Ecosystem Structure, Trophic Levels, and Energy Flow
Ecosystems and Trophic Relationships
Life takes place in the biosphere. The biosphere includes the atmosphere (specifically the troposphere), the entire hydrosphere, and the geosphere.
Defining Ecosystems
Contemplating a landscape, we can distinguish between living (biotic) and non-living (abiotic) components. These components are closely interrelated. The set of organisms and the relationships established between them constitute the ecosystem. Within an ecosystem, we distinguish:
- Biocenosis (or Community): All living beings residing in an ecosystem. Individuals of a single species form a population.
- Biotope: The place or geographical area occupied by the community. It is formed by the physical environment (water, air, soil, and rocks) and a number of environmental factors (light, temperature, humidity, pressure, and salinity).
Types of Environmental Factors
The elements and characteristics that affect the environment or the lives of organisms are classified as:
- Abiotic Factors: Non-living components, such as temperature, light, and water, which are directly dependent on the characteristics and composition of the medium.
- Biotic Factors: Factors dependent on the presence and interactions of living beings (e.g., predation, competition).
Organism Adaptations to the Environment
An adaptation is a hereditary feature of an organism that promotes its reproduction and survival.
- In animals, many adaptations are aimed at protection against temperature fluctuations. Obtaining food and defense mechanisms are also biotic factors that have driven many adaptations.
- In plants, the presence of water is the main factor that determines physiological and structural adjustments.
Trophic Relationships in the Ecosystem
The interactions that occur between the components of a community regarding nutrition are called food or trophic relationships.
Classification of Trophic Levels
The organisms that form an ecosystem obtain food in very diverse ways, defining distinct trophic levels:
- Producers: Autotrophic organisms that produce their own food (e.g., plants, algae).
- Consumers: Heterotrophic organisms that consume organic matter from other living beings.
- Primary Consumers: Herbivores.
- Secondary Consumers: Carnivores (feeding on herbivores).
- Tertiary Consumers (or Superpredators): Feed on carnivorous animals.
- Decomposers: Heterotrophic organisms that feed on dead matter and the remnants of living beings (e.g., bacteria, fungi).
Food Chains and Food Webs
A food chain consists of a series of organisms linearly ordered, where each individual consumes the preceding individual. Multiple interconnected food chains form a food web.
Matter and Energy Flow in Ecosystems
In an ecosystem, matter flows cyclically (biogeochemical cycles).
Energy flow is not cyclic. A portion of the energy released by every organism during respiration is ceded to the environment as heat and cannot be reused by the ecosystem. This results in a unidirectional flow of energy.
Population Dynamics (Growth and Decline)
Population growth or decline refers to the change (increase or decrease) in the number of individuals of a population over a specific period of time.
Ecological Equilibrium
When environmental conditions are stable, the number of organisms in the ecosystem and their biomass (the amount of living matter it contains) self-regulates. When this occurs, we say that the ecosystem is in balance.
Ecological Succession and Ecosystem Change
Ecological succession describes the process of change in the species structure of an ecological community over time. For example, after a forest fire occurs, the ground is soon occupied by grass, which develops into a meadow with bushes and shrubs. In this process, the community has passed through the meadow and scrub stages to reach a mature ecological community (the forest). This gradual change is called succession.
Impact of Human Activity on Ecosystems
Human activities significantly influence ecosystems, often negatively. Key impacts include:
- Excessive hunting and fishing.
- Pollution (contamination).
- Anthropogenic fires.
- Transformation and destruction of land (habitat loss).
Energy Sources for Human Use
Most of the energy we use to power our civilization is derived, directly or indirectly, from living things or their remains.
Fossil Fuels
Fossil fuels, such as coal, oil, and natural gas, were formed from the remains of plants and marine organisms that were buried under layers of mud millions of years ago.
Biomass as a Renewable Energy Source
Biomass energy is utilized in two main ways:
- Direct Combustion/Fermentation: Direct burning of biomass waste in power plants, or fermentation in landfills designed to produce methane gas.
- Biofuel Production: Used for vehicles, such as biodiesel (derived from sunflower, rapeseed, or other crops) and bioalcohol (derived from raw sugar crops).