Amphibian populations worldwide have recently been declining at a fast rate due to factors such as climate change, water pollution, predation, and diseases. However, according to a study from researchers at McGill University amphibians now might have to contend with another threat, i.e. invasive plants.
The Fowler’s toad (Anaxyrus fowleri) of Long Point, Ontario, listed as endangered in Canada under federal legislation, has recently been discovered to be suffering from a loss of
breeding habitat due to the invasive common reed (Phragmites australis) spreading throughout their shallow marshes.
Although the area that had been covered by the common reeds had remained isolated to less than one hectare for quite some time, an invasive strain of the reeds developed around 1995 which then soon began to occupy its neighbouring areas at about 11.1% per year. Moreover, a decline in the level of water in these marshes also promotes the proliferation of the common reeds; therefore the water levels of Lake Erie that supports the marshy breeding habitats for the Fowler’s toads are also contributing to this rapid expansion of the common reed.
In 2010, the common reed had spread to inhabit 15% of the total marsh area, i.e. an alarming 85.4 hectares compared to the <1 ha that had been occupied only 20 years before. Due to the swift coverage of marshy breeding habitats to the uninhabitable reed environment, the carrying capacity which initially could hold 176 male toads in 1989 has been declining by 8 toads a year.
In order to estimate the abundance of the Fowler’s toad in relation to this invasive plant, a thorough mark-recapture method with toe clips was utilised to identify adult male toads during each breeding season for 23 years from 1989-2011. The population of Fowler’s toads were found to shift from the regular cycle of bounded fluctuations to a gradual decline in the year 2002, and therefore demonstrates a strong relationship between the spread of these reeds and the dwindling of the toad population due to a new, lower carrying capacity.
Fortunately, there is potential for the Fowler’s toads to recuperate and successfully recover from this decline. The toads have been noted for being resilient to destructive environmental conditions and appear well adapted to the constantly changing characteristics of the marshland and reproduce with large clutch sizes of around 2,000-10,000 eggs.
Furthermore, the authors proposed different solutions to combat the decline of the Fowler’s toad and alleviate the stress on the toad populations of Canada. These solutions include creating temporary artificial breeding ponds to foster an environment for the
populations to grow, developing strategies to effectively restrict the further spread of these common reeds into the marshes of the northern shore of Lake Erie, and restoring the already invaded areas.
The decline of the Fowler’s toads is an important conservation issue in Canada as these toads are common throughout the eastern United States, but in Canada there are only three small populations of these endangered toads that are all found on the northern part of Lake Erie. If efforts aren’t made to save the Fowler’s toads of Canada, they could soon be extinct from the Canadian frontiers.
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GREENBERG, D. A., & GREEN, D. M. (2013). Effects of an Invasive Plant on Population Dynamics in Toads. Conservation Biology.