Trouble in paradise: Oil roads significantly reduce rainforest frog biodiversity

Summary:

  • The canopy of tropical rainforests harbour a rich variety of life, and remain a largely unexplored scientific frontier
  • Bromeliads are plants that grow in the rainforest canopy, and their leaves form minute ponds in which water can collect, playing host to many other species
  • Disturbance caused by road building and deforestation dramatically alters these complex arboreal ecosystems, with strongly negative impacts on biodiversity

There is an entire world in microcosm living among the branches in the rainforest canopy. This world is complex and replete with microhabitats, hence it supports many thousands of species. The canopy is largely unexplored by scientists, due in part to the difficulties of conducting a study tens of metres above the ground. One of the most important microhabitats present in the lofty world among the trees are phyotelmata- miniature pools that form in the leaves of plants that are perfectly adapted to life in the tree tops. And the most important of these plants are the bromeliads- they have specialised ‘tanks’ at their base, where overlapping leaves form a leak-proof pond of water in order to trap water. This is because most bromeliads are epiphytes- plants that live on tree branches whose roots never touch the ground, relying on airborne mist and dust for their water and nutrition.

Ranitomeya variabilis male, carrying his tadpole on his back. [Picture retrieved from http://www.dendrobates.org/images/variabilis_nominal9.jpg 17/02/2016]
Many animal species are bromeliad specialists; they can live and breed nowhere else. Among the most common specialists are frogs- they require water to hatch their eggs and rear their tadpoles- and as such they are at the greatest risk should anything happen to their arboreal nurseries. One such species is the fantastically colourful poison dart frog Ranitomeya variabilis (left): only as large as your thumbnail, potently poisonous and brilliantly adapted to the rainforest high-life. The female of this bijou little frog lays her eggs in the tank of a bromeliad, and supplies it with infertile eggs as food. Should anything endanger the tadpole, the male carries it on his back to find safety in a new bromeliad pond.

Yasuní national park, in the Ecuadorian Amazon, is the most biodiverse place on Earth, and is a fantastic place to study the rainforest canopy as its variety of life is almost unmatched. Unfortunately Yasuní is under threat by recent oil exploration due to its underground reserves of fossil fuels. A recent study published in the online journal PLoS ONE has attempted to examine the damage caused by this exploration, with a focus on the impacts of oil road construction. The investigation focussed on the response of bromeliad-dwelling frog diversity under three different ‘treatments’- intact forest, low-impact road construction (which uses geofabric as a base) and high-impact road construction (which uses felled trees as a base).. Along with this they recorded environmental variables such as the tree species that bromeliads were living on, the height above the ground that they were growing and the number of bromeliads growing in each tree. The researchers focussed on frogs living in one particular species of pool-forming bromeliad, Aechmea zebrina. Their analyses revealed a startling result: bromeliads growing near oil roads (both low and high-impact) harboured significantly fewer individual frogs from fewer species. Deforestation has many effects on rainforests- the loss of large trees reduces the local

journal.pone.0085470.g001
Bromeliads (Aechmea zebrina) in Yasuni national park, with the author collecting specimens. Retrieved from McCracken & Forstner (2014)

humidity, increases temperature and further tree mortality. As well as this, toxic fumes from oil-towing vehicles could pollute the areas surrounding the road. Both bromeliads and frogs are ‘hypersensitive’ to changes in climatic conditions, because they rely on the moist, cool rainforest air to supply them with water and prevent them from drying out. This, coupled with the reduced number of bromeliads, drastically reduces the habitat space available to canopy-dwelling amphibians; habitat loss is one of the greatest threats to frogs worldwide.

Detrimental effects of oil extraction of tropical rainforests are well documented, and as this study shows even the lowest possible impacts of oil extraction have a significantly destructive influence on these mega-diverse systems. As such, the authors suggest that no further access routes are made into Yasuní, and best-practice methods are used to try to protect this precious tropical Eden.

 

 

Reference

McCracken, S.F., Forstner, M.R.J. (2014) ‘Oil road effects on the Anuran community of a high canopy tank bromeliad (Aechmea zebrina) in the Upper Amazon Basin, Ecuador’ PLoS ONE 9(1): e85470. doi:10.1371/journal.pone.0085470

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