DEPARTMENT OF BIOLOGICAL SCIENCES, USMANU DANFODIYO
UNIVERSITY, SOKOTO
(BIO 101)
ECOLOGY
Being a First Semester Lecture Note
MARCH, 2024
What is Ecology?
Ecology is the scientific study of the relationships between organisms and their
environment, encompassing both living (biotic) and non-living (abiotic)
components. It seeks to understand how organisms interact with each other and
with their surroundings, as well as how these interactions influence the
distribution, abundance, and diversity of life on Earth. Ecology provides insights
into the functioning of ecosystems, the dynamics of populations, and the
sustainability of natural systems.
The History of Ecology
The history of ecology can be traced back to ancient civilizations, where
observations of nature and the environment laid the foundation for ecological
principles. In the 17th and 18th centuries, the establishment of natural history
museums and botanical gardens facilitated the collection and classification of
plants, animals, and fossils. Explorers and naturalists, such as Carl Linnaeus and
Charles Darwin, made significant contributions to the cataloging and
understanding of biodiversity. However, modern ecology as a scientific discipline
began to emerge in the late 19th and early 20th centuries, driven by advancements
in fields such as biology, botany, zoology, and environmental science. Ancient
civilizations, including the Greeks, Romans, and Chinese, made observations of
the natural world and recognized patterns in the distribution of plants, animals, and
ecosystems. Early naturalists, such as Aristotle and Theophrastus, documented the
diversity of life and speculated about ecological relationships.
Emergence of Ecology as a Scientific Discipline:
The term "ecology" was coined by the German scientist Ernst Haeckel in 1866,
derived from the Greek words "oikos" (household) and "logos" (study). Haeckel
emphasized the interrelationships between organisms and their environment, laying
the groundwork for modern ecological theory. In the late 19th and early 20th
centuries, pioneering ecologists such as Charles Elton, G. Evelyn Hutchinson, and
Henry Gleason conducted studies on populations, communities, and ecosystems.
Their research laid the foundation for concepts such as food webs, trophic
interactions, and species diversity. In the mid-20th century, the concept of
ecosystems gained prominence, emphasizing the interactions between living
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organisms and their physical environment. Ecologists like Eugene P. Odum and
Howard T. Odum pioneered the study of energy flow, nutrient cycling, and
ecosystem dynamics.
Global Environmental Awareness and Modern Ecological Research The latter
half of the 20th century witnessed growing concerns about environmental
degradation, pollution, and habitat loss, leading to increased awareness of human
impacts on the environment. Ecologists played a key role in advocating for
conservation measures, sustainable resource management, and biodiversity
conservation. Today, ecology encompasses a wide range of sub-disciplines,
including conservation biology, landscape ecology, microbial ecology, and urban
ecology, among others. Advances in technology, such as remote sensing,
molecular genetics, and computational modeling, have expanded the scope and
complexity of ecological research, allowing scientists to address pressing
environmental challenges and informed conservation efforts.
ELEMENTS OF ECOLOGY
Ecology, as a scientific discipline, encompasses various elements that contribute to
understanding the interactions between organisms and their environment. Here are
some key elements of ecology:
Organisms: Organisms are the fundamental units of ecology. Ecology studies how
different organisms interact with each other and with their environment, including
other living organisms and abiotic factors like temperature, water, and nutrients.
Population: A population consists of individuals of the same species living in a
particular area. Population ecology examines factors such as population size,
density, distribution, and dynamics, including birth rates, death rates, and
migration.
Community: A community comprises multiple populations of different species
coexisting in the same area and interacting with each other. Community ecology
investigates species interactions, such as competition, predation, mutualism, and
symbiosis, and their effects on community structure and dynamics.
Ecosystem: An ecosystem includes all living organisms (biotic) and their physical
environment (abiotic) interacting within a defined area. Ecosystem ecology studies
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the flow of energy and nutrients through ecosystems, as well as the cycling of
materials such as carbon, nitrogen, and phosphorus.
Habitat and Niche: A habitat is the specific environment where an organism lives
and obtains the resources it needs to survive. That is, an area occupied by a biotic
community or a natural environment in which an organism lives. Basically, there
are two types of habitat, aquatic and terrestrial habitat. A niche refers to the
specific portion occupied by a particular species or organism and the role or
function of an organism within its habitat, including its interactions with other
organisms and its utilization of resources. This entails the functional position of an
organism within the community. For example, a Caterpillar and an Aphid which
lives on the same plant occupies different functional positions or ecological niche
on the plant. The Caterpillar lives mainly on the leaves and feeds on them while
the Aphid lives on the young shoot and sucks sap from it. Although both organisms
live on the same habitat, each of them has its own living space and source of food.
Biotic and Abiotic Factors: Biotic factors are living components of an ecosystem,
such as plants, animals, fungi, and microorganisms which can be grouped into
producers, consumers, decomposers. Abiotic factors are non-living components,
including climatic factors such as temperature, precipitation, sunlight, and water
availability, edaphic factors such as topography, rock and soil type, inorganic
materials and nutrients such as carbon (iv)oxide, nitrogen, oxygen, calcium,
phosphorus etc., which influence the distribution and abundance of organisms.
Biomes: Biomes are large-scale ecological regions characterized by distinct
climate, vegetation, and animal life. It can be defined as the largest community of
living organisms. Examples of biomes include tropical rainforests, deserts,
grasslands, and tundra, each with unique ecological characteristics and species
compositions.
Ecological Succession: Ecological succession refers to the long term, gradual and
progressive process of change in community structure, species composition,
diversity and number over time in a particular ecosystem. Primary succession
occurs in areas devoid of soil or borne vegetation, while secondary succession
occurs in areas with existing soil and vegetation.
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Conservation and Management: Ecologists play a crucial role in the
conservation and management of natural resources and ecosystems. They study the
impacts of human activities on the environment, develop strategies for sustainable
resource use, and implement conservation measures to protect biodiversity and
ecosystem health.
Other components of ecology includes, atmosphere, Lithosphere, Hydrosphere as
discussed in the lecture.
THE INTERRELATIONSHIP BETWEEN ORGANISMS
Ecology examines various interactions between organisms and their environment,
including energy flow through food webs and trophic levels, nutrient cycling, and
the effects of disturbances, such as natural disasters and human activities, on
ecosystems. The interrelationship between organisms, also known as ecological
interactions (species interactions), refers to the various ways in which organisms
interact with one another within ecosystems. These interactions play a fundamental
role in shaping the structure and function of ecological communities. There are
several types of ecological interactions, each with its own impact on the dynamics
of populations and communities:
Competition: Competition occurs when two or more organisms vie for the same
limited resources, such as food, water, or territory. It can be intraspecific (between
individuals of the same species) or interspecific (between individuals of different
species). Competition can influence the distribution and abundance of species and
may lead to niche differentiation or competitive exclusion. For example different
plant species competing for sunlight, water, and nutrients in the forest.
Predation: Predation involves the consumption of one organism (the prey) by
another organism (the predator). Predators exert selective pressure on prey
populations, influencing their abundance, distribution, and behavior. Predation can
also drive adaptations in both predators and prey, leading to co-evolutionary
dynamics. For example Lion and goat, Snake and mouse, Hawk and chicks.
Mutualism: Mutualism is a symbiotic relationship in which both participating
species benefit from the interaction. Examples of mutualistic relationships include
pollination by insects (the relationship between bees and flowers, where bees
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obtain nectar and pollen for food while pollinating flowers, which allows plants to
reproduce), nitrogen-fixing bacteria in plant roots, and cleaning symbiosis between
cleaner fish and larger marine organisms. Mutualistic interactions contribute to
ecosystem stability and function.
Commensalism: Commensalism occurs when one organism benefits from the
interaction, while the other is neither helped nor harmed. An example is epiphytic
plants, which grow on the branches of trees and gain access to light without
affecting the host tree. Commensal relationships are relatively rare compared to
other types of interactions.
Parasitism:Parasitism is a relationship in which one organism (the parasite)
benefits at the expense of another organism (the host). Parasites derive nutrients or
resources from the host, often causing harm or reducing the host's fitness.
Examples include tapeworms in vertebrates and parasitic plants that obtain
nutrients from their hosts.
Amensalism: Amensalism is a type of interaction in which one organism is
negatively affected, while the other organism is unaffected. For example,
allelopathic plants release chemicals that inhibit the growth of neighboring plants,
without any benefit to themselves. An example is the release of toxins by some
plants that inhibit the growth of nearby plants
These ecological interactions are interconnected and can have cascading effects
throughout ecosystems. Understanding the dynamics of these relationships is
essential for elucidating ecological processes, predicting ecosystem responses to
environmental change, and informing conservation and management efforts.
TYPES OF HABITAT
Habitat is a specific place or natural environment where a particular species of
organism or a biological community naturally lives, thrives, and interact with their
surroundings. They can vary widely in terms of physical characteristics, such as
climate, topography, vegetation, and soil composition. Similarly, habitats can vary
widely in size, ranging from a small rock crevice to a vast rainforest, and they
provide the essential conditions necessary for an organism's survival and
reproduction. These conditions include factors like climate, food sources, shelter,
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and other resources required for the species to meet its life cycle needs. Habitats
can be categorized into various types based on their characteristics and the
organisms that inhabit them. Some common habitat types include:
Terrestrial Habitats:
Forest: Forests are characterized by dense vegetation dominated by trees. They
can be further classified into tropical rainforests, temperate forests, and boreal
forests, each with distinct plant and animal communities.
Grassland: Grasslands are vast open areas covered predominantly by grasses, with
few trees or shrubs. They include savannas, prairies, and steppes and support a
diverse array of herbivores and grazing animals.
Desert: Deserts are arid environments with low precipitation and extreme
temperatures. They can be hot (like the Sahara Desert) or cold (like the Gobi
Desert) and are adapted to drought-resistant plants and animals.
Tundra: The tundra is a cold and treeless biome found at high latitudes or high
elevations. It has a short growing season and is characterized by permafrost,
mosses, lichens, and hardy grasses.
Aquatic Habitats:
Freshwater: Freshwater habitats include rivers, lakes, ponds, streams, and
wetlands. They support diverse aquatic life, including fish, amphibians, insects,
and aquatic plants.
Marine: Marine habitats encompass oceans, seas, coral reefs, and estuaries. They
cover more than 70% of the Earth's surface and are home to an incredible variety
of marine organisms, ranging from microscopic plankton to large marine
mammals.
Urban Habitats:
Cities: Urban habitats consist of human-built environments such as cities, towns,
and suburbs. They are characterized by a mix of residential, commercial, and
industrial areas and can support unique assemblages of plants and animals adapted
to urban conditions.
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Suburbs: Suburban habitats are transitional zones between urban and rural areas,
often characterized by a mix of residential housing, parks, and green spaces. They
can provide habitat for wildlife species that have adapted to human-dominated
landscapes.
Specialized Habitats:
Caves: Cave habitats are found underground and provide shelter for a variety of
cave-adapted organisms, including bats, cave-dwelling insects, and unique cave-
dwelling fish.
Mangroves: Mangrove forests grow along tropical coastlines and are characterized
by salt-tolerant trees and shrubs. They serve as important nursery habitats for fish
and provide protection against coastal erosion and storms.
Each habitat has its own unique characteristics and supports a specific set of plant
and animal species adapted to its environmental conditions. Understanding these
habitats and their biodiversity is essential for conservation and ecosystem
management efforts.
J. D. TANKO
