We’ve all become familiar with the link between climate change and extreme weather phenomena, but did you know that climate change can also profoundly alter species numbers? For instance, it is making the female turtle population boom.
A study, published this month in Nature Climate Change, tells how warmer temperatures are leading to warmer beach sands and, as a result, more female turtles being born which is boosting the turtle population. All good so far — but there’s a catch. If the sands grow too warm, the number of females to males being born will tip dramatically, and potentially lead to serious population problems. The reason for this can be found in what determines the sex of an infant turtle.
The sex of sea turtles isn’t dependent on chromosomes like we’re familiar with in most species, including humans. Instead, the sex of a developing turtle relies on where the egg is stored or more precisely, the temperature of the sand in which its mother lays her eggs. At 29 degrees Celsius, the split between male and female infants is roughly 50%. This has been dubbed the “pivotal temperature.” Recent rises above that temperature have meant the population is skewed slightly more females to males, but so far that’s not been a problem. Still, scientists are concerned that if global temperatures continue to rise, so will female population numbers which could cause serious problems for the turtles.
Studies from as recent as 2012 appeared to show that turtle populations like the adult leather-back turtle were holding out well. Scientists concluded that fears of a dangerous imbalance might be premature but recommended continued monitoring. So why is the imbalance not already threatening the turtles? Well, it’s at least partly down to male breeding patterns and how they differ from those of the females.
Males often have breeding intervals that are more frequent than the female intervals. They also move about, and don’t mate for life. This means that their mating habits have so far meant that the more abundant female population is still being served and the reproductive cycle is continuing. Yet, scientists haven’t known how long the male mating patterns can absorb the impact of the population skew — until now.
This latest study, which examined a loggerhead turtle rookery in Cape Verde in the Atlantic, gave scientists the chance to study and project how the rising temperatures would affect turtle numbers. The news is mixed. Over the next 20-30 years, scientists in this study are confident that the number of females born will grow and that they will have more offspring, therefore continuing the population boom. That’s the good news for the short-term, but that won’t last forever.
“Ultimately, if you extrapolate long enough into the future […] once you get 100 years or more into the future, then things start to look serious,” says lead researcher Professor Graeme Hays. “You have so few males left that it’s likely to be a problem. There will be heaps of female but not enough males to fertilize all those eggs.”
That said, there is a chance that the turtles, which have shown their capability to adapt before, might shift their breeding patterns to coincide with colder temperatures or might migrate to colder areas. This could at least temporarily save their population by re-balancing the ratios to a better matched figure, but it could also have an impact on the habitats of other marine life.
The researchers recommend that humans can do their part for the turtles by restraining ourselves from building on what are known as lighter beaches, where the sand is less dense and so cooler. This would provide a safe haven from the temperature change and allow the turtle population a shot at a more even balance for longer.
It’s not only turtles that depend on temperature to determine the sex of their young, though. Many types of lizard, as well as crocodiles and alligators also utilize temperature selection. There is also fresh research on insects that use others to host their young that shows that, opposite to turtles, more male insects appear to be produced as temperatures climb. What that will ultimately mean for these insects is unclear, but all of this fascinating research gives yet another example of how the global temperature climb will affect life on earth in seemingly subtle ways that could have dramatic consequences, thus pressing the need for action to prepare and deal with the fall out before it’s too late.
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