Question: Will liberated animals upset the ecosystem?
Answer: As the answer, below are some points for reflection…
 Some liberated animals are protected in well-managed sanctuaries. Some are liberated in the open, able to move around, not in confined spaces with tightly balanced ecosystems, such as national parks and reservoirs, which is illegal in some countries. Fair considerations should be made to ensure the liberated should be able to survive. That said, if they are not saved, they could be bought to be killed and eaten within less than 24 hours, having much shorter lives.
 Politics aside… A human immigrant legally enters another country, with different living habits. Do we say this immigrant upsets the human ecosystem, and demand the immigrant to directly return? What if we are the immigrant, just looking for a more decent life? This immigrant and company are not overwhelmingly many too, in ratio. A human refugee flees a place otherwise unfairly condemned to die, and desperately wants to enter a country for safety. Do we say this refugee is a definite source of danger to everyone else, and should simply be sent back to be killed? What if we are the refugee, just wanting to live? Again, this refugee and company are not overwhelmingly many too, in ratio. Think of liberated animals as the refugee immigrants.
 The liberated is always a VERY VERY VERY small number in ratio, compared to the millions of beings killed daily worldwide. If so, is not animal liberation not more of attempting to restore nature a LITTLE, than possibly harming nature much? Is not MUCH killing and inaction by not saving not MUCH more harmful? Humans active in trapping, breeding, killing, selling, buying and eating of animals are collectively MUCH more harmful in destroying lives and the global environment. For example, years ago, humans were already upsetting the ecosystem severely, with ALL 17 fishing seas being overfished. Why not live and let (free to) live?
 Is not the daily and sometimes periodically increased transporting of many animals to other places and countries to be killed not a much greater way of upsetting global ecosystems? If it is not alright to save relatively few, is it alright to not save any at all, to simply let all beings be killed? If it is considered alright by some to kill many animals for spiritual reasons believed in, why is it not alright for others to save some animals in the name of spirituality too? Those who get killed without being rescued will not have the opportunity to be connected to a better spiritual life now, and in the future. Thus, not liberating them makes it hard to help them both physically and spiritually. While not eating animals helps them passively, liberating them helps them actively. Both are important.
 Every day, many average humans are freed from prisons worldwide, to return to their usual lives. Many of them are meat-eaters, whose demand for more meat leads to supply of many more killed animals. Many of them are ignorant that meat-consumption is the number 1 cause of the climate crisis: https://www.theguardian.com/environment/2018/dec/21/lifestyle-change-eat-less-meat-climate-change Even many who are not ignorant continue to eat meat and animal products. Are these humans who destroy the environment globally to be kept imprisoned then, or even to be executed, so as to lessen the impact of their harm? Of course not. And what about those not in prison, you and me, who might also be unreasonably active in destroying the environment, by not living with better habits? So perhaps, the question in the title above is the more relevant one.
May all beings be well and happy, free from fear and harm.