Remember "the Circle of Life" from the Lion King? Lion cub Simba is told by his father how the animals the lions hunt feed them, but one day they too will die, and will feed the grass, which in turn will feed the grazing animals that the lions hunt and... Well, you get the picture.
But that's a fairly simple picture. In nature, the relationships between all the organisms (plants, animals, microbes, etc.) in a given ecosystem are usually far more complex. Instead of a circle, the phrase "food web" is closer to the truth. Teasing out all of the interconnections, and determining how important each is to the whole is one of the trickier tasks facing scientists.
Some examples follow below the Orange Omnilepticon.
The Circle of Life is an appealing concept, but it doesn't do full justice to the intricate interrelationships between all the organisms in an ecosystem. A more accurate metaphor might be to think of an ecosystem as being like a self-assembling puzzle with many pieces. Add or subtract certain pieces from the puzzle, and the whole picture changes, sometimes in unexpected ways. It's not a static picture either - it changes over time.
The picture we see today might be very different from what it was or will be. There's always a certain degree of change happening in the world - and even more so with global climate patterns changing. What may seem a minor piece today could be critical tomorrow; who knows what the effects are of pieces that have gone missing? Seeing what's no longer there is a difficult task to manage - but we're starting to figure it out.
Cute, Fuzzy - And Important!
Edges are important, the places where one ecosystem impinges on another, where different habitats interact. Coastal biological communities are one example. In California, the marine ecosystems along the coast are under a lot of stress from human activities. Humans affect the amounts and quality of water that runs off the land into the sea. They fill in coastal marshes that many species need for habitat; they hunt and fish. We're finding out now that one particular species may play a critical role in keeping the near shore ecosystem in balance.
The BBC has picked up on recent research that indicates the California Sea Otter may be a more important element in the coastal web of life than had been previously realized. As the BBC summary of the study notes, the urbanization of the California coast means there's a lot of nutrients washing into the sea, especially nitrogen from fertilizers. This encourages the growth of algae which in turn suppresses the sea grass that would normally cover the bottom. The algae actually grows on it, keeping the sea grass from getting the sunlight it needs. (This is a problem for sea grass around the world.)
This matters because the sea grass provides habitat for a lot of other species. It helps protect the shoreline from erosion. It helps soak up CO2. And this is where sea otters come into the picture. Researchers looked at 50 years of data on sea grass growth in a section of Monterrey Bay, and what they found was, the one factor that seemed to correlate with how well the grass was doing was the number of sea otters living in the area.
The hypothesis, which they tested, is that the sea otters feed on crabs in the area, which means fewer crabs. Fewer crabs in turn means that more of the small invertebrates the crabs would normally eat survive. And those invertebrates just happen to eat algae! Where they keep the algae in check, the sea grass can grow and thrive, despite the increasing amounts of nitrogen in the water.
Sea otters turn out to be the missing piece in this puzzle. They were nearly hunted to extinction over the past 200 years, but have been recovering with the end of the fur trade. More recently there have been restrictions on where they've been allowed to recolonize their former habitat because of fears from fishermen that they would hurt fishing. The implication now seems to be that they should actually improve it, if their presence means sea grass can flourish. (Of course, it will also help if the problem of run off can be addressed too.)
The Landscape of Fear
Another example of a missing piece is better known: wolves in Yellowstone. But what's becoming clearer is that the presence of wolves is more than just a matter of how many animals they eat. Their presence also changes the behavior of those animals that are their prey - and those changes have a larger impact on the whole landscape. There's a detailed account here of what wolves have meant for Yellowstone.
Elk numbers have dropped. It's not just a matter of wolves killing and eating them that explains it. In a landscape with wolves, elk spend more time watching for predators and less time grazing. Their herd behavior changes, and so does their success rate at raising young. This reduces pressure on the plants that elk eat, so there have been changes in the numbers and variety of plants that can now thrive - and this in turn affects all the animals that depend on those plants. Further, with the return of fire to the Yellowstone ecosystem, this affects how the landscape recovers afterwards. As the paper linked above concludes:
...Thus, the preservation or recovery of gray wolves may represent an important conservation need for helping to maintain the resiliency of wildland ecosystems, especially with a rapidly changing climate.Humankind has a bias against predators (other than ourselves), and yet ecosystems are shaped by their presence or absence in important ways, at all levels - even down to spiders and grasshoppers.
Last year two ecologists from Yale University released spiders into cages of grasshoppers. However, the spiders didn’t eat even one grasshopper because their mouthparts had been glued shut. Still, the grasshoppers were terrified, and it was noted that their metabolism increased by at least 40 percent. This led to a significant change in their diet, as they ate more carb-heavy goldenrod plants and decreased their protein intake from grasses.The Landscape of Fear is potentially a powerful management tool. Hunting, fishing, forestry - there tends to be a species-centered approach, as in Trout streams, Deer hunting, etc. which may not be as efficient as looking at the whole picture.
This change in animal behavior signals what might be called a paradigm shift in ecological thinking. Just the mere fear of predation can lead to remarkable changes in an animal’s behavior. And this in turn has a big impact on the landscape. And of course, since ecosystems involve long routes of energy flow, the impact on the landscape then further impacts the lives of other animals.
... take bighorn sheep. Forest fires keep a lot of areas open and bighorn sheep need open areas. When we suppress the fire [which we want to do] the trees and the shrub grow back. That provides ideal hunting habitat for cougars. Then many say we have to control the cougar. But we don’t need to control the cougar. We need to control the habitat.Missing Pieces - or Pieces in the Wrong Place?
We need to look at the land [or habitat] and understand what balance of risky versus safe habitat will provide us a balance of predator and prey.
So landscape becomes a very, very strong management tool. Once we understand what the landscape of fear is for a particular species then we can go in an manage the habitat depending on what our conservation goals are.
The government has a serious problem with an introduced species - the horse. (And burros as well) Horses had been present in the Americas thousands of years ago, but had died out (or been hunted to extinction.) Europeans reintroduced horses and they quickly re-established themselves. The problem is, there's currently a large wild population in the west that is running into conflict with cattlemen who want the range they graze on for their livestock. The region is also in an extended drought which means the animals have less and less food available. This creates a dilemma, as much of the land they roam is under Federal control,so it becomes a question of the Feds trying serve many masters and multiple interests with limited resources.
Since the 1970s, the BLM has gathered thousands of horses each year, trying to prevent them from dying of starvation due to overpopulation. The costs have skyrocketed to $74 million a year, 60 per cent of which is spent on holding facilities that now keep some 49,000 horses and donkeys penned up. Congress is unlikely to increase the BLM budget any further, so this year it is only rounding up horses from the regions experiencing the most dire conditions. But the drought is unlikely to end before the pens reach capacity, expected before the end of 2014. Crunch time looms.The fundamental problem is too many horses, more than the land can support. The options are limited to two main choices:
• starvation from overgrazing and drought, which will bring numbers down - and leave the land in bad shape not just for the horses but all the other species that share it.
• round ups, to capture horses and reduce the number of free-roaming animals. Problems include protests from pro-wild horse groups, what to do with captured horses (adoption can't keep up with supply and selling them for slaughter isn't very popular), and the costs of feeding and caring for them when federal budgets are under attack.
One solution that is being proposed is to use birth control on wild horses. Bringing down the birth rate is certainly one method to bring wild equine populations into a better balance. The two big problems with this approach are logistics and budgets. Tracking down all of the wild horses spread over thousands of square miles, let alone administering birth control measures is neither cheap nor easy. (And there's also the question of what kind of selection bias humans might have when picking out horses for birth control.)
The missing piece in this puzzle is horse predators: wolves, bears, cougars, wolves, coyotes. The long-standing western crusade against 'varmints' has given horses free rein to multiply in the absence of predators, to the ultimate detriment of themselves and their habitat. Given the hostility to increasing wolf numbers, it's not likely that the ranching interests will look favorably on any efforts to reintroduce any predators to their historic former range, especially given the knee-jerk rejection of anything smacking of environmentalism in western red states. Given the wide-ranging response of Yellowstone ecosystems to the return of wolves though, it's likely such a restoration would be far more effective and with greater benefits than trying to treat the horse problem as an isolated puzzle piece.
The Long Result of Time
Speaking of missing pieces, recent research suggests the Amazon rainforest is still suffering the effects of an extinction event thousands of years earlier. The arrival of humans into the Americas seems to coincide with the disappearance of many large mammals (collectively called megafauna) - but there were also some climate changes going on that also affected vegetation. There's no single smoking gun that explains it all; it may well have been a combination of several things coming together.
The disappearance of really large herbivores had consequences that are still manifesting today.
Vast regions of the Amazon are growing more slowly than they were several thousand years ago because they lack the fertilising effect provided by South America’s distinctive “mega-fauna” – the very large mammals that went extinct soon after the arrival of humans.Given that we are rather counting on the Amazon in its role as a carbon sink, this is perhaps not good news for climate change. It also suggests that surviving large mammals may be carrying out a similar role today - which means their conservation is important far beyond their own individual roles. It's possible the fertility of the plains states today might in part be derived from millions of buffalo in vast herds redistributing nutrients during the course of their wanderings. In the case of the Amazon,
A study of how soil nutrients are distributed within the Amazon basin has revealed there is a dearth of vital minerals such as phosphorus because large mammals no longer roam the region to fertilise the soil with their dung.
The study, published in Nature Geoscience, calculated 98 per cent of nutrient-dispersal has been lost since the extinction of the mega-fauna, which happened around the same time that humans first colonised South America from the north.It should be noted that large mammals may be important to the oceans as well, by transporting and releasing iron in their poo.
“While 12,000 years may be a timescale that is beyond most people’s understanding, through this model we show that extinctions back then still affect the health of the planet to this day,” Dr Doughty said. “Put simply, the bigger the animal, the bigger its role in distributing nutrients that enrich the environment.
“Most of the planet’s large animals have already gone extinct, thereby severing the arteries that carried nutrients far beyond the rivers into infertile areas,” he said.
Meanwhile, Much Much Closer to Home...
The matter of missing pieces has a very intimate connection for humans at a gut level - literally. The human digestive tract - indeed most of the human body - plays host for entire microbial ecosystems. We're just beginning to appreciate how these complex ecosystems affect us. It turns out the mix of bacteria we have living in our intestines have direct effects on our health.
Individuals with fewer numbers of so-called “good” bacteria are more likely to be obese and develop obesity-related ailments such as type 2 diabetes, high cholesterol, and heart disease. That’s according to research conducted by the international MetaHIT consortium published Thursday (August 29) in Nature.In fact, it appears the critters living inside us (gut flora) affect the way our immune systems function, the way food gets digested as it passes through us, and more. There are studies that suggest bacteria may even move in with us before birth. Sorting out exactly what's inside us is tricky, because some of the bacteria are so interdependent, they can't be isolated and grown in pure cultures - and pure cultures don't show us how they interact with each other. It's DNA sequencing that's giving us a better idea of who's living in there.
This is one of the factors that makes the use of antibiotics something that should be managed carefully. A serious infection may require antibiotics to knock it down - but there can be collateral damage to the 'good guys' who actually help us. Worse, it makes things easier for bacteria that are resistant to a particular antibiotic, because they thrive while competitors die back. It turns out an effective way to treat Clostridium difficile infections is to give the afflicted person a stool transplant so they can be recolonized by helpful bacteria that have gone missing from the gut after antibiotics wiped them out. In a healthy gut, they keep C. difficile from taking over.
It would be fair to say that modern medicine isn't just about treating patients anymore - it's also about treating ecosystems. Like it or not, we're never alone - and it helps to have all the right pieces in place.
The Bigger Picture
It's one of the more rewarding elements of modern biology and science in general, to discover approaches that scale, that have general application. Understanding the way a particular ecosystem functions is likely to have applications across ecosystems in general. Understanding gained in one place may open doors in others. The importance of individuals within a species, within an ecosystem, transcends their individuality - it's their roles as members of a greater whole that makes them matter in ways we can't appreciate if we only look at them in isolation. If you can't see the forest for the trees, it's as apt to say you can't see the trees without the forest.