Lecture 12

Good. Now that you have the actual learning outcomes, I’ll answer each one directly using your notes.

1. Identify the main sources of energy in lotic ecosystems

The main energy sources in streams are:

  • Allochthonous inputs (dominant in many streams)

    • Leaves, twigs, and organic matter from surrounding land

    • Your notes: forested streams can have ~90% of energy from terrestrial sources

  • Autochthonous production

    • Produced within the stream by autotrophs (algae, macrophytes)

These energy sources form the basal resources that support the food web.

2. List the major groups of autotrophs in streams

From your notes, the main autotroph groups are:

  • Diatoms

    • Silica frustules, high-quality food (low C:N), fast turnover

  • Green algae (Chlorophyta)

    • Filamentous mats, higher C:N, lower food quality

  • Cyanobacteria (blue-green algae)

    • Photosynthetic bacteria, nitrogen-fixing, sometimes toxic (e.g., Phormidium)

  • Macrophytes

    • Larger aquatic plants contributing to primary production

3. List the major groups of aquatic heterotrophs involved in organic matter processing

From your notes:

  • Fungi (Hyphomycetes)

    • Primary decomposers of leaf litter

    • Break down material using enzymes

  • Bacteria and Archaea

    • Assist decomposition and nutrient cycling

  • Macroinvertebrate shredders

    • e.g., freshwater crayfish, stoneflies, caddisflies

    • Break down coarse organic matter (CPOM → FPOM)

These groups work together to process terrestrial organic matter.

4. Explain how longitudinal changes alter feeding groups and processes

As streams move from headwaters to lower reaches:

  • Headwaters

    • Shaded, low light

    • Energy mainly allochthonous

    • Shredders dominate

    • System is heterotrophic (P:R < 1)

  • Mid-reaches

    • More light → more algae

    • Grazers dominate (feed on periphyton)

    • System becomes autotrophic (P:R > 1)

  • Lower reaches

    • Deep, turbid, low light

    • Fine organic matter dominates

    • Collectors/filter feeders dominate

    • Returns to heterotrophic (P:R < 1)

5. Describe the River Continuum Concept (RCC) and its strengths/weaknesses

What RCC is:

A concept that explains how physical conditions and energy sources change along a river, shaping biological communities and ecosystem processes.

Strengths:

  • Provides a predictive framework for how streams function

  • Links physical gradients to biological patterns

  • Helps explain changes in feeding groups and energy use

Weaknesses (from your notes):

  • Dams disrupt the continuum (Serial Discontinuity Concept)

  • Does not account for seasonal flooding

  • Not accurate for all systems (e.g., New Zealand streams) because:

    • Short, steep catchments

    • Frequent floods

    • Headwaters not always forested

Bottom line

Everything in your notes directly maps to these outcomes. The key is:

  • Energy sources → organisms → processes → longitudinal change → RCC

If you want next, I can turn this into:

  • a one-page cheat sheet, or

  • exam answers (full paragraphs) based on these outcomes.