Tag Archives: ecology

tipping points and ecosystem collapse

This research presents seagrass meadows as an example of an ecosystem that seems to disappear suddenly, but actually reached a tipping point caused by chronic pollution.

Testing for thresholds of ecosystem collapse in seagrass meadows?

Ecological systems can be dynamic and unpredictable, with shifts from one ecosystem state to another often considered ‘surprising’. This unpredictability is often thought to be due to ecological thresholds, where small cumulative increases in an environmental stressor drives a much greater consequence than would be predicted from linear effects, suggesting an unforeseen tipping point is crossed. In coastal waters, broad-scale seagrass loss often occurs as a sudden event which is associated with human-driven nutrient enrichment (eutrophication). We tested whether the response of seagrass ecosystems to coastal nutrient enrichment represents a threshold effect. Seagrass response did follow a threshold pattern when nutrient enrichment (dissolved inorganic nitrogen) exceeded moderate levels, with a switch from positive to negative net leaf production. Epiphyte load also increased with nutrient enrichment, potentially driving this shift. Inadvertently crossing such thresholds, as can occur through ineffective management of land-derived inputs such as wastewater and stormwater on urbanised coasts, may help account for the widely observed ‘sudden’ loss of seagrass meadows. By identifying tipping points we may not only improve monitoring for adaptive management that seeks to avoid threshold effects, but also the restoration of systems that have crossed them.


David Quammen (author of one of my all-time favorite nonfiction books, The Song of the Dodo: Island Biogeography in an Age of Extinction) has a long article in National Geographic about Yellowstone National Park which touches on some of the same things.

The Greater Yellowstone Ecosystem is bigger than any other park complex in the lower 48 states. And size matters. A resonant study published in the journal Nature back in 1987, by a young ecologist named William Newmark, revealed that among 12 national parks and park complexes in the western United States, all except two had lost mammal species in the years since they had been established, but that Greater Yellowstone, as the largest, had lost fewer species than almost all others. Most of those local extinctions had resulted not from direct human persecution—as the wolves of Yellowstone had been persecuted to oblivion—but from the natural processes of extinction characteristic of islands: When habitat is constrained within a limited area, animal populations remain small, and small populations tend to wink out, over time, because of accidental factors such as disease, fire, hard weather, and bad luck. Greater Yellowstone had lost less of its mammal diversity by natural attrition than had small parks such as Zion, Bryce Canyon, and Mount Rainier. Its size, evidently, had served it well.

Newmark’s original work has been challenged in some particulars during the decades since, but its basic conclusion remains sound: Size matters. The size of the Yellowstone complex helped preserve big, fearsome, wide-ranging, combative animals such as the grizzly, each one of which demands a large territory. No other park in the lower 48, apart from Glacier National Park along Montana’s Canadian border, now supports robust populations of the three greatest living North American carnivores—the grizzly, the wolf, the mountain lion—as well as such other predaceous animals as the wolverine, the coyote, the bobcat, and the red fox. Yellowstone is our wildest park south of the border complex that includes Glacier, in part because it’s our biggest.

The other good thing about geographical bigness is that, besides giving space to large predators with broad territorial needs, it usually encompasses habitat diversity as well as sheer space, thereby sheltering a greater variety of creatures at all levels of size, living all modes of life.

Because I am interested in island biogeography and I like the idea of having seminal papers at my fingertips, I looked up the Newmark article mentioned above.

A land-bridge island perspective on mammalian extinctions in western North American parks
Nature 325, 430 – 432 (29 January 1987); doi:10.1038/325430a0

In recent years, a number of authors have suggested several geometric principles for the design of nature reserves based upon the hypothesis that nature reserves are analogous to land-bridge islands. Land-bridge islands are islands that were formerly connected to the mainland and were created by a rise in the level of the ocean. Land-bridge islands are considered supersaturated with species in that the ratio of island to mainland species numbers is higher than expected from the area of the island. As a result, the rate of extinction should exceed the rate of colonization on a land-bridge island, resulting in a loss of species that is suggested to be related to the size and degree of isolation of the island. If nature reserves are considered to be similar to land-bridge islands, because most are slowly becoming isolated from their surroundings by habitat disturbance outside the reserves, several predictions follow. First, the total number of extinctions should exceed the total number of colonizations within a reserve; second, the number of extinctions should be inversely related to reserve size; and third, the number of extinctions should be directly related to reserve age. I report here that the natural post-establishment loss of mammalian species in 14 western North American national parks is consistent with these predictions of the land-bridge island hypothesis and that all but the largest western North American national parks are too small to retain an intact mammalian fauna.

It’s easy to get depressed. Even if we preserved a lot of big open spaces, left them completely alone, and there were no such thing as pollution or climate change, a smaller nature would still be a less healthy nature. The only silver lining is that if we had a really thorough knowledge of how the shapes of preserved lands and the connections between determine their ecosystem health, we could theoretically come up with land use policies and practices to produce the best possible ecosystem health in the remaining space available.

There is research going on in this area:

A simplified econet model for mapping and evaluating structural connectivity with particular attention of ecotones, small habitats, and barriers
Wei Houa, Marco Neubertb, Ulrich Walzc
Landscape and Urban Planning
Volume 160, April 2017, Pages 28–37

Small habitats and ecotones are recognized as key structures in preserving biodiversity and maintaining landscape connectivity. However, most analyses of landscape pattern have not fully accounted for these elements. This leads to an underestimation of the landscape heterogeneity, especially at the local scale. This research aims to evaluate the structural connectivity for a source habitat (i.e., forest) with particular consideration of the roles of ecotones, small habitats, and barriers. A multi-buffer mapping procedure based on vector data is applied on two comparative test sites for mapping ecological networks (econets) which are composed of forest patches, ecotones, corridors, small habitats, and barriers. On this basis, several indices are proposed for quantitative evaluation of structural connectivity of econets. The application of the indices show that our approach can be useful for analyzing econet connectivity and identifying the roles of critical landscape elements, for example the barriers’ effect on overall forest connectivity. Within an econet, ecotones function as extension of forest edges which can increase the intrapatch connectivity; small habitats play the role of stepping stones which can enhance interpatch connections among forest habitats. The proposed econet model provides a generalized illustration of landscape connectivity and can be used to compare and monitor forest pattern.

What a Fish Knows

What a Fish Knows is what it sounds like – a book about what fish are thinking. From the publisher:

Do fishes think? Do they really have three-second memories? And can they recognize the humans who peer back at them from above the surface of the water? In What a Fish Knows, the myth-busting ethologist Jonathan Balcombe addresses these questions and more, taking us under the sea, through streams and estuaries, and to the other side of the aquarium glass to reveal the surprising capabilities of fishes. Although there are more than thirty thousand species of fish—more than all mammals, birds, reptiles, and amphibians combined—we rarely consider how individual fishes think, feel, and behave. Balcombe upends our assumptions about fishes, portraying them not as unfeeling, dead-eyed feeding machines but as sentient, aware, social, and even Machiavellian—in other words, much like us.

What a Fish Knows draws on the latest science to present a fresh look at these remarkable creatures in all their breathtaking diversity and beauty. Fishes conduct elaborate courtship rituals and develop lifelong bonds with shoalmates. They also plan, hunt cooperatively, use tools, curry favor, deceive one another, and punish wrongdoers. We may imagine that fishes lead simple, fleeting lives—a mode of existence that boils down to a place on the food chain, rote spawning, and lots of aimless swimming. But, as Balcombe demonstrates, the truth is far richer and more complex, worthy of the grandest social novel.

Highlighting breakthrough discoveries from fish enthusiasts and scientists around the world and pondering his own encounters with fishes, Balcombe examines the fascinating means by which fishes gain knowledge of the places they inhabit, from shallow tide pools to the deepest reaches of the ocean.

Teeming with insights and exciting discoveries, What a Fish Knows offers a thoughtful appraisal of our relationships with fishes and inspires us to take a more enlightened view of the planet’s increasingly imperiled marine life. What a Fish Knows will forever change how we see our aquatic cousins—the pet goldfish included.

forests as a carbon source?

This journal article talks about the possibility of a disturbing situation where climate change starts to kill trees, which are then no longer able to absorb carbon dioxide, which causes more climate change, and so on in an accelerating feedback loop.

Trees Can Limit Climate Change—Unless It Kills Them First

Scientists have considered forests a potential barrier to climate change, since plants on land take up about 25 percent of our carbon dioxide emissions. As trees in colder areas are exposed to warmer temperatures and more CO2 emissions, they will grow faster and absorb more emissions, helping to mitigate the effects of a primary greenhouse gas, the theory goes.
But, in an alarming twist, global warming is likelier to limit forests’ capacity for absorbing emissions in many parts of the continent, a study released today in the journal Ecology Letters finds. After combining climate projections with the tree records, researchers found no evidence for the boreal greening hypothesis. In fact, they found a risk of a negative feedback loop, as trees in their model reacted poorly to warmer temperatures due to drought and other disturbances.
That means as trees die faster than they can take up CO2 emissions, releasing trapped carbon, forests could become a net source of carbon, accelerating climate change. The study found that we could reach such a tipping point as early as 2050.

new book on soil

Here’s a review on a new book on soil.

Soils had not excited many ecologists until, two decades ago, soil ecologists started emphasizing that many aboveground phenomena are under belowground control. Richard Bardgett is one of the most eloquent and knowledgeable of the soil scientists who have contributed to the current enthusiasm about soils. In his recent book Earth Matters: How Soil Underlies Civilization he explains how much human societies depend on soil. He writes about how soils are formed, how they influence biodiversity and food quality, and what role they play in cities and in war, and introduces us to the interplay of soils and climate change.

connectivity and corridors

From Conservation Biology:

Connecting science, policy, and implementation for landscape-scale habitat connectivity

In an increasingly fragmented world, networks of habitat corridors are critical to support movement of organisms between habitat patches and the long-term persistence of species. The science of corridor design and the policy of corridor establishment are developing rapidly, but often independently. Here we assess the links between the science and policy of habitat corridors, to better understand how corridors can be effectively implemented, with a focus on a suite of landscape-scale connectivity plans in tropical and sub-tropical Asia. Our synthesis suggests that the process of corridor designation may be more efficient if the scientific determination of optimal corridor locations and arrangement is synchronized in time with the achievement of political buy-in and policy direction for corridor designation. Land tenure and the intactness of existing habitat in the region are also critical factors –optimal connectivity strategies may be very different if there are few, versus many, political jurisdictions (including commercial and traditional land tenures) and intact versus degraded habitat between patches. We identify financing mechanisms for corridors, and also several important gaps in our understanding of effective corridor design including how corridors, particularly those managed by local communities, can be protected from habitat degradation and unsustainable hunting. Finally, we point to a critical need for quantitative, data-driven models that can prioritize potential corridors or multi-corridor networks based on their relative contributions to long-term metacommunity persistence.

the case of the missing mammals

Where would the large mammals be if humans hadn’t come along?

How would the world look if humans had never spread out across the Earth? For a start, we’d have a lot more forest, much less pollution, and the stars would look unbelievably bright. But, as a new map shows, the planet would also be absolutely teeming with large mammals, from the Serengeti to Northern Europe and all the way across the Americas. Researchers at Denmark’s Aarhus University have created a global map which shows the distribution of large mammals as it may have been if humans had never left Africa…

The Americas used to be home to 105 large mammal species, including sabre-toothed cats, mastodons, giant sloths and giant armadillos, which all disappeared in the last 100,000 years or so. A previous study by the Aarhus University research team showed that human activity was responsible for this mass extinction

“The reason that many safaris target Africa is… that it’s one of the only places where human activities have not yet wiped out most of the large animals,” said Postdoctoral Fellow Søren Faurby, lead author on the study.

The highest levels of diversity would be in central regions of north and south America, especially parts of Texas, the U.S. Great plains and regions of Brazil and Argentina.

Unnatural Selection

Amazon description:

Gonorrhea. Bed bugs. Weeds. Salamanders. People. All are evolving, some surprisingly rapidly, in response to our chemical age. In Unnatural Selection, Emily Monosson shows how our drugs, pesticides, and pollution are exerting intense selection pressure on all manner of species. And we humans might not like the result.

Monosson reveals that the very code of life is more fluid than once imagined. When our powerful chemicals put the pressure on to evolve or die, beneficial traits can sweep rapidly through a population. Species with explosive population growth—the bugs, bacteria, and weeds—tend to thrive, while bigger, slower-to-reproduce creatures, like ourselves, are more likely to succumb.

Monosson explores contemporary evolution in all its guises. She examines the species that we are actively trying to beat back, from agricultural pests to life-threatening bacteria, and those that are collateral damage—creatures struggling to adapt to a polluted world. Monosson also presents cutting-edge science on gene expression, showing how environmental stressors are leaving their mark on plants, animals, and possibly humans for generations to come.

more on automated data synthesis

Here’s another article from Environmental Modeling and Software about automated synthesis of scattered research results:

We describe software to facilitate systematic reviews in environmental science. Eco Evidence allows reviewers to draw strong conclusions from a collection of individually-weak studies. It consists of two components. An online database stores and shares the atomized findings of previously-published research. A desktop analysis tool synthesizes this evidence to test cause–effect hypotheses. The software produces a standardized report, maximizing transparency and repeatability. We illustrate evidence extraction and synthesis. Environmental research is hampered by the complexity of natural environments, and difficulty with performing experiments in such systems. Under these constraints, systematic syntheses of the rapidly-expanding literature can advance ecological understanding, inform environmental management, and identify knowledge gaps and priorities for future research. Eco Evidence, and in particular its online re-usable bank of evidence, reduces the workload involved in systematic reviews. This is the first systematic review software for environmental science, and opens the way for increased uptake of this powerful approach.