I've read a lot about cockroaches but was unable to find how they contribute to the ecological environment. Does anyone know?
Cockroaches are an integral part of the food chain.
Cockroaches are an important source of food for a number of organisms, such as arthropods, birds, and mammals. As such, they are an important part of the food chain. Cockroaches also play an important role in nutrient recycling. Most species of cockroach are detritus feeders and with the help of endogenous cellulases play an important role in degrading plant material. Some species, such as Cryptocercus, feed directly on wood and play a major role in lignocellulose digestion in temperate forests.
They don't have to "contribute" as such. All they have to do is survive and pass on their genes to their offspring. Any benefits that they have (in terms of detritus cleaned up, etc.) or harms that they cause is purely coincidental.
There's no "desire" on the behalf of species to make things "better". All they "do" is try to survive in their existing environment but not make it "worse" for themselves. A species wouldn't survive very long if it ate all of the food in an area or if its waste products polluted the area to such an extent that they couldn't survive.
However, that doesn't mean you can simply remove a species from an environment and not cause actual harm to that environment. The environment includes all the other species that co-exist and they have all evolved in the presence of each other. This means that other animals have evolved to cope with the fact that cockroaches prey on them, others have evolved to eat cockroaches. Remove the cockroaches and the population of the first species will explode and that of the second will collapse. This will have knock on effects to other species in that environment and so on.
You must read this article:
“Most cockroaches feed on decaying organic matter, which traps a lot of nitrogen,” Kambhampati said. “Cockroach feeding has the effect of releasing that nitrogen (in their feces) which then gets into the soil and is used by plants. In other words, extinction of cockroaches would have a big impact on forest health and therefore indirectly on all the species that live there.”