The Earth’s Complex Systems and Ecosystems
1. The Earth: A Complex System
The Gaia hypothesis, described in the text at the beginning of this unit, states that the planet Earth behaves like a system. Furthermore, it can be considered a complex system, because it is made up of interacting subsystems.
Atmosphere: Mix of gases which forms the outer layer of the planet.
Hydrosphere: All the planet’s water, including water contained in living things.
Geosphere: Subsystem made up of minerals, rocks and soil
Biosphere: Subsystem made up of all living things, which depend on one another and their environment.
1.1. The Biosphere and Ecosystems
The term biosphere refers to the subsystem of the Earth which is made up of all the living things which inhabit our planet and all the relationships between them.
The biosphere also includes the interactions between living things and their environment, as well as the phenomena taking place in the environment. The components of the biosphere are organised into ecosystems. So, the biosphere can also be defined as the total of all the ecosystems on Earth.
An ecosystem is a natural system, made up of a group of living organisms (the community or biocenosis) which interact with one another and with the physical environment, or biotope, that they inhabit. The science that studies this is called ecology.
((((Biotope= SOL, FACTORES AMBIENTALES, HUMEDAD…
Biocenosis= FLORA, FAUNA, RELATIONSHIPS BETWEEN LIVING THINGS))))
1.2. Components of ecosystems: Biotopes
Biotopes are defined as the natural physical surroundings of an ecosystem, including its physical and chemical properties.
A biotope’s characteristics depend on the abiotic components of the ecosystem, that is, non-living things: soil, water, light, temperature, etc.
Temperature, Wind, Humidity, Light, Currents, Distance from sea, Latitude, Salinity, Contours, Water bodies, Altitude
Some abiotic factors may be so scarce, or even totally absent, that they impede life. These are called limiting factors.
A habitat is the place or physical area occupied by a species within an ecosystem. Habitats are determined by the area’s abiotic components.
1.3. Components of ecosystems: Biocenosis
We use the term biocenosis, or community, to refer to the set of populations of different species which inhabit a specific area, or biotope, which provides the environmental conditions they need in order to survive.
The biocenoses of ecosystems contain the following levels of organisation:
Species: group of similar organisms which can reproduce with one another and produce fertile offspring.
The individual organisms of a single species which inhabit a specific area make up the population.
A group of populations which live together in the same ecosystem form a community or biocenosis.
2. Structure of ecosystems
In ecosystems, living matter is organised into trophic levels which determine the ecosystem’s structure. The soil also stores mineral salts and a certain amount of water and oxygen, as well as necromass and other components.
2.1. Trophic Levels
Organisms which share the same kind of food belong to the same trophic level.
Trophic Levels:
Producers: Autotrophic organisms which convert inorganic matter into organic nutrients. (Photosynthesisers, Chemosynthesisers)
Consumers: Heterotrophic organisms which consume the nutrients created by the producers.
(Primary= herbivores/// Secondary= May be = Carnivores, Omnivores, Detritivores, Saprophytes, Coprophagous, Parasites/// Tertiary= Apex predators, Omnivores, Scavengers)
Decomposers and mineralisers: Heterotrophic organisms which convert nutrients into inorganic matter.
The first trophic level is made up of producers autotrophic organisms which consume inorganic matter with low energy from the soil and atmosphere. The majority of them are photosynthesisers, as they use light as their source of energy All organisms, both producers and consumers, respire in order to access the energy stored in the form of chemical bonds in nutrients.
2.2. Food chains and webs
By mapping out the exchange of matter and energy between the trophic levels of an ecosystem, we can establish its food chains and webs.
A food chain is a linear sequence of organisms of different trophic levels in which each organism consumes the preceding one.
2.3 Ecological Pyramids
Ecological pyramids are graphic representations of the general structure of an ecosystem. They are organised into trophic levels and producers always form the base layer.
Each trophic level is represented by a layer whose size is proportional to the amount of matter (biomass), energy or the number of organisms that that level contains. Depending on the factor used, they are classified as biomass, energy or numbers pyramids.
Ecological pyramids help us study the structure and functioning of ecosystems using trophic parameters. They include:
Biomass (8). This shows the amount of organic matter, alive or dead, in w trophic level or in an ecosystem. It is measured in grams of carbon per square centimetre (gC/cm) or kilocalories per square metre (Kcal/m),
among other units. Productivity (P). This is a measure of energy flow. It is measured in joules UI and is calculated with this formula: productivity biomass/time, or P=8/t. There are two kinds of productivity grass (GP) or total, and not (NP), which is productivity minus respiration (R), i.e. NP GP-R.
3. Dynamics of ecosystems
The way ecosystems work, or the dynamics of ecosystems, depends on the energy flow and the matter cycle in them. Le, how matter and energy circulate through the trophic levels.
3.1 Energy and ecosystems the 10% rule
Energy usually enters land ecosystems in the form of light from the Sun, and does so at the trophic level of the producers. Autotrophic organisms use this energy to create complex molecules, with many chemical bonds, from simpler molecules with fewer bonds. It is in these bonds that energy accumulates. Part of this energy is used by living things and part is lost in the form of heat.
The 10% rule states that the energy that passes from a given trophic level to the next is approximately 10% of the energy accumulated there.
3.2 Self-regulation in ecosystems
In ecosystems, the organisms that make up a biocenosis interact with one another. These interactions form part of ecosystems’ self-regulation mechanisms
A. Interactions in biocenoses
The relationships between the organisms in a biocenosis are classified into two general categories: interspecific relationships and intraspecific relationships.
Interspecific relationships
Interspecific relationships occur between organisms of different species. The relationships may relate to feeding, cooperation or competition.
An ecosystem’s interspecific relationships define the ecological niches that the living organisms occupy in that ecosystem.
The ecological niche of a species is the function the organisms perform in the ecosystem, which determines their survival strategy.
The ecological niche does not just mean the physical space or habitat of a species. It also refers to the set of interactions it has with the community
Intraspecific relationships
Intraspecific relationships, whether they relate to competition (-) or cooperation (+), occur between organisms of the same species.
Relationships of competition give rise to phenomena such as territorialism, while relationships of cooperation produce many different types of alliances.
B. Interactions between biotopes and biocenoses
Environmental factors in the biotope determine the survival and quantity of the organisms that inhabit it. That a why they also affect the organisms geographical distribution.
Tolerance limits
The minimum and maximum values of an environmental factor between which a species can survive are called tolerance limits. They define the tolerance interval or ecological amplitude of the species
Eurytopic species are undemanding in relation to the values of a given environmental factor. Their tolerance lists are wide and their ecological amplitude is high. These are generalist species with a wide geographical distribution
Stenotopic species are highly demanding in terms of the values of a given environmental factor. Their tolerance limits are narrow and their ecological amplitude is low. These are specialist species whose geographical distribution is limited
4. Adaptation of living things
Living things interact with both biotic and abiotic environmental conditions. and adapt in different ways in order to survive in their environment
A biological adaptation is an anatomical, physiological or behavioural trait in a species which increases the organisms’ chances of survival, or the effectiveness of their reproduction in that environment.
4.1 Types of adaptation
There are three types of adaptation:
Anatomical or morphological, such as the transformation of the limbs of whales and dolphins (marine mammals) into fins adapted for movement in water.
Physiological or functional, such as homeothermy in birds and mammals.. which allows them to regulate their body temperature internally.
Behavioural or ethological, such in courtship in birds, seeking shade, etc.
4.2. Essential adaptations
Living organisms are distributed across two main environments, water and land, where the determining conditions mean the organisms have to make essential adaptations in order to survive.
A. Essential adaptations in the land environment
The conditions considered to be determinants for survival in the land environment are light, temperature and atmospheric humidity.
B. Essential adaptations in the water environment
The conditions considered to be determinants for survival in the water environment are light, amount of oxygen dissolved in the water, salinity. density and hydrostatic pressure.
5. Evolution of ecosystems
As you already know, ecosystem populations interact with one another and with the environment’s abiotic conditions, regulating their own size and geographical distribution. This way, the community remains stable in a dynamic balance.
5.1. Ecological succession
Gradual changes take place over time in both environmental conditions and the biocenosis
We refer to the natural and consistent process of change that an ecosystem undergoes over time as ecological succession.
Ecological succession has several stages:
1. Initial or establishing stages, in which generalist species of small animals predominate. The number of ecological niches is small and little biomass is stated.
2. Intermediate or maturing stages, in which specialist populations appear. The number of ecological niches grows and the amount of stored biomass increases. The size of the organisms and the number of species also increases
3. Final stage or climax. This is the highest level of ecosystem organisation Biodiversity, the number of ecological niches and the amount of stored biomass are all high. Food webs in climax communities are complex.
5.2 Ecotones
Ecosystems have boundaries, but there are transition zones between different ecosystems.
The transition zones between two neighbouring ecosystems are called ecotones.
The phenomenon known as the edge effect occurs in ecotones. It means that there is an increase in the diversity and density of organisms that inhabit them. Ecotones have certain characteristics in common with the neighbouring biotopes, so they share species with the neighbouring communities.
((((UN ECOTONO ES LA TRANSICIÓN DE UN HÁBITAT A OTRO POR ASÍ DECIRLO, POR EJEMPLO DE HABITAT DE TIERRA, LUEGO HAY UN ECOTONO Y ESTA EL ACUÁTICO.)))
6. Cycle of matter in ecosystems: Biochemical cycles
The chemical elements that form living matter are carbon, oxygen, nitrogen, phosphorous and sulphur. Known as bioelements, they are found in the atmosphere, the hydrosphere and the geosphere. Living things use these bioelements to make their tissues.
Biogeochemical cycles are the closed circuits that the elements travel round, forming living things (bio-) and the environment (-geo-), and which are affected by changes (chemical). Matter is recycled through these cycles.
Through photosynthesis, producers incorporate energy to ecosystems by forming the bonds that transform inorganic matter into organic matter. Decomposing and mineralising organisms use these organic nutrients and return the elements to the soil, where they are stored in the form of inorganic matter.
Therefore, for organisms to live they need not just energy but also certain chemical elements, called biogenic elements, which form part of their cells and tissues.
They can be found in the biosphere, but need to be recycled constantly to ensure their availability. Without them, life would not be possible.
The cycle of matter in the biosphere is possible thanks to biogeochemical cycles.