One of the things that impact our environment, that doesn’t get its due attention, is the issue of introduced species. These are the animals who, by one means or another, find themselves in a new land. To us, the idea that we might wake up one day and find ourselves in a new country can be scary, but exhilarating. For animals, I’m not so sure it would be either of these reactions.
These animals must find water, food and shelter in situations that they may not be designed to deal with. It could mean instant death, it might mean a long time of struggle and slow decline for the animal as it fights to survive, it could mean a horrendous death in the mouth of some animal that it has never seen before, and didn’t know was dangerous. In some cases, though, it become the problem, being the dangerous animal that sneaks up and kills native species that have no idea it was there or that it would kill them.
There are, of course, some success stories regarding animals that were introduced to help with one problem or enhance some other aspect of life. There are some who just exist, quietly in the background, harming little, inconveniencing few, and there are those who have been introduced for so long, they are simply a part of the fabric of life in their new home.
These animals are sometimes imported to the new country by humans for research, scientific purposes, for sporting purposes – hunting and fishing, or for pest control. Some are brought as pets – legally and illegally. Some of them stowaway, while others are turned lose by humans who thought they would be good pets, but found out otherwise. There are also those animals who play a part in ancient medicines and rituals, that are brought for those purposes.
Once here, they can escape because of storms, floods, human mistakes, or just because the animal was too cunning or too determined to stay locked up. That’s when the problems start, and once those first animals are loose, to get rid of them is like trying to put the genie back in the bottle. A simple action of releasing a pet fish in the water can have devastating effects on plants, animals, humans, and every other aspect of the ecosystem. Once the balance is askew, you can’t get it back. Yes, some introductions of alien species have been eradicated, but before that can happen, there is always damage left in their wake, be it a native plant that is made extinct, or an entire community bankrupt, or the land structure completely changed. Lives – human, animal and plant – can and do hang in the balance.
If nothing else is taken away from this book, I hope that the lesson is that animals and plants are living, viable entities, and cannot be ignored or discarded when we take on the role of caretaker for them, no matter what the setting. Be it a specimen for a lab, a pet, or an animal intended to help eradicate pests, it is our responsibility to ensure that it does not impact the ecosystem. There are many ways we can help, because this is now a global issue. The cost of introduction is high, and is a long term commitment. Hopefully as more people become aware of that, and treat ownership or stewardship of these creatures responsibly, we will have fewer problems with introduced species.
African Clawed Frog
An African clawed frog was the first vertebrate ever to be cloned. It was also one of the first animals to be used for pregnancy tests for humans in the 1940s. This species has also been to space – in 1992 on the space shuttle Endeavor, where some were used to study reproduction and development in zero gravity.
So why would such a wide-traveled and scientifically significant creature make it into our book about aliens? Well, it’s not because of the outer space thing. It’s because they are a harmful, destructive introduced species, as are many of the other animals included in this book.
What harm can a frog do? In order to understand the problems, you have to look at the animal as a whole. From the name, we know that they come from Africa, and are fairly wide-spread there. They have special adaptations that allow them to survive through droughts and monsoons – they are able to use their claws to pull themselves to other bodies of water. They can dig into the mud and go dormant for up to a year, waiting for water to return. They prefer warmer temperatures, fresh water, and calm areas in which to lay their eggs. They prefer a place that doesn’t have larger predators.
One of the problems created by the introduction of this species is that they, themselves, are large predators, at least in frog terms, and they have a voracious appetite. They are now found in the USA, Chile, France, Mexico, Sicily, the United Kingdom, and Portugal. In virtually all these new areas, the African clawed frog is problematic. It steals habitat and food from native species, while devouring their eggs. It will also eat the mature animals if the local frog species are smaller than the African clawed ones. They are too big for most local snakes and other water predators to handle, so they can become a dominant species very quickly.
There is a second problem that comes with these frogs, this one found in their skin. They carry Chytrid Fungus, a disease that quickly kills amphibians, and that spreads very easily. Because of a naturally-occurring antibiotic in the skin of the African clawed frogs that helps any wound to heal very quickly, and because the fungus is essentially trapped there where it cannot penetrate into the skin, the African clawed frog is a perfect host for this disease.
The obvious question is, if they are so bad, why were they introduced? Frogs in general share a lot of anatomical similarities with mammals, which makes them well suited for lab use. Many were imported for this purpose. They are still used extensively in studies regarding vertebrate embryology, because their embryos are transparent, allowing scientists to observe development, and because they are prolific in egg production. Even in places where the frogs are not introduced to the wild, there are still problems caused by the introduction of the fungus to other animals, spreading it even further and killing that many more native species. Even if the African clawed frogs aren’t able to become established in a new environment, the damage caused by the attempt to adapt, because of this deadly fungus, is significant.
This frog has many very different adaptations. Instead of webbed front feet, they have no webbing between toes. This helps them to push food into their mouths. These frogs don’t hop because the back legs are long and the back feet, while webbed, have three toes with large cornified tips that look like claws. These frogs use their front fingers and these back claws to crawl along the ground. This species of frog has no eyelids. Horny plates cover their eyes. They have no tongue, and no vocal sac, so males make no noise other than a clicking sound to attract mates. They have no visible ears.
Because of these adaptations, and because to a small degree they are able to change their color to match their habitat, they are a species that create interest to people, and for that reason, they have been imported as exotic pets. As with many exotic pets, when they become too big, or too much, or too expensive to handle, or they lose their appeal, people turn them loose which accounts for some of their distribution in new areas. In some places, large gatherings of feral African clawed frogs have been found. People underestimate the size these animals can achieve. They are, by all standards, large frogs.
In the wild, these frogs start to reproduce when they are one year old. They can lay 500 to 2000 eggs at a time, and can lay up to four times each year, creating potentially 8000 new frogs every spring/summer. They are also long-lived frogs, living up to fifteen years. The harm that can be done by the release of just a few frogs could be profound.
In some states in the United States, the importation and ownership of these frogs is now prohibited. They are not used as much for some research so that demand has also lessened. In some areas that are known to be inhabited, the lakes are fenced off and drained, hoping the frogs will run out of food source and perish. The problem with this plan is, as mentioned, these frogs have the ability to burrow and go dormant for a year, waiting for the pond to refill.
In some places in California, the species has been eradicated through the use of poisons. They also propose the use of traps in areas where poisons or the introduction of other predatory species might be devastating to the unique flora and fauna already there. In France, they hope to eradicate the population before it becomes unmanageable. Chile is still considering what options it has available, again because they must ensure the safety of native species in their attempts to remove these frogs. The IUCN’s Global Invasive Species Database considers the threat of this species to be extreme. We rate it here as very detrimental both because of the frog’s nature and because of the Chytrid Fungus it brings with it.