Just a few notes I may come back to.
Ecology in the animal kingdom relates to niches - opportunities to obtain free energy by a biological mode of existence - inhabited by species. The concept is more complex for a technological civilization because it can interpose a layer of technology between its biology and 'nature' so as to operate successfully in multiple niches.
For example, tropical-savanna evolved humans can live almost anywhere on the earth by using technologies to shelter, acquire food and so on.
Interstellar space is so discontinuous from planetary environments that it seems that (almost) only technological civilizations could colonise it. So does this mean that interstellar space is in principle a monoculture of the first species to achieve it, or is there ecological room for different ways to do it, ways which could avoid conflict, or even create the possibility of symbiotic collaboration?
Just checking on the Internet, I found a couple of interesting sites.
Centauri Dreams is a grown-up discussion of these kinds of things, and it pointed me to George P. Dvorsky's Blog which is focused on the much-discussed-on-this-blog Fermi Paradox.
Dvorsky had an amusing attack on a clearly must-have book which I had been hitherto unaware of. I quote:
"This is the most ridiculous book I've seen in quite some time: An Introduction to Planetary Defense: A Study of Modern Warfare Applied to Extra-Terrestrial Invasion by Travis S. Taylor et al, described by the publisher as follows.
'This book describes a serious look at defending the planet in the event of an extra-terrestrial invasion. Travis Taylor, et al, have written the definitive book on the defense of earth against a potential alien incursion. Whatever your beliefs on the subject...the book also serves as an important primer on the potential future of warfare on every level. It is tightly grounded in current day realities of war and extrapolates thoughtfully but closely about future potentials. It should be on the reading list of anyone who is serious about national security and the future of war.'"
Dvorsky continues "There is so much wrong with all this that I don't know where to begin." ... but of course, begin he does.
More later, maybe.