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Trophic Levels

Trophic Levels

All organisms in an ecosystem occupy a trophic level in the food chain. The lowest level consists of primary producers, which synthesize their food from either solar or chemical energy. Each subsequent level obtains energy from the levels below. Detritivores can occupy any of the levels above primary producers.

What is an Ecosystem?

What is an Ecosystem?

Production Efficiency

Production Efficiency

Net production efficiency (NPE) is the efficiency at which organisms assimilate energy into biomass for the next trophic level. Due to low metabolic rates and less energy spent on thermoregulatory processes, the NPE of ectotherms (cold-blooded animals) is 10 times higher than endotherms (warm-blooded animals).

Trophic Efficiency

Trophic Efficiency

Trophic level transfer efficiency (TLTE) is a measure of the total energy transfer from one trophic level to the next. Due to extensive energy loss as metabolic heat, an average of only 10% of the original energy obtained is passed on to the next level. This pattern of energy loss severely limits the possible number of trophic levels in a food chain.

Fixed Action Patterns

Fixed Action Patterns

A fixed action pattern (FAP) is a specific, hard-wired sequence of behaviors that occurs in response to an external stimulus, called a sign stimulus. The behavior is “fixed” because it is essentially unchangeable—proceeding similarly across individuals of a species every time it occurs.

Osmoregulation in Fishes

Osmoregulation in Fishes

When cells are placed in a hypotonic (low-salt) fluid, they can swell and burst. Meanwhile, cells in a hypertonic solution—with a higher salt concentration—can shrivel and die. How do fish cells avoid these gruesome fates in hypotonic freshwater or hypertonic seawater environments?

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Related Experiment Video

Updated: Jun 3, 2025

Modeling the Size Spectrum for Macroinvertebrates and Fishes in Stream Ecosystems

Modeling the Size Spectrum for Macroinvertebrates and Fishes in Stream Ecosystems

Published on: July 30, 2019

Linking Fire, Food Webs, and Fish in Stream Ecosystems.

David A Roon¹, J Ryan Bellmore², Joseph R Benjamin³

¹Oregon State University, Department of Forest Ecosystems & Society, Corvallis, Oregon USA.

Ecosystems (New York, N.Y.)

|January 6, 2025

Summary

This summary is machine-generated.

Wildfires can impact aquatic ecosystems and fish populations through various pathways. Food web modeling reveals that fire severity and other factors influence short- and long-term biomass dynamics, with varied outcomes for stream ecosystems.

Keywords:

Aquatic-terrestrial linkages Disturbance Ecosystem modeling Fish Food webs Wildfire

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Area of Science:

Ecology
Environmental Science
Aquatic Ecosystems

Background:

Wildfire regimes are shifting, raising concerns for aquatic ecosystems and fish populations.
Predicting fish responses to wildfires is complex due to multiple interacting pathways.
Whole-ecosystem approaches, like food web modeling, are valuable for understanding these complex interactions.

Purpose of the Study:

To apply a dynamic food web simulation model to assess wildfire impacts on stream ecosystems.
To investigate how wildfire severity influences short- and long-term biomass dynamics of periphyton, invertebrates, and fish.
To identify key factors driving aquatic ecosystem responses to wildfires in headwater streams.

Main Methods:

Utilized a dynamic food web simulation model to link trophic dynamics with wildfire effects.
Simulated wildfire impacts on periphyton, aquatic invertebrates, and fish biomass.
Analyzed responses across different fire severities, time scales, and trophic levels in western Pacific Northwest streams.

Main Results:

Wildfires often increased modeled periphyton, invertebrate, and fish biomass in the short and long term.
Modeled responses varied significantly in direction, magnitude, and duration based on fire severity, time since fire, and trophic level.
Water temperature, canopy cover, riparian shading, and turbidity were sensitive factors influencing response trajectories.

Conclusions:

Wildfire impacts on aquatic ecosystems are complex and context-dependent, leading to diverse responses.
Food web modeling is a useful heuristic tool for understanding fire-ecosystem-fish linkages.
Identifying specific contexts where fires may negatively impact fish is crucial for resource management.