We often think species that exist only in small numbers are also in danger of going extinct. But it seems being rare is not always a bad thing.
Image: NABU
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There are fewer than 50 Maui's dolphins left in the world. Their relatives, the vaquitas, are even less "common." Both are on the brink of extinction. But do small numbers automatically mean a species is likely to disappear? Not according to a team of researchers from the University of California, Davis.
In a perspective paper published in the journal "Ecology Letters," they considered which factors make a species likely to thrive, even if its population is small. They also looked at what factors are likely to contribute to a species' demise.
For starters, it helps if the adult animals or plants are highly mobile. That seems obvious since, if there are few of them and they are spread out, they may have to travel far to find a suitable mate. Alternatively they need to have a good intermediary who can take their gametes (seeds, sperm or eggs) to a mate. It also helps if they can signal and/or attract a mate over a long distance.
Where fertilization takes place is important as well. If it happens inside or near an adult, that's a plus. To us and most other mammals out there that would seem obvious. But many species simply release their gametes into the air or water in the hope they will either find a mate or even just combine with their drifting counterparts.
A famous and spectacular example of this is the broadcast spawning of many types of coral, which can turn otherwise clear stretches of ocean into a cloudy soup of gametes. Such a strategy works well if there are many others like you nearby but not if you are few and far between.
Speaking of sperm and eggs, for a real edge in terms of survival, it helps if you're not too set on being male or female but open to changing your sex if the occasion calls for it. Many types of snail and worm fit the bill, as do some fish, among other animals. The advantage is obvious. If there are very few of you around and you're all male and have to stay that way, you're not going to have any offspring anytime soon.
When does rare mean thriving?
Some species are very successful at being rare. They can survive in small numbers, scattered over large distances. Sadly, that doesn't hold true for the Maui's dolphins and vaquitas.
Both species live in a single small habitat — the west coast of New Zealand's North Island and the northern part of the Gulf of California, respectively.
Furthermore, both didn't initially exist in such small numbers but human activity — specifically fishing — has pushed them to the brink of extinction.
"By learning how a species can be rare, we can also learn how to protect species that cannot be rare," said UC Davis professor Geerat Vermeij.
The paleontologist is one of the paper's authors. Since rare species are also often not as extensively investigated as common ones, however, the authors say more research is needed to test their theories.
Human activity threatens thousands of species with extinction: Red List
The International Union for the Conservation of Nature's annual Red List assesses 97,000 species — 27,000 face extinction. Poaching, invasive pests, agriculture and climate change are driving many of them to the brink.
Image: picture-alliance/dpa/WWF
Hope for mountain gorillas
Let's start with the good news. According to the latest Red List update, the number of mountain gorillas has significantly increased. The IUCN has said the number of animals has risen from about 680 a decade ago to more than 1,000 now. Intensive conservation action such as removal of snares has contributed to the rebound of the mountain gorilla, which inhabits the Congo region's jungles.
Image: Reisedoktor/Wikipedia
Whales get a reprieve
Fin whales are now considered vulnerable rather than the more worrisome label of endangered. Their number has roughly doubled since the 1970s, to around 100,000 individuals, according to the IUCN. The situation of gray whales has also been upgraded — from critically endangered to endangered. Bans on commercial whaling have made a real impact on conservation.
Image: picture-alliance/ZUMAPRESS/VW Pics
Dampened euphoria
Yet the IUCN also issued warnings about the consequences of overfishing. For example, 13 percent of grouper species worldwide and 9 percent of the approximately 450 fish species in Lake Malawi in eastern Africa are threatened with extinction. "Depleting fish stocks are a serious concern for food security, particularly for coastal communities in developing countries," the IUCN said.
In a previous Red List update, the Mauritian flying fox — an important pollinator — moved from vulnerable to endangered. The bat population fell by a whopping 50 percent from 2015 to 2016 due largely to government-implemented culling sparked by alleged damage to fruit crops. The megabat species also faces threats from deforestation, illegal hunting and an increase in cyclone activity.
Image: M. D. Parr
Invasive species threaten Australian wildlife
Invasive species are threatening a number of unique Australian reptiles. This grassland earless dragon has shifted from vulnerable to endangered. It often falls prey to feral cats, as well as changes to the intensity and frequency of bushfires. Like most native Australian wildlife, the reptile is adapted to environmental conditions that existed before European settlement.
Image: Will Osborne
A precious species
Taking its name from "The Lord of the Rings" character Smeagol — aka Gollum — the precious stream toad is also on the list of species threatened with extinction. It is listed as vulnerable, largely as a result of expanding tourist resorts and complexes in its Genting Highlands habitat in Malaysia.
Image: Chan Kin Onn
Junk food parrots
The population of keas, New Zealand's Bird of the Year 2017, is declining rapidly, mostly due to tourists who keep feeding the curious parrots junk food. As a result, the birds get used to trying novel food and end up eating poison bait meant to control pests such as rats, stoats, or possums, which destroy up to 60 percent of the birds' nests each year. You can see the connection, can't you?
Image: Imago/imagebroker
No sand eel, no kittiwake
Black-legged kittiwakes rely on certain key prey, like sand eels. But a lack of eels to eat means breeding colonies in the North Atlantic and Pacific are struggling to feed their chicks. Globally, the species is thought to have declined by around 40 percent since the 1970s. The main cause is overfishing and alterations in the ocean due to climate change.
The snowy owl is vulnerable, with recent population estimates much lower than previously thought. Climate change has hit the iconic Arctic bird hard, as it has increased snowmelt and reduced the availability of rodent prey. A quarter of bird species reassessed in the Red List, including the snowy owl, have become more endangered.
Image: Imago/CTK Photo
Reebok namesake in danger
Five species of African antelopes — of which four were previously assessed as least concern — have been declining drastically as a result of poaching, habitat degradation and competition with domestic livestock. One of these is the gray rhebok, for which the Reebok sports brand is named.
Image: UltimateUngulate/Brent Huffman
World's largest antelope in trouble
The world's largest antelope, the giant eland — previously assessed as least concern — is also vulnerable. Its estimated global population is between 12,000 and 14,000 at most, with fewer than 10,000 mature animals. This species is declining due to poaching for bushmeat, human encroachment into protected areas and expansion of agriculture and livestock grazing.
