Cane toad (Bufo marinus)

   Invasive species in an environment can pose serious threats. After the introduction of a new species, what follows is largely unpredictable and irreversible. It can cause significant damage to the ecosystem. Much is uncontrollable in nature, but it is the interest of some ecologists to maintain stability amid the chaos. A species of relevance to this topic is the cane toad, a toxic species of toad, in Australia, originally from the American continents. Cane toads were initially introduced to Australia in 1935, with the intention of controlling sugar cane insects. Following its invasion, the population of cane toads increased drastically and spread over hundreds of square kilometres.

Cane toads now range from Central and South America to Australia

 

     These cane toads caused death in various vertebrates, both directly and indirectly due to their toxins; cane toad poisons do not naturally break down after death. Reports of water supplies being poisoned by the toads were made accordingly, so studies were conducted to test the effects of long dead and desiccated toads on waters and the animals that inhabited them. Various parts of road-killed toads were placed into water labelled with a dye; the dyed water was poured into a clean tub of water. It was found that native fish and tadpoles were noticed to avoid the dyed water. Another series of experiments, this time including the cane toad tadpoles in the water, observed significantly higher mortality rates than previously recorded rates under normal conditions. The cane toads were having long lasting effects on the environment after death, creating toxic conditions  in which native species hadn’t adapted too. The conservation ecologist’s approach is explore possible ways to regulate the dire effects that the invasive species has had on the ecosystem.  Predation of the cane toads was considered ; a predator native to Australia was needed.  It was observed that the cane toad in its metamorph state (the state between a tadpole and adult) was susceptible to predation of meat ants. A study had found that 88% of metamorphs died of their injuries even if they had escaped predation.. What’s more is that the ants forage the toad remains that they cannot immediately consume, reducing the toxicity that the dead toads are known to introduce to the environment. Therefore these ants are very ideal for controlling cane toad populations and removing some of the impact of the toxic break down into the environment.

Meat ants attack a Cane toad

     Another method that proves to be effective is “CTA” (conditioned taste aversion). It is kind of like sensitizing an organism, “training” them to associate a certain “clue” (taste) with danger that the organism should then avoid if contact is made in the future. A quoll, a small carnivorous marsupial were used in an experiment. Using toads infused with a nausea inducing chemical, conservation ecologists aimed to cause quolls to get used to the fact that the toads were not good to eat. To verify if this experiment worked they captured many quolls and divided them into two groups of males and two of females. One would be conditioned with the nausea inducing chemical following CTA (toad smart) and the other not (naïve toad) in both the male and female groups. After releasing the toad smart and toad naïve quolls out into the wild, they tracked them with radio, recorded sleeping positions with GPS and embedded a mortality sensor in them to determine their survivorship. At the end of the experiment, females survival rate were higher; 84% for females and 58% for males. Toad-smart quolls had a much higher survivability; 94% in females and 88% in males. What this group concluded was that invasive cane toads pose a large threat to northern quolls, and CTA can be effective to manage predators responsible for extinctions and that more research will be needed to find out if CTA has a long term effect on toad aversion.

A quoll munching on a toxic Cane toad

     Consider the dynamic complexity and the astronomical number of factors swirling around in an ecosystem, never in equilibrium and ceaselessly changing, having evolved and adapted accordingly. The introduction of a species that had not adapted accordingly could have macroscopic effects, that are irreversible, if considerable disturbance does follow as shown in these aforementioned studies of the cane toad.. In the eyes of conservation ecologists, it is important to sustain the dynamics of an ecosystem, or consequences inevitably ensue, that imply danger to species and to us (poaching pandas), whole habitats (cane toads) and even global scales (global warming). Their work is rigorous, because of the uncontrollable and unpredictable aspect of the dynamic ecosystem, but step by step, they provide ways that preserve the regulation of life in its environment. We can’t imagine the complex way that life as a whole has integrated itself, but being a part of it, conservation ecologists recognize the importance of maintaining that integration to the best extent we can during our era here on planet earth.