Here are the sample questions for exam 3.  There will also be opportunities on the final for extra credit based on old exam questions.

Exam 3 sample questions

Weeks ago, we talked a bit about harvesting populations.  Today I’d like to revisit this topic in the light of all the many concepts we’ve covered so far:

• the simple logistic model suggests that there is a maximum sustainable yield (MSY) — though achieving this might be problematic
• setting fixed quotas at the MSY can work in theory — but is dangerous if a) the environment fluctuates, or b) estimates of stock sizes are uncertain
• setting fixed effort is safer, but leads to variable harvests
• Economically optimum yield, which maximizes profit, is often lower than MSY
• reserves can allow rescue of harvested populations via dispersal
• harvest can impact life-history as well as population numbers

Finally, we start talking about ecosystems and the links between the biotic and the abiotic world.

• We can the sum of the biotic component of an ecosystem in terms of biomass (i.e. a static amount) or productivity (i.e. a rate of change in biomass or energy through time)
• Net productivity is the difference between the rate at which new biomass is produced and the rate at which existing biomass is used through respiration
• Primary productivity is limited by a combination of sunlight, water, and the other nutrients required to build biological molecules.
• Secondary productivity is limited by the losses due to the decomposer pathway, the fecal pathway, respiration.
• The efficiency with which primary productivity is consumed, assimilated, and transformed into new consumers depends on the characteristics of the primary producers and the consumers themselves.

All matter must move through ecosystems via some combination of physical forces (e.g. erosion), chemical forces (e.g. mineralization), or consumption. The flows between terrestrial biotic, aquatic biotic, lithospheric, atmospheric components of the ecosystem depend on both the compound of interest and the actors within the ecosystem.  4 common limiting components of ecosystems are carbon, nitrogen, sulfur and phosphorous.

• The carbon and nitrogen cycle are dominated by the atmospheric phase and biotic interactions facilitate the transfer between air and land/water.
• The atmospheric and lithospheric components of the sulfur cycle are comparable and transfer is dominated by physiochemical forces; with some contribution from bacteria.
• The phosphorous cycle is dominated by the lithospheric and aquatic components.

With our new-found insight into the structure and dynamics of communities, today we’ll revisit one of the central questions in ecology: why do some places have more species than others?

• A simple way to consider this is in terms of how to pack more species in an ecosystem
  • This can occur by expanding the niche axes (these might be resources OR conditions)
  • Each species can narrow its utilization within the available niche space
  • Species can minimize overlap within the niche space
  • Even the smallest gaps within niche space can be filled (https://www.youtube.com/watch?v=zc8zCSQxBhM)
• Island biogeography seeks to explain patterns of species richess in terms of the dynamic processes that form communities — i.e. establishment and extinction
  • The balance of establishment and extinction predict stable patterns of species richness, though not necessarily stable community compositions