Limnology Final Exam Flash Cards

What are the four main groups of primary producers in lakes?

Phytoplankton, periphyton, macrophytes, chemosynthetic bacteria

What is periphyton?

Attached algae; includes epilithic (rocks), epiphytic (plants), epibenthic (sediments), and epixylic (wood) forms

Name the three morphological classifications of phytoplankton.

Single-celled, colonial, chains/filaments

What are the seven primary taxonomic groups of freshwater phytoplankton?

Cyanobacteria, Chlorophyta, Bacillariophyta, Pyrophyta, Chrysophyta, Cryptophyta, Euglenophyta

What unique structures do cyanobacteria use for buoyancy?

Gas vacuoles

What is a heterocyte (heterocyst)?

Nitrogen-fixing cell in cyanobacteria; functions only when inorganic N is low

What is an akinete?

A resting spore in cyanobacteria

What is a frustule?

The silica cell wall of diatoms (Bacillariophyta)

Distinguish epitheca and hypotheca.

Epitheca = larger upper half of diatom frustule; hypotheca = smaller lower half

What is the raphe?

A slit in pennate diatoms that allows gliding motility

What is the pellicle?

Proteinaceous outer covering in euglenoids

List three factors that control algal birth rate.

Intrinsic species rate, temperature, light, nutrients

List four factors that control algal death rate.

Senescence, disease/parasitism, grazing, physical mechanisms (sinking)

Name the three phases of the P-I curve in order of increasing light.

Light limited growth → Light saturated growth → Photoinhibition

What is photoinhibition?

Decline in photosynthesis at very high light intensities

What does Stoke's Law describe?

The sinking velocity of small spherical particles; larger/denser particles sink faster

Under what condition do cyanobacteria perform nitrogen fixation?

When dissolved inorganic nitrogen concentrations are low

Are archaea more closely related to bacteria or eukaryotes?

Eukaryotes (archaea are more closely related to eukaryotes than to bacteria)

Give three examples of prokaryotes.

Bacteria, cyanobacteria, archaea

What is the key difference between prokaryotes and eukaryotes?

Prokaryotes lack a nucleus and membrane-bound organelles; eukaryotes have both

What type of photosynthesis does NOT produce oxygen?

Anoxygenic photosynthesis (uses H₂S instead of H₂O; produces sulfur)

Why are diatoms prone to sedimentation?

Their dense silica frustules cause them to sink rapidly (Stoke's Law)

Why are diatoms useful in paleolimnology?

Their silica frustules preserve well in sediment cores

What limits primary production in the lacustrine zone of a reservoir?

Nutrients (not light; the water is clear)

What might be the most important carbon/energy source for macroinvertebrates in highest order streams?

FPOM (fine particulate organic matter)

What are three ecological roles of zooplankton?

Grazers (control phytoplankton), nutrient recyclers, fish food

Name the major groups of zooplankton.

Protozoans (ciliates, flagellates, amoeboids), rotifers, crustaceans (cladocerans, copepods), insects (Chaoborus), ichthyoplankton

What do ciliates primarily feed on?

Bacteria

What is parthenogenesis?

Asexual reproduction common in rotifers and cladocerans (e.g., Daphnia)

What is a typical filtration rate for large Daphnia?

~25 mL/individual/day

Distinguish cyclopoid vs. calanoid copepods.

Cyclopoid = predaceous; calanoid = herbivorous. Both are raptorial feeders.

What is Diel Vertical Migration (DVM)?

Daily vertical movement: deeper during daylight, near surface at night

What is the most likely cause of Diel Vertical Migration?

Predation pressure (avoiding visual predators during daylight)

What is cyclomorphosis?

Seasonal morphological changes in zooplankton (e.g., longer spines) induced by predator presence

In the two-lake Daphnia example, why did Daphnia in the lake with fish have more pointed helmets and longer spines?

Cyclomorphosis — induced by chemical cues from zooplanktivorous fish

What causes the lake without fish to lack zooplanktivorous fish?

It goes anoxic every winter, killing fish

What is an ephippium?

A resting egg of Daphnia; product of sexual reproduction

What did Brooks and Dodson demonstrate?

Presence of an efficient zooplanktivore changes zooplankton community composition and size

What is Chaoborus?

Phantom midge; predaceous insect larva (~10 mm)

What is ichthyoplankton?

Fish larvae

If a lake has abundant algae, what would you expect about planktivorous fish?

Lots of planktivorous fish (they reduce zooplankton grazing on algae)

Why is Daphnia considered a keystone species?

It is a dominant grazer that controls phytoplankton and serves as key fish prey

Approximately how much does filtration capacity increase when Daphnia body size triples?

~10× the filtering capacity

What are the two main crustacean zooplankton groups?

Cladocerans (e.g., Daphnia) and copepods (cyclopoid, calanoid)

Name three predaceous cladocerans.

Leptodora, Cercopagis (fishhook waterflea), Bythotrephes (spiny waterflea)

What are macrophytes?

Macroscopic aquatic vegetation: macroalgae, mosses, ferns, and angiosperms

Name the four major evolutionary groups of macrophytes.

Charaphyta (green algae), Bryophyta (mosses), Tracheophytes (vascular plants), Angiosperms (flowering plants)

What is Chara?

A macroalga (Charaphyta); muskgrass; possible ancestor of vascular plants

Name the three attached growth forms of macrophytes.

Emergent, submergent, floating-leaved

Give two examples of emergent macrophytes.

Typha (cattails), Phragmites (common reed), Pontederia (pickerel weed)

What is aerenchyma?

Spongy, gas-filled tissue in emergent macrophytes for buoyancy and gas exchange

Give two examples of submergent macrophytes.

Myriophyllum spicatum (Eurasian watermilfoil), Elodea

What adaptations do submergent macrophytes have?

Lack structural tissue (lignin); vestigial stomata; diminished cuticle

What is heterophylly?

Leaves that change shape depending on where they grow (submerged vs. floating vs. emergent)

Give an example of a free-floating macrophyte.

Lemna (duckweed), Utricularia (bladderwort)

What are the two alternate states of shallow lakes?

Clear water with high macrophyte abundance; turbid water with low macrophyte abundance

What trigger can cause a switch from macrophyte-dominated to algae-dominated state?

Loss of fish species that preys heavily on herbivorous/zooplanktivorous fish

How do macrophytes maintain the clear-water state?

Compete with algae for nutrients, reduce sediment resuspension, provide habitat for grazing zooplankton

What is the littoral zone?

The shallow, near-shore area where most macrophytes grow

What is Eurasian watermilfoil's growth form?

Rooted submerged aquatic vegetation

Which lake is most likely to be invaded by Eurasian watermilfoil?

Large, warm, deep lake near a boat launch

What is NOT a way to reduce watermilfoil spread?

"Only plant watermilfoil on private property" (this would spread it)

What are vestigial stomata?

Reduced or non-functional stomata; submerged plants need less gas exchange regulation

Where is Utricularia found?

Free-floating macrophyte (bladderwort)

How do floating-leaved plants like water lilies avoid desiccation?

They don't need extensive cuticle because leaves float on water surface, not exposed to air

What does a connectedness food web show?

Who eats whom (feeding links); indicates structural relationships

What does an energy flow food web show?

Major pathways of energy flow; quantitative energy transfers between trophic levels

What does a functional food web show?

Dynamically important interactions and impacts of predators on prey populations

Distinguish trophic level from trophic position.

Trophic level = discrete integer (1,2,3); trophic position = continuous measure accounting for omnivory (e.g., 2.4)

What is ecological efficiency?

Consumer production ÷ prey production (typical 7-25% per transfer)

How are stable isotopes (δ¹³C, δ¹⁵N) used in food web studies?

δ¹³C traces carbon source (energy origin); δ¹⁵N indicates trophic position

State the Trophic Cascade Hypothesis.

Number of trophic levels determines biomass distribution; predators control prey when Cpred > Pprey

What are the three conditions for a trophic cascade?

1) Consumers control prey biomass (Cpred > Pprey); 2) Relatively simple food web; 3) Size-selective predation

Predict: Adding piscivorous fish to a lake will have what effect on algae?

Decrease algae (piscivores reduce zooplanktivores → more large zooplankton → more grazing on algae)

What is biomanipulation?

Using trophic cascade concepts (fish management) to improve water quality

Does biomanipulation work alone?

No; must be combined with watershed management for long-term effectiveness

Distinguish bottom-up vs. top-down control.

Bottom-up = nutrients control producers; top-down = predators control lower levels

In Lake Mendota, why does phytoplankton decline in spring/summer?

Zooplankton grazing increases; fish hatch later, temporarily reducing zooplankton

Where is PCB most concentrated in fish?

Fatty tissues (PCBs are lipophilic)

What is the typical energy transfer efficiency from algae to zooplankton?

~25% (in example: 8,000 → 2,000 cal/m²/d)

What is the typical energy transfer efficiency from light to algae?

~1% (in example: 730,000 → 8,000 cal/m²/d)

What does the y-axis on a stream hydrograph represent?

Discharge

In a lake with abundant algae, what characteristic of the food web would you expect?

Lots of planktivorous fish

What is the top-down prediction for a 4-level food web (piscivores → zooplanktivores → zooplankton → algae)?

High piscivores → low zooplanktivores → high zooplankton → low algae

What is the top-down prediction for a 3-level food web (zooplanktivores → zooplankton → algae)?

High zooplanktivores → low zooplankton → high algae

Define riffle and pool.

Riffle = shallow, fast, turbulent; Pool = deeper, slower, finer sediment

What is the riparian zone?

Land adjacent to a stream; influences organic matter input, shade, nutrients

What is the hyporheic zone?

Subsurface region where groundwater and surface water mix; biogeochemical hotspot

What is water discharge?

Volume of water flowing past a point per time (m³/s); Q = A × v

What are the four components of a hydrograph?

Rising limb, falling limb, storm flow, base flow

What is a pollutograph?

Plot of pollutant concentration vs. time

What is stream order?

Hierarchical classification: 1st order (headwaters) → higher order when two equal orders join

What does the River Continuum Concept predict about low-order streams?

Heterotrophic (P/R < 1); dominated by allochthonous CPOM; shredders abundant; canopy limits light

What does the River Continuum Concept predict about mid-order streams?

P/R ~ 1; grazers abundant (periphyton production)

What does the River Continuum Concept predict about high-order streams?

Autotrophic (P/R > 1) or heterotrophic; dominated by FPOM; collectors abundant

Name the four stream invertebrate feeding guilds.

Shredder, grazer, collector, predator

What do shredders eat? Where are they most common?

CPOM (coarse particulate organic matter; leaves, wood); low-order streams

What carbon source do shredders in low-order streams primarily use?

Allochthonous (terrestrial) inputs

What do grazers eat?

Periphyton (attached algae)

What do collectors eat?

FPOM (fine particulate organic matter)