The metapopulation concept, while simplistic, was a powerful conceptual advance in population ecology. Metapopulation dynamics means that local persistence can emerge as a consequence of regional interactions — which fundamentally changes the way we have to think about measuring and managing ecological systems.

1. • A species may be able to persist regionally, even though local conditions and resources do not support all populations
   • Levins codified this idea in the concept of a metapopulation — a population of populations
   • Balance between migration (i.e. dispersal) and extinction rate determines the patch occupancy of metapopulation
   • Real dispersal is more structured than Levins’ assumptions, but generic predictions can be used to interpret field observation

Practical applications of the metapopulation concept have been used in the design of reserves for conservation — codified in the SLOSS, or Single Large Or Several Small debate — and the control of infectious diseases.

Marine Metapopulations

Metapopulation dynamics of infectious disease

On Friday, we’ll discuss these two papers in the context of the topics we’ve been covering in class:

https://www.pnas.org/content/106/Supplement_1/9987.long

https://www.nature.com/articles/ncomms14504

So, read them before Friday.

As promised, here is a list of sample questions for exam 1.  Many questions on the exam will be drawn from this list — I promise that the exam will be considerably shorter than this!  Note that the exam will cover the material though Friday, 27 Sept.

Exam-1-Test-Bank

There was a request for more information on optimal reproductive allocation. Here I’ve linked a pdf of the section on this topic from from Ted Case’s excellent book “An Illustrated Guide to Theoretical Ecology” which is really required reading for anyone that wants to pursue a career in ecology.  It is laid out in greater detail than what we covered in class.

Case_reproductive_allocation

Today we’ll finally let populations open up — that is, they will no longer be restricted to births and deaths within the population and we’ll consider the consequences of interactions between populations.  Dispersal, or movement from one population to another, is the primary mechanism of interaction among populations of the same species.  With this phenomenon added, we can then consider the patterns at the regional scale of the collection of populations, or the metapopulation.

1. • Populations are rarely completely isolated from each other — dispersal is the movement of individuals from one population to another
   • The growth and decline of populations must also account for gains due to immigration and loses due to emigration
   • Dispersal may often be density dependent
   • Dispersal may be passive, vectored, or active
   • Realized dispersal is consequence of potential dispersal, filtered by conditions and resources
   • Dispersal can “rescue” populations for which demographic rates do not allow positive growth
   • A species may be able to persist regionally, even though local conditions and resources do not support all populations

Today we continue our discussion of life histories and consider the tradeoffs inherent in reproducing now or later.

• • Classification of survival curves (Type I, II, III)
  • Allocation to life history strategies might be impacted by environment or presence of other species — particularly if allocation is plastic
  • Environmental settings that lead to lower juvenile survival, tend to lead to lower reproductive effort
  • Environmental settings that lead to lower adult survival, tend to lead to higher reproductive effort

Today we take the population dynamic principles from the last few lectures and revisit what they mean for selective pressures on how species balance out the dual tasks of staying alive and reproducing — formally, an organism’s life history, or the lifetime pattern of growth, differentiation, storage, and reproduction.

1. • Reproductive value quantifies the potential to produce offspring against the probability of surviving long enough to do so.
   • Trade-offs are inherent in different solutions to survival and reproduction
   • r and K strategies are a dichotomy that recognize a trade-off between allocation to reproduction (r) and allocation to growth (K)
   • Conditions and environments that select for different strategies are dynamic in time
   • Lack clutch size implies trade-off between number and quality of reproduction; i.e. too many offspring are hard to provision
   • Simple Lack clutch size is often not observed, because of cost of reproduction to survival and future reproduction
     • fitness is measured in terms of R0, rather than each clutch (for iteroparous species)

The logistic model for population growth

1. • In the logistic model, per capital growth always declines as population size increases, but absolute growth is maximized at intermediate population size
     • recruitment is the number of new individuals added per time
   • Maximum sustained yield is the population size at which recruitment is maximized
   • We expect individuals to do better at low density, but not always
   • Allee Effect occurs when per capita growth is limited at low population density
   • Increasing density may impact characteristics of individuals — lower per capita resource leads to smaller body size — or the interactions between individuals — leading to indirect consequences other than resource limitation

Now that we have a conceptual model for population growth, we can tear it apart.  Competition for limited resources implies that populations will not grow indefinitely — taking that as a starting point, we can derive a conceptual model for the more realistic setting of populations growing under resource constraints.

1. • More individuals competing for finite resources results in lower per capita resource
   • Competition can be characterized in terms of the interaction (interference v. exploitation) or the outcome (scramble v. contest)
   • Competition can limit birth rate, death rate, or both — when they are equal, the population is constant at the carrying capacity

This well timed articles was published just in time for our discussion on Wednesday.

https://www.nytimes.com/2019/09/08/us/trump-black-rhino-trophy-hunter.html?fallback=0&recId=1QcyV0aTtdTqUrGsQ4vbM2GglTo&locked=0&geoContinent=NA&geoRegion=PA&recAlloc=control&geoCountry=US&blockId=home-discovery-vi-prg&imp_id=632179619&action=click&module=Discovery&pgtype=Homepage