Limnology Fall 2003 -- Practice Questions For Second Exam

The format of the second exam will be similar to the first exam, with the addition of a matching (choose the correct taxonomic group) section in the short answer portion (Part 2)

Part 1 -- Definitions – Define the following and explain their limnological significance

1. Resource spiraling

- A conceptual framework for describing resource use in streams -- looks at downstream transport of nutrients -- the spiral length is a function of the distance an atom is transported before it is captured by organisms and the distance moved while in the organisms.
-Some possible significances:

2. Vertical migration

-Movement of zooplankton up and down in the water column (most common pattern is to move up at night and down during the day)
-Significance: Is an adaptation of some zooplankton to avoid predation by visual (e.g., fish) predators

Part 2
Find the organism in the list below that best corresponds to the characteristic, and put its letter in the blank (List only ONE organism per question and use each answer only ONCE; there will be extra organism names left over – don’t panic!)

a. Chlamydomonas              d. Rotifers               g. Myriophyllum
b. Anabaena                        e. Chara                  h. Porifera
c. Calanoida                        f. Typha                   i. Ephemeroptera

1.           Sex determination is based on ploidy level (i.e., haploid, diploid) in these animals.
2.           This algae can perform nitrogen fixation.
3.           A type of macrophyte that can live in water deeper than 10 meters (given sufficient light).
4.           Often found in stream ‘drift.’


Part 3 – Short Essays

1. Describe at least one possible adaptive cause of cyclomorphosis and give an example of the effects of cyclomorphosis in this case (4 points)

Possible answers:

(1) To avoid sinking -- phytoplankton (or zooplankton) may develop spines or longer forms to increase their resistance to sinking (increasing form resistance in Stoke's Law that governs sinking rates).  In warmer waters (during summer) when water density is lower and sinking rates higher, we would predict that there should be an increase in longer forms.

(2) Resistance to vertebrate predation -- cyclomorphosis might involve a changing to forms that are less visible when vertebrate predators are abundant.  For example, in Lake Gatun, Panama, Zaret found a seasonal change in shape of the zooplankton Ceriodaphnia from a form with a large eye to a form with a small eye.  He determined that the large eyed morph was much more vulnerable to predation by a fish (Melaniris).  When he fed India ink to the small eyed morph to make a 'pseudo-eye', the altered small eyed Ceriodaphnia with the ink spots were also more visible and were eaten by fish.

(3) Resistance to invertebrate predation -- cyclomorphosis to forms with spines, helmets, etc. may be an adaptation to avoid predation by invertebrates -- For example, there are two forms of the zooplankton Bosmina, and one form has short mucrones (tailspine) and antennae.  The other form has long mucrones and antennae.  The long form has been shown to be resistant to predation by the copepod Epischura, because the antennae interfere with the copepod's ability to turn and eat the Bosmina.  The long form Bosmina escape more frequently and then 'play dead' and avoid recapture.  So, a switch from short to long forms in this case and others, may be adaptations to avoid predation by invertebrate predators that can not capture or ingest spiney zooplankton.

2. Give three examples of morphological adaptations in stream insects that may help them survive in stream environments (6 points)

Possible answers:

(1) Insects may be flattened or streamlined (this may decrease their resistance to flow and the possibility that they are swept away by currents, but it can also be an adaptation for living under rocks)
(2) Some insects have suckers or hooks for grasping rocks (tarsal claws)
(3) Some insects, such as chironomid larvae, make tubes out of sticky substances or silk-like substances that keep them attached to rocks.
(4) Some insects, such as caddis flies, make heavy cases (for example out of stone or wood) that provide ballast (weight) and allow them to remain on the bottom

(Hint:  There’s sure to be at least one graph on the exam as well)