If you abandon alien species
The most of the pet that you have is from foreign countries. So it means the most of the pets are alien / foreign species. Some reasons why people released pets are having an "exhausted mind" "bat breeding conditions" "accidents" etc.
But have you ever think environmental influence which comes from our released pets?
The first influence is destruction of the ecosystem. Foreign species’ reproductive ways and adaptability are stronger than Japanese native species. So, they kick out such species/ animals and adjust to native environment. Also, they give bad effects to predatory animals. It is really a difficult thing to restore the ecosystem.
The second influence is genetic pollution.This pollution vanishes the native species’ genetic information/ ability. Erased genetic information is equal to the extinction. Japanese beetle is a famous example. To be specific, Okinawa subspecies beetle's gene get damaged from Main island beetle's gene. As a result hybridization species diffuses in Okinawa. It means subspecies DNA gets extinct on the genetics.
The last influence is health hazard.Some foreign species likely to have venom. In Japan, some people have toxic spiders for pet. Every year some buyers miss spiders. In fact, some people from origin countries die because of the poisonous spiders. We have to be well informed about toxic /poisonous foreign pets.
Impulsive people's behavior will leave a large trace in the environment. We have to consider about this problem before having a pet. Also, people who already have pet need to reconsider.