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A survey of ordinary differential equation models investigating environmental and sustainability issues in the history of Easter Island appeared in 2011. One of the results discussed was a model by Basener et al. which investigated the relationship between humans, the forest stock, and the non-native Polynesian rat that was introduced by early settlers. This paper surveys recent developments in research using differential equation models to understand the interactions between people, rats, and forest stock.

SummaryThe Birkhoff ergodic theorem, proved by George David Birkhoff in 1931, allows us to investigate the long-term behavior of certain dynamical systems. In this article, we explain what it means for a function to be ergodic, and we present Birkhoff's theorem. We construct models of activities typically found at carnivals and compare and contrast them by analyzing their ergodic theory properties. We use these carnival models to show how Birkhoff's ergodic theorem can be used to help a photographer set up her equipment to take pictures of all children on a carousel and to aid a magician in finding a lost jewel in a sticky mess of taffy.

We discuss properties of the Julia and Fatou sets of Weierstrass elliptic ℘ functions arising from real lattices. We give sufficient conditions for the Julia sets to be the whole sphere and for the maps to be ergodic, exact, and conservative. We also give examples for which the Julia set is not the whole sphere.

We prove that there are families of rational maps of the sphere of degree n2(n=2,3,4,…) and 2n2(n=1,2,3,…) which, with respect to a finite invariant measure equivalent to the surface area measure, are isomorphic to one-sided Bernoulli shifts of maximal entropy. The maps in question were constructed by Böettcher (1903--1904) and independently by Lattès (1919). They were the first examples of maps with Julia set equal to the whole sphere.

We prove that there are families of rational maps of the sphere of degree n2(n=2,3,4,…) and 2n2(n=1,2,3,…) which, with respect to a finite invariant measure equivalent to the surface area measure, are isomorphic to one-sided Bernoulli shifts of maximal entropy. The maps in question were constructed by Böettcher (1903--1904) and independently by Lattès (1919). They were the first examples of maps with Julia set equal to the whole sphere.