Global climate change is real. We are living in an age of
overwhelming evidence. For example, last December I was wearing shorts and a
t-shirt in upstate Ohio – not normal. But while we have been aware of this
threat for some time, the effects of climate change on many groups of organisms
are poorly understood. One such group is amphibians; those sometimes slimy,
hopping, misunderstood (you can’t get warts from a toad) creatures. Amphibians
are one of the most sensitive groups of organisms on the planet to environmental
change. Approximately 40% of amphibians are threatened or endangered and
climate change has been implicated as a major driver of amphibian declines.
That is why a group lead by Benjamin Scheele of Australia National University set
out to determine how climate change has affected the endangered northern
corroboree frog (Pseudacris pengilleyi).
The corroboree is a small frog with a limited distribution,
occurring largely within nationally protected areas. So, factors implicated in
amphibian declines like habitat loss and environmental contamination should not
affect these individuals. However, a decline of 42% was observed over 13 years
in southern Australia. Initially, research indicated that the extinctions were
the result of Batrachochytrium
dendrobatidis (Bd), an emerging
infectious amphibian disease that has been linked to declines worldwide. While Bd was an initial driver of the
extinctions, Bd now persists in
populations without causing further declines. Perplexed, researchers turned to
climate change as the primary culprit.
One misconception about climate change is that it just causes
warmer temperatures. While largely true, climate change also affects
seasonality and subsequent precipitation. Because amphibians like the corroboree
breed and lay their eggs in waterbodies, environmental desiccation (dryness due
to reduced precipitation) reduces the chance of offspring survival into the
next generation. With this in mind, the team set out to analyze 10 years of
previous data and conducted their own surveys. They divided their sampling
areas between three primary sites: frogs present, extinct (historically
present), and historically absent. They also divided each site into pools, with
or without frogs, and each pool into nests (present, possibly present, or
absent). What they found was striking.
Over the course of 10 years, annual and autumn precipitation
declined by 20% and 38%, respectively, with sharp increases in mean annual
temperatures. These changes altered the amount of water that entered waterbodies
with runoff declining 40%, indicating a period of unprecedented drought. Not
surprisingly, the team found positive correlations between sites with frogs and
the presence of water. Conversely, in areas of increased dryness, tree
invasions occurred, indicating the longevity of the drought conditions. Taken
together, the results showed that the climate extreme primarily affected the corroboree
through habitat desiccation, lowering future survival.
So what does this mean for us? Well, it’s a question I
really hate to answer because it shouldn't matter – we caused the problems and
they are our problems to remedy. However, there are many direct benefits that
we gain from amphibians. Amphibians, especially frogs, are a crucial part of
the food web; they help fight the spread of, and provide remedies for, human
diseases. Many insects spread diseases such as dengue fever, West Nile, and
malaria, and these insects are also a primary part of frog diets. So, less
frogs leads to more disease-carrying insects and higher prevalence of disease. Also,
frogs produce skin secretions that have been used in medicines that treat
conditions such as high blood pressure and peptic ulcers, and diseases such as
diabetes and HIV. Frogs are also important bioindicators. Their skin is extremely
permeable and susceptible to aquatic pollutants. Thus, the health of frogs is
thought to be an accurate predictor of environmental health – the environment
in which we live.
We have been aware that climate change is a real problem. In
this study, Scheele and his team have provided evidence that the recent
declines in the corroboree can be linked to warming temperatures, reduced
rainfall, and increased habitat desiccation that ultimately reduced survival.
The researchers propose that in order to mitigate the negative effects of
climate change, efforts must be made to provide suitable habitats that will be
able to persevere in the changing world. However, no matter the solution, we
are the driving force behind many of the factors (including climate change)
that are responsible for the current amphibian declines and must take steps to
ameliorate our effects on natural systems before species like the corroboree
are gone for good.
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