Disclaimer: What? Pokemon belongs to Nintendo? Oh darn.
Topics in Pokemon Biology: Biocombustion
One trait widespread amongst pokemon, regardless of their actual taxonomic relationship, is biocombustion. Biocombustion results from the formation of flammable liquids and gasses within a pokemon's body, which catch fire when exposed to oxygen. Due to the reactive nature of these chemicals, biocombusting pokemon hold two or more precursor chemicals in separate sacs in the body, known as 'fire sacs,' and only mix them immediately prior to release.
Many biocombusting pokemon breathe fire through the mouth, and these species have their fire sacs located in the throat. Others secrete one of the precursors as oil on their skin or fur, then release the other precursors when needed, causing their skin to alight. Many pokemon with external fires can consciously control the amount of flame they produce, but for others it is involuntary.
The obvious challenge facing any biocombusting pokemon is to prevent itself from being burned by its own flames, in the mouth or on the skin. To cope with this, the pokemon secretes flame retardants into its tissues, and even incorporates them into its fur or scales. Thus, while the liquid or gas burns, the pokemon itself is unharmed.
Biocombustion affects more than just the individual pokemon, however. The ability to produce flame at will is a driving force in landscape dynamics, affecting every aspect of the ecosystem. This is because fires can escape, and wildfires can result at a much higher rate than would occur otherwise (note that electrogenic pokemon can cause fires as well). Some plants respond to the presence of biocombusting pokemon by becoming fire resistant. Thick bark and deep, insulated roots are common in areas where these species roam. Other plants take advantage of the clearing of brush and production of fertilizing ash by spreading their seed after fires, even producing seeds that cannot sprout without being exposed to smoke. But where biocombusting pokemon are especially common, woodlands often cannot persist at all, giving way to scrub or grassland, which can recover faster after a fire passes through.
In this way, biocombusting pokemon can be considered as ecosystem designers, and even as keystone species. Wherever they occur, the ecosystem changes in response.