Lecture 14 Biomes

Question 1

Ecosystem function measured by

Answer 1

Net primary productivity - biomass produced by primary producers

Nutrient mineralisation
(available N in soil)

Carbon sequestration (C sinks)

Decomposition

Question 2

Seagrass meadow (Posidonia oceanica)

Answer 2

Stores the most carbon in top m of soil. Living material reduces water movement and captures drifting detritus. Dead material resistant to decomposition. Seagrass “mattes” retain sediments and protect beach from erosion

Question 3

Other environments with high C storage

Answer 3

Tundra, boreal forest, salt marshes

All due to low decomposition rates

Question 4

Role of biodiversity in ecosystems

Answer 4

Co-occurring species occupy diff niches
E.g. access diff types and depths of soil Nitrogen

More species - more individuals accessing resources

Total plant cover increases w/greater species richness (as seen in cedar creek grass plots USA) available N used more efficiently and remaining N in soil declines

Question 5

Niche packing

Answer 5

Niche complementarity

Question 6

Sampling effects

Answer 6

Can contribute to pos BD(biodiversity) to EF (ecosystem function) relationship

More species added to system

Question 7

Relationships between biodiversity and ecosystem function BD-EF

Answer 7

Vary among species and measure of function

Positive high redundancy - lots of species doing the same thing - loss of diversity at high level does not lead to large reduction in function until critical low reached

Positive low redundancy - loss of diversity at high levels leads to large reduction in function - further loss has less effect (as monoculture establishes)

Positive proportional loss - each species loss leads to equal loss in function (no compensation)

Negative relationship - common in observational studies w/realised diversity

No relationship

Negative proportional - every species lost leads to proportional increase in function.

Question 8

Faster growing species

Answer 8

Faster growing species outcompete others have neg diversity increased productivity

Question 9

Large impact species

Answer 9

Keystone
Strong ecosystem wide effects disproportionate to their size e.g. wolves in Yellowstone NP

Foundation
Large and abundant so have large ecosystem effects e.g. trees and seagrass

Engineering species
Physically alter environment e.g. beavers

Keystone and foundation species control net primary production through food web.
Keystone predators top down. Resources affect primary producers bottom up. Trophic cascade pattern in Yellowstone could also be bottom up from aspen recovery - more manipulative experiments required

Question 10

Sea otters and kelp forests

Answer 10

Sea otters consume urchins that graze kelp maintaining kelp populations

Loss of otters leads to urchin overrun areas known as urchin barrens where kelp is unable to establish itself - effectively an urchin desert

Question 11

Alternative stable states

Answer 11

Diff self replacing communities in ecosystem can dominate
Shifts between them occur at large perturbations
Once shifted state is stable and only a large perturbation can shift system back - phase may be discontinuous

Kelp state maintained: predator abundance controlled by otters limiting urchin migration and grazing

Barren state maintained: predator abundance urchins settle fertilise and recruit their destructive grazing prevents successful kelp recruitment

Question 12

Alternate stable state

Answer 12

Diff states of ecosystem as a theoretical landscape. In the kelp/barren example sea otters are a system variable. Shifting the system to a new state - over a ‘peak’ to a new ‘hollow’
community can also be shifted to another state if the landscape itself changes (parameter/enviro factor) changing the curve

Question 13

Eutrophication

Answer 13

Eutrophication in shallow lakeside to nitro/phospho fertilisers:

Overabundance of nutrient in water leading to algal bloom

Question 14

Hysterisis

Answer 14

Past effects influence future trajectory, return to initial state cannot be achieved simply by reversing initial perturbation - the ‘trough’ may be too deep to return from

Question 15

Ecosystem summary

Answer 15

Defined as : all interacting organisms in an area and their abiotic environment

Assimilation, production and trophic efficiency set limits on energy higher up trophic levels and biomass that can be supported: limits special abundance

Function influenced by biodiversity

Can shift to alt stable state after perturbation

Hysteresis : shift back to former state not possible w/ simple reversal of perturbation