Swimming across a crocodile-filled river full and dodging venomous snakes in search of rare carnivorous plants is all in a day’s work for Dr. Adam Cross, restoration ecologist at Curtin University in Perth, Australia. Cross conducts much of his fieldwork in Western Australia’s Kimberley region, where he sidesteps deadly wildlife and endures broiling 104-degree Fahrenheit temperatures in suffocating humidity in search of elusive carnivorous plants.
A quarter of the world’s 860 known carnivorous plant species are at risk of extinction as a result of climate change and threats like land clearing and poaching, according to a study Cross and his colleagues recently published in Global Ecology and Conservation.
Carnivorous plants are unique because they gain nutrients from prey. They mostly lure and eat insects, though some can also derive nutrients from small animals. The popular Venus flytrap is a well-known example, luring small insects such as flies to its open leaves with a sweet nectar scent; once the fly brushes up against a trigger hair, Venus snaps the leaves shut, trapping the fly, which it then dissolves with digestive enzymes.
‘Sensitive, specialized’ and existing in narrow ecological niches
Sensitive and specialized, carnivorous plants typically grow in “nutrient-impoverished habitats where carnivory offers a competitive advantage,” according to the Cross report.
“Carnivorous plants, more so than almost any other group of plant, occupy extremely narrow ecological niches because carnivory is basically a strategy that has evolved to allow plants to be competitive in typically nutrient-poor soils and in habitats where other plants often find it very challenging to be competitive,” Cross says.
Some carnivorous plants have unique and intriguing mutually beneficial relationships with other species. Cross points to carnivorous plants in South Africa of the Roridula genus that aren’t capable of digesting their own prey. Instead, they rely on an insect called Pameridea that eats other insects trapped in the plant’s sap before extruding its waste on the plant, allowing the plant to ultimately derive nutrients from the insects it trapped.
In Borneo, a Nepenthes pitcher plant has such a mutualistic relationship with Hardwicke’s woolly bats. The bats seek leafy outgrowths atop the pitchers and roost in them, depositing their waste into the pitcher, which then digests the nutrients. Other Nepenthes pitcher plants in Borneo have such relationships with mountain tree shrews. The plants produce a secretion that the shrews access by awkwardly hovering with their rear ends over the pitcher. The secretion makes the small animals violently excrete straight into the pitcher, which then uses the nutrients. With such unique relationships with other species, it’s possible the loss of a single carnivorous species could ripple across ecosystems.
“There’s a whole raft of these really unique co-developed mutualisms,” Cross says. He points out we don’t know the specific impact of removing one species from the ecosystem, but “there’s a whole raft of species that just wouldn’t exist without this association.”
Many species are adapted to grow only in very specific locations, such as particular microhabitats, elevation ranges, and even geological formations. Of the 860 known species, Cross’s study found 89 species live only at one single known location. They are extremely limited in terms of their range, which often leaves them with perilously few options in the face of climate change and other dangers.
Accumulating threats to fragile plants
The study examined threats to 790 of the species, finding the top threats to include agriculture and aquaculture (with 170 species impacted), other natural systems modifications (168 species), and climate change and severe weather (158 species). After those come energy production and mining, human intrusions and disturbance, and biological resource use. Nearly a quarter of the species studied faced impacts from at least three threats. Out of the species analyzed, 8% were critically endangered, 6% endangered, 12% vulnerable, and 3% near threatened.
Climate change’s rising temperatures, severe fires, and droughts – each becoming more frequent, long, and severe – all pose a threat to these fragile plants. In South Africa, the Cape Floristic Region faced “exceptional droughts” from 2015-2017, and it is home to 20 carnivorous plant species, including 15 endemics that live nowhere else. The plants are already generally quite restricted in range and, with more of their habitat becoming unsuitable, some may perish. Shifting rainfall patterns also impact numerous species, especially since many of them live in very sensitive wetland ecosystems. Additionally, climate change could also affect pivotal parts of ecosystems such as the insects they feed on, pollinators, and seasonal shifts in budding, hibernation, flowering, and more.
After a disruption such as habitat degradation or land use changes, carnivorous species are often the first to vanish, providing a clue that more problems may be brewing. They serve as “harbingers of anthropogenic degradation and destruction of ecosystems,” according to the article by Cross and his colleagues.
A gauntlet of challenges awaits in the field
To study these plants, Cross has to access the remote spots on the globe where they live. To reach his Kimberley, Australia, field site, where he travels once or twice a year, Cross and colleagues must first fly 1,400 miles from Perth to Kununurra and then hop on a tiny mail plane that only travels to the area once a week. If the air strip isn’t too wet – and it sometimes is because the area can receive over 15 inches of rain in a single day – the plane can land, dropping off the researchers for a week or two. Unless they get stuck and have to stay longer, which happens from time to time.
While the area is accessible via a single road during the dry season from April to October, light aircraft flights are the only way to get there the rest of the year. Extensive planning is required for such remote fieldwork, and Cross sends supplies like nonperishable foods well ahead of time. They must send ahead what they need because once they arrive, besides the station’s caretakers, there are no other people for over 60 miles.
A typical day at the field site involves rising early with the sun and getting together everything the team will need for a day out on foot and quad bike collecting plant and seed samples and recording observations. In addition to packing gallons of water, GPS devices, and sample collection gear, they also double-check for snakebite first aid kits. Cross says their research area is home to seven of the world’s 10 most venomous snakes – including the top three – so preparation is vital. Freshwater crocodiles also live in nearby rivers, which the researchers have to swim across at times, but he finds ease in knowing there are no saltwater crocodiles. Furthermore, “the freshwater crocodiles usually tend to avoid people – they’re more scared of us than we are of them. It would be a very different story if there were saltwater crocodiles around.”
Researching carnivorous plants involves running a gauntlet of challenges in addition to dodging critters, including locating existing data about known species, which can be buried deep in various reports and written in numerous languages. Finding species in the field, both known and yet-to-be-discovered, can be complicated because some species are visible on the landscape only for a few weeks each year, leaving a very short window for surveys.
Challenging work … but ‘incredible botanical experience’
Collecting and preserving specimens in the field can also be tough. Cross and his team collect specimens in the extreme field environment, carefully packaging samples to endure torrential rainstorms, swims across swollen rivers, and hours of bouncing on a quad bike along a rough dirt track. The samples sit in high temperatures and humidity until they can be flown out on a mail plane. It often takes several weeks for them to ultimately reach the lab and, with luck, they arrive in usable condition rather than as a pile of rotten vegetation. “It’s challenging enough to collect things like herbarium specimens and make sure they’re correctly pressed at the best of times,” Cross says.
It’s a challenging work environment, to say the least. But it’s all worthwhile, according to Cross. “[It’s an] incredible botanical experience,” he says. “I think one in every eight collections of plants from the Kimberley during the wet season currently yields a new species to science.” Some of these species can also help inspire human innovation. A type of nonstick cookware was derived from scientists’ observations about carnivorous plants.
Cross points out the importance of preserving these sensitive species, not just so humans can derive technology to fry eggs with ease, but also to protect vital ecosystems. “There’s an increasing body of literature that suggests that ecosystem health and the integrity of our ecology is intrinsically tied to human health and the well-being and livelihoods of human communities,” Cross says. “So if we continue down this pathway of exploitation and destruction we’re actually damaging our own communities and well-being as well. So with carnivorous plants representing a harbinger for decline – because they’re often so sensitive and the first to disappear or decline in the face of degradation – we should really be paying a lot more attention to the integrity of carnivorous plant populations as an indicator for the changes that we are wreaking on natural systems.”