Stream Ecosystem Ecology

Question 1

Explain why streams are open ecosystems, and compare them to lakes (which are closed ecosystems).

Answer 1

A is lakes. They are well-bounded (closed) ecosystems because community, resource and physical boundaries are the same. The shoreline is the boundary for all of those.
B is rivers. We can see community boundaries is within the river water, resource boundaries is the river and the terrestrial around the river, physical boundaries are all the stream orders in the river.

Question 2

Name autochthonous and allochthonous fluxes in a lake.

Answer 2

Sunlight is autochthonous flux
Upstream and terrestrial ecosystems are allochthonous fluxes

Question 3

Energy budget in a lake are:
· I = Import (POM, CPOM, FPOM, DOM)
· PP = Primary Production
· E = Export (POM, CPOM, FPOM, DOM)
· CR = Community Respiration
· ΔB = Change in Biomass of Organic Matter
· PP/CR ratio = balance between production and respiration
· I/E ratio = balance between imported and exported energy.

Explain how these change from upstream to downstream.

Answer 3

○ When stream order go up:
§ The import (I) goes up
§ Primary production (PP) goes up
§ Export (E) goes up
§ Community respiration goes up
§ I/E goes down
PP/CR goes up

Question 4

Explain Production/Respiration

Answer 4

The ratio of gross productivity to respiration in a community of species
○ When P/R < 1 (less than one) it means there are more organisms that use CPOM for energy rather than primary production, so here respiration is higher.
○ When PR > 1 (more than one) it means there are more primary producers and following that there are more organisms that use primary producers for fuel, so productivity is higher.

Question 5

What is the limiting factor for primary producers in a stream?

Answer 5

Light

Question 6

Explain and draw the decomposition of a leaf in a stream.

Answer 6

· CPOM from terrestrial ecosystems is a huge nutrient source in streams
· Microbes are the first one to start decomposing (eating) CPOM, forming a microbial film
· Microbial film attract shredders, so the shredders are the next to decompose CPOM
○ There is a debate on whether shredders want the microbial film or the CPOM, but it is probably both that they want
· Then what the microbes and shredders do not decompose become FPOM

Question 7

Name leaves that have slow, medium, and fast breakdowns

Answer 7

· Fast breakdown – Many weedy macrophytes (water lilies, naiad pondweed)
· Medium breakdown – Most deciduous (broadleaved) trees
· Slow breakdown – Conifers, some deciduous trees (oaks), grassy macrophytes (bullrushes, sedges, reeds)

Question 8

What does temperature do for decomposition rates?

Answer 8

Increased temperature increases decomposition rates
Because of shredders increased metabolism when temperature is higher, they will need more nutrients

Question 9

In which ecosystems does microbial decomposition most important?

Answer 9

Microbial decomposition more important in tropical streams.
Primarily due to the consistently warm temperatures and high humidity in tropical regions which significantly promote microbial activity, leading to faster decomposition rates of organic matter in these ecosystems.

Question 10

In which ecosystems does ivertebrate decomposition most important?

Answer 10

Invertebrate decomposition more important in temperate streams
Temperate regions often have a higher abundance and diversity of aquatic invertebrates, particularly shredders, which play a key role in breaking down organic matter like leaf litter, making them a significant driver of decomposition in these ecosystems

Question 11

Is breakdown rate higher or lower for leaves with lower C:N

Answer 11

Breakdown rate higher for leaves with lower C:N
Because nitrogen is preferred nutrient in organisms

Question 12

Explain nutrient spiraling, and write the equation.

Answer 12

How nutrients travel down the stream
○ First they will be free floating in the water, but at some point an organism (biota) will intake them. That is the whole spiral, and when they are excreted a new spiral will begin.
○ Total spiraling distance=S_W+S_B

Question 13

Draw the connection between species diversity, ecosystem function, and flow diversity in primary producers.

Answer 13

Flow diversity impacts species diversity
○ Flow is more diverse in up stream orders
Species diversity impacts ecosystem function

Question 14

Draw the connection between species diversity, ecosystem function, and flow diversity in collectors.

Answer 14

Species diversity impacts flow diversity
Flow diversity impacts ecosystem function