This presentation is loosely based on Elith et al.'s (2010) paper by the same name. It explains the rationale behind the MaxEnt approach to species distribution modeling with presence-only data in an intuitive way with some simple examples.
It's worth noting that I initially wrote this presentation before the connections between MaxEnt and Poisson regression were fully understood. This is a very exciting result, so I may post an updated version at some point in the future.
In the mean time, ecologists that are interested in this connection should make sure to check out this blog post by David Warton: http://methodsblog.wordpress.com/2013/02/20/some-big-news-about-maxent/