Introduction
It should be noted that almost any living organism that has been alien in a particular environment can be considered an invasive species. They move to a new habitat from different parts of the planet where they used to live, and new conditions allow them to adapt to the setting successfully. After invasive species adapt to new conditions, they begin to conquer the territory and actively multiply displacing native populations (Enger & Smith, 2016). Many researchers emphasize that invasive species can adversely affect local flora and fauna, for this reason, they are often considered predators. Nonetheless, this effect does not appear immediately but in the course of several years with the increase in the population of the invasive species. The purpose of this paper is to review cane toad as an invasive species and to analyze its peculiarities.
Characteristics
The basic characteristics of invasive species type are that they are non-native and they do not have the threats to their further dissemination. As a rule, such dangers are the vultures or disease-causing living organisms that can serve as natural checks to the increase in the populace (Enger & Smith, 2016). Importantly, invasive species do not face any strong predators or organisms in the new habitat that might threaten their breeding. Another characteristic of this type of species is that the majority of them are generalists. It implies that they can adapt and live in various habitats and settings. Moreover, such as animals, plants, or organisms mature quickly, breed intensely, and their young have a high survival rate (Enger & Smith, 2016). In terms of other particular characteristics, invasive species have strong and efficient dispersal systems, and they can easily win in the competition with native organisms.
Summary, Origin, and Relocation
The cane toad is one of the representatives of invasive species that threaten the life of flora and fauna. Cane toad (or Rhinella marina) was introduced in Australian Queensland in 1935 in order to fight with insect pests of sugar cane. The number of toads released on the territory was close to 60000; however, sugarcane plantations did not become suitable conditions for this species, and they spread throughout the territory while ignoring insect pests (Cogger, 2014). Thus, the introduction of an invasive species to control the size of another invader was not only ineffective but also led to uncontrolled consequences.
This type of toad has warty, keratinized skin. Individuals of this species have dark brown skin with spots. The belly of the amphibian usually has a yellowish tinge. The cane toad has characteristic round glands and supraorbital ridges. On the hind legs, the individuals have leathery membranes. Due to the fact that this is a nocturnal amphibian, the toad has horizontal pupils. It should be stressed that this amphibian type is toxic. An individual of this species can weigh up to two kilograms and reach 23 centimeters in length (Cogger, 2014). Initially, the cane toad is from Central and South America; however, as noted above, it was brought to the islands to reduce the number of beetles that devoured sugar cane plantations. In no way influencing the number of beetles, the toad bred in a vast territory and led the local fauna into decline (Simberloff, 2013). This amphibian has a good appetite and can hunt lizards, marsupial mammals, songbirds, and the eggs laid by saltwater crocodiles.
The peculiarity of this kind of toad is that its skin has toxic secretions; for that reason, Australian predators could not eat it. Consequently, as in the case of other invasive species, the number of this amphibian remains artificially high in the new environment due to the absence of predators capable of feeding on them or predators that are resistant to toxins (Cogger, 2014). Despite the attempts made by Australians to fight the toad, at present, no measure has brought significant success. For instance, to combat these amphibians, the local population tried using dry cat food. Residents poured food near the location of the toads, while scientists attracted to this place the ant species that could attack the amphibians and their offspring. As a result of the attacks, about 80% of all the progeny of the cane toad died; nonetheless, the surviving individuals bred very quickly (Cogger, 2014). In addition, the native population considered fighting them with the help of viruses. However, in the long term, such a measure could cause a chain reaction and result in irreparable damage to the local fauna. Therefore, this method has not been applied yet.
Limiting Factor
It should be emphasized that invasive species could be considered a limiting factor especially in the case of the cane toad. A limiting factor is an aspect that prevents the species from uninterrupted growth in the number of the populace. As stated by Enger and Smith (2016), certain aspects that prevent the population from growing can come from outside the species itself. Such an agent should be considered an extrinsic limiting factor. In particular, predators should be referred to as this type of limiting factor (Simberloff, 2013). Therefore, due to the fact that cone toads affect the populations of certain species types directly, they should be considered an extrinsic limiting factor for the native organisms.
Further on, invasive species are a density-dependent limiting factor. Despite the fact that cone toads can breed rapidly, which means that predators have higher chances of catching them, this type of toad is toxic. It implies that no predator apart from humans can influence the density of cane toad. On the other hand, as the population growth of this species is uncontrolled, it means that the greater their population is, the more they can eat themselves threatening the population of other species such as lizards, birds, and so on (Simberloff, 2013). Thus, the size of the predator population remains the same or decreases while the size of invasive species continues to grow. Nevertheless, a density-dependent limiting factor also implies the growth in disease epidemics (Enger & Smith, 2016). As illnesses are more likely to spread faster in larger populations, it means that toads are more likely to transmit parasites among their kind.
Conclusion
Therefore, it can be concluded that new ways of invasions of potentially dangerous alien organisms continue to emerge. At present, scientists cannot offer effective or universal control measures to cease the spreading of invasive species. The criticality of the situation lies in the fact that they are a serious enemy of local populations since invaders are highly competitive. As in the example of cane toads, the invasive species thrive in new territories monopolizing food sources. Their consolidation in new territories and further distribution entails undesirable environmental, economic, and social consequences. Therefore, the scientific world, governments, and people, in general, are highly concerned about finding ways to combat the critical occurrence.
References
Cogger, H. (2014). Reptiles and amphibians of Australia. Melbourne, Australia: Csiro Publishing.
Enger, E., & Smith, B. (2016). Environmental science (14th ed.). New York, NY: McGraw-Hill.
Simberloff, D. (2013). Invasive species. New York, NY: OUP USA.