OK, here's what I've come up with. Let me know if there's something I should add to it, or if it's ready to go as-is.
Bullywug
The ecology of the bullywug would detail their role in disrupting a swamp environment, maintaining loose territorial boundaries and eating interlopers. The ordinary bullywugs hate their larger, more intelligent cousins, who organize well and conduct raids on other civilizations. We will explore the bullywugs’ declining relationship with their sleeping god, Ramenos. We will write up a racial feat that provides a special bonus to charges when hopping.
References: Monsters of Faerun, Monstrous Manual, Complete Book of Humanoids
Dryad
The ecology of the dryad will explore how these beautiful fey protect their forest and groves. Some dryads are neutral in alignment, and keep a veritable army of amorous slaves. We will present the Hamadryad, a more powerful version of the dryad with a range of druidic abilities and total mastery over her forest. We will also detail the goddess Verenestra, a goddess of the natural beauty of female faeries. We will mention the dryad’s origins in Greek mythology.
References: Monster Manual, Monstrous Manual, Dragon #87, Dragon #251
Ki-rin
The ecology of the ki-rin describes the sky-bound existence of these champions of goodness. They sometimes make lairs in locations so high they are almost impossible to reach without flying. We will present two related creatures, the T’uen-rin (an extremely powerful version of the ki-rin from Arcadia), and the Dragon Horse (a less powerful cousin of the ki-rin with no horn, from the Elemental Plane of Air. We will also detail their benevolent sky-god, Koriel. We will explain the ki-rin’s origins in the various mythologies of Asia.
References: Oriental Adventures, Monstrous Manual
Satyr
The ecology of the satyr shows how these wild merry-makers bring their sylvan homes to life. We will describe their infamous all-night-long revels, which leave mortals hung over and with lighter pockets. We will present their more powerful, chaotic cousins, the korred, whose laugh leaves humans stunned. We will detail their reveler deity, Damh, one of the gods of the Seelie Court. We will include a note on the lusty satyr’s origins in Greek and Roman mythology.
References: Monster Manual, Monstrous Manual, Dragon #155, Complete Book of Humanoids
Treant
The ecology of the treant will describe how a grove of treants tend to its old hardwood forest. We will mention how the treant’s roots can be found in Tolkien’s Ents. We will detail their relationship with the druidic Verdant Lords (from Masters of the Wild). We will mention their relation to other intelligent tree monsters such as the quickwood, black willow, hangman tree, and gakarak (and present stats for at least one of them). We will detail the Father-Tree, Emmantiensien.
References: Monster Manual, Monstrous Manual, Dragon #79, Dragon #283