, who have the largest and brightest tails mate more often. The components of the biosphere are categorized as biotic, abiotic, and energy components. Abiotic components include non-living elements such as the lithosphere, atmosphere, and hydrosphere, while biotic components include plants, animals, and microorganisms.
The living communities include animals, bacteria, plants, fungi, and human beings. It is derive from the Greek word “bios” and “sphaira” which means “Life” and “Earth’s shape” respectively. The term was coined by Eduard Suess, an English Austrian scientist, in his book titled “The Face of Earth” in which he discussed the relationships betwee living things and how the Earth supports them.
The biosphere encompasses everything from the deepest tree roots to the shadowy depths of the ocean, dense rainforests, and lofty mountaintops. It is also calle the ecosphere. It can be up to 12500 meters above sea level and at least 8000 meters deep in the ocean. Aside from natural biosphere, ones have also been create, such as Biosphere 2, which is perhaps the biggest close ecosystem ever by humans.
Origin and evolution of the biosphere
The first prokaryotes flourished in an oxygen-free biosphere some 3.8 billion years ago. These primitive ancient prokaryotes included single-celled creatures such as bacteria and archaea. Some prokaryotes evolved a distinctive chemical process known as photosynthesis and converted water and carbon dioxide into simple sugars and oxygen with the help of sunlight. The organism’s ability to perform photosynthesis is autotrophy. More species, therefore, were able to use the carbon dioxide in the atmosphere and eventually supplied the atmosphere with oxygen. These creatures ranged from single-celled algae to multicellular autotrophs, such as vascular plants.
The atmosphere gradually changed into a mixture of oxygen and other gases that could support new types of life. More complex living forms were able to evolve as a result of the biosphere receiving more oxygen, such that they acquired different ecological niches. Numerous species of plants and other photosynthetic organisms, which formed the autotrophs of the food chain, increased. Likewise, animals that eat plants or other animals that behave as heterotrophs also developed. Also, to decompose dead plants and animals, bacteria and fungi (decomposers) evolved.
Components of Biosphere
The components of the biosphere are categorize as biotic, abiotic, and energy components. Abiotic components include non-living elements such as the lithosphere, atmosphere, and hydrosphere, while biotic components include plants, animals, and microorganisms.
Abiotic components of Biosphere
I. Lithosphere (Geosphere)
- It forms the terrestrial portion of the biosphere.
- It is the stiff, rocky outer layer of the Earth which is made up of the crust (the rocks that make up the continents and the ocean floor) and the upper mantle’s solid outer layer. These layers support life by giving shelter and sustenance from tiny bacteria to big mammals and lofty trees.
- It also stretches to a depth of almost 60 kilometers, and its lower mantle and core are the only parts that do not support life and are not a part of the biosphere.
- It is the region that contains different gases like oxygen, carbon dioxide, and other gases.
- This gaseous envelope makes it possible to see insects, birds, and other creatures soar high or fly above 2000 meters in the sky.
- With the increase in height, the concentration of oxygen level goes on decreasing, which limits the availability of organisms in the atmosphere. The region in the atmosphere up to which animals or other forms survive or sustain makes up the biosphere.
- Besides providing oxygen for respiration, the ozone layer of the atmosphere plays a crucial role in protecting living forms from the sun’s harmful ultraviolet rays.
- It forms the aquatic portion of the biosphere as all the water components of the Earth, such as waterways, ponds, oceans, etc., are included in it.
- However, several solid forms, such as glaciers, are also included under the hydrosphere.
- It maintains the ecosystem by temperature regulation on Earth and supplying water to all living things.
- Every component of the hydrosphere is responsible for the existence of living forms.
Biotic components of Biosphere
- Plants: These are autotrophic organisms that manufacture their food themselves through a process called photosynthesis. These are the primary producers, becoming the only primary source for all living organisms.
- Animals: These are heterotrophic organisms that depend on primary producers or other animals for their food, release energy and reserve it for future purposes. Thus, they are known as consumers.
- Microorganisms: They serve as decomposers that obtain their nutrition through the breakdown of waste or dead and decayed bodies. Fungi, bacteria, algae, viruses, etc., are under this category.
Energy components of Biosphere
It is the third and most important part of the biosphere, without which life on this planet would not have been conceivable. All biological forms on this planet depend on it for generation and reproduction. Every living thing functions like a machine that transforms one form of energy into another while also using it to do work. Sun is the ultimate source of energy for all living organisms in the biosphere for existence.
Factors affecting Biosphere
- Earth tilting: Tilting of the earth causes seasons and seasonal fluctuations. Seasons are crucial to the continuation of life on Earth as it determines the type of species that will survive in an area.
- Distance between the Earth and the Sun: Lesser the distance from the Sun, the warmer the place, and the greater the distance between the Sun and the Earth, the cooler the place will be.
- Natural disasters: Catastrophes such as landslides, floods, volcanic eruptions, earthquakes, etc. ruin life and property, thereby creating an imbalance in the ecosystem.
- Some smaller factors: Several minor factors, such as changes in climate, humidity, temperature, precipitation, etc., carry the potential to alter the land and living conditions. These factors are responsible for the changes at the molecular level.
The future of the biosphere is dependent on the activities and interactions carried out by the population with its environment. With the increasing population and their notorious activities, such as haphazard utilization of available natural resources, pollution, forests fire, etc., the ecosystem balance gets disturbed.
Protected areas designed for the conservation of plants and animals recognized by UNESCO are known as biosphere reserves. They protect the local wildlife and its diversity. Terrestrial, marine and coastal ecosystems are all included in biosphere reserves. These reserves advocates strategies that balance biodiversity solution and sustainable human usage. It promotes sustainable development appropriate for integrating people and nature and where solutions are sought for biodiversity conservation, economic growth, research, and education. In Yangambi, the Democratic Republic of the Congo, the first biosphere was discovered. Other biosphere reserves are Fuerteventura Reserve in Spain, Gran Arenal Biosphere Reserve in Australia, and Bliesgau Biosphere Reserve in Germany.
Importance of Biosphere
- The components of the biosphere are categorized as biotic, abiotic, and energy components. Abiotic components include non-living elements such as the lithosphere, atmosphere, and hydrosphere, while biotic components include plants, animals, and microorganisms.
- The plants of the biotic communities supply us with raw materials such as food, fuel, and fibers to survive.
- The decomposers of the biosphere play a lead role in the decomposition and biological modification of toxins and other harmful components.
- Naturally available compounds in the terrestrial biosphere help to provide pharmaceutical compounds in the pharmaceutical industries.
- The biosphere’s composition can be studied and managed to serve as an effective marker for regulating the amount of terrestrial pollution.