NatureWatch: Tales of growth and survival

To get big, grow slow

A decade-long study of whale sharks (Rhincodon typus) has determined that the biggest fish in the world are female.

While males of the species grow quite quickly before plateauing at an average of eight or nine metres, females proceed more slowly to around 14 metres. Some grow to 18.

“[E]ven though they’re big, they’re growing very, very slowly; it’s only about 20 or 30 centimetres a year,” says Mark Meekan from the Australian Institute of Marine Science (AIMS), who led the research reported in Frontiers in Marine Science.

He and colleagues visited Western Australia’s Ningaloo Reef for 11 seasons to track 54 whale sharks – a feat made possible by their unique “fingerprint” of spots that can be used to identify individuals – and made more than 1000 measurements.

For the females, there are huge advantages to being big, Meekan says, not least the ability to carry lots of pups. “Only one pregnant whale shark had ever been found, and she had 300 young inside her. That’s a remarkable number; most sharks would only have somewhere between two and a dozen.”

The findings also explain why gatherings of whale sharks in tropical regions are made up almost entirely of young males, Meekan says. “They gather to exploit an abundance of food so they can maintain their fast growth rates.”

Mountains aren’t for eating

It seems that even in tough times, Africa’s megaherbivores don’t climb. It was known that giraffes and elephants prefer to forage on the savanna rather than head up a mountainside, but a new study has confirmed just how much.

Monitoring a 120-hectare area around Kenya’s Mpala Research Centre, a team led by the Smithsonian Tropical Research Institute, US, discovered that even in the dry season, when resources are scarce, both species would rather travel further afield than think of scaling a slope.

The aim is maximum food with minimal effort expended: perhaps understandable when you eat a lot (as much as 270 kilograms a day for elephants) and are big enough to not really have to bother about predators.

The pattern is revealed in greater damage to vegetation on the plains, particularly Acacia mellifera trees, which grow all over the savanna landscape and are a common meal for megaherbivores.

The upside, the researchers say, is that this may help preserve steep slopes as habitat refugia, with a greater diversity and density of vegetation than more visited areas.

“This study has broadened our understanding of the role of topography in explaining diversity patterns of plants,” said Duncan Kimuyu from Kenya’s Karatina University, corresponding author of a paper in the journal Biotropica.

Climate threat to Komodo dragons

Global warming and sea-level rise threaten the extinction of the world’s largest lizard, the Komodo dragon, according to a new international study.

Varanus komodoensis already has restricted habitats, the researchers say in a paper in the journal Ecology and Evolution, and this must be better incorporated into conservation strategies.

Only 4000 individuals are thought to survive in the wild. They are endemic to five islands in southeast Indonesia: Komodo, Rinca, Nusa Kode and Gili Motang, which are part of Komodo National Park, and Flores, the largest, which has three nature reserves.

However, the new modelling predicts “local extinction” on three of the five, according to lead author Alice Jones, from Australia’s University of Adelaide.

She and colleagues from Australia, Indonesia, Italy and the US used Komodo monitoring data and climate and sea-level change projections to build spatially explicit demographic models that project the species’ future range and abundance under multiple climate change scenarios. They ran over one million model simulations.

“Our models predict a reduction in range-wide Komodo dragon habitat of 8%-87% by 2050, leading to a decrease in habitat patch occupancy of 25%-97% and declines of 27%-99% in abundance across the species’ range,” the authors write in their paper.

Conservation managers in coming decades may need to consider translocating animals to sites where Komodo dragons have not been found for many decades, says co-author Damien Fordham, from the University of Adelaide. “This scenario can be tested easily using our approach.”

The project was jointly led by Australia’s Deakin University, and involved collaboration with the Komodo National Park and the Eastern Lesser Sunda Central Bureau for Conservation of Natural Resources.

Unique find well off the beaten track

This is a very rare butterfly and it leads a pretty tough life.

While working in some “hard to reach areas” of Momsky National Park in far eastern Russia, researchers led by Roman Yakovlev from Siberia’s Tomsk State University came across what they thought was an isolated population of the rarest Palaearctic butterfly species, the Arctic Apollo (Parnassius arcticus).

That, in itself, would have been quite something – but things weren’t quite right. The curious specimens were larger on average, had more elongated wings compared to the Arctic Apollo, and were missing the distinct dark spot on the wings.

After in-depth morphological and molecular genetic analyses, the scientists concluded that it was in fact a completely new subspecies – since named Parnassius arcticus arbugaevi – distinguished by a number of external and DNA differences.

The population is only known to inhabit the Momsky Range, in North-Eastern Yakutia, where it lives on dry scree slopes with poor vegetation at an elevation of 1400 metres.