Floridian Frog Acoustic Battles!

Invasive Alien frog populations are causing commotion with competitive exclusion across Southern Florida! 

The forests of Florida are densely populated with a vast variety of treefrog species. Being able to produce uninterrupted and unaltered calls to other members of the same species is very important for mating. The sound a frog makes is very specialised and allows both potential mates to know what type of frog they are and where they are situated. Therefore, if an Invasive Alien Species comes along with a call of the same frequency and tends to produce it at the same time of night, this could lead to confusion and missed mating opportunities as they battle it out.

Pinewood Treefrog 

Cuban Treefrog 

Green Treefrog

Tennessen et al explore the arrival of Invasive Alien Species such as Cuban Treefrogs and their impact on native ones like Green and Pinewood Treefrogs. In particular they focussed on the acoustic calls they both make looking for any changes in the patterns of their sounds, relating it to competitive exclusion. 

Competitive Exclusion

As defined by Gause, competitive exclusion is when one group of organisms can potentially exclude another group from their habitat or particular resources. This can produce two responses;

1. the other group becomes entirely excluded and has to migrate or becomes extinct 

2. the other group modifies their lifestyle in order to share the resources and coexist

Either way, the species with the competitive advantage, such as an Invasive Alien Species, will be able to impact the life of other species. 

In this case the Cuban Treefrogs invaded the South Florida forests and starting interfering the acoustic resources of other native treefrogs. Tennessen et al conducted a study involving Cuban, Pinewood and Green Treefrogs where they played the calls of each species to the other and recorded their responses. When the Cuban Treefrog's acoustics were played to the Pinewood Treefrog, no change or modification to their call was recorded. This was because they both produce their calls at different frequencies and tended to make sounds at different times. This therefore meant there was no overlap in the communication between members of the same species and therefore no competition. However, when the Cuban call was played to the Green Treefrogs it was found the native species shortened the duration of their cals and increased the call amplitude.

 Tennessen et al  display this result in the figure above. The top graph (a) shows the Green Treefrog vocal behaviour before the Cuban Treefrogs call was played to them and the bottom on (b) shows the frequencies of their calls afterwards. This shows that the Green Treefrog has infact modified its call in response to the invasive species being there. This adaptive behaviour shows the second response mentioned in the competitive exclusion explanation above and is a key example of how Invasive Alien Species do not always lead to extinction.