Harvested Populations
What is the equation that describes maximum sustainable yield (MSY)?
MSY = K/2
Describe what a biocontrol is, and list an example of an unsuccessful biocontrol.
Biocontrols are ‘natural’ means of controlling invasive species, by way of usually introducing predators of invasives to a given region. An unsuccessful example of this were cane toads, which were meant to curb beetles in sugar cane farms, but became destructive to the environment more generally.
Describe an example of alternative stable states in nature
Grassland -> woodland
Coral reef -> algae dominated reef
Name two factors that may influence discrepancies between lower income countries and higher income countries.
Differences in access to hospitals, clinics, medicine, contraception
Differences in cultural values that lead to discrepancies in the population sizes of different-aged human populations
Differences in access to education
Describe adaptation vs. acclimation
Adaptation occurs at a population level, whereas acclimation occurs at an individual level.
Provide an example of prey switching exhibited by humans.
Haddock to flounder fishery switch;
Baleen whale fishery switches
Name three qualities that make a species better at expanding it’s range (and becoming… invasive!!)
Being a good disperser
High effective population size (lots of genetic diversity => fodder for adaptation)
Phenotypic plasticity (allowing for a buffer before true adaptive changes)
Existence of empty niche space
What are the two most drastic human impacts on natural systems, as relevant to our restoration discussion?
Suppression of fire, removal of large grazers
What was this plot introduced to explain in regards to human populations? (graph)
The progression of human demography through time, in response to social, economic, and cultural factors that coincide with the “”””development””””” of a place.
Provide the equation used to estimate the instantaneous rate of increase (r) from a discrete time step
Nt = N0*lambdat
lambda = er and r = ln(lambda)
What led to the North American megafaunal extinction?
Appearance of Beringia (land bridge to NA) and increased human population.
Are all introduced species invasive? Why or why not?
No, not all introductions produce invasive species. Invasive species are usually characterized by having little to no controls on their population growth, meaning there are few competitors, predators, and/or fairly untapped resources. They also usually incite some form of ecological damage.
Describe one restoration success story.
Reintroduction of wolves to Yellowstone NP: increased diversity and robustness of native flora, especially woody plants (long-term census data)
Reintroduction of bison to Yellowstone NP: increased soil microbial activity (long-term exclusion plots)
Has the carrying capacity of humans changed across history? Why or why not?
Yes; rapid developments in the scaling up of the production of food, medicine, clean drinking water, etc has allowed for humans to expand their population rapidly in modern times. This reflects an increase in carrying capacity that allows for the continued growth of global human populations.
Why don’t populations stay at K forever?
Time lags allow populations to overshoot K, leading to oscillations or chaos.
Describe an example of the impact of harvesting on a species’ traits
Decrease in body/horn size in bighorn sheep;
Decrease of number of tusks in African elephants
Decline in sport fish body size
If you were a natural resource practitioner, how would you decide which life stages of a threatened species was most important to bolstering their long-term population growth? List two variables/metrics you would measure and describe each one.
Sensitivity: the absolute change in lambda in response to absolute change in matrix element aij
Elasticity: the proportional change in lambda in response to the proportional change in matrix element aij. Important because it’s scaled to one, so highest elasticities will most strongly influence lambda!
Why is it that a community could change from one stable state to another? Why is it often difficult to return back to the original stable state?
If a community is perturbed so much it exceeds a ‘tipping point’, it is likely the dynamics of the system will begin to canalize the generation of a new stable state rather than fall back to the original state (visualized by the hump shaped graph). Returning often requires LOTS of energy/time/$$ to get there (often infeasible).
Extrapolating from this plot, there is a purported ‘5th stage’. What would we call this 5th stage? (graph)
‘Population in decline’, characterized by birth rates that are below replacement rates, and a larger elderly population than young population.
Fill in the blanks regarding the Theory of Island Biogeography:
Close islands →
Far islands →
Small islands →
Large islands →
Close islands → high immigration,
Far islands → low immigration
Small islands → high extinction,
Large islands → low extinction
What kind of human actions lead to increased jellyfish populations, and how do they do so?
Habitat modification to prevent shoreline erosion: more polyp settling habitat.
Ballast water translocation spreads jellyfish larvae.
Overfishing reduces competition between jellyfish and fish.
Eutrophication → increased phytoplankton, more food for jellyfish.
Warming expands jellyfish habitat
Describe a feature of ecological communities that contributes to them being susceptible or resistant to invasion.
Connectance is a feature that describes how highly linked species are in a community. It is quantified as # links/spp2). Higher connectance = harder to invade for many reasons: biotic resistance, better adapted species to competition, fewer vacant niches/unused resource flows, etc.
How does our understanding of climax communities and alternative stable states complicate our understanding of restoration?
Climax communities don’t have a ton of support empirically (not consistently seen in studies), and we know alternative stable states are a reasonable expectation for many ecosystems. This makes our ‘end goal’ for which habitat we want to restore more ambiguous – how do we choose the species and habitats to bring back?
In the following plot, describe which would have no growth, slow growth, and rapid growth (graph)
Rapid > slow > zero
What were two main findings in the the connectivity experiments conducted at the Savannah River Site, South Carolina?
Connectivity both reduced extinction and increased colonization rates over the course of the ~20 year experiment.