Focus on how primary production interacts with immune systems and contributes to ecosystems.
Central theme: Movement of energy and nutrients throughout ecosystems.
Trophic Levels
There are several levels in an ecosystem characterized by the role of organisms concerning what they eat and what eats them.
Primary producers: Organisms that produce energy through photosynthesis; typically plants and algae.
Primary consumers: Herbivores that consume primary producers; known as the second trophic level.
Secondary (and higher) consumers: Carnivores that eat herbivores; include the third, fourth, and higher trophic levels.
Trophic levels can reach higher than six, but most ecosystem services occur within the first five or six levels.
Detritivores: Organisms that consume dead organic matter (detritus).
Play a crucial role in decomposing matter that is not consumed by herbivores.
Their function is exceedingly vital on land where a large amount of organic production ends as detritus.
Dead Organic Matter
Definition of detritus: Dead organic material that is crucial for detritivores and cycles within the ecosystem.
Decomposers include bacteria and fungi, which break down detritus into simpler compounds for nutrients recycling.
Invertebrates aid in this process by shredding the material.
Clarification on trophic levels regarding detritivores:
Detritus represents the first trophic level, while detritivores represent the second trophic level, comparable in position to herbivores.
Energy Flow in Ecosystems
The source of energy in ecosystems can be categorized into two types:
Autotrophic (autochthonous): Energy produced internally by organisms like plants and algae.
Allochthonous: Energy that comes from external sources, such as dead leaves falling into water bodies (streams).
Energy flow is complicated by the fact that most energy is lost when moving between trophic levels, often in forms such as heat, as stated in the second law of thermodynamics.
There is always an energy loss during trophic transfers which can lead to biomass pyramids.
Example: Energy transfer is illustrated through biomass pyramids, where there is a sharp decline in biomass at each trophic level.
Aquatic systems do not consistently follow the same pyramid structure due to various lifespans of producers and consumers.
Aquatic vs. Terrestrial Systems
Trophic levels and efficiency differ between aquatic and terrestrial ecosystems due to structural adaptations of plant life and factors like light competition.
In terrestrial systems, only about 13% of the produced biomass is consumed, while in aquatic systems, over one-third is typically consumed.
Plants on land, such as trees, face gravity, making them structurally heavier and harder to consume compared to more buoyant, palatable algae in water.
Herbivory Dynamics
Question of why herbivore populations do not keep growing despite the abundance of potential food sources (the ‘world is green’ paradox).
Constraints include
Predators: Control herbivore populations, reducing overpopulation.
Plant defenses: Secondary compounds, thorns, and spines impede herbivory.
Nutritional content: Terrestrial plants have a higher carbon to nitrogen ratio, making them harder to assimilate compared to herbivorous diets, affecting consumption efficiency.
Trophic Efficiency
Trophic efficiency defined as the measure of energy transfer between trophic levels.
Components of trophic efficiency:
Consumption Efficiency: The percentage of the lower trophic level consumed.
Assimilation Efficiency: Percentage of ingested food that is absorbed into the body.
Production Efficiency: The portion of assimilated energy converted into new biomass.
Higher efficiency ratios can be observed in aquatic systems compared to terrestrial. Carnivores generally have higher consumption efficiency than herbivores.
Herbivores face challenges from plant materials like cellulose that inhibit efficient digestion.
Ecological Dynamics and Examples
Case study visibility: Noticing population dynamics in sea lions based on dietary changes indicating the quality of the food consumed over time.
Shift from high-fat herring to lower-fat cod correlates to smaller body sizes and decreased birth rates, resembling the concept of nutritional decay due to decreased food quality.
Trophic Cascades
Distinguishing between bottom-up controls (resource availability influencing producers) and top-down controls (predators influencing the food web top.)
Examples of these cascades have been observed in both aquatic and terrestrial systems— one being the introduction of non-native species and how it impacts local biodiversity, stability, and structure of food webs.
The various roles predators play on herbivore populations can cascade down through the food web affecting plant communities and nutrient cycling.
Biodiversity and Ecosystem Stability
Discussing how an increase in biodiversity can enhance the stability of trophic levels above.
The portfolio effect: Allows diversity at one level to ensure variation is buffered across higher trophic levels.
Pollutant Dynamics in Ecosystems
Persistent organic pollutants (POPs) can bioaccumulate in organisms along the trophic levels from producers through to apex predators.
Example: Inuit studies in the Arctic showing unexpectedly high levels of PCBs in indigenous diets due to the marine food web.
The role of organisms like salmon in transporting and augmenting pollutant burden through their life cycles illustrates the complex interconnectivity within food webs.
Conclusion
The discussion encapsulates an intricate network of energy dynamics, trophic interactions, and the complex implications of biodiversity within ecosystems.
Understanding the detailed relationship between various organisms allows for better insight into ecological preservation and management efforts.