Impacts on the environment
1) Impacts due to digestion of Cane toads
As mentioned before, Cane toads have a gland besides their heads, which let out a poison, which can be lethal to any animal that consumes or even goes near the Cane Toad (Purves). Not only is the adult Cane toad poisonous but so are all of the cycles of the Cane Toad starting from even the eggs, to the tadpoles, to the juveniles, to the cane toad (Puhalovich). Even though there are animals such as the keel black snake are immune to this venom, it can be very deadly to those who are vulnerable causing problems in breathing, paralysis, and death (Puhalovich). As the Cane toad was introduced there are many examples of animals that had a decrease in population because they had consumed the Cane toad.
The first example is on the northern quoll. The northern quoll is a species that lives in northern Australia and it is now marked as endangered due mostly because of the introduction to the Cane Toad and the poison that is inside of the Cane Toad (“Dasyurus hallucatus”). According to a study done by Professor of Conservation Biology John Woinarski of Charles Darwin University and David M Watson a associate professor at Charles Sturt University, the decline of the northern quoll can be shown. How they did this experiment was that they had 77 monitored sites having sites in the Kakadu National Park where the cane toad would arrive and sites were toads would not arrive (Woinarski). As soon as the toads arrived, there was no change in the control variable but within a year of the toads’ arrival only 4 out of 30 initial Quoll’s were remaining (Woinarski). As more and more corpses were found in the monitored sites, they realized that the corpses all had similar bleedings in the nose and ear and red lips, which is the symptom of Cane Toad Poison (Woinarski). After two years since the cane toad was released, the sites where the toad was released there were no more northern quolls left (Woinarski). This symbolizes that Cane toad poison actually does have an affect on the population growth of a species. Figure 16 shows a northern quoll creeping on a cane toad.
Another example of an impact due to digestion of the Cane toad is the Agamid family, which is the lizard family (Puhalovich). It was analyzed by John Woinarski of Charles Darwin University that various species of the agamid family such as the frilled neck lizard and the gilberts dragon as well as in general 59% of the agamid family in Australia decreased in population due to the arrival of the Cane toad and its poisons (Puhalovich). This is due to the poison in the Cane Toad’s glands which kill’s its consumer unless the species is immune to it like the keel black snake.
Also, the final example of an impact due to digestion of the Cane toad is Goannas. Goannas are a group of monitor lizards and there are over 20 different species of these lizards in this group (“Australian Goannas, Our Monitor Lizards”). According to Dr. Scott Burnett, who is a professor of ecology at the University of Sunshine cost, there was 64% decrease in the population of the Argus monitor only 7 months in to the introduction of the cane toad (Puhalovich). Also, there were higher drops of 77% for the next year of the Argus monitor as well (Puhalovich). It is said that 85% of the lizard group, the Varanids were at a risk to die due to the arrival of the cane frog (Puhalovich).
One can see that the cane frog didn’t only affect one species due to their poison; it affected many different types of species.
2) Impact of predation by Cane Toads
As mentioned in previous topics on nutrition, it was mentioned that adult Cane frogs consume various different species ranging from insects like ants, spiders, beetles to animals such as toads, frogs, and snakes to even mammals like birds and earthworms (“Cane Toad”). Also, it was mentioned that an adult frog eats about 200 food pieces a day, which is a huge amount of food (“Cane Toad”). Because cane toads will eat almost everything that is put ahead of them, predation by Toads are a huge problem when dealing with the impact it had on the environment.
First of all, an example of an impact of an environment regarding predation by toads can be proven by a study done by Dr. Christopher Boland, professor of biology and environment, of the Australian Nation University. Boland mentions that a bird species called Merops Ornateus, were affected by the predation by the cane toads (“The biological effects, including lethal toxic ingestion, caused by Cane Toads”). Boland found out that Cane Toads destroyed 33% of the nests of the Merops Ornateus, also called the Rainbow bee-eaters (“The biological effects, including lethal toxic ingestion, caused by Cane Toads”). Also, they would often eat the eggs and the baby birds as well (“The biological effects, including lethal toxic ingestion, caused by Cane Toads”).
Another example of an impact of an environment regarding predation by cane toads can be supported by facts about the large appetite that Cane Toads have first of all, it was described by Byron Shire council that one Cane toad was recorded to eat 24 rainforest snails and another cane toad was recorded to eating a large amount of 270 ants in one day (“Cane Toads”). This supports the fact that the Cane Toads have a very big appetite and this might endanger many of its prey since before the cane Toads arrived, they weren’t used to being consuming in this much of a quantity (“Cane Toads”).
There are also many other examples of impacts on the environment by predation such as a study done by Dr. Michael Crossland, professor of Ecology, at the University of Sydney, which proved that Cane toads’ tadpoles, predate on frog tadpoles. (Puhalovich) Another example is that Planigale maculate, which are carnivore mice, was discovered as one of the cane toad’s dietary items by a professor named Michael Archer, professor of Biological Environmental sciences at the University of New South Wales (Puhalovich).
3) Competition due to same resources
Competition is one of the essential things that happen when an invasive species comes in to a local area. This is because if more population of different species comes that aren’t used to being in that country and go in to a niche, this causes competition and will lead to competitive exclusion. This is the case for the Cane Toad and various other species that are going to be mentioned having competition with the Cane Toads.
First of all, the ornate burrowing frog was found to have competition for habitats with the Cane Toad as found out by Dr. Michael Crossland, professor of tropical Ecology, at the University of Sydney (Puhalovich). He mentions that before the cane toad was introduced, the ornate burrowing frog had laid eggs and lived a cycled life (Puhalovich). However, as the cane toad was introduced, it was found out that tadpoles of the ornate burrowing frog didn’t survive when the Cane toad frog tadpoles had already taken the spot (Puhalovich). Crossland concluded that this infers that there was competition because the frog tadpole and the toad tadpoles were fighting for a resource, in this case shelter, and the more dominant cane toad tadpole had won over the habitat (Puhalovich). One can look at figure 18 to look at the Limnodynastes ornatus or the ornate burrowing frog.
Another experiment was done with frogs in general to support that competition is one of the essential things that happen when an invasive species comes in to a local area. This experiment was done by Dr. Ian Williamson, who is the professor of biosciences, at the Queensland University of Technology in Brisbane, Australia (Puhalovich). He did an experiment with 4 different types of frogs to see what happened when they were face with the Cane Toad to compete for the same resources (Puhalovich). He did this using an artificial pond to record the data (Puhalovich). The results were found out that tadpole growth was reduced in three different types of frogs except for a last fourth one with the Cane Toad present (Puhalovich). Also, there seemed to a decline in numbers of one of the frogs, which was the green tree frog (Puhalovich). This symbolizes the competitive exclusion that was going on with the green tree frog and the Cane Toad (Puhalovich). One can see that not all species experienced competition when the Cane Toad was present but it was evident that most did as can be seen in the study.
There was another short general experiment that was done to support the fact that competition is one of the essential things that happen when an invasive species comes into a local area. This can be seen by a quick general a study done by Professor Ross Alford, professor of environmental sciences at James Cook University and Lin Schwarzkopf, who is the professor of biology and tropical biology at the James cook University (Puhalovich). For example, Alford and Schwarzkopf mentions in a finding from a study that when the Cane Toad were present with native species, the cane toad population would increase rapidly (Puhalovich). This would infer at competition because of competitive exclusion and how one species flourishes more while one diminishes (Puhalovich).