Litoria gracilenta - The Graceful Tree Frog is an ephemeral breeder. They emerge to breed in temporary streams and ponds that form after summer storms.(Image: K. Kriger, Save The Frogs!)
The summer afternoon storms of subtropical Queensland are an awe inspiring sight and sound of nature. If you’re lucky enough to have some trees and ponds around your house, the wet balmy night will be filled with the crawk – crawk – crawk of male Green Tree Frogs (Litoria caerulea) seducing prospective partners.
These Green Tree Frogs are lucky and seem to be able to get along with us, living in our constructions like shower blocks, drains, and toilets. While I felt lucky to experience these loving sounds of nature, only 5 kms from Brisbane’s CBD, I wondered about the diversity of frog calls that I would have heard if I was here 200 years ago, before Brisbane was a metropolis.
The arrival of Europeans heralded massive landscape changes; natural habitats have been converted to agriculture and suburbia. In many cases these changes either removed or severely degraded frog habitat around Australia. The logging of forests, damming of rivers and the development of land often removes the vegetation surrounding ponds and streams, adds pollutants and sediments and, can change the flow of water. Of course these changes can affect the quality of the habitat for frogs. For example the vegetation around streams can act as a shelter for tadpoles from predators; removing it increases their chances of being eaten by fish.
Some frogs like the one pictured, actually lay their eggs in ponds or streams that are not permanent (ephemeral). They lay eggs in streams or ponds that actually dry up after a short period. They are known as the ephemeral breeders.
Ephemeral ponds and streams are good places to lay frogs’ eggs and for tadpoles to grow up in, because they are often isolated and new. There are no or few predatory fish. Take a look in a puddle, see any fish? Fish need streams to be connected so that they can move around. Ephemeral ponds are generally not linked or connected, they’re much more like a string of puddles.
Pristine frog habitat with riparian vegetation (Image: TalkingNature.com)
Deepening stream channels to increase water flow (which is often done to ‘improve’ stormwater drainage for new urban developments), is not good for these frogs. It can cause temporary or ephemeral ponds to become permanent. A permanent connection to a river allows the predatory fish to access the frog breeding ponds, eating the eggs and tadpoles. Tadpoles that have not evolved to cope with predatory fish have little chance of survival. The evolutionary strategy of the ephemeral breeders backfires when man connects the ponds and streams.
A recent scientific review of habitat destruction in Australia revealed that the populations of 20 out of 41 species of frogs were at risk of declining as a result of habitat degradation. Altering habitat has serious implications for the biodiversity of Australia’s frogs. This study also showed that ecological managers need to better understand how habitat alteration affects the different populations of Australian frogs [1]. Understanding how habitat alterations affect the stream ecology makes us better able to live with nature.
Tonight, as I listen to the crawk – crawk – crawk of male green tree frogs, I will try to imagine the cacophony of calls that were once heard from the many other frog species that are no longer in Brisbane.
[1] Hazel, D (2003) Wildlife Research 30(3) 193 – 205 doi:10.1071/WR02075
K. Kriger is founder of Save The Frogs! Visit his frog conservation website.
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Deepening stream channels to ‘improve stormwater drainage’ is also bad because the high-flux storm flows scour the stream bottom, removing vegetation that serves as protective habitat for tadpoles.
http://savethefrogs.com
About the frog picture featured in this post:
I took the photo of that Graceful Treefrog in the wallum swamps behind the Gold Coast (Tugun/Coolangatta) Airport in 2005.
Queensland Dept of Transportation has since put a major freeway through that area, destroying habitat, increasing noise pollution that drowns out frogs’ mating calls, and exposing any remaining wildlife to toxic runoff. There was little resistance to the proposed freeway even though multiple endangered frog, mammal and plant species lived there. SAVE THE FROGS! (http://savethefrogs.com) works to promote a society that respects and appreciates nature, so that citizens take action and oppose the blatant destruction of wildlife habitat, rather than allow those with financial stake to do as they wish, as was the case at the Gold Coast airport.
Sad times, the economy will win out everytime
but I’ll be listening out for our local frogs, unfortunately i think the dreaded toads have run of our neighbourhood though
Hi Maria,
Sometimes ‘the economy’ realises that there’s more value over the long term to leave things alone. That’s happening in places like the Great Barrier Reef and in other places around Australia.
Many people are starting to realise that nature has a significant, economic and social value.
Lets encourage it and hope it grows. Spread the word about TalkingNature.com
Cheers
James
I really liked your blog! super
I found your blog on google and read a few of your other posts. I just added you to my Google News Reader. Keep up the nice work Look forward to reading more from you in the future.
Interesting to ponder a further complicating factor in habitat connectivity. So many when they discuss this topic tend only to think of connecting forests, which is of course very important, but different kinds of habitat are important to different kinds of animals. In the case of these particular frogs, a lack of total connectivity is apparently best, while presumably it is still preferable to have a chain disconnected ponds not too far away from one another, to cater for multiple breeding couples in the locality, and so that their progeny will later be likely to have a few options to expand into. Incidentally, I live about 100km south of Brisbane and am currently listening to whistling tree frogs though my window (one of the few species that continue to call through winter).