Simon Fraser University researchers have discovered a potential explanation that sheds light on why a third of amphibians are at risk of extinction. Following a year-long study, the biologists found that amphibian groups that diversify rapidly are more prone to extinction.
Amongst the other vertebrate species, such as mammals, birds, reptiles, and fish, this pattern is only found in amphibians.
“For many amphibians, the amount of distance they can travel is often limited and they are also typically sensitive to water availability. These traits likely contribute to why amphibians are one of the most threatened vertebrate classes in the world,” according Greenberg, a PhD candidate in the biology department at SFU.
The study by Greenberg and professor Arne Mooers looked at amphibian groups on a global scale to understand how evolution may influence extinction.
“The goal of this study was to ask how diversification rate influences extinction risk, by testing whether diversification influences the proportion of currently threatened species in amphibian genera,” said Greenberg.
The biologists discovered that amphibian groups that diversify rapidly have a greater share of species that are at risk of extinction. The reason for this appears to be related to the nature of these rapidly diversifying groups, in that they consist of species that are highly specialized to certain environments.
“If a species is specialized to a certain environment and their environment gets altered, their choice is to either [adapt] to those conditions, move, or go extinct,” said Greenberg.
Amphibians are dubbed ‘ecosystem indicators’ because they are thought to be very sensitive to changes in the environment including air quality, light intensity, moisture, and temperature. With current climate change and increased habitat loss occurring worldwide, many species are being affected and amphibians are, in turn, one of the most at-risk groups.
Specialist species, which predominate in rapidly diversifying groups, are potentially at a greater risk of extinction if they cannot adapt to changing conditions as their options are more limited.
“The ability to rapidly speciate and colonize new environments was beneficial for these groups, but now this a liability as these species may be disproportionately lost under human-driven environmental change,” explained Greenberg.
Initially, slowly diversifying species were hypothesized to be more at risk of extinction based on studies of mammals and birds, but Greenberg’s research showed the opposite in amphibians.
Groups that have rapidly diversified are more likely to go extinct. “This makes a lot of sense: groups that diversify rapidly should lose species rapidly too because several traits that are thought to increase speciation, such as low connectivity and genetic exchange between populations, also are tied to extinction in the present,” said Greenberg.
When conducting this study, Greenberg also noticed that there are 20 rapidly diversifying amphibian groups where every single species in that genus is threatened with extinction. Applying models to estimate evolution history loss indicated that just saving one species from each of those 20 groups would save about 1.4 billion years of independent evolutionary history, he found.
What this means is that scientists and conservationists may need to rethink the way they currently conserve species. “Conservation could benefit greatly by focusing on a long-term evolutionary perspective, instead of the short-term time frames we usually consider to preserve biological diversity,” said Greenberg.
Humans are the primary cause of the current decline in the amphibian species as invasive species and foreign pathogens are introduced to new environments. “This is very significant because it can cause massive die-offs of species that don’t share an evolutionary history with these pathogens and therefore often lack the necessary immune defenses to fend off infection,” explained Greenberg.
In addition, land conversion, climate change, and pollution also play a role in the decline of amphibians.
Greenberg urged that more efforts need to be stepped up to understand why certain amphibians are rapidly diversifying. The study also revealed another significant piece: that speciation and extinction may be positively related and high diversity amphibians are also poised to be disproportionately lost.