Human and Invasive Species

Small Indian Mongoose

Adorable? This Small Indian Mongoose was introduced to control rats in places such as Mauritius and Hawaii in late 1800s. Such efforts, however, have caused extinction of some endemic birds, reptiles and amphibians.

I came across this database on invasive species that published the 100 worst invasive species on the planet - from aquatic plant to mammals:

Click the link above for reference

 First of all, what are invasive species?

"Invasive species are plants or animals that do not belong where humans have intentionally or accidentally brought them. " - WWF

Humans, with or without intention, have introduced some of these species to places and have caused extinctions to some other species. 

I remember reading an article about crayfish last year, Thomas Breithaupt, an employee at the UK Environment Agency, found up to 20 signal crayfish per square metre in some areas. Humans introduced them from America for aquaculture purposes 30 years ago. What's important is that such concentration of the non-native species will lead to the 'outcompetion' of other species. In fact, humans spread invasive species in different ways, and the frequency has increased. For example, the rate of invasion into San Francisco Bay rose from one to three invader per year in 1961-1995. Invasive species found their route through foreign sources or across watershed boundaries. Over 400 species were introduce during the 1961 - 1995 compared to just 67 in 1850 - 1900.

Frequency of occurrence for vectors of introduction for alien invasive species that are threat facts for listed fish species in Canada

In Canada, most invasive species in freshwater were introduced due to sport fishing. In fact, 85% of the introductions that affected native species were intentional, while 88% of these were related to sport fishing. Although in general, over 75% of the species face not only threat from invasive species, such factor appeared to be the only contributor to the extinction of North American fish taxa. Invasive species were also considered to be the second greatest threat to imperilled species in America. Dextrase and Mandrak mapped the significance of invasive species, they affected more than half of the listed species in Canada. 

Number of listed fish species and the proportion that are threatened by alien invasive species in each freshwater ecological area in Canada (Height = number of listed species, solid = number of listed species threatened by invasive species)

Humans often introduce non-native species with good intention, but result in bad consequences, including the potential extinction of local species. Apart from Small Indian Mongoose and signal crayfish, zebra mussels were also deliberately introduced to some aquatic environments. They are famous for being efficient filter feeders that increase water clarity. However, the mussels bioaccumulate toxins that are harmful to native species like fishes and birds that consume them. 

Recently, there has been raised awareness of the harmful effect from invasive species, and has encouraged discussions upon solutions. National Wildlife Federation suggested three main focuses: 

1. Prevention of their introduction in the first place

2. Create monitoring systems for detecting new infestations

3. Move rapidly to eradicate newly detected invaders

These initiatives are relatively easy to come up with, but difficult to implement. Actual practices, such as biological control of invasive pests, were used in Hawaii. Yet, this method is controversial, as it caused extinction of some other non-target species. For instance, the introduction of 16% of 313 parasitoid species to eradicate holometabolous pests attacked other native species in North America.  

Facing non-native species, many species are outcompeted and have therefore gone extinct. On another note, human intervention in removing the invasive species they introduced is argued to cause further adverse impact on native species. Hopeless?

We can just anticipate that better solutions, which would not contribute further to extinction, will be put in effect soon.